WO2013104755A1

WO2013104755A1 - Method and system for a spatially resolved representation of elastic properties of soft biological matter

Info

Publication number: WO2013104755A1
Application number: PCT/EP2013/050487
Authority: WO
Inventors: Jürgen FINSTERBUSCH; Anna-Lisa KOFAHL; Karl Georg MAIER; Sebastian THEILENBERG; Deniz ULUCAY; Carsten URBACH; Judith WILD
Original assignee: Rheinische Friedrich-Wilhelms-Universität Bonn; Universitätsklinikum Hamburg-Eppendorf (UKE)
Priority date: 2012-01-11
Filing date: 2013-01-11
Publication date: 2013-07-18
Also published as: EP2802893A1

Abstract

Method for a visually perceptible graphic representation of elastic properties of soft biological matter, preferably of soft brain tissue, wherein the soft matter is moved at every point in time in a movement known in all six degrees of freedom, thereby producing acceleration, and a magnetic resonance imaging method is simultaneously used, and the movement of the soft biological matter is detected by means of the magnetic resonance imaging method in at least one layer. For this purpose, a system with a raising and lowering device (22) that can be positioned in an MRI head coil is used.

Description

Method and system for the spatially resolved representation of elastic properties of soft biological matter

The invention is directed to a method for visually perceptible, pictorial representation of elastic, in particular viscoelastic, properties of soft biological matter, in particular a biological system, preferably the soft Gehimmasse a human brain.

Furthermore, the invention is directed to a system for the visually perceptible visualization of elastic, in particular viscoelastic, properties of soft biological matter, in particular a biological system, preferably the soft brain mass of a human brain, comprising a magnetic resonance tomograph with an MRI coil and a soft biological Matter carrying and disposable in the MRI coil device.

Finally, the invention is directed to the use of a system of the aforementioned kind for carrying out a method mentioned above. Elastography is used to represent the properties of the tissue of a body, for example, the brain or (or) the Gehimmasse. This technique always involves a periodic mechanical excitation (frequency about 50 Hz) and the imaging of the wave propagation generated in the brain by means of a nuclear spin method, for example by means of magnetic resonance tomography, also known as nuclear spin tomography. The matching devices are called Magnetic Resonance Imaging (MRI) or Magnetic Resonance Imaging.

The disadvantage is that due to the strong increase of the attenuation (vibration damping) with increasing frequency while only a resolution in the centimeter range is achieved and in the bilddarstellenden part of the nuclear penis, if any, only global changes in the brain can be represented.

Two known methods for determining the elastic properties of tissue are the theological measurement and the magnetic resonance clastography. These two methods can also be used to determine the vi skoelasti properties of the brain.

A disadvantage of these known methods is that they are set certain limits, as far as the validity, reproducibility and accuracy of the measurements are concerned. In rheological measurements of the human brain this is examined for elastic properties under the influence of shear, compressive and tensile stress. For logical reasons, this type of measurement is only possible on brains in vitro. In vitro in this context means for a measurement to take place outside of a living organism.

For a rheological measurement, the different tissue segments are cut out and examined for the different stresses. This gives you direct access to the brain. This type of direct investigation has already proven itself in other areas. However, it has proved disadvantageous that the measurements depend very much on the preparation of the removed tissue. The fact that the brain is no longer supplied with blood hardens after a few hours. The loss of water and temperature regulation, which normally takes place in a brain in vivo, also has an effect on the elastic properties, so that reproducible measurements can only be obtained to a limited extent and only inaccurate statements about the elastic behavior can be made. The data measured under laboratory conditions are thus difficult to transfer to the natural behavior of a brain in vivo. In vivo means that processes take place on the living organism and thus take place on the living organ.

Magnetic resonance elastography (M E) is so far the only method to examine the brain in vivo in terms of elastic properties, so that elastic properties of the brain tissue can be represented. Shear waves in the brain are excited at a frequency of 20 Hz to 500 Hz via an external generator. To generate the mechanical waves, there are different methods (electromechanical excitation, piezoelectric system, pneumatic excitation by a speaker). The stimulation usually takes place via a bite plate or a vibration plate under the head. The propagation of shear waves in the brain is recorded by means of an MRI and subsequently evaluated. From the propagation speed, the elastic properties can be derived.

By means of MRE it is possible to detect a changed tissue strength of the brain in persons suffering from multiple sclerosis. Even in Alzheimer's patients a change in strength could be measured. A diagnostic added value through knowledge of the viscoelastic properties of the brain in vivo is thus clearly established. The disadvantage of this method, however, is that the effective resolution is used with the

Frequency of waves increases, but then be attenuated more. Thus, the resolution can not be increased arbitrarily. Because of the skull bone direct access to the brain is denied, it is thus always a long-wave excitation from the outside, an internal excitation is not possible.

In summary, it can be concluded that both methods are satisfactory

Do not allow investigation of the human brain.

The invention is based on the object to provide a solution which makes it possible to minimize or even eliminate disadvantages described above, and also to provide a means to examine viscoelastic properties of the human brain in vivo and the spatial distribution of the viscoelastic properties of the human brain.

The object of the generic method is inventively achieved in that the soft biological matter with a defined, at any time in all six degrees of freedom known and / or detected movement is moved to generate acceleration with simultaneous use of magnetic resonance imaging method and the movement of the soft biological Matter is detected by means of the magnetic resonance imaging method in at least one defined and / or detected layer / plane of the biological system and an image of the magnetic resonance imaging method using a motion-sensitive sequence and the movement of the soft biological matter is synchronized with the motion-sensitive sequence or recording frequency.

In a system of the type described in more detail, the object is achieved in that the device is designed as a lifting and lowering device on which the soft biological matter is fixed in position fixable and positionable in the MRI coil positionable, wherein the lifting and Lowering device a positioning element, which can be arranged fixed in the coordinate system of the spatial coding of the MRI scanner, and a movement element, which is able to follow the possibility of being able to follow gravity in free fall, is movably arranged on the positioning element and on which the soft biological matter can be arranged, includes.

Finally, the object is still achieved by the use of a system according to any one of claims 1 6 to 29 for carrying out the method according to one of claims 1 to 15. The method according to the invention and the system according to the invention are also used below under the term MR rheology.

The invention makes use of the advantages of the methods of rheological measurement and magnetic resonance elastography (MRE) and tries to combine the advantages of the two methods mentioned above. However, it does not meet the previously described disadvantageous limits. It is possible to examine soft biological matter, in particular a biological system, preferably a soft brain tissue of a human brain, and thus the body or body parts, such as the human brain.

Soft biological matter is understood to mean biological material, human or animal tissue, fluid or other non-hard matter that is MRI-like.

According to Luhmann's system theory, a biological system is understood in the context of the present invention to mean every living being that is separated from the environment by its body. Simplified, every body of a living being thus represents a biological system. Here, however, the term biological system is not limited to living beings, but can also include dead living beings. However, a very important aspect of the invention is the human, or the human body as a biological system, in particular the soft brain mass in the human head. But also animals and especially mammals fall under the concept of the biological system.

In particular, the investigation on the human head and human brain, in particular the soft human brain mass, will be described by way of example in the following.

In order to achieve the above objects, a method according to the invention and a system according to the invention are developed according to the preceding embodiments, which allow a new insight into the viscoelastic properties of the brain.

The advantage here is that the knowledge of the elastic properties of the brain and their spatial distribution in the brain or in the soft brain mass for medical diagnosis of great benefit. So it is possible that, for example, the early detection, diagnosis and observation of dementias, hydrocephalus, brain tumors and Benefit from multiple sclerosis or make this possible. The method is also medically safe, non-invasive and free of ionizing radiation.

It is furthermore advantageous that increased blood flow through neuronal activity and thus, for example, also signs of Alzheimer's can be measured and represented by means of the system and the method.

Furthermore, it is advantageously possible to record a complete layer of the body or head within a very short time, for example in milliseconds or seconds, whereby the body or head is only lowered once per layer. This is possible because the pulses and field gradients follow one another, for example in the millisecond range.

With the aid of the method and system according to the invention, elastic properties or relationships or structures of the human brain can be examined and displayed non-invasively, so that an invasive procedure is not necessary. Furthermore, the spatial distribution of the elastic properties, in particular of the viscoelastic properties, of the human brain can be examined and represented. The human brain also includes the soft brain tissue.

Necessary is a minimal but sufficient acceleration of the brain or soft brain mass while performing a magnetic resonance imaging imaging procedure with the head in the scanned area of the magnetic resonance imaging apparatus. Furthermore, the invention can also be carried out on other parts of the body or even the entire body of a person according to previous explanations.

The system according to the invention and the method according to the invention thus also make possible the in vivo representation of elastic properties of the human brain. The system includes a magnetic resonance tomograph and is operated synchronously to the acquisition sequence. In this case, the head is preferably raised in the supine position pneumatically by means of a device and lowered again. A motion-sensitive recording sequence allows the representation of the relaxation of the brain after lowering into the rest position. Here, an internal excitation in the form of a creeping process is to be achieved by an externally controlled free fall of the head. The metrological advantage of free fall, In particular, the measurements at the beginning of free fall, is that the measurements are relatively independent of the mechanical vibrations in the scanner and especially from the patient bed.

For example, considering the head as the system to examine, one can think of the skull as a hard shell and the brain as a soft core with viscoelastic properties.

According to the invention, the special construction of the head, in particular of the human head, is used as a hard shell and interpreted as a rigid container, and with the brain suspended resiliently and dampened therein, or in a suspended and dampened suspended state. Each volume of elements of the brain or brain mass is elastically coupled and subcritically subdued. In principle, the brain can be described using the classical theological models of Maxwell, Kelvin and Ringham.

The cranial bone follows the falling motion instantaneously and thus at exactly the same moment as the brain crawls. The resulting movements of the various tissue segments are dependent on the viscoelastic properties and the couplings of the segments with each other.

By means of a motion-sensitive magnetic resonance sequence, the characteristic motion behavior of the tissue segments is measured in a spatially resolved manner in vivo. Thus, for example, it is possible to measure the brain tissue according to previous execution. By analyzing this movement behavior of the various regions in the brain, it is possible to deduce their viscoclast-like properties.

In one embodiment, the method according to the invention provides that the spatial distribution of the elastic, in particular viscoelastic, properties of the soft biological matter in the biological system is evaluated and imaged using the magnetic resonance imaging method.

The biological system is preferably a human body,

Furthermore, the inventive method provides that a head is moved as part of the biological system with a brain therein with acceleration of the Gehimmasse as the soft biological matter of the biological system. The examination on the human head is thereby performed preferably because the human head has a rigid shape in which the soft human brain exists. In investigations on soft human body parts, such as legs with a movable surface, these body parts are packed so dimensionally stable due to the movement so that they are lowered rigidly and without deformation.

In a further embodiment, the method according to the invention provides that the soft biological matter, in particular the soft brain mass, is moved and displayed in vivo.

The acceleration of the soft biological matter, especially the soft brain mass, preferably takes place under the influence of gravity of the earth. This realizes a freefall. By raising the soft biological matter, such as the head and brain, pneumatically, so that there is pressure after lifting in the pneumatics, pressure drop and reduction can be achieved. to realize a vacuum on vacuum by means of pneumatics. The body is thus accelerated in free fall. Alternatively, it is possible that the head with brain is actively accelerated from a rest position and then actively decelerated, whereby the deceleration of the head with brain undergoes a negative acceleration. This can be carried out, for example, by means of a mechanical, electronic or a combination of the two. For example, an elevation of the head from the rest position to a certain higher level is possible during which the method according to the invention is carried out.

In a further embodiment, the inventive method provides that the soft biological matter, in particular the soft Gehimmasse, fixed dimensionally stable during the measurement or the outer shape is known at any time of the measurement. The measurement is preferably a measurement series or a measurement period. A dimensionally stable fixation means, for example, a dimensionally stable packing of soft biological matter. Due to the dimensionally stable fixation errors can be avoided during the measurement.

The method according to the invention provides, in a further embodiment, for the motion-sensitive sequence to have at least one 90 ° pulse and at least one 180 ° pulse and at least one field gradient, preferably two graded fields. This makes it possible to use nuclear magnetic resonance for medicine as an imaging method. For this purpose, however, the measured signal is spatially resolved, individual small regions, to be assigned to so-called voxels. This is done by clever switching of magnetic field gradients, which are superimposed on the static field of the magnetic resonance tomograph.

The field gradient is preferably switched in the direction of the movement of the soft biological matter. Thereby, a representation of the viscoelastic properties in the brain according to the invention is possible.

In a further embodiment, the inventive method provides that the soft biological matter, in particular the Gehimmasse, and at least a part of the biological system, in particular the head having the brain mass, before generating the acceleration by a distance from a rest position in the direction against gravity is raised to a moving position and held there. A movement position is a position in which the matter is positioned at a standstill before the subsequent movement. From this position, a movement is started under the influence of acceleration to return to the rest position. Thus, a movement position is also referred to as an acceleration position.

Preferably, the head is raised by a distance between 0.5 mm and 4 mm, preferably between 1 mm and 3 mm.

In a further embodiment, the inventive method provides that the soft biological matter is moved in the free fall of gravity from the movement position to the rest position, the brain reaches this rest position with a time delay relative to the head.

According to the invention, it is provided in a first alternative that the time of lowering of the soft Gehimmasse head having been selected so that the head is lowered during or after the first field gradient back to the rest position, the head and the Gehimmass after lowering with the second field gradients are applied.

Alternatively, it is provided according to the invention in a second alternative that the time of lowering the head having the soft brain mass is selected so that the head is lowered back to the rest position before the first field gradient, wherein the head and the soft brain mass after lowering with the first and second field gradients are applied.

When the head is lowered after the 180 ° pulse according to the first alternative, other properties are measurable than the second alternative. Preferably, in addition to the soft brain mass of a human brain, the head is also moved with a defined movement known and / or detected at all times in all six degrees of freedom to generate an acceleration with the simultaneous use of an imaging nuclear spin tomography method. For the synchronization, preferably at least one container, in particular at least one tube, is used, by means of which the measured images of the soft biological matter, in particular the soft brain mass, are synchronized. This makes it possible that the container acts as a phase standard and the phase zero point for the layer to be examined pretends. It is expedient according to the development of the system according to the invention if the positioning element has at least one support and at least one half-ring and that the movement element has at least one shell, wherein the soft biological matter can be fixed in a dimensionally stable manner on the shell.

In an advantageous embodiment, the shell is movable by means of the half-ring in the system, wherein the shell is movably arranged on the half-ring.

During the measurement, the soft biological matter, for example, the human brain with the soft brain, must be fixed in the system in the coordinate system of the magnetic resonance tomograph, so that no further degree of freedom arises in the direction of movement and pure vertical guidance parallel to the direction of movement is possible , The fixed fixation must thus be positioned so that it is fixed in position to the (resonance) magnet, but is still movable for the lowering movement.

By means of the shell, it is possible to position the head of the person so that it is arranged centrally, for example by arranging the tip of the nose, inside the device or the measuring device. Furthermore, it is possible to fix the head in such a shell that no rotation of the head during free fall occurs in the context of the movement. Furthermore, the head can be positioned in the shell so that after movement of the head, it remains in the shell.

In a further advantageous embodiment, at least one field gradient, preferably two field gradients, is connected at least in the direction of movement of the movement element. Thereby, a representation of the viscoelastic properties of the brain according to the invention is possible. It is advantageous for the development of the invention, when the lifting and lowering device has a pneumatic, by means of which the moving element, preferably the shell, can be raised and lowered. Thereby, a continuous movement is possible, which is further linear and can be carried out without interruption. Preferably, the pneumatic is switched from pressure to vacuum, so that a free fall of the soft biological matter from the raised position, in which there is pressure in the pneumatic, to the rest position is possible.

In a further advantageous embodiment, the shell has a mass of about 10% of the head weight (including the Gehinimasse) of a human.

Advantageous and expedient for the system according to the invention is furthermore when the moving element, preferably the shell, between 0.5 mm and 4 mm, preferably between 1 mm and 3 mm, can be raised and lowered. It is possible to use a folding mechanism or a linear movement device.

For the structural design of the system, it is particularly advantageous and expedient if the support and the half-ring consist of polyoxymethyl s. Furthermore, it is particularly advantageous and expedient for the structural design of the system if the shell has at least one aramid.

It is advantageous in that the lifting and lowering device is therefore made lightweight, but stiff, since polyoxymethylene and aramid are used.

It is useful according to the invention, when the system comprises a movement measuring device, in particular an optical monitoring, by means of which

Movement of the lifting and lowering device is measurable.

For the structural design of the system, it is particularly advantageous if the optical monitoring has at least one light-emitting diode, preferably three light-emitting diodes, at least one light guide, preferably three light guides, and at least one light detector, preferably at least one photodiode, in particular three photodiodes.

It is useful according to the invention, when the system has a measuring unit for measuring the properties of the soft biological matter, in particular the soft brain mass of the brain, so that by means of the movement of the soft biological matter in the device, the properties of the soft biological matter in In vivo are measurable and representable. Thus, properties of the soft biological matter, in particular of the human brain, can be displayed simply and quickly by means of the measuring device. The measuring unit preferably comprises at least one RF antenna or at least one control signal from the control computer of the MRT, at least one Leuclit diode, at least one light guide and at least one Lichtdeketor, preferably at least one photodiode.

In a further advantageous embodiment, the system comprises at least one container, in particular at least one tube, with a signal-generating content, preferably with a hydrogen content, in particular hydrogel, comprising water and agar, or preferably with glass wool or wool, wherein by means of the container and the filling of which is the phase normal for the displayed layer of soft biological matter can be determined. A signal generating content generates a signal during the measurement. A hydrogen content is a content that generates a signal due to the hydrogen content.

In another embodiment, the agar has an agar concentration of 4 g of agar / 1 liter of water to 6 g of agar / 1 liter of water, preferably 5 g of agar / 1 liter of water. By means of the container and the previously described concentration, it is possible to compare the ascertaining measured data and the associated images with each other. The container serves as the phase zero of each layer of soft biological matter to be examined.

It is expedient according to the invention, when the system is in power connection and / or operative connection with a negative pressure and / or pressure-providing pneumatic and / or Bewegungsmeßeinrichtung, in particular optical elements, and / or electrical components and / or brought.

The invention will be explained in more detail by way of example with reference to drawings.

1 shows a schematic section of a device according to the invention and a method according to the invention,

2 shows a principle of the device according to the invention and of a method according to the invention in detail,

3 shows a structural image and two phase images, FIG. 4 shows the principle of the contrast in the phase image, FIG. 6 shows an overview image for the rotation of the magentization vector, FIG. 6.3 shows a spin-echo representation, FIG. 6.4 shows a visual stimulus as a graphic, FIG. 6.5 shows a spin echo sequence,

FIG. 6.6 shows a simplified scheme of a motion-sensitive EPI sequence, FIG. 6.7 shows several rheological models, FIG.

7.1 shows a principle of a device according to the invention and of a method according to the invention in detail,

FIG. 7.2 shows an alternative principle of a device according to the invention and a method according to the invention in detail, FIG.

8.1 a support and a half ring according to the invention,

FIG. 8.2 shows a support, a half-ring and a shell according to the invention, FIG. 8.3 shows phase normals in a system according to the invention, FIG.

FIG. 9.1 shows a phase image without movement, FIG.

9.2 a phase diagram with movement,

FIG. 9.3 shows a gray scale representation,

9.4 an amplitude image, FIG. 9.5 a phase image to the layer from FIG. 9.4, FIG.

Fig. 9.6 Comparison of the gray value curve,

Fig. 9.7 Representation of distorted phase standards,

Fig. 9.8 representation of undistorted phase normal,

Fig. 9.9 Representation of four phase norma, 10 shows a support, a half-ring and a shell according to the invention,

11 edition, half ring and shell in several views,

Fig. 12 edition, half ring and shell in another view and

Fig. 13 edition and half ring in another view. For the necessary understanding of the system and method according to the invention, in addition to the invention, the theoretical fundamentals of magnetic resonance imaging and their imaging are briefly explained below, as well as the relevant properties of magnetic resonance tomography, for which it is necessary according to the invention to measure movements. It also shows the elastic properties of the brain. With reference to the above, two different methods are further presented that are capable of describing viscoelastic properties of the human brain.

The description of the figures further describes in detail the methods and the associated system according to the invention which enable a new contrast representation of the viscoelastic properties of the brain. Furthermore, in the figure description, the structure of the invention is described in detail and presented the creation of a phase standard.

In addition, basic phase images generated in the measurements according to the invention are described. Furthermore, the possibilities of the method are described.

First, the known from the prior art components of a magnetic resonance tomograph are generally shown. It is known from the prior art that a magnetic resonance tomograph comprises, for example, a vacuum container, a cold shield, a cold head, a compressor, a superconducting shim coil, a superconducting field coil, an iron brain, a gradient coil set, a transmission filter, an RF coil, a local coil, has a transceiver and a patient bed. The gradient coils are used for slice selection and spatial encoding.

By means of such an MRI, one can produce sectional or slice images of the human (or animal) body.

For this purpose, a sequence is used, which is a combination of high-frequency pulses and gastric gradient fields, the sequences being switched on and off many times in a predetermined order every second. Sending and receiving the High-frequency pulses, for example, by means of coils, such as a head coil. The applied principle is based for example on the spin echo sequence,

At the beginning, a 90 ° pulse is emitted by means of the MRT, whereby the magnetization generated by the MRT is deflected by 90 ° transversely to the external magnetic field. The magnetization begins to revolve around the original axis.

The resulting high-frequency signal can be measured outside the body.

This decreases exponentially, because the proton spins dephase and overlap increasingly destructively. The time after which 63% of the signal has decayed is called T2 -Re 1 axat ionsze i t

(Spin-spin relaxation). By means of a suitable 180 ° rephasing RF pulse, one can cause part of the dephasing to be undone at the time of the measurement, so that more spins are again in the same phase.

In addition, depending on the sequence parameters, the signal may also depend on the so-called Tl relaxation time (spin-lattice relaxation), which is a measure of the rate at which the original longitudinal orientation of the spins reverts to the external magnetic field.

Tl and T2 times according to previous embodiments are also in the example

PCT / EP2007 / 010002 (WO 2008/067905 Al).

An MRI examination generally always includes Tl- and T2-weighted image series in at least two spatial planes.

In order to be able to assign the signals to the individual volume elements (voxels), a spatial coding is generated using linearly spatially dependent magnetic fields (gradient fields). It is exploited that for a given particle, the Larmor frequency depends on the magnetic flux density (the stronger the field component perpendicular to the direction of the particle rotation pulse, the higher the Larmor frequency). In a measuring coil, an alternating voltage is induced by the rotating Transversalmagentisierung whose frequency is the Lamorfrequenz.

The gradients together thus cause a coding of the signal in three spatial levels. The received signal, for example by means of a coil in the MRI, belongs to a specific layer of the body and contains a combination of frequency and phase coding, which the computer can convert into a two-dimensional image with a Fourier transformation.

Previous versions of the MRT and the method are known from the prior art or, for example, from PCT / EP2007 / 010002 and will be explained in detail below if necessary.

First, for a basic understanding, the invention will be briefly described.

As shown in FIG. 1 in the partial image a), the brain G in the hard cranial bone can be regarded as a strongly damped harmonic oscillator, each segment or each considered and defined volume part (brain) of the brain G being represented as an inert mass (model) by a cuboid), which is coupled with an elastic spring 1 (elastic spring) and a damper 2 (darnper). When the hard head shell of the head K abruptly accelerates or decelerates abruptly, the brain G or the brain mass experiences an acceleration or deceleration, which, however, is delayed or differently formed with respect to the hard head shell. In particular, the brain continues to vibrate G or the immune system until it settles down. In this case, the speed V of Gehimbewegung and the time until the idle state is reached, depend on the spring constant (elastic spring 1) and the damping 2, as shown by the partial image c) in Fig. 1. In the context of an imaging magnetic resonance tomography method, the head K is first raised by a distance d (partial image a) of FIG. 1) by means of a pneumatically actuated head laying device 6, wherein the position is determined by a fast optical measuring device, preferably on the head support device 6 is arranged, is displayed. After reaching the upper start and rest position shown in the sub-figure a) of Fig. 1, the head K by the distance d in the embodiment down to the horizontal position, as shown in the partial image b) of Fig. 1, in the sense dropping rapidly by this small distance d. At the same time, however, the imaging process of the magnetic resonance tomography apparatus, in whose bi-loading part the head K is arranged and placed at this time, also runs during this movement.

The "fall time" and the "fall angle" or "drop height" are adjustable and are preferably provided with a diffusion sensitive / motion sensitive, single shot (EPI) (eefao planar imaging) Synchronized sequence of the current magnetic resonance imaging method. The motion of the brain G or the particular brain segment or volume of matter considered is represented as encrypted gray-scale in phase images during the presence and presence of the diffusion-sensitive / motion-sensitive sequence / acquisition sequence (partial image c) of FIG. 1).

The measuring principle according to the invention is further explained with reference to FIG. 2, wherein the representations in the upper partial image (partial images a) to c) of FIG. 2 at the times ti, t ₂ and t _{3 are} respectively the partial images a) to c) of FIG 1 correspond. The measuring principle shows a variant of the measurement according to the invention. To the. Time tj according to FIG. 2 sub-picture d), the head is in the upper position and is raised by dz = 3 mm. At time t ₂ , the device folds down, the skull bone follows the movement instantaneously (blue curve 3). The downward movement of the brain is delayed (red curve 4). Each element 5 of the brain G moves with a different time constant corresponding to the elastic coupling 1 and damping 2. This delayed movement of the brain can be represented by means of a motion-sensitive sequence as an image contrast in the MRI system (magnetic resonance tomography system).

The acceleration of the head K is shown below.

A pneumatically controlled device is installed for moving the head into the head coil in the magnetic resonance tomograph (MRT, Magnctresonan / .tomographen). It must be ensured that the device is fitted without play in the head coil. The pneumatics must be designed in such a way that the movement of the head takes place only over large-area actuators in order to avoid vibrations and deformation of the entire device.

The head K is fixed on an exactly adapted to the shape of the head pad of the head-laying device 6 shown in FIG. 2, which is rigidly connected to a moving device. The head K is raised (measured above the vertex) by approximately 3 mm, the joint 7 is located in the region of the lumbar spine according to partial image a) to FIG. 2. The position of the folding device is measured optically in real time. For the measurement, a modulated light signal is conducted via a glass fiber to the measuring position. There the beam cross-section is widened over a trapezoidal light guide. With an identical light guide, the light signal is caught behind a 2 mm wide air gap and guided with a second optical fiber into the control area of the MRI (magnetic resonance tomograph). In the 2 mm wide air gap There is a plastic panel attached to the folding device. The analog height signal thus generated is optically detected and displayed on a digital oscilloscope.

The movement of the folding device of the head-elevating device 6 takes place via rapidly switchable, electrodynamic pneumatic valves. Via throttle valves, the time constants for raising and lowering the head can be set individually.

The following describes the recording of the movement.

The movement of the head K is synchronized with the acquisition sequence of the magnetic resonance tomograph or nuclear magnetic resonance tomograph. The time of lowering is adjustable (accuracy 0.5 ms), the lower rest position (time t ₂ ) - must be reached before the 90 ° pulse 8a in this Ausführungsheispiel.

The image is recorded with the help of a motion-sensitive sequence (for example, spin-echo, EPI, etc.), wherein the two vertical bewegungsempfmdlichen, magnetic field gradients 9a, 9b at each time point t ₃ within a 100 ms wide time interval after lowering the head K are set can. This makes it possible to measure the individual time constants of each volume element 5 of the brain G absolutely.

The image contrast generating quantity Äh determines the image contrast and the information in the phase image. Fig. 4 shows the underlying calculation formula. Thus, a spatially resolved representation of the human brain can be realized.

Hereinafter, another application example according to the invention will be described. The following measurements were carried out on a 1, 5 T Kemspintomographen, for example, a 1, 5 T Magnetom Avanto Kemspintomographen Siemens, using a conventional head coil. The sequence parameters of the EPI sequence used are: TR: 1000 ms, TE: 150 ms, fat saturation, b value: 100 s / mm, gradient length: 20 ms, time interval of the gradient: 66 ms, voxel size, 1 mm x 1 mm x 5 mm. The parameters of the movement: stroke of the head K: 3 mm, reaching the lower position 3 ms before the 90 ° pulse 8a and 15 ms before the first motion-sensitive gradient 9a. The measurements were carried out on a 66-year-old male volunteer.

The images of FIG. 3 on the left side (partial image a)) show a transverse structure image (amplitude image) of the transverse plane examined. In the middle (partial image b) of FIG. 3), a phase image of the same layer / plane is shown, which was recorded without preceding movement. Structures within the head K are not recognizable. The Gehimmasse / brain G is shown as a homogeneous gray field due to the failure to move during the concern of the motion-sensitive sequence / gradient. On the right (partial image c) of FIG. 3), a phase image with preceding movement of the same layer / plane of the head K is shown. The structures visible there are recognizable on the structure picture. In particular, dark areas of the brain are recognizable in the right part of the brain. The contrast stems from the differences or changes in the elastic properties of the individual brain areas made visible by the method according to the invention.

The method according to the invention for visualizing elastic properties of the human brain by means of or based on a material science method is thus simple to perform, non-invasive and not uncomfortable for the patient. The visual contrast or contrast difference depends on the combination of elasticity (elastic spring) and the damping constant of the respective brain area.

In addition, it should be noted that in Fig. 2, the curve 3 shows the decay curve of the head K, i. the hard head shell, and the curve 4 the corresponding curve for the brain G is shown. The first 1-hole req uen / .pul s 8a of the MRI defines the respective measurement plane / measurement layer (transverse plane) in the brain G. The 90 ° pulse 8a is followed in the usual way by a 180 ° pulse 8b. The acceleration of the head K in the direction of distance d can be achieved not only by pivoting the head rest according to FIG. 2, but also by displacing the head rest.

Below is another Kur / beschreibiing the system according to the invention for vivo representation.

The head K to be examined rests in a mechanical lifting / lowering device 22 according to FIG. 5, which pneumatically raises and lowers the head K. The current position is optically measured in three places. The device is controlled by an electronic system that switches the pneumatics synchronously to the recording sequence.

All components of the system for carrying out a method according to the invention can be found in the block diagram of FIG. 5.

Below is a description of the mechanics. The mechanics are designed to be used in a standard Head Spool 39 (Siemens Medical Solutions) within a 1.5 T MRT, for example within a Siemens Magnetom Avanto Tomographs, can be operated. By means of such a head coil 39, for example, the imaging sequences are received in the MRT.

The mechanics is divided into two parts.

The lower, a part consists of a thin support 23, which is fitted into the round opening shape of the head coil 39. Attached to it is a half-ring 24, which defines both the position in the longitudinal direction, as well as connections 20a, 20b for the later-described pneumatic 40 and the optical monitoring 41 includes. The half ring 24 forms the other, second part. The mechanism is shown by way of example in FIG. 5, FIG. 8.1, FIG. 8.2, FIG. 8.3, FIG. 10 to FIG. On the support 23 are shown in Figure 8.1, two rubber tubes 21 a, 21 b, which can be filled or evacuated via the pneumatic ports 20a, 20b with air. At both

Side of the half-ring 24 are bores 43 a, 43 b in which over the same pneumatic ports 20a, 20b cylindrical pistons 25a, 25b can be raised and lowered. This is shown in FIG. The half-ring 24 and the support 23 are made of polyoxymethylene (POM) (POM is also known under the trade name TECAFORM AH natur, Ensinger).

On the tubes 21 a, 21 b and the cylinders 25 a, 25 b lying on a shell 26, on which the head K is positioned. The shell 26 was made by hand as a sandwich laminate of aramid-reinforced plastic. The sandwich consists of a 3-millimeter-thick aramid honeycomb (Kevlar® honeycomb) sandwiched between two approximately one-millimeter-thick laminates of aramid fabric (Kevlar® fabric, trade name Style 284 from ECC) and epoxy resin (trade name Epoxy Resin L and Hardener L from R & G Faserverbundwerkstoffe GmbH) is located. The entire sandwich was produced in one operation in an aluminum mold. The shell 26 according to FIG. 8.2 serves as a support for the head K. The shell 26 is supported on the shell 26 by means of a vacuum pad (not shown in FIG. 8.2) (MR (gastric resonance)).

Standard accessories; Siemens Medical Solutions).

On the sides of the half ring 24 and in the rear region of the support are stops 28a, 28b made of POM, which limit the stroke of the shell 26 adjustable to a maximum of 3 mm. These stops 28a, 28b are designed as an angle that protrude over the support. On half ring 24 (front stops) are according to Figure 8.2 and Figure 12 through this angle from above Nylon screws 29a, 29b used. They form the actual stop, which is adjustable thereby. The stop on the support (rear stop) can be adjusted by different thickness POM pieces.

The pneumatic system according to the invention will be described below. The lifting and lowering device 22 is pneumatically driven. For this purpose, according to FIG. 5, a membrane pump 1 1 (vacuubrand MZ 2T) in two pressure vessels 12 a, 12 b generates a super-negative pressure (20 kPa or -25 kPa with respect to the ambient pressure). Underpressure and overpressure are set by means of mechanical pressure control valves 13a, 13b (own structures) and can be read on two pressure gauges according to FIG. Pressure and suction side are connected to manually adjustable throttle valves 15a, 15b via a common supply line 16 to the lifting / lowering device 22. The suction side is additionally provided with an electromotive switching valve 14 (Leybold). By default, this valve 14 is closed, so that the lifting / lowering device 22 is under pressure and the shell 26 is in the upper position. If the switching valve 14 is opened, the device 22 is vented and the shell 26 decreases.

For adjusting the time constants of raising and lowering, the pressure and suction sides are equipped with manual throttle valves 15a, 15b. In Überdruckteil a Überdrackbegrenzer 44 is installed in the form of a place sheet, which vented automatically due to design at an overpressure of 40 kPa. All components in the pneumatic circuit 40 according to FIG. 5 are equipped with standard vacuum small flange

Technology connected.

In the air supply line to the lifting and lowering device 22 in the MRI room 17, as well as in the control room 18, manual vent valves 37, 37a are installed in the pneumatic circuit. Thus, both the operator and the patient himself at any time the pneumatics are switched off.

The electrical control will be described below.

The excitation J JF signals of the MRI 19 are received with an RF antenna 35 in the scanner room 17. The anti-Semitic signal is amplified (EG & G ORTEC Model AN302 / NL) and the MRI's FIF pulses are detected in a De-ay-Trigger (Delay Trigger DT 104, Paul Scherrer Institute) and a control pulse is generated via an electronic relay (Power supply via Triple Power Supply EA-PS 3332-03) the switching valve 14 of Pneumatic opens synchronously to the recording sequence. Antenna signal and control signal are checked with oscilloscope 32 (Tektronix TDS 5034).

The optical monitoring will be described below.

For timely exactly adjustable synchronization of the lifting / lowering device 22 with the MRT sequence, the mechanism is equipped with an optical display. For this purpose, from the control room 18, the light of three commercially available LEDs 30a, 30b, 30c (AVAGO Technologies I ILMP HG35- I W0DD) using coated plastic optical fibers 31a, 31b, 31c (outer diameter 2.2 mm, core diameter 1 mm ) to the mechanics. At the front stops 28a, 28b, the optical fibers are widened into a wedge. The light emerges from the wedge and is collected after 2 mm by a second, also widened light guide. In the gap, an aperture moves with the head shell, which dimmers the incoming light depending on the position. At the back stop, the light exits directly from the light guide and is captured directly by a second light guide. This moves with the Kopfschaie 26 in front of the first light guide. The collected light is passed back into the control room 18, the respective light signal with a photodiode 33a, 33b, 33c (Burr-Brown OPT101) detected and displayed on the oscilloscope 32. There speed and the stroke of the head shell 26 can be tracked temporally resolved. The light-emitting diodes 30a, 30b, 30c, the light guides 31a, 31b, 31c and the photodiodes 33a, 33b, 33c are part of the optical monitoring 41. The light-emitting diodes 30a, 30b, 30c are connected to a function generator 34 (Voltcraft FG-506). operated at a frequency of 30 kHz.

Further details on the magnetic resonance tomography used are described below.

The measurements are performed on an MRT 19, here a Siemens Magnetom Avanto MRT, with a grand field strength of 1, 5 Tesla. For image acquisition, a simple, diffusion-sensitive spin-echo sequence (SE) and a diffusion-sensitive echo-planar imaging sequence (EPI) are used.

The relevant properties of magnetic resonance imaging are presented below.

For the method presented here, it is necessary to measure movements. How this can be achieved by MRI is also described below. The last part deals with the elastic properties of the human brain. Fig. 6.1 shows the energy split by the ern-Zeeman effect for a proton in an external magnetic field. The magnetic dipole moment μ pre / edit around the direction of a static, external magnetic field Bo. The energy difference between the two states is ΔΕ = γι h B ₀ . In order to transfer the spins in the other state, this energy must be applied or removed.

Protons in the magnetic field behave like quantum mechanical, magnetic gyros with a magnetic moment μ. If the angular momentum axis of the proton and the direction of an external magnetic field Bo are not parallel, a precession movement of the magnetic moment about the magnetic field axis follows with the angular velocity coo = γι Bo, equation (2.1) which is also called the Lamor frequency, γι describes the gyromagnatic relationship has a value of γι = 42.577 MHz · T ¹ for protons.

The grand laws of quantum mechanics require a quantization of the angular momentum I (vector) and its z-component, so that with the Planck's quantum h and the magnetic quantum number ni for the angular momentum I _z in / - direction

I _z = m _{ h with nii = ± 1/2, -I <mj <I. Equation (2.2)

In an external, static magnetic field Bo (vector) = B ₀ · e _z (vector), for protons with spin I = 1/2 two energy levels E = + 112 v _\ h Bo (core Zeeman effect) result. The energetic distance of the levels, ie the energy needed for transitions, is described by ΔΕ = γι h B ₀ (FIG. 6.1).

Electromagnetic waves that are radiated resonantly at the Lamor frequency co ₀ and have the energy E = ho = hcoo * h γι Bo can now create a transition between the two levels.

The occupation of the upper and lower levels in the ground state takes place according to the Boltzmann statistics. If a multi-stakeholder system is considered, one can summarize the magnetic moments of the spin ensemble to a magnetization vector M and go into the classical representation. The irradiation of a resonant, electromagnetic wave is then used to spiral the magnetization vector from the / - direction into the xy plane. The radiation duration τ determines the angle of rotation u - γΒ ι τ with respect to the z-axis with B _ä equal to the induced by the EM wave alternating field (Figure 6.2.). Achieved α 90 °, the associated pulse is referred to as a 90 ° pulse. A pulse with twice the strength results analogous to a 180 ° pulse. The amount of magnetization vector projected onto the xy plane can be thought of as a rotating dipole whose signal can be measured with an antenna perpendicular to it.

By such a high-frequency pulse (RF pulse) energy is supplied to the system and it is in a disturbed, energized state of energy. There it releases energy via spin-lattice or spin-spin interaction and returns to its grand state. These processes are also known as longitudinal and transverse relaxation. They are described by the associated time constants T) and T ₂ and are responsible for the fact that the signal builds up again in the z direction or decays in the xy plane. The system returns to the initial state.

Fig. 6.2 shows rotation of the magnetization vector M due to the irradiated Bi field

(Vector). After the irradiation time τ, the magnetization has rotated by α = γΒι τ.

Nuclear magnetic resonance can be used for medical diagnosis, since different types of tissue differ in the relaxation times Tf and T ₂ and can thus be differentiated. A detailed description of the relaxation processes is known in the art or in the literature.

The following describes the echo signal.

Fig. 6.3 shows in detail a spin echo. The 90 ° pulse causes a rotation of the equilibrium magnetization from the z direction into the x-y plane (step A according to FIG. 6.3). The spins run at different angular velocities due to inhomogeneities

(Larmor frequencies) apart, they dephase (steps B, C) and the signal decays. The irradiated 180 ° pulse after time T _{E / 2} rotates the spins about the x-axis so that the faster spins are again behind the slow ones (step D). The faster spins pick up the slow ones again (step E). After the time ΊΥ; the spins rephase to the so-called echo (step F). The amplitude of the falling signal decreases with the specific relaxation time of the tested sample volume (green curve 45).

The reading of the signals takes place via so-called echoes. The actual signal decay occurs much faster due to magnetic field inhomogeneities than the pure relaxation processes. They lead to an accelerated dephasing of the spins. This signal drop is also referred to as free induction decay (PID). By generating an echo signal, one achieves a signal decay independent of the inhomogeneities. The process is explained in Fig. 6.3. It can thus be seen that the spins initially rotated into the xy plane (step A) precede because of inhomogeneities with different angular velocities (Larmorfrcquenz.cn) and dephasing (steps B, C). By injecting a 1 8 () ° pulse, the spins are rotated 180 ° about the x axis, causing the faster spins to be behind the slower ones (step D) and catching up again (step E). This rephases the spins and provides a measurable signal, called an echo (step F). The signal drop of the echo maximum thus takes place only by the actual relaxation (green curve 45). These can now be used to determine the relaxation time.

Gradients and spatial encoding are described below. In order to be able to use nuclear magnetic resonance for medical purposes as an imaging method, the measured signal must be spatially resolved and assigned to individual small regions, so-called voxels. This is done by clever switching of magnetic field gradients, which are superimposed on the static Bo-Feid. As explained at the beginning, the Lamor frequency depends on the strength of the magnetic field (equation 2.1). A gradient now causes a variation of the field strength along an axis, whereby a location-dependent Lamor frequency arises.

The layer excitation is described below.

The gradient Gz = eBz / dz causes an increase of the field strength in the / direction and thus shifts the Lamor frequency in each z plane over coo = γι (Bo + Gz · z). Equation (2.3) Fig. 6.4 shows a layer excitation. The z gradient in / - direction excites a thin layer in which the condition ω ₀ = (oil is satisfied.

Since a transition between the energy levels takes place only when a high-frequency field is irradiated, which coincides with the now location-dependent Lamorfrequenz the spins, the 90 ° -PuIs so only the layer in which the condition ω ₀ = CÖL is satisfied (Fig. 6.4). The width of the layer depends on the strength of the gradient and the bandwidth of the radio-frequency pulse.

The phase coding will be described below.

For the coding in the y direction, a gradient Gy = <3by / öy is applied for a certain time T _y . This increases location-dependent the Lamorfrequenz CÖL ⁼ y (B ₀ + G _y y), so that there is a relative phase difference ΔΦ = yGy Ty Ay. Ay describes the distance between them different spin ensembles. If the signal of a layer with N different, known gradients is measured, the N-lines in the y-direction can be assigned their signal contribution.

The following describes the frequency encoding.

During the actual readout of the signal, a third gradient is switched in the x-direction Gx = cBx / <3x. Thus, each voxel with a different frequency sends COL (X) = γ (Β ₀ + G _x x) depending on the x position. The measurement results in a frequency spectrum from which the signal of its frequency is reassigned to the voxels in the x-direction by means of a Fourier transformation.

The sequences are described below.

The circuit of several RF pulses and gradients for generating an image is called a sequence. In the following two sequences are presented, which can be used for imaging.

The spin echo sequence is described below.

FIG. 6.5, part a), shows the circuit of a spin echo sequence (SE sequence). Upon irradiation of the 90 ° pulse, a slice selection takes place by the spatial encoding gradient in the / direction. Since the 180 ° pulse acts on the entire sample volume, another gradient in the / direction is switched in during this, in order to restrict the range to the slice selected at the 90 ° pulse. Between the 90 ° pulse and the 180 ° pulse, the phase gradient is switched in the y direction. For a recording with N lines, N passes with different gradient strengths are necessary. During the reading of the echo signal, the frequency coding takes place. To do this, a gradient is switched in x-direction. This provides different frequencies in each voxel. By means of a Fourier analysis, the signals from different voxels can be assigned to their x-position on the basis of their frequency.

In summary, it can be stated in accordance with the foregoing that sub-image a) thus shows a spin-echo sequence in detail, during which the magnetization collapses into the xy plane during the 90 ° and 180 ° pulses , a gradient is switched in /.- direction to select a layer. For the phase coding, a gradient in the y-direction is applied before the 180 ° pulse. An image with N lines requires N passes with different gradients in the y-direction. During the reading of the echo signal, the frequency is encoded by a gradient in the x direction. Partial image b) shows: In order to measure a movement within the examined volume, gradients are arranged symmetrically around the 180 ° pulse, which thereby generate a location-dependent dephasing. If a movement has taken place, the second gradient can not completely cancel the dephasing so that a phase change ΔΦ = yGe T _B Ah arises proportional to the movements. GB describes the gradient strength in the direction of movement, TB their irradiation duration. Ah indicates the positional difference created by the movement.

In order to detect movements in the measuring volume, two additional, so-called motion-sensitive gradients can be switched in the direction of movement (partial image b) of FIG. 6.5). The principle is based on the method of the first diffusion measurements. In an SE sequence, these gradients are switched symmetrically around the 180 ° pulse. The first, like the phase encoding gradients, causes a location-dependent phase change along an axis. The 180 ° pulse then rotates the magnetization in the opposite direction. The second gradient with the same polarity would completely reverse the dephasing if the examined volume did not move. If, however, the location of the spins changes between the two gradients due to a movement in the examined sample volume, the phase shift is not completely reversed by the second gradient. The measured phase change Δ (equation 2.4) is proportional to the position shift Ah = hl - h2. GB describes the gradient strength in the direction of movement, TB its duration.

ΔΦ = yGn TB hi - yG _β XB j. Equation (2.4)

Gray values are then assigned to the signal amplitudes and phase positions thus measured and spatially assigned, so that a sectional image (amplitude image) can be generated from the amplitudes, on which the structures of the examined volume can be seen. From the phases, a sectional image (phase image) can be generated, in which the movements are made visible.

The EPI sequence is described below.

The echo planar imaging (EPI) sequence is one of the fastest pulse sequences available on an MRI and is shown in Figure 6.6. It differs mainly in the echo generation of a spin-echo sequence. She does not rely on a 1 80 ° pulse to rephase the spins, but works with gradient echoes. Via a frequency-encoding gradient in the x-direction, the spins are first dephased, Prephasing called, then rephasing this by a gradient in the opposite direction and thus to produce the desired echo. Due to the double irradiation time of this gradient, the second half again serves for prephasing for a further phase encoding step. With interposed phase encoding gradients in the y direction, a complete, 2-dimensional image can thus be generated from a single excitation, since a whole series of echoes occurs.

Fig. 6.6 shows in detail a simplified scheme of a motion-sensitive EPI sequence. In the case of the EPI sequence, the spins are first pre-pregraded by gradients in the x direction and then rephased in order to produce an echo. An intermediate phase encoding gradient in the y direction provides for the complete generation of a two-dimensional image. As in the case of the SE sequence, a 180 ° pulse is radiated for the movement sensitivity around which symmetrically distributed two gradients lie in the direction of movement.

In order to make this sequence sensitive to movement as well, a 180 ° pulse with the two gradients lying symmetrically around it is irradiated in the direction of movement before the pre- and rephasing, as in the SE sequence.

Water trapped in adipose tissue has a different Lamor frequency, which is called chemical shift. This leads to undesirable structural shifts in the imaging. To avoid this, since the chemical shift in fatty tissue has too great an effect, the fatty tissue is saturated before the actual measurement. The exact operation of fat saturation is known in the art or in the literature.

The following describes the elastic properties of the brain

The tissue of the brain is a substance that has both elastic properties of a solid and viscous properties of a liquid. It is called viscoelastic and can be described by different models. The science of the behavior of elastic, viscous and plastic bodies is called rheology.

Pure elastic properties are described by the elastic modulus. The modulus of elasticity is defined by the Flookesche law as E = σ / ε, ie as a proportionality constant between stress σ and strain ε. This results in a relationship between acting force and change in length over F oc E · AL. In rheology, elastic behavior is represented by a spring (FIG. 6.7, partial image a)).

The viscous properties are described in rheology by an attenuator (FIG. 6.7, partial image a)). The damping is due to the viscosity of the fluid.

Unknown systems, such as those found in the brain, can be formally described by combinations of springs and dampers and approximated as arbitrarily as desired (Fig. 6.7, partial image b)). This characterizes both the elastic and viscous properties of the system.

In Fig. 6.7 some rheological models are shown.

To part of a) of Fig. 6.7: spring and damper are in accordance with previous explanations basic elements in the rheology and describe elastic and viscous behavior.

To sub-image b) of Fig. 6.7: Unknown systems usually have more than one behavior.

By combinations of springs and dampers, more complex properties, such as e.g. present in the brain, approximated as closely as possible and thus characterized. Shown in FIG. 6.7 is partial image b) basic combinations of rheology, ie simple standard models of rheology.

The known methods rheological measurements and magnetic resonance elastography were previously described in detail in the general section.

Subsequently, the method according to the invention and the associated systems are consequently presented in detail. In Fig. 7.1 partial image a), the principle of the method according to the invention is shown schematically and further elaborated. Within the receiving coil of an MRI, the head K is raised by a few millimeters (upper position). In this condition, the brain G and the skull bone are in balance. Subsequently, the head K is dropped (lower position). This results in a disruption of the balance of forces, viscoelastic stored tissue structures in the brain G move relative to the skull bone. If the hard skull bones down again, it settles much faster than the soft core, the brain G. This creeps depending on the viscoelastic properties. In this case, different types of tissue can exhibit different behavior, which is recorded by the measurement of the movement by means of the MRI. Fig. 7.1 sub-picture b) shows the timing. At time U, the head K is raised and in an equilibrium state. Then it is dropped, with the hard skull bone (blue, curve 3) coming up first and resting relatively quickly (t ₂ ). The soft brain regions follow the delayed motion, depending on their viscoelastic properties, delayed while synchronously initiating a motion-sensitive sequence. This represents, depending on the time of the additional gradients in the direction of movement (t ₃ ), different behavior of different tissue structures in a phase image (green curve 10 and red curve 4).

In summary, it can thus be stated that FIG. 7.1 thus shows in detail the principle of MR rheology, wherein at the beginning of a measurement according to the preceding embodiments, the head raised is in an equilibrium state. Subsequently, the head is dropped, whereby the skull bone is again relatively quiet after striking because of its hardness and the associated damping. Tissue segments with different viscoelastic properties, represented by two different springs and dampers, follow the fall movement with different lowering behavior.

Partial image b) thus shows the representation of the time sequence according to the preceding statements. The raised head K, which is in an equilibrium state (ti), is dropped from a small height (distance d) (t ₂ ), the hard skull bone coming up first and resting relatively quickly (blue curve, 3). Delayed a motion-sensitive sequence (eg EPI sequence) is started, which makes the movement Ah of the tissue segments during this period in a phase image visible. Different, viscoelastic properties (red curve 4 / green curve 10) can thus be recognized. At time (t ₃ ), the necessary additional gradients are switched in the direction of movement. An alternative approach, the method method is shown in FIG. 7.2, which reproduces in Fig. 7.1, upper partial images a) and b), which is why in this respect reference is made to the preceding description for Fig. 7.1.

The alternative procedure is now described in sub-diagram c) of FIG. 7.2, wherein reference numerals indicated in FIG. 7.2 relate to the same curves or elements as are given in the description for FIG. 7.1, provided the reference numerals are identical. As previously described with reference to FIG. 7.1, the principle of "MR rheology" is to record a relaxation movement of the brain G, triggered by a case of low altitude, by means of motion-sensitive magnetic resonance tomography MR.

In the alternative procedure according to FIG. 7.2, the head K is pneumatically lifted and lowered in a time-controlled manner by means of the apparatus or device described in connection with FIGS. 10 to 13. The hard skull K follows the movement instantaneously, the Gehini G will crawl for a while.

In the procedure according to FIG. 7.1, the time of lowering is selected such that the cranium is timed before the 9 () ° excitation pulse of the MR sequence (magnetic resonance sequence) in the lower position (time t ₂ , middle partial image of the partial image a ) of FIG. 7.1 and curve 3 in FIG. 7.1b) (partial image b) of FIG. 7.1)). The subsequent movement-sensitive gradients then record different relaxation behavior of the brain G. Thus, a spatial encoding occurs through the gradients related to the examined slice / plane of the brain. With the chosen fall time the last part of the relaxation curve is examined. In this case, the question of "how does the movement end" is illuminated, in which the height difference between the two gradient pulses of each volume element can be represented as image contrast by means of the two vertical gradient financial gradients shown in Figure 7.1 The spatial resolution is determined by the spatial resolution of the magnetic resonance tomograph , for example, 1, 5 mm resolution, where a measured gray value is the height difference between the two magnetic field gradients, and a constant gray value means that the brain does not move between the two magenta field gradients.

In the procedure according to FIG. 7.2, the fall time is selected such that the lowering point takes place only after the 1 80 ° pulse 8b and after the first gradient 9a (drop of the curve 3 in partial image c) of FIG. 7.2). This examines the same relaxation curve, that is, it looks at how the brain G reacts to the fall and moves from "above" to "below", but now the beginning of the movement ("how does the movement start") is observed In addition, the elastic properties of the brain can be measured and represented, and the synchronization is improved. <br/><br/> The technical advantage of the examination at the beginning of free fall is that the measurements are relative are independent of the mechanical vibrations in the tomograph and especially of the patient bed. Mitteis the embodiment of FIG. 7.2, it is thus possible to directly absorb the acceleration of the brain at the beginning of the free fall or to look into this.

Furthermore, another spring Γ, a further damper 2 ^' and a further element 5 ^' are shown elsewhere in the head K in FIGS. 7.1 and 7.2.

Furthermore, the lowering of the head according to FIG. 7.1 and FIG. 7.2 preferably takes place by means of a stroke movement by the distance d.

By means of the method illustrated in FIG. 7.1 and FIG. 7.2, the internal stress state can be represented within cranial bones. Hereinafter, the structure of the system according to the invention according to the preceding

Embodiments described with reference to the variant in Figs. 7.1 and 7.2.

In order to technically realize the measuring method presented in the previous chapter, several components are required, which are described individually below. This includes in particular a suitable mechanism on which the head can rest and which makes it possible to perform a lifting and lowering of the head controlled in the MRI. The movement is generated pneumatically, applied overpressure corresponds to the upper position, negative pressure corresponding to the lower. Through throttle valves, the exact shape of movement can be adjusted in both directions.

Subsequently, the pneumatic will be described first. Overpressure and depression are provided by a diaphragm pump 11 (vaeuubrand MZ 2T) according to FIG. 5. About connected plastic hoses two reservoir 12a, 12b are brought with a volume of approximately 15 liters to an overpressure of 20 kPa or negative pressure of -25 kPa compared to the ambient pressure. By mechanical pressure control valves 13a, 13b, the pressures are adjustable and can be read on manometers. To control the lifting and lowering speeds, the pressure and suction sides are equipped with throttle valves 15a, 15b, which can be adjusted manually. An electro-pneumatic switching valve 14 (Leybold) allows switching from positive to negative. Its electrical control will be explained below. The pressure and suction sides then run via a common supply line (rubber hose 16) from the control room 18 to the MRT room 17 with the MRT 19. Hereinafter, the lifting and lowering device 22 will be described. A Y splitter in the MRT room 17 according to FIG. 5 divides the common feed line into two tubes 21a, 21b, which can be plugged into the lifting and lowering device 22 (FIGS. 10, 12, 13). The device is designed so that it can be accurately placed in the head coil of the tomograph (Siemens Medical Solutions).

A part of this, hereinafter referred to as a support 23, serves as a holder for recessed rubber hose 21 a, 21 b, which are connected to the pneumatics.

The other part, hereinafter referred to as half ring 24 is connected to the support 23, ensures a secure fit of all components and includes, in addition to the possibility to connect for the coming of the Y-splitter tubes 20a, 20b, two pistons 25a, 25b , These are also connected to the pneumatic and in them a cone is embedded on the upper side.

When applied overpressure, the rubber tubes 21 a, 21 b are inflated and the piston 25 a, 25 b pressed upwards. As a result, a shell 26 resting thereon can be raised at three different points until it reaches the upper position.

FIG. 13 shows in detail a support 23 and a hollow ring 24 consisting of polyoxymethylene. The support 23 is adapted to the head coil of the scanner. The associated half-ring 24 serves to fix the support 23 and includes the connections of the pneumatics. To these two pistons 25a, 25b are connected in the half-ring 24 to guide the neck-near part of the shell 26. The rubber hoses 21a, 21b let into the support 23 are connected to the same pneumatics and can be inflated and evacuated.

The shell 26 consists of a sandwich laminate of aramid-reinforced plastic. For this purpose, a 3 mm thick aramid honeycomb (Kevlar® honeycomb) of approximately one millimeter thick laminates of aramid fabric (Kevlar® fabric) and epoxy resin was enclosed. To give it the necessary shape, it was made in a matching aluminum mold.

The shell 26 is shown together with the support 23 and the half ring 24 in Fig. 10 and Fig. 1 1 and Fig. 12.

At the positions 27a, 27b, where it projects beyond the pistons 25a, 25b, cones are mounted on the underside, which fit into the recessed cone of the pistons 25a, 25b. As a result, the shell 26 is located on the tubes 21 a. 21 b and the piston on. so that Rotational movements and Verwmdungen are almost impossible. Furthermore, these materials do not affect tomographic imaging and are extremely lightweight.

By means of stops 28a, 28b, the fixing elements 27a, 27b are kept secured on the pistons 25a, 25b against slipping off of the pistons 25a, 25b and / or the half-ring 24 and / or the support 23.

The implementation of the construction by means of this shell 26 plays an important role, since a system is needed for the free fall, which is free from external influences such as friction and suction force. So now, if the pneumatics switched to suppression, the pneumatic ports 20a, 20b (hoses) are emptied and the piston 25a, 25b sucked down. This happens fast enough so that the shell 26 loses direct contact with these parts. This ensures that the shell 26 and the head resting thereon can fall freely. The cone embedded in the pistons 25a, 25b and the cones mounted on the shell 26 ensure that the shell 26 is centered at the bottom after each fall and thus always at the same position. Since the head must not move during the impact, it rests on a vacuum pad (standard MR accessory, Siemens Medical Solutions). This is filled with small Styrofoam hedgehogs and can be evacuated at a vacuum port of the scanner. As a result, the styrofoam balls are contracted, so that the cushion forms a precisely fitting connection between the head and the wider shell 26. Thus, it provides the necessary stability of the head.

In order to limit the stroke of the shell 26 upwards 23 stops 28a, 28b as shown in FIG. 10 are laterally attached to the half-ring 24 and at the head end of the support. The two

Stops 28a, 28b on the half ring 24 are mounted in angled form and protrude there right and left on the shell 26. An attached nylon screw 29a, 29b is screwed from above against the shell 26 and thus limits the stroke to an adjustable height. The stop, which is mounted on the support, is also angular. The stroke is limited here by different, festschraubbare pieces of different thickness.

With the exception of the shell 26, all components of the device 22 presented above are made of polyoxymethylene (POM). This fulfills all requirements placed on the device 22, in particular that it can be used without interference in the MRI 1.

Fig. 10 shows in detail an aramid reinforced plastic shell. The aramid honeycomb (Kevlar® honeycomb) and a laminate of Kevlar® fabric and epoxy resin form an extremely lightweight but stable, mangetresonan-suitable construct. On this, the head is fixed with a vacuum pad, so that unwanted movements can be minimized and the head can be raised and lowered.

The optical monitoring will be described in detail below. In order to monitor the position of the shell in time, the lifting and lowering device 22 has an optical monitoring. The light from three LEDs 30a, 30b, 30c is over

Optical fiber 31a, 31b, 31c to the lifting and lowering device 22 shown in FIG. 5 passed. In each case a light guide goes to the stops on the half-ring 24. There, they are plugged into a holder whose output is connected to a Plexiglas wedge. This expands the light signal so that a larger signal area in the stroke direction is achieved. At a distance of 2 mm there is another wedge that recaptures the light. On the shell 26, however, a shutter is mounted, which is mounted so that it protrudes exactly between the two wedges. Depending on the position of the shell 26 is dimmed by different amounts of light. For reasons of space, only two light guides are guided past one another on the third stop. Depending on the position of each other, more or less light is transmitted. The light collected in the wedges or in the light guide is returned to the. Directed control room, where the signal strength is made visible by connected to an oscilloscope 32 photodiodes 33a, 33b, 33c. Thus, the position of the tray 26 can be monitored at each of the three locations.

The light-emitting diodes 30a to 30c are operated via a frequency generator 34 (Voltcraft FG-506) at a frequency of approximately 30 kHz. Thus, if necessary, by a Oscilloscope 32 upstream bandpass unwanted frequencies of other light sources can be filtered out.

This position monitoring allows a time adjustment of the fall process to a recording sequence, which is explained in the following section. The electronics will be described in detail below.

The previously explained sequences can be repeated as often as desired in a time-adjustable distance TR. The timely precise control of the switching valve for coordinating the raising and lowering operation is synchronized with the HF pulses of the tomograph via the electronics presented here. The RF pulses are received as shown in FIG. 5 via an RF antenna 35, which is mounted in the MRT room 17, and then in an amplifier (EG & G ORTEC Model AN302 / NL) and converted into a control pulse. Since the falling process of the shell is to be completed in a variant before the 90 ° pulse of the tomograph, a delay of any length can be set via a digital delay generator (BNC Model 7020) so that shell 26 and head K arrive shortly before the next 9th ° -puis hit down. The delayed control pulse is applied to an electronic relay which opens the switching valve 14. The RF pulses will also be made visible on the oscilloscope 32. All these elements / components are part of the "logic" 36, unless they are specifically or explicitly shown in Fig. 5. The logic 36 is part of the electrical components 42nd

The following are safety considerations. The MRI examination is harmless to the human body. The magnetic fields acting on the organism are harmless. Since the case takes place perpendicular to the static magnetic field and the gradients are switched only after the free fall, there can be no induction currents in the body.

The occurring loads due to the case are harmless for the head K. It is assumed that the head K comes to rest within a braking distance of 0.5 mm, resulting in a maximum of six times the acceleration of gravity for 25 ms, which acts on the head K. This also occurs in everyday life and represents no problem for the human body due to its extremely short duration. Should the subject still feel unwell, he can press an alarm button that belongs to an MRI by default and alerts the staff in the control room.

In addition, the subject has direct access to a safety valve 37 in the pneumatics.

By pulling out a plug in the Y-splitter, the subject can at any time prevent the supply of air to the lifting and lowering device 22. The built-in stops 28a, 28b are also designed so that they withstand the maximum, prevailing in the pneumatic circuit pressure and thus limit the maximum lifting height.

The plastics used pose no danger. The light-emitting diodes (LEDs) 30a, 30b, 30c installed for optical monitoring have only a low power and are thus absolutely harmless, moreover they are located outside the field of vision of the subject.

Damage to the subjects is therefore excluded, so that the presented method could safely be used for early diagnosis.

The phase standard will be described below. Since the phase position is consistent only within one image, two images can not be compared with each other from the outset. So you can not say which phase belongs to which movement. In order to be able to compare images directly with one another, one needs a point that has demonstrably not moved during the sequence in order to be able to normalize to it.

In the context of the present invention, a so-called phase standard has been produced for this purpose, whose construction and construction will be briefly explained below.

In order to have such a phase zero point in each layer to be examined, a PVC pipe 38a, 38b of about (about) 15 cm in length and 1.5 mm in diameter as shown in figure 8.3 is used, which is fastened longitudinally next to the head. In order to bind the signal generator water so that no flows occur within the tube, two approaches were followed.

The first involves the use of a hydrogel of water and agar, which is also known as a gelling agent. The necessary cooking process is known from the prior art.

In the second approach, the tube was filled with glass wool or (or) cotton wool to prevent internal water movement.

In order to close the tubes 38a, 38b, fitting plugs were provided, which are provided with a retractable screw. This allows the pipes to be filled to the brim without air inclusions. To mount the tube in the head coil 39, a holder 40 a, 40 b was built, which can be mounted from the inside to the coil 39. This is a U-shaped POM piece. On one side, the piece was designed so that the tube 38a, 38b can be pinched there. On the other side with the U-shaped opening are several holes in which a threaded rod pulls this part of the U-piece together and thus clamps on the Kopispule (Fig. 8.3). Thus, the position of the tube is variable and can be clamped as close to the head.

Fig. 8.3 shows in detail clamped phase normal A, B in the head coil 39. PVC pipes 38a, 38b with phase standards are clamped in a U-shaped holder 40a, 40b. This can be clamped to the coil 39 and placed in any positions close to the head. In the measurements, the head K is approximately at the position where the inserted bottle is located.

The measurements and the results are shown below. For this purpose measurements are presented, which were achieved with the introduced method. These give a qualitative insight into the possibilities for generating a new contrast by the method according to the invention and the system according to the invention.

Subsequently, the novel contrast is first displayed. The simplest classification of the contrast possible with MR rheology is shown in a comparison of an image with a preceding movement and a picture without movement.

A phase image without movement is shown in Fig. 9.1. The noise outside the head should not be considered further. As can be seen, the phase angle is not quite homogeneous due to the uneven field within the head. The influence of this field inhomogeneity on the phase image with motion can be removed by subtracting the phase image without movement from that with motion. The editing of phase images is possible with a self-written program (author Marcus Radicke).

Such a processed differential image can be seen in Fig. 9.2. In addition to the creation of the difference image of the two images (with and without movement), the phase angle was also rotated in such a way that there is no direct transition from white to black in the image. These occur because phase angles greater than 359 ° start again at 0 ° and receive a corresponding gray value. The image with motion was created at a fall height of one millimeter on a male subject aged 27 years with a motion sensitive EPI sequence. The sequence parameters are: TR: 2500 ms; TE: 150 ms; b value: 250; Gradient length: 20 ms; Time between first and second gradient: 60 ms, voxel size 2x2x5 mm.

Fig. 9.1 thus shows in detail a phase image without motion. Without movement there is almost no contrast. The not quite homogeneous gray gradient is due to small magnetic field inhomogeneities according to previous explanations. Fig. 9.2 thus shows in detail a phase image with motion. The phase image reduced by the inhomogeneous course clearly shows different behavior of inner and outer tissue structures. The drawn yellow line 46 indicates the area investigated below.

The comparison of the two FIGS. 9.1 and 9.2, which were taken approximately at half the frontal height, shows qualitatively distinct differences. In FIG. 9.2 (phase image with movement), structures are distinguished which can not be seen in FIG. 9.1 (phase image without movement). It can be clearly seen the separation of the two halves of the brain. In addition, it can be seen that the tissue inside a half behaves differently than tissue near the skull bone. To further clarify this, a graph has been created which represents the gray levels on the horizontally drawn line 46 (Figure 9.3). With the help of a program (Image J, Version 1.46r) using the "Plot Profile" function, the gray values along the line were read out and plotted against the pixel. Large values reflect dark gray values, small values bright. The two valleys left and right have a large difference to the edges and the center. This is a particularly good illustration of the different behavior of inner brain tissue to outer tissue. The finer structures will be discussed below.

Fig. 9.3 thus shows in detail a gray value representation of a section in the x-direction. It can be clearly seen, according to previous statements, the separation of the two halves of the brain and the differentiated behavior of the inner areas. The gross separation between inside and outside are superimposed on more information.

The comparison with a structure recording will be described below.

Each measurement in a layer also includes a structure recording or a so-called amplitude image, as shown in FIG. 9.4. In this, the internal structures of the human brain can be clearly recognized. A previously described, processed phase image, from the same layer as the amplitude image, can be seen in Fig. 9.5. It shows a spatially resolved representation of each examined view.

This is a recording of a 27-year-old probandi!) With the following sequence parameters: TR: 2500 ms; TE: 150 ms; b value: 200; Gradient length: 20 ms; Time between first and second gradient: 40 ms, voxe size: 2x2x5 mm. Again, the separation of the two halves of the brain and the different behavior of structures inside and outside can be seen.

Fig. 9.4 thus shows in detail an amplitude image of a selected layer. Left-up in Fig. 9.4 a phase normal B can be seen. The yellow line 47 shows the area that is compared with the phase image. Thus, Fig. 9.5 shows in detail a phase image with motion associated with the layer of Fig. 9.4. Here, too, the phase standard B can be seen left-up. The yellow line 48 shows the area that is compared with the amplitude image.

A close comparison of both Figs. 9.4 and 9.5 shows that the method is capable of examining finer structures.

FIG. 9.6 shows the gray values of the vertical lines 47, 48 from FIGS. 9.4 and 9.5. The line 47, 48 lies over the same pixels and runs from top to bottom.

The course of the gray values is compared below. It is not important to find a synchronous behavior of both lines 47, 48, but to determine whether a change in the amplitude image can also be found in the phase image. The consideration of the two lines 47, 48 in Fig. 9.6 suggests a correlation between changes in the phase image and changes in the amplitude image.

Fig. 9.6 thus shows in detail the comparison of the gray-level course of the amplitude image and phase image along a vertical line 47, 48. The gray values of the amplitude image Ap are shown below, the phase image P above. The exact value plays no role in the comparison. Changes in the phase history seem to change in the

Amplitude curve to correlate.

The measurements of the phase standard are described below.

The phase normal, as described here, is the result of several experiments and measurements and was pursued by two different approaches.

Initially used, higher concentrations of agar in water resulted in a strong distortion. This is shown in Fig. 9.7.

In the middle is a bottle filled with a signaling fluid, which is used for sample measurements. In the figures, above and below reflections of these can be seen, which are not relevant here. Both tubes contain a hydrogel with an agar concentration of 7.5 g agar / 1 l water (7.5 g / l). The round shape of the tubes 38a, 38b is very distorted to recognize. Not to be seen in FIG. 9.7 are two more phase standards filled with glass wool (highly compressed), water and copper sulphate. These are located further down the side of the bottle. The positioning of the hydrogel-filled tubes 38a, 38b adjacent the bottle (Figure 9.8) shows that there are no more distortions there. This thus seems to be dependent on the position in the head coil 39.

In Fig. 9.9 four phase normal A, B, C, D can be seen. These are two hydrogel-filled tubes 38a, 38b, at a concentration of 5 g / l, which were positioned immediately adjacent to the bottle. On the other hand, the tube (D) on the top left is covered with a little glass wool and pure water, the tube top right (C) with little cotton wool and pure water. All four give a clear signal and have no flow inside. A slight distortion, however, can be found in both upper tubes (C, D).

The phase normal B with the low agar concentration of 5 g / l can also be seen in FIGS. 9.4 and 9.5. In this case, although they are located further out, they have a much smaller distortion, in contrast to those with a concentration of 7.5 g / 1.

Fig. 9.7 thus shows in detail the representation of distorted phase normals C, D. The phase normals C, D are filled with agar and water hydrogel with an agar concentration of 7.5 g / l according to previous embodiments. They show strong distortions. Phase normals filled with water, copper sulphate, and large amounts of glass wool are immediately adjacent to the bottle but are not represented by the EPI sequence. In the middle is the bottle for use in test recordings.

FIG. 9.8 thus shows a detail of undistorted phase normal A, B in detail according to the preceding embodiments. The same phase standards were used as in FIG. 9.7. In the position next to the bottle they are not distorted.

Fig. 9.9 thus shows in detail in accordance with previous embodiments, a representation of four phase standards A, B, C, D. The tube top-left (D) is filled with water and a small amount of glass wool, the top-right (C) with Water and a small amount of cotton wool. The two tubes (A, B) next to the bottle are filled with hydrogel of agar and water at a concentration of 5 g / l. In the middle is the bottle used during test recordings.

The novel contrast is described in detail below.

The method of MR-rheology is able to show different elastic properties in the brain G, as the above measurements make clear. The generated phase images and in particular their gray value representations show the possibilities of Rheology on. The different behavior of tissue inside a hemisphere suggests different viscoelastic properties of this region. A direct structural comparison of an amplitude image with the associated phase image shows that even small, internal structures can be examined using the method of MR rheology. In order to be able to make quantitative statements about the viscoelastic properties of these structures, it is first necessary to interpret the gray values in order to read them

To close movement speed or the displacement of the tissue. Furthermore, it has to be considered which rheological models can best be assumed for the viscoelastic properties. The combination of a spring, together with a damper is not enough. For a more detailed description, a three-dimensional view of this problem must be made, so that much more complex models are needed.

It has not been possible to demonstrate according to the preceding statements that the course of the phase angles depends on many parameters of the measurements. Therefore, for quantitative statements it must also be considered which TR and Tj times are meaningful. The strength of the motion-sensitive gradients and the distance also play an important role. During measurements it could be determined that some combinations of the setting cause a wobble of the couch. This has a negative impact on imaging. Also, the fall height affects it, as a case of greater height inevitably pulls a stronger movement of the lounger by itself. In addition, the height of the fall also changes the movement of the brain G itself. The higher this is, the further the tissue will deflect. This also raises the question as to when exactly the motion-sensitive gradients should be switched, on the one hand to absorb the movement as early as possible, but on the other hand enough time to pass, so that the shell and the hard skull bones no longer move. With all these parameters, the values used to create the phase images in the previous chapter give good results. Their variation and exact behavior must be further investigated.

Below further information on the phase standard

As can be seen in all hydrogel tubes with their signal-generating content, the phase angle is homogeneous, so that movements inside are successfully prevented. The different measurements from the hydrogel tubes also showed that the distortion that occurs depends on the concentration of the agar. At high concentrations it is stronger, probably due to chemical shift is caused. But since the distortion is also in fillings with pure water and cotton wool or glass wool comes about, albeit much lower, this is not the only reason. It was found that it is also dependent on the position in the opfspuie. Field inhomogeneities appear to be larger in areas farther from the center of the coil, thus providing a distorted appearance. In addition, it is possible that the 4-channel coil has problems in the reconstruction of the outdoor areas.

The use of cotton wool or glass wool to prevent the flow was also a possibility for the phase normal. The initially used admixture of copper sulfate actually served to increase the signal strength. An excessively high concentration of copper sulphate and the low level of signaling water in tubes filled with highly compressed glass wool led to the opposite effect. The signals were very weak and did not exist, depending on the sequence used (EPI). This is attributable to the copper sulfate, which at the concentration which was still too high, greatly reduced the Ti time, so that in the large number of echoes produced in the EPI sequence, not enough signal was available in the later echoes. However, the later experiments with pure water and a small amount of glass wool or cotton wool also produced a usable phase standard, as shown by the homogeneous phase angle in the phase standards. However, in contrast to the use of agar, it can never be completely ensured that currents are completely suppressed. From all measurements, the use of agar and water with a concentration of 5 g / 1 turns out to make the most sense, as here currents are reliably prevented, the risk of air bubbles is relatively low and there is only a very small distortion.

Previously, the method of R-rheology was introduced and the necessary structure in detail documented technically.

The limitations of other methods to study viscoelastic properties in the brain motivate a method in which an internal stimulus takes place. The proposed construction allows a free fall of the head K and shell 26 by their separation from the remaining components. After the fall, the use of aa midvanced plastic, the chosen shape of the shell, the centering cones fixed to it in the outer areas and the use of a vacuum pad ensure that the head is always in the same place after each fall. The fall process can therefore be reproduced as often as desired. The built-in, optical monitoring allows accurate position monitoring, so that over the used Electro-pneumatics of the lifting and lowering controlled and repeated as often as you like. The temporally synchronized, movement-sensitive measurements are able to visualize the movement of the brain in a phase image. With a fall height of one millimeter, the subjects did not experience any discomfort. On the other hand, the phase images produced show a clear separation of the two halves of the brain and a different behavior from the brain regions further inwards and those further out. A comparison between an amplitude image and the associated phase image makes it clear that changes in the phase image can be assigned to changes in the amplitude image. But this also makes it obvious that more complex, theological models have to be used for a precise description. The prepared and tested phase standard can be used for further evaluations. It offers a clue to the phasing of several images can be normalized.

In further measurements, measurements with different parameters and different layers can be compared with each other via the phase standard. In addition, the investigation of the exact movement of the brain from the time of impact until the re-adjustment of the balance of power inside is possible. It is also important to further examine the effects of the parameters to be set and to check whether influences such as measurements at different times of the day, the amount of liquid added before the measurements or differences in the sex and age of the subjects play a role. These questions will be dealt with in a planned study soon. Also, further improvements in the design are planned.

The method thus offers a promising future possibility to study the viscoelastic properties of the human brain in vivo.

Claims

claims:

1. A method for visually perceptible, pictorial representation of elastic, in particular viskoclastischer, properties of soft biological matter, in particular a biological system, preferably the soft Gehimmasse a human brain ((!)),

characterized,

that the soft biological matter is moved with a defined motion known and / or detected at all times in all six degrees of freedom to generate acceleration using a magnetic resonance imaging technique, and the movement of the soft biological matter is determined by at least one of the defined magnetic resonance tomography methods or detected slice / plane of the biological system is detected and an image acquisition of the magnetic resonance tomography Veriahrens using a motion-sensitive sequence and the movement of the soft biological matter is synchronized with the motion-sensitive sequence or recording frequency.

2. The method according to claim 1, characterized in that with the magnetic resonance imaging method, the spatial distribution of the elastic, in particular viscoelastic properties of the soft biological matter in the biological

System is evaluated and mapped.

3. The method according to claim 1 or claim 2, characterized in that the biological system is a human body.

4. The method according to any one of the preceding claims, characterized in that a head (K) is moved as part of the biological system with a therein befmdlichen brain (G) with acceleration of the brain rnasse as the soft biological matter of the biological system.

5. The method according to any one of the preceding claims, characterized in that the soft biological matter, in particular the soft brain mass, is moved in vivo and visualized.

6. The method according to any one of the preceding claims, characterized in that the acceleration of the soft biological matter, in particular the soft brain mass, takes place under the influence of gravity of the earth.

7. The method according to any one of the preceding claims, characterized in that the soft biological matter, in particular the soft Gehimmasse, fixed dimensionally stable during the measurement or the outer shape is known at any time of the measurement.

8. The method according to any one of the preceding claims, characterized in that the movement-sensitive sequence at least one 90 ° pulse (8a) and at least one 180 ° pulse (8b) and at least one field gradient (9a, 9b), preferably two field gradients (9a , 9b).

9. The method according to any one of the preceding claims, characterized in that the field gradient (9a, 9b) is switched in the direction of movement of the soft biological matter.

10. The method according to any one of the preceding claims, characterized in that the soft biological matter, in particular the brain mass, and at least a part of the biological system, in particular of the brain mass having head (16) before generating the acceleration by a distance (d) a rest position is raised in the direction of gravity in a movement position and held there.

1 1. A method according to claim 10, characterized in that the head (K) by a distance (d) between 0.5 mm and 4 mm, preferably between 1 mm and 3 mm, is raised.

12. The method according to spoke 10 or spoke 1 1, characterized in that the soft biological matter in the free fall of gravity is moved from the movement position to the rest position, the brain (G) delayed in time relative to the head (K) this rest position reached.

13. The method according to claim 12, characterized in that the time of lowering of the soft Gehimmasse having head (K) is selected so that the head (K) during or after the. first field gradient (9a) is lowered back into the rest position, wherein the head (K) and the brain mass after lowering with the second field gradient (9b) are applied.

14. The method according to spoke 12, characterized in that the time of lowering of the soft brain mass having head (K) is selected so that the head (K) before the first field gradient (8a) is lowered back to the rest position, wherein the Head (K) and the soft brain mass after lowering with the first and second field gradient (8a, 8b) are applied.

15. The method according to any one of the preceding claims, characterized in that in addition to the soft brain mass of a human brain (G) and the head (K) with a defined, at any time in all six degrees of freedom known and / or detected movement to generate an acceleration is moved with the simultaneous use of an imaging Kemspintomographieverfahrens.

16. A system for the visually perceptible, pictorial representation of elastic, in particular viscoelastic, properties of soft biological matter, in particular a biological system, preferably the soft brain mass of a human brain (G) comprising a Magentresonanz.tomographen (MRT, 19) with an MRI coil (39) and a device carrying the soft biological matter and disposable in the MRI coil (39),

characterized,

in that the device is designed as a lifting and lowering device (22) on which the soft biological matter can be fixed in a positionally stable manner and positionably positionable in the MRT coil (39), wherein the lifting and lowering device (22) has a positioning element which is stationary in the coordinate system of the spatial encoding of the manganese resonance tomograph (MRT, 19), and a movement element, which is capable of being able to follow gravity in the free fall, is movably arranged on the positioning element and on which the soft biological matter can be arranged ,

17. System according to spoke 16, characterized in that the positioning element has at least one support (23) and at least one half-ring (24) and that the moving element has at least one shell (26), wherein on the shell (26) the soft biological matter is dimensionally stable fixable.

A system according to claim 17, characterized in that the shell (26) is movable in the system with the half-ring (24) at its center, the shell (26) being movably mounted on the half-ring (24).

19. System according to one of the preceding claims, characterized in that at least in the direction of movement of the movement element at least one field gradient (9a, 9b), preferably two field gradients (9a, 9b), is connected.

20. System according to any one of the preceding claims, characterized in that the lifting and lowering device (22) has a pneumatic (40), by means of which the moving element, preferably the shell (26), can be raised and lowered.

21. System according to spoke 20, characterized in that the moving element, preferably the shell (26), between 0.5 mm and 4 mm, preferably between 1 mm and 3 mm, can be raised and lowered.

22. System according to any one of the preceding claims, characterized in that the support (23) and the half-ring (24) consist of Polyoxymefhylen.

23. System according to any one of the preceding claims, characterized in that the shell (26) has at least one aramid.

24. System according to any one of the preceding claims, characterized in that the system comprises a movement measuring device, in particular an optical monitoring (41), by means of which the movement of the lifting and lowering device (22) is measurable.

25. System according to claim 24, characterized in that the optical monitoring device (41) has at least one light-emitting diode, preferably three light-emitting diodes (30a, 30b, 30c), at least one light guide, preferably three light guides (31a, 31b, 31c), and at least one Light detector, preferably at least one photodiode, in particular three photodiodes (33a, 33b, 33c), comprising.

26. System according to one of the preceding claims, characterized in that the system comprises a measuring unit for measuring the properties of soft biological

Matter, in particular the soft brain mass of the brain (G), so that by means of the movement of soft biological matter in the device the

Properties of soft biological matter in vivo are measurable and representable.

27. System according to one of the preceding claims, characterized in that the

System having at least one container, in particular at least one tube (38 a, 38 b), with a signal-generating content, preferably with a hydrogen content, in particular hydrogel, comprising water and agar, or preferably with glass wool or wool, wherein means of the container and the filling of which is the phase Normai for the displayed layer of soft biological matter can be determined.

28. System according to claim 27, characterized in that the agar has an agar concentration of 4 g of agar / 1 liter of water to 6 g of agar / 1 liter of water, preferably 5 g of agar / 1 liter of water.

29. System according to one of the preceding claims, characterized in that the system in power connection and / or operative connection with a negative pressure and / or pressure-providing pneumatic (40) and / or movement measuring device, in particular optical elements (30 a, 30 b, 30 c , 31 a, 31 b, 31 c, 32, 33, 34, 41), and / or electrical components (42) is and / or can be brought.

30. Use of a system according to one of claims 16 to 29 for carrying out the method according to one of claims 1 to 15.