WO1997038329A1

WO1997038329A1 - Optical imaging system

Info

Publication number: WO1997038329A1
Application number: PCT/US1997/005669
Authority: WO
Inventors: George P. T. WILENIUS; David Malcolm
Original assignee: Xitec, Inc.
Priority date: 1996-04-10
Filing date: 1997-04-04
Publication date: 1997-10-16

Abstract

There is provided an optical imaging system (10) for generating imaging information from incoming radiation that has passed through a particular object. The optical imaging system (10) includes scintillating screen (12) for converting the incoming radiation to visible light, an image intensifier (14) for increasing the intensity of the visible light and a lens and taper combination (20, 30) for coupling the scintillating screen (12) to the image intensifier (14). The lens and taper combination (20, 30) has a fiber optic taper (30) for forming a viewable image based on the visible light and a lens (20) for directing the visible light to the fiber optic taper (30). Further, the optical imaging system (10) includes an output system for presenting the viewable imaging for clinical analysis.

Description

OPTICAL IMAGING SYSTEM

BACKGROUND OF THE INVENTION

I. Field of the Invention The present invention relates generally to optical imaging systems for converting radiation, such as x-rays or gamma-rays, to visible light. More particularly, the present invention relates to a high quality diagnostic fluoroscopic imaging system having high photocollection efficiency with a low level of radiation exposure to the subject. Optical imaging systems for medical diagnoses typically use radiation technologies, such as x-rays and gamma-rays. Such optical imaging systems are often used for extremity imaging in orthopedic, podiatry and sports medicine. For example, a typical optical imaging system may transmit x-rays through a body part, such as a patient's hand, and generate a video or printed image of the body part for analysis. One concern with radiation-based optical imaging systems is the possible damage to the body part due to the radiation's high intensity flux. Existing optical imaging systems require large dosages of high intensity flux to achieve images that are acceptable for analysis. However, such large dosages of radiation may cause problems to the health of the patient, as well as the environment. Moreover, there is a need for an imaging system that is efficient, for example light in weight, less bulky and, thus, conducive to a portable imaging system.

One optical imaging system is a fluoroscopic x-ray imaging system that has microchannel plate image intensifiers. Such an x-ray imaging system employs a phosphor screen for converting x-rays to visible light, a light intensifier for amplifying the visible light and an optical coupling to direct the visible light from the phosphor screen to the light intensifier. The optical coupling affects the intensity of the x-ray beam required to generate a quality image. Accordingly, a patient would be exposed to less x-ray radiation in an x-ray imaging system that has an efficient optical coupling. Thus, it is clearly desirable for an optical imaging system to have an efficient optical coupling, and thus improved photon collection efficiency.

Modern conventional medical image intensifiers use electron optics and, thus, provide excellent radiation performance. The present invention provides such excellent radiation performance in a smaller, less expensive and lower weight package.

π. Description of the Prior Art

The most difficult aspects of any imaging system is the collection of the visible light generated at the phosphor screen and coupling the phosphor screen to the image intensifier. For existing imaging systems, either a lens or a group of fiber optics are used to couple the phosphor screen to the image intensifier. For example, U.S. Patent No. 4,142,101 to L.I. Yin, which issued on February 27, 1979, titled LOW INTENSITY X-RAY AND GAMMA-RAY IMAGING DEVICE, provides an optical

imaging device that operates at low doses of radiation. The optical imaging device includes a phosphor screen for converting radiation-to-visible light and a visible light intensifier coupled to the phosphor screen by a fiber optic plate. The visible light intensifier includes a photocathode for converting the visible light to electrons, a micro¬ channel plate amplifier for amplifying the electrons and an output phosphor for converting the amplified electrons back to visible light. This patent uses a fiber optic plate to couple the phosphor screen to the visible light intensifier, and provides no recognition of the need for efficient optical coupling.

Lenses gather a very small fraction of the light generated at the phosphor screen due to the physical limitations imposed by the lens aperture and the lens-to-object distance necessary for image formation. Photometric calculations show that approximately 0.75% of the light photons generated at the phosphor screen will be collected by a f/1 lens and focused on an image intensifier with a 25 mm input diameter. With an 18 mm intensifier, the corresponding percentage would fall to 0.41%. Fiber optics have a greater photon collection efficiency than lenses. However, only the core glass of the fiber optics conducts light while light falling on the sheath of the fiber optics and the extra-mural absorber are lost. Calculations based on formulae presented by Walter E. Sigmund in Fiber Optic Tapers in Electronic Imaging. (Electronic Imaging West, Pasadena, CA; April, 1989) indicate that 0.78% of the photons generated will be delivered to a 25 mm intensifier by a tapered fiber optic bundle, but that this would fall to 0.40% with an 18 mm intensifier. The overall collection efficiency of a taper is not better than an f/1 lens.

Accordingly, existing imaging systems, including the optical system described in the above cited U.S. Patent No. 4,142,101, do not provide an efficient optical coupling. In addition, improvements in photocollection efficiency should also result in

improvements in image brightness. While the photocollection efficiency described above is the true measure of optical system efficiency, the image intensifier reacts to input image brightness and a brightness gain results from the fact that the image is minified. For the above systems with either 25 or 18 mm intensifiers, an f/1.0 lens will produce an image luminance approximately equal to 25% of the object brightness and a fiber optic taper will produce an image luminance of approximately 75%.

Generally, lenses and fiber optics have the following characteristics. When the object size is very large, the use of fiber optics is not practical for reasons of cost and practicality. A large fiber optic, such as one having a 215 mm input diameter, has not yet been manufactured and, if undertaken, would be cost prohibitive. Also, when the taper ratio, i.e. input diameter vs. outer diameter, is large, the photocollection efficiency of the fiber optic is no better than a conventional lens. In addition, fiber optics are only effective at transmitting light when the angle of incidence of the light is less than the numerical aperture of the fiber.

The present invention is an optical imaging system that includes a combination of a lens and fiber optics to obtain a significant improvement in optical or photon collection efficiency over existing systems which have either a simple lens or a group of fiber optics. The optical imaging system components are a phosphor screen, an image intensifier, and means for coupling the phosphor screen to the image intensifier. The phosphor screen converts x-ray radiation to visible light, and the image intensifier may operate in a magnetic field environment. In addition, the optical imaging system may include an output device to display or print the information converted by the phosphor screen and amplified by the image intensifier.

SUMMARY OF THE INVENTION Against the foregoing background, it is a primary object of the present invention to provide an optical imaging system that includes a converter for converting radiation to visible light and means for efficiently collecting the visible light and

directing it to an intensifier that has a high collection efficiency. It is another object of the present invention to provide such an optical imaging

system in which a combination of a lens and fiber optics is used to collect the visible

light and direct the visible light to an intensifier having a lens with a very low F number.

It is a further object of the present invention to provide such an optical imaging system that generates diagnostic quality images and uses intensifiers that are not susceptible to magnetic fields.

It is yet another object of the present invention to provide such an optical imaging system that is not bulky, lightweight, and relatively inexpensive.

It is a still further object of the present invention to provide such an optical imaging system that is portable.

It is a yet further object of the present invention to provide such an optical imaging system that includes a zoom feature for adjusting the position of the lens relative to the fiber optics.

It is still yet a further object of the present invention to provide such an optical

imaging system in a medical device for x-ray imaging of body parts.

To accomplish the foregoing objects and advantages, the present invention, in brief summary, is an optical imaging system for generating imaging information from incoming radiation that has passed through a particular object. The system comprises

means for converting the incoming radiation to visible light, an image intensifier for increasing the intensity of the visible light, and means for coupling the converting

means to the image intensifier. The coupling means includes a fiber optic taper for forming a viewable image based on the visible light and a lens for directing the visible

light to the fiber optic taper. In addition, the optical imaging system includes an output

system for presenting the viewable image for clinical analysis.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and still further the objects and advantages of the present

invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawings: Fig. 1 is a diagrammatic view representing first and second preferred embodiments of the present invention;

Fig. 2 is a diagrammatic view of transmitted light losses that may occur in the

fiber optic taper of Fig. 1; Fig. 3 is a graph of a test analysis of taper input size based on varying screen

sizes for a typical 50 mm lens design;

Fig. 4 is a graph of a test analysis of a hypothetical 75 mm lens that was scaled

from the 50 mm lens design of Fig. 3;

Fig. 5 is a diagrammatic view of illumination by an object of the lens of Fig. 1;

Fig. 6 is another diagrammatic view of illumination by an object of the lens of

Fig. 1;

Fig. 7 is a graph showing image luminance of the present invention of a 100 mm

object; and Fig. 8 is a graph showing image luminance of the present invention for a 150

mm object.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is an optical imaging system including a combination of a lens and fiber optics or fiber optic tapers to provide efficient photocollection or photon collection efficiency. Preferably, the optical imaging system is used in a fluoroscopic x- ray device for measuring extremities of the human body, such as a mini C-arm x-ray device. Although the preferred embodiments, described below, are directed to mini C-

arm x-ray devices, it is to be understood that the present invention has application to a

wide variety of optical imaging systems. For example, in addition to providing smaller

size and cost advantages for mini C-arm type devices, the present invention provides economic cost advantages for larger x-ray devices as well.

The photon collection efficiency of a lens having a fixed size and focal length is a function of the minification required of the lens. Accordingly, the greater the nullification, the less the photon collection efficiency. Also, fiber optic tapers are effective at transmitting light when the sine of the angle of incidence of the light is less than the numerical aperture of the fiber. Therefore, the fiber optic taper is used in

conjunction with a lens to reduce the amount of minification required and, hence, improve the photon collection efficiency of the lens. At the same time, the transmission

properties of the fiber optic are maintained by ensuring that the sine of the angle of the rays of light impinging on the fiber optic is at an angle less than or equal to the

numerical aperture of the fiber. Referring to the drawings and, in particular, to Fig. 1, there is provided an

optical imaging system of the preferred embodiment which is generally represented by reference numeral 10. A scintillating or phosphor screen 12 is positioned at one end of the system 10 and an image intensifier 14 is positioned at the other end. The optical imaging system 10 combines a lens 20 and a fiber optic taper 30 that together form a coupling means between the phosphor screen 12 and the image intensifier 14. The fiber

optic taper 30 has a conical type shape with a large diameter end 32 positioned adjacent

the lens 20, and a smaller diameter end 34. Accordingly, the components of the optical

imaging system, from left to right, are the phosphor screen 12, the lens 20, the fiber optic taper 30 and the image intensifier 14. In a preferred embodiment, the phosphor

screen 12 is made of gadoliniumoxy sulphide, terbium doped, more commonly referred to as a rare earth phosphor.

For operation of the optical image system 10, radiation from an energy source is transmitted through an object, such as a portion of a person's body, and received by the phosphor screen 12. The phosphor screen 12 is a conversion means for converting the radiation into visible light that is directed to the lens 20. The lens 20 forms an image of the object at the large end 32, which is shown as a viewed image at a small end 34 of the fiber optic taper. The visible light entering the lens 20 is refracted at a

first principal plane 22, and the visible light exiting the lens is, again, refracted at

second principal plane 24 For the present invention, the location of the second

principal plane 24 is positioned as far back as possible from the front vertex 26 of the

lens 20. Various dimensions of the present invention are given in Fig. 1. φ₀ represents the diameter of the phosphor screen 12, and u is the distance from the phosphor screen 12 to the first principal plane 22 of the lens 20. H is the distance from a front vertex 26 of the lens 20 to the first principal plane 22, H' is the distance from the front vertex to the second principal plane 24, v is the distance from the second principal plane 24 to

the large end 32 of the fiber optic taper 30, φ_t is the diameter of the large end 32, and φi is the diameter of the small end 34.

When the fiber optic taper 30 is interposed between the lens 20 and the image, then the minification required of the lens is substantially reduced. Also, the collection efficiency increases as the square of this reduction and the image brightness correspondingly improves. As the size of the image, for an object of fixed size, is increased, the lens is moved closer to the object and, hence, subtends a larger angle with respect to any point on the image. Thus, there is an increase in the photon collection efficiency. The degree of improvement obtained by this technique is limited when the sine of the angle of the most oblique ray entering the fiber optic taper 30 exceeds the numerical aperture of the fiber optic taper, the visible light will not be transmitted to the image intensifier 14. This is not a sharp cut-off, but is rather a dirnming of the image at its edges in which the center brightness is enhanced.

The focal length of the lens is dictated by the screen size. For the present invention, the focal length ranges from about 25 mm to about 125 mm and, preferably, the focal length is from about 50 mm to about 80 mm. As described below, the focal lengths for the first and second preferred embodiments are 50 mm and 58 mm, respectively. the focal length is from about 50 mm to about 80 mm. As described below, the focal lengths for the first and second preferred embodiments are 50 mm and 58 mm, respectively.

The first preferred embodiment of the present invention is a system design

having the following primary parameters that would provide both 100 and 150 mm field of views in a single intensifier assembly:

TABLE 1: 100/150 mm System

Screen Diameter (mm) 100 150

Taper Diameter (mm) 42 42

II Diameter (mm) 17.5 17.5

Lens - Focal Length (mm) 50 50

- f/number 1.2 1.2

Field of View (degrees) 47.7 47.0

Relative Brightness - Center 0.758 0.749

- 80% of radius 0.505 0.440

- Outer Edge 0.364 0.312

Object to Lens Distance (mm) 113 172

(inches) 4.45 6.77

Lens to Image Distance

(Includes taper and image intensifier) (mm) 58 51

(inches) 2.28 2.10

Overall Image Chain Length (mm) 290 342 f includes taper and image intensifier]

(inches) 1 1.42 13.46

The second preferred embodiment of the present invention is another system design having the following primary parameters that would provide 150 and 230 mm field of views in a single intensifier assembly:

TABLE 2: 150/230 mm System

Screen Diameter (mm) 150 230

Taper Diameter (mm) 44 44

II Diameter (mm) 17.5 17.5

Lens - Focal Length (mm) 58 58

- f/number 1.2 1.2

Field of View (degrees) 40.4 40.8

Relative Brightness - Center 0.722 0.745

- 80% of radius 0.464 0.430

- Outer Edge 0.349 0.319

Object to Lens Distance (mm) 204 309

(inches) 8.03 12.16

Lens to Image Distance (Includes taper and image intensifier) (mm) 55 49

(inches) 2.16 1.93

Overall Image Chain Length (mm) 383 483 [includes taper and image intensifier]

(inches) 15.08 19.02

In addition, the first and second preferred embodiments includes the following properties for the fiber optic taper 30:

TABLE 3: Propert ies for the Fiber Optic Taper

SPECIFICATION DESCRIPTION

Glass Type SFO 32A

Large O.D. Fiber Size 25 μm or less

Minimum Clear 50 mm to 25 mm Apertures

Gross Distortion < 5%

Shear Distortion < 0.004

Magnification Tolerance 2.00 ± 0.11

O.D. Large End 53 mm + 0.0 mm - 0.13 mm

O.D. Small End 26.5 mm (ref.)

Length of Taper 43.5 mm ± 0.5 mm

Image Alignment 0.020 TIR maximum

Optical Finish 10 fringes or better - 20/10 scr/dig

Radioactive Material < 500 ppm Thorium Oxide

Numerical Aperture 1.0 at Small End

Chickenwire (CW) Width of continuous CW shall not exceed 2 fibers. CW greater than 2 fibers wide will be treated as a blemish (length/width).

ZONE 1 ZONE 2 ZONE 3

SIZE 25 MM (DIA.) 25-40 MM 40-50 MM

< 0.070 disregard disregard disregard

0.070-0.140 3 5 6

0.140-0.200 2 3 4

0.200-0.250 1 2 3

> 0.250 0 0 1

Blemishes SIZE ALLOWED

0.010" none

0.006"-0.010" 10

0.003"-0.006" 30

0.001 "-0.003" 40

Other All other specifications as per Schott FP87-1 standard taper specification.

In another embodiment that has been tested, the field of view was 215 mm with a 56 mm custom f/1.02 lens designed and built by Optics for Research Inc. The

embodiment included a 36 mm fiber optic taper and a 17.5 mm, proximity focused,

microchannel plate image intensifier. For the present invention, the F number ranges from about 1.0 to about 5.6.

More preferably, lenses having an F number from about 1.0 to about 1.2 are desired to maintain low levels of intensity and, thus, minimize the intensity of the x-ray beam. At this time, the lowest available F number with proper field of view is about 1.0. It is envisioned that a smaller F number is better, provided we get a field of view, however a smaller F number is not commercially available.

Referring to Fig. 2, additional losses may be incurred in the fiber optic taper 30, namely losses within the numerical aperture of the fiber and transmission and cladding fraction losses. The transmission loss of the core 36 of a typical fiber optic taper is only 2% per inch of length. The primary loss in any fused fiber optic results from the

light being only transmitted by the core 36. In other words, light is not transmitted by the cladding 38 or extra mural absorbers (EMA), such as black glass, incorporated into

the fiber optic taper 30. EMA captures light that escapes from the fibers because it is

outside of the numerical aperture and if not captured would reduce image contrast and

resolution. For the preferred embodiments, shown in the above table, not all of the light is

contained within the numerical aperture This condition depends on the final selection

of taper input size. The taper input size is as large as possible in order to have optimal

optical performance. For example, a 250 mm system with a 75 mm lens has an image brightness that is about 36% greater than that of a 150 mm system with a 50 mm lens. The taper input size is limited by undesirable effects created by vignetting in the lens and variation of luminance over the diameter of the image. Thus, as the size of the taper input is increased, the field of view of the lens is exceeded and the edges become dimmer.

Referring to Fig. 3, for the preferred embodiment, a test analysis was performed on a 50 mm lens made by Nikon for its 35 mm SLR cameras in which limits have been

apphed based on the above vignetting effects and luminance variations. The field of

view was limited to 46 degrees and the ratio of center to edge luminance was limited to 2: 1. Up to and including 100 mm screen sizes, the system was limited by the ratio of center-to-edge brightness; beyond that point, it was limited by field of view. Since the taper size varies only slightly between certain screen size ranges, such as from about

100 mm to about 150 mm, a zoom feature may also be incoφorated into the present invention. Referring to Fig. 4, the lenses of the present invention may be virtually any size by simply scaling an existing design, such as the above 50 mm lens shown in Fig. 3.

Fig. 4 shows the same analysis as above for the 50 mm lens in which a hypothetical 75 mm lens is scaled from the 50 mm lens design. In this case, the taper size is limited by

center-to-edge brightness considerations throughout the screen size range. Although

the taper size varies much more throughout the entire size range, the variation between

reasonable zoom increments, such as from about 100 mm to about 150 mm, is not large and is still reasonable to build dual image size systems. Thus, there is no fundamental limit to the screen size of the image intensifier of

the present invention, such as a 500 mm intensifier or larger, since all components

including the lens, fiber taper and microchannel plate intensifier, can be scaled to larger sizes. Although larger fiber optic tapers tend to be expensive, such costs generally become more reasonable in time with advances in technology and mass production. In addition, the cost of building a scaled image intensifier screen is much less than the cost

of building large conventional intensifiers in vacuum envelopes, particularly medical intensifiers.

In an alternative embodiment, not all light can be contained within the numerical

aperture but EMA would be needed and there would be brightness trailoff. Also, light

would escape between fibers resulting in a loss of contrast. Hence, the additional losses result from the fraction of the cladding 38 so that the estimated total transmittance of the fiber optic taper 30 will be at least 0.75.

Concerning the effects created by variation of luminance over the diameter of the image, the present system may include a filter for shaping the x-ray beam intensity across the diameter of the image to compensate for non-uniform gain across the image. The filter preferably has a cone-like shape in which the thickest portion is in the center

and the thinnest portion is at the edges. The filter is inserted into the x-ray beam to

counterbalance the above variation in image illuminance.

In addition, the present system may include a proximity focused microchannel

plate intensifier that has a uniform gain across its' diameter. Although not mandatory,

such proximity focused intensifier may be used in applications where the presence of

magnetic fields may distort the images. Accordingly, the photometry of the lens and taper combination has been numerically analyzed. Thus, it is necessary to begin with an understanding of the flux of light from a small source. Kingslake's reference, Optical System Design by Rudolf Kingslake (Academic Press, 1983) provides that the flux of light from a small source

is:

F = I ω (1)

where F is the flux, I is the intensity of the source and ω is the solid angle in which the

flux is measured.

Referring to Fig. 5, the lens 20 is illuminated by an object 16 at a distance of u - H from the front vertex 26 of the lens. Also, a small plane source of area Ao and

luminance B is in the plane of the object. For example, AQ corresponds to the area and

B corresponds to the luminance of the phosphor screen 12. The lens 20 is divided into a series of concentric rings 40 and each ring is, in turn, divided into small segments or

lens elements 42.

To determine the illuminance of the image at any point, it is necessary to

integrate the illuminance, due to source A₀ , for each lens element 42. The distance between the lens element 42 and the source A₀ is d.

In a three dimensional Cartesian coordinate system, the source A₀ can be

described as being located at i, yi, zi and the lens element 42 at x₂, y , z₂. The center of the object 16 and lens elements 42 are at:

Object Element Lens Element

Xι = R (2a) <5r _{fΩ l} δθ. (3a)

X, = (r + — ) cos(6> + — ) '

2 2 yι = o (2b) (3b)

X₂=(r + -)sin(ø + — ) ² 2 2

Z]=u-H (2c) Z₂=0 (3c)

The intensity of a plane source falls off at increasing angles of view, because of

Lambert's cosine law of intensity. The angle of view of the small element in the

object plane is the angle between the ray in question and a line peφendicular to the element. Space analytic geometry defines the angle between two lines as: a.a_j+b.b_j+c.c. cos(α) =

J[βf+bf ₊cf] [aϊ+b*+cπ W

where a_n:b_n:c_n are the direction of the line, defined as:

a_n = X2 - i (5a) b_n = y₂ - yi (5b)

where the subscript 1 refers to the intersection point, and the subscript 2 refers to the

other end of the lines.

When one line is peφendicular to the object plane, equation (4) becomes:

where α' denotes the angle to the midpoint of an element 42.

The intensity in the direction of the lens element 42 is: I(α') = AoB cos(α') (7)

Referring to Fig. 6, the solid angle ω can be determined by calculating the

angles between the lines that define how the finite lens element 42, at its' corners,

subtends the source, δ is associated with δr, δB' is associated with δθ at r and δB" is

associated with δθ at r + δr.

The finite element, that subtends the source, is approximately a trapezoid. The area of the trapezoid projected in the direction of the source is:

and the solid angle, ω, is:

(δβ'+δβ") ω = δa (9)

At the lens 20, the finite element is assumed to be a plane surface, and Lambert's

cosine law of illuminance applies, introducing another cosine term. The incremental

flux entering the lens 20 at each element 42 on the lens surface is:

- ∞5F = A _{A 0} nB cos 2 _r (α i ) δ.a^ (δ-¹β- —+δβ —" -) (10)

The total flux of visible light entering the lens 20 is:

Fo 0 = ∑ _--i'r^"=0" ∑ -i-⁽"θ=0^* δF • 1 1 -t

where ri is the radius of the lens aperture. The flux of light falling on the image is

equal to the flux of light entering the lens 20, except for transmittance losses in the lens, and the fiber optic taper 30. The illuminance of the image, relative to Lambert brightness, is:

where m is the image magnification and

Finally, the entrance angle of the light ray directed into the fiber optic is

considered. This is done in the same manner that the angle of view between the lens element 42 and the source A₀ was calculated. The location of the image at the fiber optic taper 30 is defined by: xι = - m R (15a) yι = 0 (15b) zι = - v (15c)

Equation (6) is used to calculate the entry angle, Y, in the fiber optic taper 30. For the

ray to pass through the taper 30, the following condition must be met:

The above equations are used to calculate the distribution of image brightness

for 100 and 150 mm screen sizes. For the preferred embodiment, a computer program was used to facilitate these calculations by numerically dividing the lens 20 into

31,400 finite elements. Using the computer program, the brightness of an object placed a far distance from the lens was calculated, a situation in which the simplifying

assumptions usually made are valid. Kingslake shows that for a lens with 100% light

transmission, the brightness of the image is:

E ₌ _ (18) πB AN¹

where N is the f/number of the lens. For an f/1.2 lens, the above equation provides an

image brightness result of 0.17361. In particular, the computer program calculated the centerline brightness of a large object placed 50 m from the lens, with an image

magnification of 0.001, to be 0.17365. Thus, the computer program provides highly

accurate results and support to the results presented. The above equation

approximately describes the image brightness that is expected from a lens only system.

As will be seen below, a typical system with a lens/taper combination will yield 4.3 times the image brightness of a lens only system and will equal the performance of a

taper only system, but at a much lower cost, and with large image sizes.

The above equations have calculated the distribution of image brightness for

100 and 150 mm screen sizes. The results of the calculations give a center image

brightness of about 15% greater than predicted by simple lens theory and an edge

brightness about 50% less.

Figs. 7 and 8 show the results of the above described calculations. The image

brightness is maintained at greater than 60% of its' central value over 80% of the

image with a 42 mm taper. This results in a 45% improvement in central image

brightness. Larger fiber optic tapers might be used, but then the field of view of the lens will be exceeded substantially and vignetting problems will occur. A small fringe arising from the increase in taper size, is that the length of the assembly is reduced by just over 1 inch.

Optical bench measurements of relative brightness at the center of the image gave results approximately 30% less than predicted by the finite element analysis. This difference arises from the intrinsic errors involved in the finite element process or from the difficulties in making the measurement with currently available equipment. However, whether based on measurement or theory, it is clear that increased taper size leads to improve optical performance and, hence, lower x-ray to light conversion factors. Thus, the present fluoroscopic x-ray imaging system, unlike any known system, found that the principal plane location should be as far back in the lens as possible. It achieves a much higher collection efficiency using light photon techniques in combination with fiber optic taper 30. Furthermore, the imaging system avoids magnetic shielding and its deleterious effects. It also results in a less bulky system that

is, therefore, less in weight and less in cost. The less bulky, less in weight imaging system is, therefore, readily incoφorated into a portable device.

The invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined

in the appended claims.

Claims

Wherefore, what is claimed is:

1. An optical imaging system for generating imaging information from incoming radiation that has passed through a particular object, said optical imaging

system comprising: means for converting the incoming radiation to visible light;

an image intensifier for intensifying the visible light, means for coupling said converting means to said image intensifier, said coupling means including a fiber optic taper for forming a viewable image based on the visible light and a lens for directing the visible light to said fiber optic taper; and an output system for presenting said viewable image for clinical analysis.

2. The optical imaging system of claim 1, wherein said fiber optic taper is

physically and optically connected to said image intensifier.

3. The optical imaging system of claim 1, wherein said lens is positioned

between said converting means and said image intensifier.

4. The optical imaging system of claim 1, wherein said lens includes a principal image plane and a principal object plane, and wherein said principal image plane is in front of said principal object plane. 5. The optical imaging system of claim 1, wherein said converting means is a scintillating screen.

6. The optical imaging system of claim 5, wherein said scintillating screen comprises a rare earth phosphor.

7. The optical imaging system of claim 1, wherein said converting means has a screen diameter that is about 100 mm to about 215 mm.

8. The optical imaging system of claim 7, wherein said converting means has a screen diameter that is about 100 mm.

9. The optical imaging system of claim 7, wherein said converting means has a screen diameter that is about 150 mm.

10. The optical imaging system of claim 7, wherein said converting means is

about 215 mm.

11. The optical imaging system of claim 1 , wherein said fiber optic taper has a large end and a small end, and wherein said lens forms an image of the particular object at the large end and a viewed image at the small end. 12. The optical imaging system of claim 11, wherein the large end of said fiber optic taper is about 42 mm.

13. The optical imaging system of claim 11 , wherein the small end of said fiber optic taper is about 17.5 mm.

14. The optical imaging system of claim 1, wherein a focal length of said lens is from about 25 mm to about 125 mm.

15. The optical imaging system of claim 14, wherein a focal length of said lens is from about 50 mm to about 80 mm.

16. The optical imaging system of claim 15, wherein the focal length of said lens is about 50 mm.

17. The optical imaging system of claim 15, wherein the focal length of said lens is about 58 mm.

18. The optical imaging system of claim 1 , wherein said lens has an F number from about 1.0 to about 5.6.

19. The optical imaging system of claim 18, wherein the F number is greater than zero and up to about 5.6. 20. The optical imaging system of claim 19, wherein the F number is from about 1.0 to about 5.6.

21. The optical imaging system of claim 20, wherein the F number is from about 1.0 to about 1.2.

22. The optical imaging system of claim 1, wherein the optical imaging system is used in a fluoroscopic x-ray device.

23. The optical imaging system of claim 22, wherein the fluoroscopic x-ray device images extremities of a human body.

24. The optical imaging system of claim 22, wherein the fluoroscopic x-ray device is used in a mini C-arm X-ray device.

25. The optical imaging system of claim 1, further comprising means for filtering the illuminance of the visible light to compensate for non-uniform gain throughout a cross-section of the visible light.

AMENDED CLAIMS

[received by the International Bureau on 21 July 1997 (21.07.97); original claims 18 cancelled; original claims 1, 4, 10 and 19 amended; remaining claims unchanged (4 pages)]

1 An optical imaging system for generating imaging information from incoming radiation that has passed through a particular object, said optical imaging system comprising

means for converting the incoming radiation to visible light,

an image intensifier for intensifying the visible light,

means for coupling said converting means to said image intensifier, said couplmg means including a fiber optic taper for forming a viewable image based on the visible light and a lens for directing the visible light to said fiber optic taper, wherein said lens includes a principal image plane and a principal object plane, said principal image plane being in front of said principal object plane, and

an output system for presenting said viewable image for clinical analysis

2 The optical imaging system of claim 1 , wherein said fiber optic taper is physically and optically connected to said image intensifier

3 The optical imaging system of claim 1 , wherein said lens is positioned between said converting means and said image intensifier 4 The optical imaging system of claim 1 , wherein said lens further comprises a front vertex, said second principal plane being positioned at the furthest possible distance from said front vertex.

5. The optical imaging system of claim 1, wherein said converting means is a scintillating screen.

7. The optical imaging system of claim 1 , wherein said converting means has a screen diameter that is about 100 mm to about 215 mm.

10. The optical imaging system of claim 7, wherein said converting means has a screen diameter that is about 215 mm. 11 The optical imaging system of claim 1 , wherein said fiber optic taper has a large end and a small end, and wherein said lens forms an image of the particular object at the large end and a viewed image at the small end

12 The optical imaging system of claim 1 1 , wherein the large end of said fiber optic taper is about 42 mm

13 The optical imaging system of claim 1 1, wherein the small end of said fiber optic taper is about 17 5 mm

14 The optical imaging system of claim 1 , wherein a focal length of said lens is from about 25 mm to about 125 mm

15 The optical imaging system of claim 14, wherein a focal length of said lens is from about 50 mm to about 80 mm

16 The optical imaging system of claim 15, wherein the focal length of said lens is about 50 mm

17 The optical imaging system of claim 15, wherein the focal length of said lens is about 58 mm 19 The optical imaging system of claim 1 , wherein the F number is greater than zero and up to about 5 6

20 The optical imaging system of claim 19, wherein the F number is from about 1 0 to about 5 6

21 The optical imaging system of claim 20, wherein the F number is from about 1 0 to about 1 2

22 The optical imaging system of claim 1 , wherein the optical imaging system is used in a fluoroscopic x-ray device

23 The optical imaging system of claim 22, wherein the fluoroscopic x-ray device images extremities of a human body

24 The optical imaging system of claim 22, wherein the fluoroscopic x-ray device is used in a mini C-arm X-ray device

25 The optical imaging system of claim 1, further comprising means for filtering the illuminance of the visible light to compensate for non-uniform gain throughout a cross-section of the visible light

STATEMENT UNDER ARTICLE 19

This application now contains claims 1 through 17 and 19 through 25. Claim 1, 4, 10 and 19 have been amended. Claim 18 has been cancelled. Claims 2, 3, 5 through 9, 11 through 17, and 20 through 25 are unchanged.

Claim 10 has been amended to make clear that the converting means has a screen diameter that is about 215 mm. Also, claim 18 has been cancelled as it is a duplicate of dependent claim 20; and claim 19 which previously depended from claim 18 has been amended to depend from claim 1. Claim 1 has also been amended to define further that the lens of the present invention includes a principal image plane and a principal object plane, and that the principal image plane is m front of the principal ob ect plane. This aspect of the invention is supported by the original disclosure at page 8, lines 16 through 22 and page 9, lines 1 through .

Claim 4 has also been amended to recite that the lens further comprises a front vertex and that the second principal plane is positioned at the furthest possible distance from the front vertex. This aspect of the invention is also supported by the original disclosure at page 8, lines 16 through 22 and page 9, lines 1 through 7.

With respect to the above amended claims, it is clear that no new matter has been inserted into the application.

The search report cites as particularly relevant, considered alone, the following United States patent:

U.S. Patent No. 4,521,688 to Yin ("the Yin patent"), which issued on June 4, 1985, titled THREE-DIMENSIONAL TOMOGRAPHIC IMAGING DEVICE FOR X-RAY AND GAMMA-RAY EMITTING OBJECTS, , applied to claims 1 through 24 of the application; this patent was further considered relevant to the examination of claim 25 of the application when considered in combination with the other cited patents.

The search report cites as particularly relevant, when combined with other documents, the following U.S. Patents:

U.S. Patent No. 3,755,672 to Edholm et al . ("the Edholm et al. patent"), which issued on August 28, 1972, titled EXPOSURE COMPENSATING DEVICE FOR RADIOGRAPHIC APPARATUS, applied to claim 25 of the application.

U.S. Patent No.3,665,191 to Moody ("the Moody patent"), which issued on May 23, 1972, titled FILTER FOR COMPENSATING EFFICIENCY DIFFERENCES IN AN OPTICAL SYSTEM, applied to claim 25 of the application.

Independent claim 1, as amended, provides an optical imaging system for generating information from incoming radiation that has passed through a particular object. The optical imaging system includes a converter that converts the incoming radiation to visible light and an image intensifier for intensifying the visible light. The converter is coupled to the image intensifier across a fiber optic taper for forming a viewable image based on the visible light and a lens for directing the visible light to the fiber optic taper. The lens includes a principal image plane and a principal object plane. The principal image plane s in front of the principal object plane. The optical imaging system also includes an output system for presenting the viewable image for clinical analysis.

The purpose of the present invention is to provide an optical imaging system with significantly improved optical and photon collection efficiency over existing imaging systems, resulting in increased image brightness. The present invention also provides an imaging system that is less bulky, i.e., less weight and less cost, and, thus, can be readily incorporated into a portable device. The above features are accomplished by utilizing a lens (i.e., light photon techniques) and fiber optics combination in which the lens has a principal object plane located in front of the principal object plane.

The Yin patent is directed to a three dimensional and tomographic imaging device for X-ray and Gamma-ray emitting objects. The imaging device includes a multiple-pin hole aperture plate held spaced from an x-ray or gamma-ray to visible-light converter which is coupled to a visible-light intensifier. The spacing between the aperture plate and the converter is chosen such that the mini-images of an emitting object formed by the pinholes do not substantially overlap as they impinge on the converter. The output of the image intensifier is digitized and directed to a digital computer for processing. The computer then displays a three- dimensional image of the object, based on the processed information.

The search report primarily focuses on column 5, lines 23 through 29 of the Yin patent which merely suggests that the converter may alternatively be coupled to the intensifier across a combination of a lens system and a fiber optics plate (tapered or not tapered) . However, the Yin patent does not disclose the type of lens or the manner in which the lens and fiber optics plate are coupled between the converter and the intensifier. Unlike the present invention as recited in claim 1, the Yin patent does not disclose or suggest a lens including a principal image plane and a principal object plane and, moreover, the principal image plane being in front of the principal object plane.

Moreover, the Yin patent merely suggests that a lens system and fiber optics combination would allow for a converter of a different size than the intensifier input. The Yin patent does not teach or suggest how a lens and a fiber optic taper can be utilized in an imaging system to increase the brightness of the image, as proviαed in claim 1 of the present invention. The Yin patent also αoes not teach cr suggest how a lens and fiber optic taper can be employed to decrease the overall size and weight of the imaging system such that it can readily be incorporated into a portable device, as provided m claim 1 of the present invention. Accordingly, the subject matter disclosed _.n the Ym patent would neither teach nor suggest the invention of claim 1. The remaining patents cited, the Edholm et al . and Moody patents, are directed to a radiation filter and no combination thereof would suggest the present invention of claim 1.

Claims 2 through 17 and 19 through 25 depend from claim 1 and are distinguished from the cited art for the reasons stated above.

In addition, claims 7 through 17 and 19 through 21 recite particular configurations of the components of claim 1 to increase image brightness and to decrease the size and weight of the overall imaging system. Claims 7 through 10 recite a specific screen diameter for the converting means. Claims 11 through 13 recite the size and shape of the fiber optic taper. Claims 14 through 17 recite specific the focal length of the lens. Claims 19 through 21 recite the F number of the lens. As previously discussed, the Yin patent merely suggests a lens system and fiber optics combination to allow a different converter size than the intensifier input. It is important to understand that the mere combination of a lens system and fiber optics system does not provide increased image brightness or even decreased size and weight of the overall imaging system, as provided in the above claims. Therefore, claims 7 through 10, 12 through 17 and 19 through 21 are further distinguished from the cited art.

In view of the foregoing, applicant respectfully submits that all claims presented in this application are patentably distinguishable over each cited patent and the cited combination of patents. Accordingly, applicant respectfully requests favorable consideration of the claims of the present application.

Due to the amendments to claims 1, 4, 10 and 19 and cancellation of claim 18, applicant is submitting herewith replacement pages 21 through 24 for the above application.