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WO1997038329A1 - Dispositif d'imagerie optique - Google Patents

Dispositif d'imagerie optique Download PDF

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Publication number
WO1997038329A1
WO1997038329A1 PCT/US1997/005669 US9705669W WO9738329A1 WO 1997038329 A1 WO1997038329 A1 WO 1997038329A1 US 9705669 W US9705669 W US 9705669W WO 9738329 A1 WO9738329 A1 WO 9738329A1
Authority
WO
WIPO (PCT)
Prior art keywords
imaging system
optical imaging
lens
image
fiber optic
Prior art date
Application number
PCT/US1997/005669
Other languages
English (en)
Inventor
George P. T. WILENIUS
David Malcolm
Original Assignee
Xitec, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Xitec, Inc. filed Critical Xitec, Inc.
Publication of WO1997038329A1 publication Critical patent/WO1997038329A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/12—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices with means for image conversion or intensification

Definitions

  • 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.
  • 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 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.
  • 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.
  • 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.
  • lenses and fiber optics have the following characteristics.
  • 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.
  • the taper ratio i.e. input diameter vs. outer diameter
  • the photocollection efficiency of the fiber optic is no better than a conventional lens.
  • 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
  • the image intensifier may operate in a magnetic field environment.
  • 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.
  • an optical imaging system that includes a converter for converting radiation to visible light and means for efficiently collecting the visible light and
  • 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
  • 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
  • the optical imaging system includes an output
  • 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
  • Fig. 3 is a graph of a test analysis of taper input size based on varying screen
  • Fig. 4 is a graph of a test analysis of a hypothetical 75 mm lens that was scaled
  • 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. 7 is a graph showing image luminance of the present invention of a 100 mm
  • Fig. 8 is a graph showing image luminance of the present invention for a 150
  • 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.
  • 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.
  • a fluoroscopic x- ray device for measuring extremities of the human body, such as a mini C-arm x-ray device.
  • optical imaging systems in addition to providing smaller optical imaging systems. For example, in addition to providing smaller optical imaging systems.
  • 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
  • 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
  • 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.
  • optic taper 30 has a conical type shape with a large diameter end 32 positioned adjacent
  • the imaging system from left to right, are the phosphor screen 12, the lens 20, the fiber optic taper 30 and the image intensifier 14.
  • the phosphor screen 12 In a preferred embodiment, the phosphor
  • screen 12 is made of gadoliniumoxy sulphide, terbium doped, more commonly referred to as a rare earth phosphor.
  • 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
  • principal plane 24 is positioned as far back as possible from the front vertex 26 of the
  • ⁇ 0 represents the diameter of the phosphor screen 12
  • 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
  • ⁇ t is the diameter of the large end 32
  • ⁇ i is the diameter of the small end 34.
  • the minification required of the lens is substantially reduced.
  • the collection efficiency increases as the square of this reduction and the image brightness correspondingly improves.
  • 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.
  • 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.
  • 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.
  • the focal lengths for the first and second preferred embodiments are 50 mm and 58 mm, respectively.
  • 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:
  • first and second preferred embodiments includes the following properties for the fiber optic taper 30:
  • 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).
  • the field of view was 215 mm with a 56 mm custom f/1.02 lens designed and built by Optics for Research Inc.
  • embodiment included a 36 mm fiber optic taper and a 17.5 mm, proximity focused,
  • the F number ranges from about 1.0 to about 5.6.
  • 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.
  • 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.
  • 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
  • EMA extra mural absorbers
  • EMA captures light that escapes from the fibers because it is
  • the taper input size is as large as possible in order to have optimal
  • 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.
  • a test analysis was performed on a 50 mm lens made by Nikon for its 35 mm SLR cameras in which limits have been
  • a zoom feature may also be inco ⁇ orated into the present invention.
  • 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
  • the present invention such as a 500 mm intensifier or larger, since all components
  • 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.
  • 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
  • the filter is inserted into the x-ray beam to
  • the present system may include a proximity focused microchannel
  • proximity focused intensifier may be used in applications where the presence of
  • 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.
  • AQ corresponds to the area
  • the lens 20 is divided into a series of concentric rings 40 and each ring is, in turn, divided into small segments or
  • the source A 0 can be
  • the center of the object 16 and lens elements 42 are at:
  • object plane is the angle between the ray in question and a line pe ⁇ endicular to the element.
  • equation (4) When one line is pe ⁇ endicular to the object plane, equation (4) becomes:
  • ⁇ ' denotes the angle to the midpoint of an element 42.
  • the solid angle ⁇ can be determined by calculating the
  • ⁇ is associated with ⁇ r
  • ⁇ B' is associated with ⁇ at r
  • ⁇ B" is
  • the finite element that subtends the source, is approximately a trapezoid.
  • the area of the trapezoid projected in the direction of the source is:
  • the finite element is assumed to be a plane surface, and Lambert's
  • the total flux of visible light entering the lens 20 is:
  • the illuminance of the image is:
  • Equation (6) is used to calculate the entry angle, Y, in the fiber optic taper 30.
  • the brightness of the image is:
  • N is the f/number of the lens.
  • 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.
  • 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
  • Figs. 7 and 8 show the results of the above described calculations.

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  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

Abstract

Cette invention concerne un dispositif (10) d'imagerie optique conçu pour générer des informations propres à la formation d'images à partir d'un rayonnement incident ayant traversé un objet particulier. Ledit dispositif d'imagerie optique (10) comporte un écran (12) scintillant conçu pour transformer le rayonnement incident en lumière visible, un intensificateur (14) d'image conçu pour accroître l'intensité de la lumière visible et une combinaison (20, 30) composée d'une lentille et d'un raccord progressif permettant de coupler l'écran (12) scintillant à l'intensificateur (14) d'images. Ladite combinaison (20, 30) de lentille et du raccord progressif est constituée d'un raccord (30) progressif en fibres optiques destiné à la formation d'une vue-écran à partir de la lumière visible et d'une lentille (20) servant à diriger la lumière visible vers le raccord (30) progressif en fibres optiques. Ledit dispositif (10) d'imagerie optique comporte enfin un système d'affichage permettant de présenter la vue-écran aux fins d'analyse clinique.
PCT/US1997/005669 1996-04-10 1997-04-04 Dispositif d'imagerie optique WO1997038329A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US62980996A 1996-04-10 1996-04-10
US08/629,809 1996-04-10

Publications (1)

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WO1997038329A1 true WO1997038329A1 (fr) 1997-10-16

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000055601A1 (fr) * 1999-03-16 2000-09-21 Packard Instrument Company, Inc. Imagerie d'echantillon
GB2350439A (en) * 1999-04-20 2000-11-29 Security Design Associates Imaging device having optical taper on an input face
GB2348018B (en) * 1999-03-16 2002-01-23 Cambridge Imaging Ltd Sample imaging

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3665191A (en) * 1968-12-16 1972-05-23 Canadian Patents Dev Filter for compensating efficiency differences in an optical system
US3755672A (en) * 1970-11-30 1973-08-28 Medinova Ab So Exposure compensating device for radiographic apparatus
US4521688A (en) * 1983-01-21 1985-06-04 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Three-dimensional and tomographic imaging device for x-ray and gamma-ray emitting objects

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3665191A (en) * 1968-12-16 1972-05-23 Canadian Patents Dev Filter for compensating efficiency differences in an optical system
US3755672A (en) * 1970-11-30 1973-08-28 Medinova Ab So Exposure compensating device for radiographic apparatus
US4521688A (en) * 1983-01-21 1985-06-04 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Three-dimensional and tomographic imaging device for x-ray and gamma-ray emitting objects

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000055601A1 (fr) * 1999-03-16 2000-09-21 Packard Instrument Company, Inc. Imagerie d'echantillon
GB2348018B (en) * 1999-03-16 2002-01-23 Cambridge Imaging Ltd Sample imaging
US6730901B1 (en) 1999-03-16 2004-05-04 Packard Instruments Company Inc Sample imaging
GB2350439A (en) * 1999-04-20 2000-11-29 Security Design Associates Imaging device having optical taper on an input face

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