US3906229A

US3906229A - High energy spatially coded image detecting systems

Info

Publication number: US3906229A
Application number: US369377A
Authority: US
Inventors: Gordon D Demeester; Harrison H Barrett; David T Wilson
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1973-06-12
Filing date: 1973-06-12
Publication date: 1975-09-16
Anticipated expiration: 1992-09-16
Also published as: GB1473189A; DE2427199C3; IT1016105B; FR2233655B1; CA999983A; NL7407118A; JPS5034283A; FR2233655A1; DE2427199A1; CH588710A5; DE2427199B2

Abstract

A system for detecting fine detail of large objects with high energy particles in which spatially coded masks are located at a plurality of positions between the object and a detecting system. The apertures in the masks are much larger than the wavelength of the high energy particles and the detector, such as a film, detects a hologram-like shadowgraph which is subsequently developed and the image reconstructed therefrom by means of light from a substantially monochromatic source.

Description

United States Patent DeMeester et al.

HIGH ENERGY SPATIALLY CODED IMAGE DETECTING SYSTEMS Inventors: Gordon D. DeMeester, Marlboro;

Harrison H. Barrett, Lexington; David T. Wilson, Billerica, all of Appl. No.: 369,377

14 1 Sept; 16, 1975 8/1973 KIOIZ 350/162 21 4 1974 Barrett 250 460 OTHER PUBLICATIONS Primary Examiner-Harold A. Dixon Attorney, Agent, or FirmJseph D. Pannone; Milton D. Bartlett; David M. Warren ABSTRACT A system for detecting fine detail of large objects with 5?} 55.81.JJJJJJJJJJiJJJJJ;i5???.???T??%5f?i2 hhh ehhhgy hhhhhh h which .hhhhhhy hhhhh hhhhh 581 Field of Search 350/162 ZP; 250/237 G, i heated at a phlrality Posltions between i 250/321 312 452, 460 482 513, 364 336, ect and a detecting system. The apertures 1n the 308 masks are much larger than the wavelength of the h1gh energy particles and the detector, such as a film, de- 56] References Cited tects a hologram-like shadowgraph which is subsequently developed and the image reconstructed there- UNITED STATES PATENTS from by means of light from a substantially monochrol,38 l Tollsey matic ource 3,263,079 7/l966 Mertz et al 350/162 ZP 3,669,528 7/1972 Richardson 350/162 21 11 Claims, 4 Drawing Figures FILM DEVELOPMENT 46 PATENTEBSEP 15 ms 3,906,229

FILM

DEVELOPMENT 46 DEVELOPE AND BLEACH HIGH ENERGY SPATIALLY CODED IMAGE DETECTING SYSTEMS BACKGROUND OF THE INVENTION Apparatus for determining the location and condition of structures and/or organs in living bodies by detecting high speed particles emanating from regions of the body which have selectively absorbed radioactive compounds requires substantial exposure of the body to potentially harmful radiation and, hence, apparatus which reduces the dosage required to obtain an image of the structure or organ of. sufficient definition and intensity to permit accurate diagnosis of the condition and location of the structure or organ is of paramount importance. Such definition is also a function of the length of time during which the body can as a practical matter be retained in an immobile position since movement of the body will cause substantial reduction in definition of the reconstructed image.

SUMMARY OF THE INVENTION This invention provides for a spatially coded pattern from a source of high energy radiation such as, for example, living tissue which has assimilated a radioactive pharmaceutical which is spatially coded, for example, by passing through a plurality of apertured mask zone plates positioned at spaced locations between the living tissue object and a detector.

The term zone plate, as used throughout the specification and claims, means a structure through which radiation passes in selected regions to produce'a beam of radiation having different amplitude levels in different regions of the cross section of the radiation beam passing through the zone plate. A Fresnel zone plate means a zone plate in which the cross-sectional pattern has a predominant component comprising at least a portion of the Fresnel zone pattern.

The apertures in the masks, which are defined as those regions of the mask substantially transparent to high energy level radiation," have widths many times the wavelength of the radiation to be detected so that radiation passing through the apertures is substantially undiffracted and the resulting shadowgraph detected by the detector constitutes a spatially coded shadowgraph pattern from which an image of the object may be derived. I

The term radiation energyv level, as used throughout the specification and claims, means the energy level of individual packets of photons of radiant energy, said level being directly related to the inverse of its wavelength by Planck's constant. The term' high energy level radiation, as used throughout the specification and claims, means radiation having an energy level higher than the energy level of radiation in the visible spectrum. The upper limit of the visible spectrum is hereby defined as having a 1000 Angstrom free space wavelength.

The shadowgraph produced by the spatially coded pattern has its spatial frequency components improved over a wide range of spatial components so that large objects, for example the entire lung cavity of the patient, can be detected in great detail. More specifically, such a system having improved match of the spatial frequency components of the object to the spatial frequencies detecting and image production system comprises two zone plates which are off-center sections of a Fresnel zone pattern. One zone plate is positioned adtecting surface which may hereinafter be referred to as the shadowgraph plane.

Further in accordance with this invention, the aperture sizes and locations of the two zone plates are preferably such that staight lines extend from a point substantially at the center of the shadowgraph plane through all corresponding locations of the zone plates. To accomplish this, for example, the zone plate positioned substantially equidistant between the detecting surface and the object zone plate has the apertures thereof identical to the apertures of the object zone plate except that the apertures in the equidistant zone plate are one-half the size of the apertures in the object zone plate.

The efficiency of the detecting process is preferably increased by converting the radiation from high energy level radiation to radiation within the visible spectrum which is then detected by any desired means such as,

for example, a recording film.

This invention further comtemplates the use ofa coding system in an image reproduction system in which the shadowgraph recorded on the film is reduced in size one to two orders of magnitude by a photo reduction process. The shadow spacings will diffract radiation in the visible spectrum from a monochromatic source passing therethrough. More specifically, for example, if the largest aperture width of the zone plate adjacent the object is approximately one millimeter, the number of rings is 50 to 60, and the narrowest aperture width spacing is onethird of a millimeter, then the equidistant zone plate projects shadowgraph line pair spacings of less than a millimeter on the film and reduction in size by photo-optical techniques on the order of 20 to 1 produces line pairs in the red regions of the visible spectrum so that monochromatic light from a conventional laser source having a wavelength in the red portion of the spectrum may be effectively diffracted.

In accordance with this invention, diffraction efficiency may be further increased by bleaching the film to produce a phase hologram-like transparency which diffracts substantially all of the monochromatic light passing therethrough.

This invention further discloses that the discontinuities of the shadowgraph at the edges of the recording media which may appear in the reconstructed image are preferably removed by using a rectilinear shape to define the outer edge of the shadowgraph detecting surface while using curved perimeters to define the outer limitations of the apertured masks such that the edges of the detecting surface appear as crossed straight lines in the reconstructed image spaced from the image of the object and may be removed by appropriate iris masks in' the optical reconstruction system.

BRIEF DESCRIPTION OF THE DRAWINGS Other and further objects and advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings wherein:

FIG. 1 illustrates an embodiment of the invention in which a shadowgraph is recorded on a film as a spaally coded amplitude pattern which is reproduced in :duced size on a film which is then bleached to con- :rt the amplitude hologram to a phase hologram from hich images of the object may be reproduced;

FIG. 2 is a transverse sectional view through the high iergy particle detecting system of FIG. 1 illustrating 1e apertures in the object mask;

FIG. 3 is a transverse sectional view of the detecting 'stem of FIG. 1 taken through line 3-3 of FIG. 1 lowing the apertured system of the equidistant mask; id

FIG. 4 is a transverse sectional view of the detecting ructure of FIG. 1 looking toward the detecting film id illustrating the rectilinear outline of the detecting lm.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2, there is shown a )urce of radiation 20 which is illustrated herein, by ay of example only, as the chest of a living person. ortions of the chest area have been rendered radioacve by administering any of the well-known radioactive harmaceuticals to the person. As is well known, sected body elements such as the liver, lung regions or lood vessels have an affinity for selected radioactive harmaceuticals. Such an affinity varies, for example, ependent on the type of disease and the region afcted by the disease.

Positioned adjacent to radiation source 20 is mask 22 Jnsisting, as illustrated in greater detail in FIG. 2, of plurality of curved bars 24 of material opaque to the idiation separated by spaces 26 equal in width to the idth of the bars. As illustrated herein, the total open rea of the mask 22 is made approximately equal to the ital opaque area of the mask and may be referred to a Fresnel zone pattern. The material of the bars 24 chosen such that the radiation from the source 20 hich hits bars 24 will be absorbed but those portions fthe radiation which are directed to the spaces 26 beveen the bars 24 will pass through.

While the mask 22 may be placed at various dismces from the source 20, it is preferably positioned as ose as convenient to the source 20 which is the object eing detected. Hence, mask 22 may be referred to as re object mask. Mask 22 may be made, for example, y depositing a layer of lead on an aluminium plate and lachining off portions of the lead to expose portions fthe aluminum. Aluminum will transmit substantially l the high energy radiation impinging thereon and, ance, such exposed aluminum regions constitute radizion aperture 26.

It should be clearly understood that the thickness of re lead layer and the choice of the support plate may a made of any desired dimensions and spacing and, in :neral, are a function of the radioactive isotope being ed. For example, with an absorption of one millicurie feither radioactive technetium or radioactive iodine, )od resolution may be obtained with widths and spaclgs on the order of one-tenth of a millimeter to one :ntimeter.

The quality of the final image detected varies as a mction of the length of exposure of the detector sysm to the patient, preferably such exposure being in IC range of from one to twenty minutes and recording and 10 counts of high energy radiation particles. owever, since the number of counts detected in accordancewith this invention is several orders of magnitude larger than the counts detected in the pinhole or collimating absorption lens system, greater definition may be achieved.

The pattern formed by the bars 24 defining the apertures is a fragmented portion of a Fresnel pattern. The bars 24 extend in arcuate form to the edges of the circular ring defining the perimeter of mask 22. As illustrated herein, for purposes of clarity, only a few bars and spaces are shown, and adequate results may be achieved with such a system. However, applications have found that masks with more than fifty bars and apertures are preferably used to produce high definition images from the shadowgraph formed, as illustrated herein, directly on a film from a crystal scintillation layer.

The width of the narrowest spacing 26 is several orders of magnitude greater than the wavelength of the radiation. For example, if the width of the narrowest aperture is on the order of one millimeter, any radiation beyond the visible range will have a wavelength many orders of magnitude less than a millimeter and, hence, any diffraction effects of mask 22 on such radiation will be substantially undetectable.

As illustrated herein, the pattern of bars 24 and spaces 26 forms an off-center section of a Fresnel zone pattern. More specifically, the diameter of mask 22, as shown in FIG. 2, is approximately equal to the distance from the center of the Fresnel zone pattern to the center of the mask 22. Such an offset offsets the image during the reconstruction process and is preferably great enough to separate the multiple images produced as well as to separate detecting surface edge artifacts from the desired image.

Mask 22, which may be referred to as the object mask, is supported in a housing 30 which spaces the element 22 a predetermined distance S from a second spatial coding mask 32. Mask 32, which may be referred to as the intermediate or equidistant mask, is formed in a similar manner to that of mask 22 and has a pattern which is the off-center section of a Fresnel zone pattern as illustrated in FIG. 3. In general, the patterns of the

masks

22 and 32 are by way of example only, and any desired patterns or portions of patterns which are symmetrical about axes substantially parallel to the average direction of motion of the radiation through the masks could be used. While, as illustrated herein, masks 22 and 23 are planar, they may if desired, be made as portions of spherical surfaces or cylindrical surfaces or other geometric shapes.

As may be seen from FIG. 3, mask 32 is an off-center section of a Fresnel zone pattern identical to that of zone plate mask 22 but scaled to substantially one-half the size of zone plate 22, with the remainder of the space between the support housing 30 being filled with the portion of the aluminum backing plate covered with lead which absorbs substantially all gamma radiamined point on the holographic image plane is intersected by a plurality of straight lines passing through different mask apertures of

masks

22 and 32, respectively, as illustrated, for example, by point 28. Since there are a plurality of such points which are essentially arcs of circles in the holographic image detector plane, particles emitted from the object will form maximum intensity by which is meant maximum number of radiation particles for that coding frequency even though object 20 is of relatively large size. It may also be seen that various other arcuate configurations may be similarly projected on the detector plane and the sum total of these forms a shadowgraph containing all the spatial frequency components of the spatial code pattern upon which the intelligence data representing the particular outline and radiation intensity of the object are superimposed. Such a pattern is an amplitude or intensity pattern and, hence, may be detected by a detector system 36.

As shown in FIG. 4, housing 30 is formed from a circular cross section to a rectangular cross section in the region where it supports the detecting system 36. It has been found that if a circular section is used for the detecting shadowgraph region, a reconstruction by optical means produces a series of circular patterns which, to some extent, interfere with or degrade the image. By the use of a rectilinear pattern, as indicated in FIG. 4, the reconstruction contains straight-line artifacts indicative of the straight-line borders of the periphery of the shadowgraph, and these intersect to form a cross with positive and negative images appearing in opposite quadrants of the cross so that by the use of an iris only one desired image may be selected and the remaining data, including the artifacts, eliminated.

The size and spacing of the

masks

22 and 32 and the size of the rectilinear detector plane may be selected from a wide range of possible configurations. For work with human bodies, the following size has been found useful:

Diameter of mask 22 25 to cm.

Effective diameter of mask 32 12 to 15 cm.

Rectilinear dimensions of the detecting surface 25 cm. X 30 cm.

Spacing distances S S 9 cm.

The number of bars 24 which can, as a practical matter, be formed in

masks

22 and 32 depends upon the thickness and material of the masking medium.

Detector system 36 is illustrated herein as being substantially planar but, if desired, may have a spherical, cylindrical or other geometric surface shape. As illustrated herein by way of example only, detector system 36 comprises a layer of film 38 sandwiched between two thin layers 40 of crystal material such as cesium iodide or calcium tungstate which produces scintillations of light when struck by gamma radiation. A backing support plate 42, preferably of light reflecting metal, is used to support the layers of crystal 40 and the film 38 positioned therebetween. The front surface of the crystal 40 on the opposite side of film 38 from the support plate 42 may also have a thin layer of light reflecting material such as an aluminum or silver surface coated thereon and, if desired, the entire package of support plate 42, film 38 and crystals 40 may be assembled as a unitary package or cassette.

In operation, gamma rays from object 20 pass through

masks

22 and 32 as well as through crystal 40. Some of the gamma rays will produce scintillations of light in one or the other of the crystal layers 40 having an intensity strength enough to partially expose the elemental areas of the film adjacent the regions of the crystals producing the light scintillation. Preferably, the crystal layers 40 are made only a few millimeters thick so that definition in the pattern recorded on the film 38 is maintained in the millimeter range.

While the film 38 is preferably in a cassette, it is shown herein as a portion of a roll of film 44 drawn through the crystals 40 to illustrate the process steps involved. After exposure, the film 38 is developed in accordance with conventional practice by passing through a developer bath 46. Any desired degree of development can be used. Preferably, however, the film is developed sufficiently to provide maximum contrast between light and dark areas. However, different degrees of development may be used to accentuate different total intensities of the detected shadowgraph.

The film 38 is then placed in a reducing system 48 which may be of a conventional type in which a light source 50 emanating from a ground glass screen 52 passes through film 38 and is focused on a film 58 through a lens 54 on the opposite side of film 38 from the light source 50. The focal length of lens 54 is chosen such that the light rays converge as passing therethrough and the shadow of film 38 is projected in reduced form on film 58 to expose film 58 and reproduce a negative of the pattern developed on film 38 in reduced form on film 58.

In accordance with this invention, the pattern on film 58 is reduced sufficiently so that the projection of the spacing of bars 24 in the pattern recorded on film 38 will be sufficiently close to produce a substantial degree of refraction of a visible light beam passing therethrough. This has been found to produce a substantial improvement in image reproduction, both from the standpoint of image distortion and image clarity or intensity.

Film 58 may, if desired, also be in the form of a cassette but is shown herein in the form of a roll of film to illustrate the subsequent steps of the process. Film 58 is passed through a conventional develop and bleach step illustrated at 60. The film 58 is of any desired conventional type which is developed to produce substantially the same or a greater degree of contrast as the original developed film 38 and is then bleached with any conventional film bleach to convert all of the light absorbing regions to a compound having a thickness and/or index of refraction different from the other regions of the film. In accordance with this invention, bleaching, in addition to enhancement of light transmission, is used as part of the conversion process from a shadowgraph pattern produced by noncoherent radiation into a refracting lens suitable for coherent light image reproduction in which size reduction of the image is used to further enhance the quality and clarity of the reproduced image.

The film 58 is then used to reproduce an image of the object 20 by a coherent light reproduction system 62. System 62 may be of any desired type and, as illustrated herein, comprises a source of coherent light 64 such as a helium neon laser whose output is focused by a lens 66 through a pinhole iris 68 to remove spatial noise. Light projected through the pinhole 68 passes through a converging lens 70 and then through the developed and bleached film 58 which diffracts the informational content of the picture away from the center line of the ll'lOlE and lens system 70 by a distance r. so that it ;ses through a hole having a diameter in an iris 72 1 appears as a reconstructed image in an image plane any desired detection system such as a ground glass een 74. The distance of screen 74 may be varied ,h respect to the film 58 to produce from the pattern :orded on film 38 various slices corresponding to 'ious distances of object from the detector system [he aperture size d and its offset r from the iris 72 functions of the diameter of the zone plate masks and 32 and the distance which the center of the zone tte patterns are offset from the center of the Fresnel 1e pattern. For example, if, as illustrated, the diameof each of the zone plates is equal to the offset of center of that zone plate from the center ofits Fresl zone pattern, the pattern size d in the iris 72 is prefibly substantially equal to the offset distance r,. from center of the system. As illustrated herein, the iris 72 is positioned substanlly in the plane where the pinhole liht from iris 68 MM be focused by the lens 70 in the absence of film which may be referred to as the Fourier plane. Hower, other locations of the iris 72 may be used and/or ier means of separating the desired image from arti- :ts and/or undesired images. The image produced on screen 74 may be viewed diztly and/or several pictures taken for various distces of screen 74 from the Fourier plane by means of :amera 76. Alternatively, a television pickup camera 1y be used to view the reproduced image and/or to )re images in a computer memory from which if deed, simultaneous three-dimensional views of the ob- :t 20 may be reproduced. in accordance with this invention, individual scintilions of light from the crystals 40 will not completely pose an elemental area of the film. Thus, overlapping tterns produced by adjacent point sources will subtntially all be recorded with optimum intensity and a nimum occurrence of the conditions where elemenareas of film are completely exposed so that addilnal scintillations of light occurring after such comate exposure go undetected. The film 38 may be sufficiently thick for a given exsure time for such complete recording without satution to occur since the portions of the film which are are completely exposed simply remain transparent to ht in the reduction process. It should be noted that ose portions which are still transparent pass the most ht so that the reduced film 58 is a negative of the iginal film 38 causing a greater darkening of the neg- .ve 58. However, this also does not result in reduction image intensity since substantially all of the opaque gions are substantially completely bleached and the t result is simply a small average increase in the retction of the film. The substantial signal amplification obtained by the duction in size of fiom 58 from film 38 and the :aching allows this system to be used for direct shad- Igraph recording, thereby allowing an improved defition of the image derived therefrom. The definition .provement varies as the total number of counts rerded which is a function of the time of exposure of e detecting system. Because of the large number of unts available compared with the prior pinhole or llimator type cameras, relatively thin scintillator ystals 40 may be used, thereby permitting a shadowgraph detection definition substantially higher than those previously available. As a result, the fineness of the bar spacing of the finest bar of zone plate mask 32 may be made substantially as fine as it is practical to fabricate such structures while still projecting patterns on the detecting surface which are within the spatial frequency pass band of the detecting system. For example, with a 20 to 1 reduction in size of the hologram from film 38 to film 58, a high definition image of an object may be derived using high energy level incoherent radiation from a living tissue source, and the image constructed using coherent light in the image-forming process will be readily visible to the naked eye.

Theory of Operation In our aforementioned copending application, the radiation emitted by the object passes in succession through a periodic half-tone screen and an off-axis section of a Fresnel zone plate. Both the half-tone screen and the zone plate are constructed so that the bars or zones are alternately transparent and opaque to the radiation. Such a system produces a coded shadowgraph strictly by geometric shadowing. The zone plate and half-tone screen are sufficiently coarse that no appreciable diffraction occurs. When the spatial frequencies are properly chosen, a strong Moire fringe pattern is formed on the shadowgraph or image plane. This finge pattern, although formed by shadowing rather than diffraction, is closely analogous to a hologram. The original three-dimensional radiation source can be reconstructed by illuminating a transparency derived from the shadowgraph with coherent light.

The formation of the Moire fringe pattern can be better understood by considering the radiation paths. Assume that the spacing from the half-tone screen to the zone plate is equal to the spacing from the zone plate to the image plate, and that the spatial frequency in the center of the zone plate is just twice the frequency of the half-tone screen. Then there will be a point in the image plane for which the transparent zones in the center of the zone plate project onto the transparent bars of the half-tone. The radiation transmitted to this point through the center of the zone plate will be a maximum. At a nearby point for which the center transparent zones project onto opaque bars, the transmission will be a minimum. In general, a fringe pattern will be formed with both the amplitude and phase of the fringes depending on the source distribution.

In accordance with the present invention, one of the highest fringe contrasts has been obtained when the half-tone screen was a zone plate exactly twice as large as the other zone plate. The fringe amplitude is now proportional to the Fourier transform of the source multiplied by a quadratic phase factor and is closely analogous to a Fraunhofer hologram.

The two-zone-plate system has several practical advantages. The strongest fringes occur in the center of the hologram. Therefore, if either the resolution or the sensitivity of the image detector falls off at the edge of its field, comparatively little information is lost.

Because of Fourier transform property, various spatial filtering operations can easily be performed by masking the hologram plane. For example, low frequency suppression can be accomplished by masking off the center of the hologram. Also, since the finges are macroscopic, a hologram could be examined visually and those regions where the fring contrast is low can be masked off. This operation is a rough approximation to matched filtering and can enhance the signalto-noise ratio in the reconstruction.

In the aforementioned copending application Ser. No. 289,707 there is disclosed a system in which fine detail of objects, such as thyroid glands, can be readily detected with a plurality of spaced aperture structures, one of which is a portion of a Fresnel zone plate and another of which is a bar mask or half-tone screen having a constant spatial periodicity.

Such a gamma camera uses an off-axis portion of a Fresnel zone plate and a bar pattern, such that center spatial frequency of the zone plate segment, f and the spatial frequency of the half tone, f are related by the proportion, 1/f )=(s =s (l/f where s is the distance from the bar pattern to the zone plate and s is the distance from the zone plate to the detecting or image plane.

When the distances s and 3 are comparable to or smaller than the zone plate aperture, and the zone plate rings and half-tone or bar pattern have a thickness comparable to their spacings, only those gamma rays passing fairly near normal are effective is generating an exposure on the film, die to vignetting and also to HR losses because diagonal rays must go farther and are weaker.

It has been found that the spatial frequency match of the zone plate and bar pattern are poorly satisfied at the edges of the field both because the zone plate and half tone are not parallel and also because the zone plate frequency and half-tone frequency do not match at the edges of the field. The result is field nonuniformity, the center of the field being imaged better than the edges.

In accordance with this invention, the straight bar pattern is replaced by another zone plate on a scale such that spatial frequency match conditions are satisfied.

More specifically, useful results can occur when the radius of the first edge, r,, of each zone plate satisfies the following proportion in order to obtain the frequency match r 22 taking r, 22 1% [one Since the two zone plates are the same function (scaled appropriately), the result is the correlation function of the two identical (except for scale) patterns. If the zone plates were infinite in extent, the correlation would be an impulse, lying on a line connecting the centers of the zone plates. If we look in the film plane, therefore, we see the Fourier transform of the object plane.

This completes the description of the embodiments of the invention illustrated herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, any distortion produced in the system which is reduced by reduction in size of the film may also be reduced by other means such as correcting lenses. A variety of other spatial coding patterns other than Fresnel zone patterns may be used, and the reconstruction may be accomplished by computer using appropriate transform programs. Also, it is contemplated that this invention may be used to form images of the shadows of organs having substances which absorb gamma radiation emanating from a source external to the living organism.

Accordingly, it is contemplated that this invention be not limited by the particular details of the embodiments illustrated herein except as defined by the appended claims.

What is claimed is:

l. The method comprising the steps of:

introducing radioactive material into an organ of a living body; and

forming a spatially coded pattern of high energy radiation level particles emitted from said radioactive material by selectively absorbing said high energy particles in a plurality of regions spaced along the average direction of motion of said particles through said regions by means comprising a plurality of zone plates each of which has a zone pattern of selective absorption of said particles which is substantially symmetrical about an axis substantially parallel to said average direction of motion of said particles through said zone plates.

2. The method in accordance with claim 1 including the step of:

deriving the image of said radioactive material in said organ from at least components of said spatially coded pattern.

3. The method in accordance with claim 2 wherein said step of deriving an image comprises:

spatially detecting at least a portion of said pattern.

4. The method in accordance with claim 3 wherein said step of deriving said image comprises:

converting the energy level of said particles radiated from said organ to radiation of a lower intensity than the intensity of said high energy level particles.

5. The method in accordance with claim 4 wherein said step of deriving said image comprises:

recording a spatial pattern having at least a component of said spatially coded pattern.

6. The method in accordance with claim 5 wherein said step of deriving said image comprises:

deriving said image with a beam of substantially coherent light.

7. The method in accordance with claim 6 wherein said step of deriving said image comprises:

projecting said beam of substantially coherent light throu a medium whose transmissivity varies as a function of at least component of said spatially coded pattern.

8. The method in accordance with claim 1 wherein said step of forming said spatially coded pattern comprises:

spatially coding at least portions of said radiation with a plurality of space masks comprising offcenter sections of Fresnel zone patterns.

9. The method in accordance with claim 8 wherein:

the centers of said Fresnel zone patterns lie substantially in a line intersecting the detector plane.

10. The method in accordance with claim 1 and including: the step of spatially detecting at least portions of said high energy radiation level particles passing through said zone plates.

11. The method in accordance with claim 10 wherein: said spatially detecting step comprises converting the energy level of said particles radiating from said organ to radiation of a lower intensity than the intensity of said high energy particles.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 906, 229 Dated September 16, 1975 Gordon D. DeMeester, Harrison H. Barrett and David T. Wilson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor(s Col. 2, line 36: "onethird" should be "one-third" Col. 4, line 11: "applications" should be "applicants" Col. 4, line 37: "S should be "S Col. 7, line 2: "diameter in" should be "diameter d in" C01. 7, line 17: "pattern" should be "aperture" Col. 7, line 21: "liht" should be "light" Col. 8, line 27: "finge" should be "fringe" Col. 8, line 37: "plate" should be "plane" Col. 8, line 66: "finges" should be "fringes" Col. 9 line 15'' "S S should be "S S Col. 9, line 23: "is" should be "in" Col. 10, line 47: "throu" should be "through" Col. 10, line 48: "least component" should be "least a component" Signed and Ercalcd this third Day Of February 1976 [SEAL] Arrest:

. RUTH c. MASON C. MARSHALL DANN Arresting Officer Commissioner oflatents and Trademarks FORM F o-1050 (104:9) USCOMM DC 60376 P69 9 U.S. GOVERNMENT PRINTING OFFICE i969 0-366-334

Claims

1. The method comprising the steps of: introducing radioactive material into an organ of a living body; and forming a spatially coded pattern of high energy radiation level particles emitted from said radioactive material by selectively absorbing said high energy particles in a plurality of regions spaced along the average direction of motion of said particles through said regions by means comprising a plurality of zone plates each of which has a zone pattern of selective absorption of said particles which is substantially symmetrical about an axis substantially parallel to said average direction of motion of said particles through said zone plates.

2. The method in accordance with claim 1 including the step of: deriving the image of said radioactive material in said organ from at least components of said spatially coded pattern.

3. The method in accordance with claim 2 wherein said step of deriving an image comprises: spatially detecting at least a portion of said pattern.

4. The method in accordance with claim 3 wherein said step of deriving said image comprises: converting the energy level of said particles radiated from said organ to radiation of a lower intensity than the intensity of said high energy level particles.

5. The method in accordance with claim 4 wherein said step of deriving said image comprises: recording a spatial pattern having at least a component of said spatially coded pattern.

6. The method in accordance with claim 5 wherein said step of deriving said image comprises: deriving said image with a beam of substantially coherent light.

7. The method in accordance with claim 6 wherein said step of deriving said image comprises: projecting said beam of substantially coherent light throu a medium whose transmissivity varies as a function of at least component of said spatially coded pattern.

8. The method in accordance with claim 1 wherein said step of forming said spatially coded pattern comprises: spatially coding at least portions of said radiation with a plurality of space masks comprising off-center sections of Fresnel zone patterns.

9. The method in accordance with claim 8 wherein: the centers of said Fresnel zone patterns lie substantially in a line intersecting the detector plane.