Digital radiographic imaging system and method therefor

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A digital radiographic image recording system which comprises:

(a) a movable scintillator body having a dense, self-supporting and substantially void-free single flat layer configuration which is substantially transparent to the optical radiation emitted by said medium, said scintillator body comprising a polycrystalline scintillator ceramic with a high X-ray absorption value and a material density of at least 99% so that substantially all X radiation impinging thereon will be converted therein to optical radiation without excessive scattering and loss of the converted optical radiation,

(b) a stationary X-ray source to expose said scintillator body to an X-ray fan beam moving in a linear non-arcuate travel direction after passage through an object,

(c) a photodetection member positioned physically contiguous with said moving scintillator body and movable therewith so that both scintillator body and photodetection member move synchronously together with the moving x-ray fan beam in the same linear non-arcuate travel direction for conversion of said moving fan beam to an optical image for simultaneous detection of said optical image in a point-by-point and line-by-line manner,

(d) said movable photodetection member having a plurality of charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear non-arcuate travel direction as the moving X-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by optical radiation impinging on the individual charge transfer device located in the same column in the opposite travel direction to the travel direction of said moving photodetection member and with said synchronous signal shifting being carried out by a time delay and integration mode of operation to form an electrical analog representation of said optical image without experiencing substantial optical attenuation, the pixel arrangement in said photo-detection member also being unbroken so that all impinging optical radiation will be collected, the synchronous signal shifting further being carried between adjoining charge transfer devices such that signals are shifted from a device having received optical radiation to the next adjoining device at the same velocity rate as the physical movement, and

(e) digital processing means for immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof with higher quantum detection efficiency, resolution and contrast.

2. A digital radiographic image recording system as in claim 1 wherein said time delay and integration mode of operation for said moving photodetector member is achieved with a spatial orientation of the individual charge transfer devices such that the individual charge transfer devices forming a row are aligned in an offset but overlapping positional relations with respect to the next adjoining row of individual charge transfer devices.

3. A digital radiographic image recording system as in claim 2 wherein a like spatial relationship is maintained between all alternate rows of individual charge transfer devices in said photodetection member to form a parallel alignment for the column orientation of said charge transfer devices in said photodetection member.

4. A digital radiographic image recording system as in claim 1 wherein the charge transfer devices are charge coupled devices.

5. A digital radiographic image recording system as in claim 1 wherein the synchronized signal shifting between adjoining charge transfer devices proceeds serially throughout each column of charge transfer devices in said photodetector member and with the output signals from each column being further stored in the digital processing means of said radiographic image recording system.

6. A digital radiographic image recording system as in claim 1 which further includes visual display of the digitized information.

7. A digital radiographic image recording system as in claim 6 wherein said visual display is operatively associated with said means for digital recording of the optical image.

8. A digital radiographic image recording system as in claim 1 wherein said scintillator body comprises a sintered polycrystalline rare earth doped rare earth oxide ceramic exhibiting high density, optical clarity, and a cubic crystalline structure.

9. A digital radiographic image recording system as in claim 8 wherein said rare earth oxide is selected from the group consisting of Gd.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3 and Lu.sub.2 O.sub.3.

10. A digital radiographic image recording system as in claim 9 wherein said rare earth dopant ion is selected from europium, neodymium, ytterbium and dysprosium.

11. A digital radiographic image recording system as in claim 8 wherein said ceramic comprises between about 5 and 50 mole percent Gd.sub.2 O.sub.3, between about 0.02 to about 12 mole percent of at least one rare earth activator oxide selected from the group consisting of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Tb.sub.2 O.sub.3, and Pr.sub.2 O.sub.3, the remainder being Y.sub.2 O.sub.3.

12. A digital radiographic image recording system as in claim 1 wherein said scintillator body comprises a composite of x-ray stimulable phosphor crystals suspended in a matrix of a solid synthetic organic polymer having an optical refractive index closely matching the optical refractive index of said phosphor crystals while also being substantially transparent to the optical radiation being emitted by said phosphor crystals.

13. A digital radiographic image recording system as in claim 12 wherein said phosphor is barium fluorochloride activated with europium ion and said synthetic organic polymer is a polysulfone.

14. A digital radiographic image recording system as in claim 12 wherein the phosphor crystals occupy a minimum weight fraction in said member of at least 50%.

15. A digital radiographic image recording system as in claim 12 wherein the polysulfone polymer is a homopolymer.

16. A digital radiographic image recording system as in claim 12 wherein said phosphor crystals comprise a europium activated barium fluorohalide further containing a sufficient level of an impurity ion selected from Group 1A and 3A elements in the periodic table of elements to reduce the optical refractive index of said phosphor.

17. A digital radiographic image recording system as in claim 16 wherein said impurity ion is incorporated as a halide compound of the impurity element.

18. A digital radiographic image recording system as in claim 16 wherein the europium activator level is in the approximate range from 0.1-2.0 weight percent based on the weight of said phosphor.

19. A digital radiographic image recording system as in claim 16 wherein the level of impurity ion is in the approximate range from 0.3-3.0 weight percent based on the weight of said phosphor.

20. A digital radiographic image recording system as in claim 16 wherein the phosphor is europium activated barium fluorochloride.

21. A method to record a digital radiographic image which comprises:

(a) forming an optical image by scanning an object exposed to a stationary X-ray source with a moving scintillator body in a linear non-arcuate travel direction during exposure of said object to a moving X-ray fan beam to form said optical image as a point-by-point and line-by-line composite of the subject being scanned,

(b) said scintillator body having a dense, self-supporting and substantially void-free single flat layer configuration which is substantially transparent to the optical radiation emitted from said medium, said scintillator body comprising a polycrystalline scintillator ceramic with a high X-ray absorption value and a material density of at least 99% so that substantially all X radiation impinging thereon will be converted therein to optical radiation without excessive scattering and loss of the converted optical radiation,

(c) simultaneously transmitting said optical image when formed to a moving photodetection member aligned with said moving x-ray fan beam and moving synchronously in the same linear non-arcuate travel direction as said moving x-ray fan beam,

(d) said moving photodetection member being positioned physically contiguous with said moving scintillator body and movable therewith so that both scintillator body and photodetection member move synchronously with the moving x-ray fan beam in the same linear non-arcuate travel direction for conversion of said moving X-ray fan beam to an optical image for simultaneous detection of said optical image as an electrical analog representation thereof and without experiencing substantial optical attenuation,

(e) said moving photodetection member also having a plurality of charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear non-arcuate travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by optical radiation impinging on an individual charge transfer device located in the same column in the opposite direction to the travel direction of said moving photodetection member and with said synchronous signal shifting being carried out by a time delay and integration mode of operation, the pixel arrangement in said photodetection member also being unbroken so that all impinging optical radiation will be collected, the synchronous signal shifting further being carried out between adjoining charge transfer devices such that signals are shifted from a device having received optical radiation to the next adjoining device at the same velocity as the physical movement, and

(f) immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof with digital processing means at higher medium detection efficiency, resolution and contrast.

22. A method as in claim 21 wherein said time delay and integration mode of operation for said moving photodetection member is achieved with a spatial orientation of the individual charge transfer devices such that the individual charge transfer devices forming a row are aligned in an offset but overlapping positional relationship with respect to the next adjoining row of individual charge transfer devices.

23. A method as in claim 21 wherein a like spatial relationship is maintained between all alternate rows of individual charge transfer devices in said photodetection member to form a parallel alignment for the column orientation of said charge transfer devices in said member.

24. A method as in claim 21 wherein the synchronized signal shifting between adjoining charge transfer devices proceeds such that signals are shifted from a device having received optical radiation to the next adjoining device after the latter device has received optical radiation.

25. A method as in claim 21 wherein the synchronized signal shifting between adjoining charge transfer devices, proceeds serially through each column of charge transfer devices in said composite member and with the output signals from each column being further stored by the digital processing means.

26. A method as in claim 21 wherein the signal shifting is carried out with charge coupled devices.

27. A method as in claim 21 which further includes digital imaging of the optical image.

28. A digital radiographic image recording system which comprises:

(a) a movable scintillator body having a dense, self-supporting and substantially void-free single flat layer configuration which is substantially transparent to the optical radiation emitted by said medium, said scintillator body comprising a polycrystalline scintillator ceramic with a high x-ray absorption value and a material density of at least 99% so that substantially all X radiation impinging thereon will be converted therein to optical radiation without excessive scattering and loss of the converted optical radiation,

(b) a stationary X-ray source to expose said scintillator body to an X-ray fan beam moving in a linear non-arcuate travel direction and after passage through an object,

(c) a photodetection member positioned in direct physical contact with said movable scintillator body and moving therewith so that both scintillator body and photodetection member move synchronously with the moving x-ray fan beam in the same linear non-arcuate travel direction for conversion of said moving X-ray fan beam to an optical image for simultaneous detection of said optical image in a point-by-point and line-by-line manner without experiencing substantial optical attenuation,

(d) said movable photodetection member having a plurality of charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear non-arcuate travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to synchronously shift the signals being generated by optical radiation impinging on the individual charge transfer devices located in the same column in the opposite direction to the travel direction of said movable photodetection member and with said synchronous signal shifting being carried out by a time delay and integration mode of operation to form an electrical analog representation of said optical image, the pixel arrangement in said photodetection member also being unbroken so that all impinging optical radiation will be collected, the synchronous signal shifting further being carried out between adjoining charge transfer devices such that signals are shifted from a device having received optical radiation to the next adjoining device at the same velocity rate as the physical movement, and

(e) digital processing means for immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof with higher quantum detection efficiency, resolution and contrast.

29. A method to record a digital radiographic image which comprises:

(a) forming an optical image by scanning an object exposed to a stationary X-ray source with a moving scintillator body in a linear non-arcuate travel direction during exposure of said object to a moving X-ray fan beam to form said optical image as a point-by-point and line-by-line conversion of the subject being scanned,

(b) said scintillator body having a dense, self-supporting and substantially void-free single flat layer configuration which is substantially transparent to the optical radiation being emitted from said medium, such scintillator body comprising a polycrystalline scintillator ceramic with a high x-ray absorption value and a material density of at least 99% so that substantially all X radiation impinging thereon will be converted therein to optical scintillator without excessive scattering and loss of the converted optical radiation,

(c) simultaneously transmitting said optical image when formed to a moving photodetection member aligned with said moving x-ray fan beam and moving in the same linear non-arcuate travel direction as said moving x-ray fan beam,

(d) said moving photodetection member being positioned in direct physical contact with said moving scintillator body and movable therewith so that both scintillator body and photodetection member move synchronously with the moving x-ray fan beam in the same linear non-arcuate travel direction for conversion of said moving x-ray fan bean to an optical image for simultaneous detection of said optical image as an electrical analog representation thereof and without experiencing substantial optical attenuation,

(e) said moving photodetection member also having a plurality of charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear non-arcuate travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by the optical radiation impinging on an individual charge transfer device located in the same column in the opposite direction to the travel direction of said moving photodetection member and with said synchronous signal shifting being carried out in a time delay and integration mode of operation, the pixel arrangement in said photodetection member also being unbroken so that all impinging optical radiation will be collected, the synchronous signal shifting further being carried out between adjoining charge transfer devices such that signals are shifted from a device having received optical radiation to the next adjoining device at the same velocity rate as the physical movement, and

(f) immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof with digital processing means at higher quantum detection efficiency, resolution and contrast.

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RELATED PATENT APPLICATIONS

A co-pending application Ser. No. 07/046,443, filed May 6, 1987 now abandoned, assigned to the same assignee as the present invention, discloses a high efficiency type x-ray image converter member which can be employed in practicing the present invention. Specifically, said converter medium comprises a scintillator body having a layer configuration and made up of x-ray stimulable phosphor particles suspended in a substantially void-free matrix of a particular solid organic polymer. The phosphor and polymer constituents in said composite medium have substantially the same optical refractive index characteristics so as to be substantially transparent to the optical radiation being emitted by said phosphor constituent when retrieving a latent radiographic image previously stored in said medium. In still another co-pending application Ser. No. 07/046,442, filed May 6, 1987, now abandoned also assigned to the present assignee, there is disclosed a like type scintillator body wherein the phosphor composition has been modified to reduce its optical refractive index and thereby provide a closer match to the optical refractive index characteristics of various solid organic polymers. More particularly, said further improved scintillator body contains a europium activated barium fluorohalide phosphor material modified to further include a sufficient level of an impurity ion selected from Group 1A and 3A elements in the periodic table of elements to reduce the optical refractive index of said modified phosphor.

BACKGROUND OF THE INVENTION

This invention relates generally to an improved digital radiographic imaging and recording system which is especially useful in medical radiographic applications and more particularly to a system of said type wherein a moving fan beam of X radiation is employed in combination with photodetection means to digitize and record the optical image formed immediately responsive to X radiation.

As previously indicated, scintillator materials emit visible or near visible radiation when stimulated by x-rays or other high energy electromagnetic photons hence are widely employed in various industrial or medical radiographic equipment. In medical applications it is desirable that the scintillator output be as large as possible to minimize exposure of the medical patient to the x-ray dosage. A known class of scintillator materials considered for use in computerized tomography applications is monocrystalline inorganic compounds such as cesium iodide (CsI), bismuth germanate (Bi.sub.4 Ge.sub.3 O.sub.2), cadium tungstate (CdWO.sub.4), calcium tungstate (CaWO.sub.4) and sodium iodide (NaI). Another known class of scintillator materials comprises polycrystalline inorganic phosphors including europium activated barium fluorochloride (BaFCl:Eu), terbium activated lanthanum oxybromide (LaOBr:Tb), and thulium activated lanthanum oxybromide (LaOBr:Tm). A still third class of already known scintillator materials found useful in computerized tomography comprises various dense sintered polycrystalline ceramics such as rare earth doped yttria/gadolinia (Y.sub.2 O.sub.3 /Gd.sub.2 O.sub.3) and polycrystalline forms of said previously mentioned phosphors including BaFCl:Eu, LaOBr:Tb,CsI:Tl, CaWO.sub.4, and CdWO.sub.4.

In U.S. Pat. No. 4,383,327, there is disclosed a scanning slit electronic radiographic system employing a linear array of electronic radiation detectors to digitize and record the optical image formed in an image intensifier device when stimulated by X radiation after passage through a medical patient. It is recognized in said prior art disclosure that an image intensifier device is subject to various problems of scattered radiation producing distortion and loss of information details in the optical image being formed. It is still further recognized in said prior art disclosure that such radiation scattering in the image intensifier device requires an increased exposure of the patient to radiation in order to prevent such degradation of the image quality and which is an undesirable consequence for medical radiographic applications. The emerging optical image from said image intensifier device in said prior art radiographic system is optically focused upon remotely located charge coupled devices forming the photodetection means in said system thereby occasioning additional detection efficiency losses in the optical information being retrieved such as resolution and contrast losses. The physical orientation of charge coupled devices forming the photodetection means in said prior are radiographic system consists of parallel aligned columns and rows in a spaced apart configuration. Such a spaced apart configuration creates void spaces whereby still further optical information can be lost for an inaccurate representation of the optical information being retrieved.

A staggered physical orientation for said photodetection means is disclosed for a digital radiographic system of the same type in a publication entitled "X-ray Image Sensor Based on an Optical TDI-CCD Imager" authored by J. deGroot, J. Holleman, and H. Wallinga and issued by Oldelft Optical Industries. Said improved photodetection means is reported to be physically coupled to the exit window of an image intensifier device to provide a more unbroken and thereby more accurate representation of the optical information being retrieved. By further reason of the relatively complex and fragile nature of the image intensifier device being employed in both prior art radiographic imaging systems, however, said devices are seen to remain stationery while being operated with the patient being moved during exposure to the x-ray fan beam such as positioned on a movable table aligned therewith. Understandably, any involuntary movement of the medical patient in either prior art radiographic imaging process creates still another source of error, such as blurring, in the optical image being formed.

It remains desirable, therefore, to provide an improved digital radiographic imaging system of this general type which is not subject to the inherent limitations experienced when using an image intensifier device.

It is another important object of the invention to provide a more compact and rugged as well as simplified equipment system and method for digitally recording a radiographic image as formed and in a manner providing improved quantum detection efficiency.

Still another important object of the present invention is to provide such an improved digital radiographic imaging system that is relatively inexpensive as well as more reliable to construct and operate while further not experiencing loss in the principal benefits now achieved with a radiographic technique of this type.

SUMMARY OF THE INVENTION

Novel composite x-ray conversion and photodetection means have now been discovered for a digital radiographic imaging and recording system which provides enhanced quality for the optical image being formed responsive thereto. More particularly, said improved composite medium comprises a movable scintillator body having a dense, self-supporting and substantially void-free layer configuration which is substantially transparent to the optical radiation emitted from said medium and which is positioned physically contiguous to a photodetector member moving synchronously therewith so that both scintillator body and photodetection means are exposed to a moving x-ray fan beam in the same linear travel direction for conversion of said moving x-ray fan beam to an optical image for simultaneous detection of said optical image in a point-by-point and line-by-line manner. Said moving x-ray fan beam is generated in the present digital radiographic imaging system with an x-ray source having a movable scanning bar member combined therewith which includes a slit opening and moves in a linear travel direction. The movable photodetection member in the present digital radiographic imaging system comprises a plurality of bi-directional charge transfer devices arranged in electrically interconnected columns and rows, said columns being aligned in the same linear travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by optical radiation impinging upon an individual charge transfer device located in the same column in the opposite direction to the travel direction of said moving photodetection member and with said signal shifting being carried out by a time delay and integration mode of operation to form an electrical analog representation of said optical image. Accordingly, the presently improved digital radiographic imaging system basically comprises said movable scintillator body having a dense self-supporting and substantially void-free layer configuration which is substantially transparent to the optical radiation emitted from said medium, an x-ray source to expose said scintillator body to an x-ray fan beam moving in a linear travel direction and after passage through an object, a photodetector member positoned physically contiguous with said movable scintillator body and movable therewith so that both scintillator and photodetector member move synchronously with the moving x-ray fan beam in the same linear travel direction for conversion of said moving x-ray fan beam to an optical image for simultaneous detection of said optical image in a point-by-point and line-by-line manner, said movable photodetector member having a plurality of bi-directional charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by optical radiation impinging on an individual charge transfer device located in the same column in the opposite direction to the travel direction of said moving photodection member and with said signal shifting being carried out by a time delay and integration mode of operation to form an electrical analog representation of said optical image, and immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof by digital processing means. In said presently improved digital radiographic imaging and recording system said time delay and integration mode of operation for said moving photodetector member is achieved with a spatial orientation of the individual charge transfer devices such that the individual charge transfer devices forming a row are aligned in an offset but overlapping positional relationship with respect to the next adjoining row of individual charge transfer devices and with the preferred embodiments maintaining a like spatial relationship between all alternate rows of individual charge transfer devices in said photodetector member to form a parallel alignment for the column orientation of said charge transfer device in said photodetector member. The preferred charge transfer devices are charge coupled devices exhibiting the operational characteristics hereinafter described but with already known charge injection devices also being contemplated as capable of performing in a like manner. As also to be described more fully hereinafter in connection with the preferred embodiments for practicing the invention, the synchronized signal shifting between adjoining charge transfer devices proceeds such that signals are shifted from a device at the same velocity as the scan movement albeit in the opposite direction.

General operation of the above defined present radiographic imaging and recording system comprises forming an optical image by scanning an object with a moving scintillator body in a linear travel direction during exposure of said object to a moving x-ray fan beam to form said optical image as a point-by-point and line-by-line composite of the object area being scanned, said scintillator body having a dense, self-supporting and substantially void-free layer configuration which is substantially transparent to the optical radiation being emitted from said medium, simultaneously transmitting said optical image when formed to a moving photodetector member aligned with said moving x-ray fan beam and moving synchronously in the same linear travel direction as said moving x-ray fan beam, said moving photodetector member being positioned physically contiguous with said moving scintillator body and movable therewith so that both scintillator body and photodetector member move synchronously with the moving x-ray fan beam in the same linear travel direction for conversion of said moving x-ray fan beam to an optical image for simultaneous detection of said optical image as an electrical analog representation thereof and without experiencing substantial optical attenuation, said moving photodetector member also having a plurality of bi-directional charge transfer devices arranged in electrically connected columns and rows, said columns being aligned in the same linear travel direction as the moving x-ray fan beam while said rows being aligned substantially transverse thereto in order to also synchronously shift the signals being generated by optical radiation impinging on an individual charge transfer device located in the same column in the opposite direction to the travel direction of said moving photodetector member and with said signal shifting being carried out by a time delay and integration mode of operation, and immediately converting said electrical analog representation of said optical image to a recorded digital representation thereof by digital processing means. In the preferred operating embodiments, digital computer means are employed for recording the optical image as formed by the composite x-ray image converter and detection means and which can further include electronic signal processing circuitry to further enhance the quality of the finally recorded radiographic image by various already known information processing techniques. Accordingly, the electronic analog signals generated by said photodetection means employed in said preferred radiographic imaging process are transmitted to said digital image processing means which can still further include contemporaneous visual display operatively associated with the digital image processing means such as a vidicon camera or cathode ray tube. As can be noted from the elimination of any requirement for an image intensifier device in carrying out the above defined digital radiographic imaging and recording process, there is achieved a higher quantum detection efficiency, resolution and contrast in the retrieved optical image together with an unbroken pixel array for the radiographic information being retrieved.

To provide enhanced quality for the optical image formed in accordance with the present invention, it is required that the scintillator body material absorb most of the X radiation being employed so that radiographic information details do not escape as well as have a substantially void-free solid medium so as not to produce excessive scattering and loss of the converted optical radiation. Said desired x-ray conversion behavior is achieved in the presently useful scintillator materials with a high absorption value at a material density of at least 99% or greater to provide superior resolution capability for the optical image generated in accordance with the present invention.

As previously indicated, a relatively broad class of solid state scintillator materials has been found useful as the conversion medium in digital radiographic imaging and recording system. A preferred general class of polycrystalline ceramic scintillator materials deemed suitable for the present x-ray conversion medium is disclosed in U.S. Pat. No. 4,525,628, also assigned to the present assignee, as exhibiting superior conversion efficiency compatible with modern computerized tomography or other digital imaging requirements. Said general class of ceramic scintillator materials comprises rare earth oxides doped with rare earth activators which yield a cubic crystal structure of high density and optical transmittance with the preferred rare earth oxides being selected from the group consisting of Gd.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3, and Lu.sub.2 O.sub.3 and wherein the rare earth activator ion is selected from the group consisting of europium, neodymium, ytterbium and dysprosium. Representative ceramics further specified in said general class of superior solid state scintillator materials include Gd.sub.2 O.sub.3 activated with europium ion and Gd.sub.2 O.sub.3 combined with Y.sub.2 O.sub.3 which is also activated with europium ion. An entirely dissimilar class of solid state monocrystalline scintillator materials is also disclosed in said aforementioned reference which can be used as the present x-ray conversion medium despite higher costs and difficulties of preparation as well as somewhat inferior performance characteristics. Said lesser preferred single crystals are grown from a melt and include NaI:Tl, CaF.sub.2 :Eu, Bi.sub.4 Ge.sub.3 O.sub.2, CsI:Tl and CdWO.sub.4.

A more limited class of the above defined polycrystalline ceramic scintillator materials which is preferred for the present x-ray conversion medium is disclosed in U.S. Pat. No. 4,473,513, also assigned to the present assignee. More particularly, said scintillator body comprises a sintered polycrystalline yttria (Y.sub.2 O.sub.3)-gadolinia (Gd.sub.2 O.sub.3) ceramic exhibiting high density, optical clarity, uniformity and a cubic crystalline structure which further includes one or more oxides of the rare earth elements selected from europium, neodymium, ytterbium, dysprosium, terbium, and praseodymium as activators along with oxides of other metal ions selected from zirconium, thorium, and tantalum to serve as transparency-promoting densifying agents. A typical ceramic of said type comprises about 5 to 50 mole percent Gd.sub.2 O.sub.3, between about 0.02 and 12 mole percent of at least one rare earth activator oxide selected from the group consisting of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Pr.sub.2 O.sub.3, the remainder being Y.sub.2 O.sub.3. Both of said above identified commonly assigned patents are further specifically incorporated by reference into the present application to avoid further necessity for added description herein of a suitable medium in which to achieve said conversion of the impinging X radiation to an optical image having enhanced visual characteristics.

A different preferred class of scintillator materials deemed suitable for the present x-ray conversion medium is disclosed in the above enumerated co-pending applications. Accordingly, said scintillator body may comprise a composite of x-ray stimulable phosphor crystals suspended in a matrix of a solid synthetic organic polymer having an optical refractive index closely matching the optical refractive index of said phosphor crystals while also being substantially transparent to the optical radiation being emitted by said phosphor crystals. A representative x-ray converter medium of said type is barium fluorochloride activated with europium ion while said synthetic organic polymer is a polysulfone. In said typical medium, the phosphor crystals occupy a minimum weight fraction of at least 50% whereas the polysulfone polymer is a homopolymer. A different x-ray converter medium of this same type utilizes phosphor crystals of europium activated barium fluorohalide further containing a sufficient level of an impurity ion selected from Group 1A and 3A elements in the periodic table of elements to reduce the optical refractive index of said phosphor. In said latter medium, the europium activator level is preferrably maintained in the range from 0.1-2.0 weight percent based on the weight of said phosphor whereas the impurity ion level is preferably maintained in the approximate range from 0.3-3.0 weight percent based on the weight of said phosphor. Said phosphor modification can be achieved as further described in said aforementioned co-pending applications, both of which are also specifically incorporated by reference into the present application, by simply combining a halide compound of the impurity element with the already formed phosphor material.

As well be illustrated below in greater detail for the hereinafter described preferred embodiments, the digital recording of an optical image having enhanced visual characteristics further requires that the photodetection means operatively associated with the present scintillator medium co-operate in a particular manner. As previously indicated, it is essential that said co-operating photodetection means be positioned physically contiguous to said scintillator body so that substantially all optical radiation emerging from the latter medium be detected and which can possibly be most easily achieved when the individual members are joined in direct physical abutment. As also previously indicated, the pixel arrangement in said photodetection means is required to be unbroken so that all of the impinging optical radiation will be collected and which can also possibly be achieved with a staggered column orientation of the individual detector arrays. For digitally recording an optical image having enhanced visual quality in accordance with the present improvement, it becomes still further required that said photodetection means be operated so that the optical radiation being received is pro