GB2076250A - Mechanical X-ray scanning - Google Patents

Abstract

Apparatus for obtaining CT scans employs a rotating unit operative to produce a scanning pencil beam of X-ray radiant energy by use of a mechanical scanning device consisting of a first collimator which shapes radiation emitted from an X-ray source into a fan- shaped beam of X-rays, and a second collimator comprising a disc- shaped chopper wheel which is rotated through the fan-shaped beam. A single pencil beam is produced and caused to scan through an angle, sufficiently great to embrace a cross section of a body being examined, onto at least one elongate detector forming a portion of the rotating unit and located on the side of the body opposite to the X- ray source and mechanical scanning device. The system can also be used to generate its own localization images and to perform digital radiography on those images and, because of the relative rotation feature, can be employed in this mode of to obtain anterior-posterior, lateral or oblique images at any desired angle. <IMAGE>

Description

SPECIFICATION Radiant energy imaging apparatus Systems have been suggested heretofore for obtaining computed tomography (CT) scans for medical or other purposes. In general, these known systems are comparitively com plex structurally, very expensive, and tend to subject a patient to a comparitively high do sage level of radiation if X-ray images of adequate quality to effect an X-ray diagnosis are to be obtained. The present invention is concerned with the provision of an apparatus which, when employed as a CT scanner, is capable of producing X-ray images which are comparable to and in some cases better than those produced by present-day commercial CT equipment, and which achieve these results at far less cost and by subjecting the patient to a far smaller level of dosage than is customary at the present time.These advantages are achieved by the provision of equipment which employs a mechanical scanner, of the general type described in Stein et al Patent No.

RE 28,544 (originally U.S. Patent No.

3,780,291) which is operative to produce a pencil beam of X-rays that scans a single efficient detector.

CT equipments employing flying spot scanning techniques have been suggested heretofore. One such arrangement is de scribed, for example, in an article entitled "Low Dosage X-Ray Imaging System Employ ing Flying Spot X-Ray Microbeam (Dynamic Scanner)" by Tateno and Tanaka, Radiology 121: October 1976, pp 189-195. The Ta teno et al system, although described as being capable of achieving quality X-ray images at lower dosages than are customarily employed in XCT equipment, uses a special noncommer ciai X-ray tube characterized by sophisticated electron optics analogous to those employed in high voltage electron microscopes and elec tron beam machining equipment, relies on an electronic scanning technique, and contem plates the use of a two-dimensioned detector.

These characteristics of this previously-de scribed system make the system far more expensive than the system of the present invention, which utilizes an extremely simple mechanical scanning arrangement. In addi tion, inasmuch as the Tateno et al system employs a two-dimensional detector, it is inca pable of rejecting scattered radiation, in con trast to the system of the present invention wherein, by use of a single, efficient one dimensional detector, such rejection is auto matically accomplished.

Further advantages accrue to the present invention, as compared to the scanning tech nique of Tateno et al which employs a device that produces a flying-spot X-ray beam by "pinhole" projection of an electronically scanned focal spot in the X-ray tube. In order to produce an X-ray field large enough to subtend a patient cross-section for a CT scan, the beam must diverge over a considerable distance from the pinhole collimator. The required distance is equivalent to locating the pinhole at the focal spot (X-ray source) of the present invention. Since the beam cross-section at any point represents a pinhole image of the focal spot, the relatively large distance from pinhole collimator to patient results in a relatively large beam cross-section, with a concurrent loss of resolution.The close proximity of the collimation system to the patient in the present invention in an important improvement, since the beam size is essentially a projection of the small collimator from a distant source.

Another system suggested heretofore, for producing CT images by use of a flying spot technique, is described in Hounsfield U.S.

Patent No. 3,866,047 for "Penetrating Radiation Examining Apparatus Having A Scanning Collimator". The Hounsfield apparatus contemplates the provision of a mechanical scanning device comprising a pair of elongated shutters which are mounted for mechanical reciprocation in synchronism with one another. Each shutter member is provided with a plurality of slots which coact with one another to produce a plurality of angularly spaced radiation beams simultaneously, each beam being caused to scan through a comparatively small angle onto a comparatively small detector which is associated with that beam.

The Hounsfield reciprocating shutter arrangement is far more complex mechanically than the comparatively simple collimator which is employed in the present invention, and requires critical alignments of the plural slots which are utilized in the spaced shutter of the Hounsfield mechanical scanner. Moreover, since Hounsfield contemplates the simultaneous generation of a plurality of angularly displaced X-ray beams, and the simultaneous scanning of all of those beams across a like plurality of detectors, the arrangement poses problems of possible loss of data at the boundaries between adjacent detectors. Two specific problems may be identified: (1) the boundaries produce a geometric inefficiency which results in wasted dose to the patient, and (3) The missing information along the beam paths through the boundaries can result in artifacts in the reconstructed CT image.

Further problems with the multiple beam arrangement of Hounsfield are related to the need for accurate matching or normalization of the plural detectors over the full dynamic range of the signal, without which severe artifacts can result in the reconstructed image.

A number of phenomena, as for example cathode resistivity and dynode fatigue, are known to produce nonlinearities and gain changes in photomultiplier tubes, the use of which is contemplated by Hounsfield. Similar problems may occur with other plural detectors which are less efficient that the scintillator-photomultiplier combination. In order to reduce the dynamic range, and thereby alleviate the normalization, Hounsfield has incorporated a "plastics block" (item 26 in his Figures) and suggested the use of a water bag filling the space between the plastics block and the patient. The use of such devices introduces extra expense and mechanical complexity, and results in wasted dose because of photon absorption (and consequent loss of information) between the patient and the detector.

The present invention utilizes a single, effi cient detector and a simple mechanical scanning arangement to obviate all these problems of the prior art.

Summary of the Invention The radiant energy imaging apparatus of the present invention comprises an X-ray system adapted to be moved rotationally as a unit about a support structure which is provided to support a body or other object to be examined by means of penetrating radiation.

The X-ray unit comprises a source of X-rays located on one side of the support means, a single elongated radiant energy detector located on the opposite side of the support means and extending in a direction transverse to the axis of rotation of the X-ray system, and a mechanical scanning device located between the X-ray source and the support means for configuring radiation emitted by the source into a single pencil beam of X-rays, and for scanning that single pencil beam along the direction of elongation of the single detector through an angle which is sufficiently large to subtend a complete cross section of a body or object on the support means. The mechanical scanning device is of the general type described in Stein et al U.S. Patent RE28,544 reissued September 2, 1975, on the basis of U.S.Patent No. 3,780,291 issued December 18, 1973, and comprises a first collimator device for shaping radiation emitted by an X-ray source into a fan-shaped beam of X-rays, and a second collimator comprising a disc-shaped chopper wheel fabricated of a radiation opaque material and having one or more X-ray transparent slots therein through which a pencil beam of X-rays can pass, said pencil beam being scanned along said single linear detector as the second collimator rotates. The chopper disc can take the form shown in the aforementioned Stein et al patent or, in the alternative, it can comprise a drum-shaped structure of the type shown in Jacob U.S. Patent No. 4,031,401.

Each of these patents is assigned to American Science and Engineering Inc., Cambridge, Massachusetts, the assignee of the present invention.

The X-ray system, comprising the X-ray source, mechanical scanning device, and sin gle elongated detector, is adapted to be moved in various directions for various differ ent purposes. The system may be moved, for example, in translation along a line parallel to the axis of the support means to provide conventional radiographic projection in a man ner analogous to that achieved by the Medical MICRO-DOSE~ X-ray system manufactured by American Science and Engineering, Inc., Cambridge, Massachusetts. In this mode of operation, because of the fact that the X-ray system is adapted to be rotated through any desired angle relative to the body support structure, images can be readily obtained as AP, PA, lateral or oblique images at any desired angle.

The mode of operation described above can also be employed to produce localization im ages preparatory to the CT scanning opera tion, i.e., the X-ray system may be translated as a unit parallel to the axis of the body support structure, and the conventional im ages obtained during this mode of operation can can be monitored to localize the system at a particular region of the body where a CT slice is to be taken, whereafter the X-ray system is caused to effect a continuous substantially constant speed of rotation relative to the body support structure to a CT scan of the selected slice. This relative rotation between the scan ner and the object being examined can be achieved by rotating either the scanning mechanism, the object, or both.The axis of relative rotation may, moreover, be selected for any desired applications, and may be either horizontal, vertical or at a selected an gle therebetween.

The system preferably includes means for adjusting the size of the CT scan field, either by mechanical manipulation of the fan beam and chopper wheel collimation system, or by displacing the position of the X-ray unit or selected portions thereof relative to the axis of rotation so as to vary the spacing between said axis of rotation and the X-ray source and/or detector.

The system can also be used to generate several CT scans simultaneously by using one or more fan beam collimation slits, all of which are traversed simultaneously, for exam ple, by a slit in a rotating chopper wheel, and by directing a plurality of parallel flying-spot beams or a single beam of sufficient dimes- sions onto several contiguous linear detectors.

The multiple detectors used in this configura tion, wherein each elongated detector sub tends more than the full field of its CT cross section, are not subject to the same severe normalization problems that were described with respect to the plural detectors in the aforementioned Hounsfield patent. This is be cause (a) each CT slice is obtained by a single detector and (b) each detector can be cali ) brated many times during a single CT scan by shaped collimator 12, fabricated for example as a composite of lead and tungsten, having an elongated comparatively narrow opening 13 at its upper end.The fan beam is further collimated by an X-ray opaque chopper wheel 14, fabricated for example of lead-filled aluminimum with tungsten jaws, that is provided with a plurality of slits 15 extending radially inwardly from the outer edge of said wheel 14 is mounted for rotation about a central axis as indicated by arrow 16, and is so positioned that an edge of the wheel overlies and completely covers slot 13 in collimator 12, except for the region of overlap of the slits 13, 15. For purposes of illustration i.e., in order that the slot 13 may be more readily seen in Figs. 1 and 2, this completely overlying relationship has not been shown in said figures, and reference is accordingly made to the drawings in Stein et al U.S. Patent RE 28,544 in this respect.

The lead and tungsten employed in collimators 12, 14 fully attenuate X-rays except in the the region of overlap of the slits, and the motion of the wheel 14 causes the slits 15 to traverse the fan beam repeatedly, thereby generating a single scanning pencil beam of X-rays 17 whose cross sectional dimensions are determined by the shapes of slits 13 and 15 in their region of overlap. This pencil-X-ray beam is partially attenuated by the subject on table 10, and the unattenuated X-rays are absorbed by an elongated photon detector 18, comprising a single efficient detector of the type described in the aforementioned Stein et al patent, as the pencil beam 17 scans from a position adjacent one end of detector 18 toward a postion adjacent the other end thereof.During this scanning operation, the entire X-ray system, including the Xray source, the chopper wheel, and the detector, is moved as a unit in the direction indicated by arrows 19, i.e., in a direction transverse to the direction of elongation of detector 18, along the length of the patient, who remains stationary on table 10, to produce multiple rows of data in the nature of a TV raster which data is supplied from detector 18, as at 20. These output signals produce a radiograph on the video (TV) monitor (not shown) e.g., by intensity modulating the CRT electron beam on a storage oscilloscope, or on a scan converter storage tube of known type.

Alternatively, the output signals may be digitized and stored in a computer accessible memory, and processed by computer to produce a digital radiograph or other display device.

The single detector 18 is a scintillation crystal coupled to one or more photomultipliers whose outputs are combined, and nearly 100% of the X-rays which are not attenuated by the patient are detected. The electrical signals obtained at the output of the photomultipliers are pulses, with the amplitude of using data obtained when the flyng spot beam impinges on the detector outside the circle of its CT image field. The outputs of several detectors can be employed to produce a plu rality of independent CT images simultane ously, thereby reducing the time otherwise required to generate a series of CT images of any one patient.This ability may be particu larly useful for the generation of so-called saggital and coronal reconstructions from multiple slice data, inasmuch as obtaining the data simultaneously obviates any problems related to motion of the patient between successive scans. In an alternative mode of operation, the outputs of two or more detectors in a contiguous group can be combined to effectively adjust the width of a single slice under examination.

Brief Description of the Drawings The foregoing objects, advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings wherein: Figure 1 is a diagrammatic illustration of a prior art Medical MICRO-DOSE~ X-ray system; Figure 2 is a diagrammatic illustration of the radiant energy imaging apparatus constructed in accordance with the present invention; Figure 3 illustrates the system of Fig. 2 used as a CT scanner; and Figure 4 is a diagrammatic illustration of a modified detector arrangement which can be employed in the arrangement of Fig. 2 to obtain multiple slice scans.

Description of the Preferred Embodiments As described previously, the present invention is concerned with a radiant energy imag ing apparatus for obtaining CT scans and other types of scan for medical and other purposes. It is based on the scanning mecha nism and the single efficient detector em ployed in the Medical MICRO-DOSEB X-ray system manufactured by American Science and Engineering, Inc., Cambridge, Massachu setts. That prior system is illustrated in Fig. 1 of the drawings.

The apparatus shown in Fig. 1 comprises a ,table or support structure 10 adapted to sup port the body of a patient who is to be examined by means of penetrating radiation, and an associated X-ray system adapted to produce a pencil beam of X-rays which is caused to scan across the patient's body. The X-ray system corresponds in general to the system which is shown in Stein et al U.S.

Patent RE28,544, the disclosure of which is incorporated herein be reference, and comprises a conventional rotating anode X-ray tube 11 whose output is collimated into a narrow fan beam by means of a wedge each pulse being proportional to the energy of a single detected X-ray photon. Since the rate of X-ray photons incident on the detector is large, these pulses add together to give a net signal which, at any instant of time, is proportional to the incident X-ray flux in the attenuated X-ray pencil beam. The electrical signal from the detector, during one scan of the pencil beam from one end of the detector to the other, corresponds to a one-dimensional radiographic image of the object, analogous to one scan line on an ordinary television monitor.The second dimension of the image is generated by virtue of the motion of the source-collimator-detector plane with respect to the patient. The series of line images is sequentially stored in digital form and, after the X-ray exposure is complete, the radiographic data are read out line-by-line onto the television monitor. The readout is sequentially ordered in the same manner in which the data are read into storage so that the image on the monitor screen is the X-ray shadowgraph of the subject being examined.

In the prior art apparatus shown in Fig. 1, the X-ray system is adapted to be moved in translation only, i.e., in the direction of arrows 19. However in accordance with the present invention, the X-ray system of Fig. 1, like parts of which are designated by like numerals in Fig. 2, is mounted to exhibit a variety of degrees of motion under the control of various drive means known per se and therefore not shown in Fig. 2 for purposes of simplicity.

The translateral motion indicated by arrow 19 may be retained in Fig. 2 when it is desired to have the system of the present invention exhibit the capabilities already described in reference to Fig. 1 and/or when the system of Fig. 2 is to provide CT scans preceded by the generation of localization images. Basically, however, the system of Fig. 2 is characterized by an arrangement wherein the translateral motion indicated by arrow 19 is replaced by or supplemented by a rotational motion of the patient relative to the scanner, as indicated by arrows 21, about an axis of rotation 22 which is the nominal axis of a patient supported on table 10. In practice, either the patient or the scanning mechanism, or both, may be rotated.When the scanning mechanism is to be rotated about axis 22, it is rotated as a unit, i.e., line detector 18 on one side of table 10 is physically connected to the X-ray generating mechanism and collimator structure on the other side of said table, by means of an appropriate interconnecting structure which is indicated by broken line 23.

When used as a CT scanner, the CT scan achieved by the system of Fig. 2 is essentially similar to that of so-called two motion, or translate-rotate, CT scanners, but without the usual mechanical disadvantages and complexities of known such devices which require reciprocating mechanical translations of X-ray source, collimator and detector(s) to take place between incremental rotational motions of the assembly. In the present invention, the two motions (sweeping beam and rotating scanning assembly) are performed smoothly, continuously and simultaneously. The number of traverses of the pencil beam during one rotation of the scanner relative to the patient establishes the number of "views" of the CT scan.The data read out from the detector 18 is reconstructed by methods well known in the CT art, e.g., appropriate algorithms are described in the article Fan Beam Reconstruction Methods by B. K. P Horn, proceedings IEEE, December 1979, pp. 1616-1623.

One traverse of the beam along detector 18 typically takes approximately 1/180 seconds, and the typical rotation of the object being examined relative to the X-ray scanning system may be accomplished in approximately 5 to 10 seconds, giving a total of between 900 and 1800 views during a complete rotation of the X-ray scanner relative to the patient.

These figures are given by way of example only, and in one embodiment of the invention the scan occurred at the rate of 30 scans per second, and the complete relative rotation of the scanning system and object being examined occurred in a time period of 15 seconds, to produce 450 views. The general operation of the sytem, in accordance with these aspects of the invention, is depicted in Fig. 3 wherein, again, like numerals are used to designate like parts.The significant points to note by reference to Fig. 3 are that the X-ray source 11 and mechanical scanner 1 2, 14 coact to produce a single scanning pencil beam of X-rays, which is scanned linearly in the direction of arrow 24 from one end to the other end to line detector 18, and which, in the course of this scanning operation, subtends an angle which embraces a complete cross section of the body or object generally designated 25 that is being moved rotationally (see arrow 21) relative to the X-ray scanner.

The size of the CT scan field can be adjusted by mechanical manipulation of the fan beam and chopper wheel collimation system 1 2, 14, i.e., by changing the slit sizes in the collimators. Alternatively, the field size canoe adjusted (referring to Fig. 3) by moving the axis of rotation of object 25 closer to the source 11 thereby to effect a smaller field and a higher resolution, or by moving the axis of rotation closer to the detector 18 to achieve a larger field and a lower resolution. These possible movements of the X-ray source 11 and/or the detector 18 relative to table 10 have been designated in Fig. 2 by arrow 26.

Typically, the total dosage to which the scanned region of the body is exposed during the taking of a CT scan is approximately 100 mR. This dosage is from 1/10th to 1/100th of the dosage which occurs in present-day commercial CT scanners, but the picture which is achieved by the present invention at this very low dosage has nevertheless been found to be comparable to, and in certain reSpects better than, those which are achieved at far greater cost and at far higher dosages by present day commercial scanners. In addi titn to achieving these significant advantages, the present invention retains a number of the advantages of the priort art system shown in Fig. 1.More particularly, it achieves sub millimeter spatial resolution, nearly total rejec tion of scattered radiation, and dose efficiency approaching 100%.

Another major advantage of the system shown in Fig. 2 is that it serves as its own localization system, and has the abilty to per form digital data processing in either of two modes, i.e., it is a dual purpose, digital radi ograph/CT system. Moreover, because of the relative rotation feature represented by arrows 21, the system can be used not only to generate its own localization images, and to perform digital radiography on those images, but can readily obtain images as AP, PA, lateral or oblique images at any desired angle.

As indicated previously, the relative rotation between the object or patient and scanner may be achieved by rotating either the scann ing mechanism, the object, or both. Moreo ver, the axis of rotation may be selected and oriented as desired for any prevailing applica tion and, in particular, it may be horizontal as depicted in Figs. 1 and 2, or vertical. A vertical orientation of the scan axis exhibits certain advantages in that it facilitates rotation by permitting the spinning chopper wheel 14 to precess in the earth's gravitational field.

The radiation source employed in the inven tion can be a conventional X-ray tube, or a radioisotope source, or a synchrotron. Regard less of the source employed, however, the simplifications which are accomplished by the present invention result in part from the use of a rotating type collimator which can take the form shown in the drawing, or the form described in Jacob U.S. Patent No. 4,031, 401, or which, if desired, can take the form of a rotating cylinder having helical radiation transparent slots therein.

The detector employed has essentially 100% detection efficiency and 100% geo # metrical efficiency, unlike most CT scanner arrays. The spatial resolution of the CT image is high. Transverse resolution (in the plane of the slice) and axial resolution (slice thickness) are both sub-millimeter, and this resolution is achieved without sacrificing dose efficiency.

Moreover, radiographic images and CT im ages may be obtained by locating detectors outside the plane of the scan, and then using the detected scattered radiation to generate an image, as is described for example in the aforementioned Stein et al patent. Such back scatter imaging is possible in the present invention since there is a single known geometric position of the scanning pencil beam at any instant of time, and the scatter from its path through the object principally controls the strength of the scattered signal at that time.

The system shown in Fig. 2 can be used moreover, to generate several CT scans simultaneously. This is accomplished by an arrangement of the type generally depicted in Fig. 4 wherein a plurality of line detectors such a 18a, 18b and 1 8c are disposed in side-by-side, parallel, contiguous relation to one another, and the pencil beam (shown in cross section 17a in Fig. 4) is so dimensioned that it impinges on the plurality of detectors simultaneously as it is swept in the direction 24 from one end to the other of the contiguous detectors.The pencil beam 17a can comprise a plurality of parallel beams which are associated respectively with the detectors 18a-18c, or a single beam which is elongated in cross section in a direction transverse to the scan direction 24, and these beam configurations can be achieved by providing one or more fan beam collimation slits in the mechanical scanner 1 2, 14, or by increasing the width of the slot 13 in collimator 12, and correspondingly increasing the length of the slot 15 in collimator 14.

By using an arrangement of the type shown in Fig. 4, a plurality of outputs 20a are obtained simultaneously from the plural detectors 1 8a-1 8c, and these plural simultaneous outputs can be processed in varying fashions to achieve various different results. For example, the plural outputs may be processed individually to produce multiple slice pictures simultaneously. Alternatively, the outputs of two or more detectors in a contiguous group can be combined and processed thereby, in effect, to adjust the width of a particular slice being examined.

The present invention lends itself to other techniques as well. For example, by using different filtering or detector characteristics for contiguous planes, or by using a low energy detector backed up by a high energy detector in the same plane, dual energy data may be obtained simultaneously. This may be used for either CT or digital radiographic images.

The subtraction of the two images taken with different energy responses can be used to emphasize iodinated contrast material. Utilizing this feature combined with multiple slices allows an image of, for example, blood vessels in a volume rather than a slice.

While I have thus described preferred embodiments of the present invention, it must be understood that the foregoing description is intended to be illustrative only and not limitative of the present invention. Many variations have already been described, and other will be apparent to those skilled in the art. For example, although the implementation of the invention has been described in connection with medical diagnostic imaging, the invention is also applicable to any nondestructive testing application. All such variations and modifications are intended to fall within the scope of the appended claims.

Having thus described by invention, I claim:

Claims (16)

1. A radiant energy imaging apparatus for examining a body by means of penetrating radiation, said apparatus comprising support means for supporting a body to be examined, an X-ray system adapted to be moved rotationally as a unit relative to said body about an axis of rotation defined by said support means, said X-ray system comprising a source of X-rays located on one side of said support means, a single elongated radiant energy detector located on the opposite side of said support means and extending in a direction transverse to said axis of rotation, and a mechanical scanning device located between said X-ray source and said support means for configuring radiation emitted by said source into a single pencil beam of X-rays and for scanning said single pencil beam through an angle relative to said source along the direction of elongation of said single detector, the length of said single detector and position of said single detector and mechanical scanning device being selected to cause said single pencil beam of X-rays to subtend an angle which embraces a complete cross section of a body on said support means as said pencil beam of X-rays is scanned along said single detector, and drive means for effecting rotation of said X-ray source, said mechanical scanning device and said single detector as a unit relative to said body to be examined about said axis of rotation.

2. The radiant energy imaging apparatus of claim 1 wherein said mechanical scanning device comprises a first collimator for shaping radiation-emitted by said source into a fanshaped beam of X-rays which beam has an elongated cross section extending in a direction parallel to the direction of elongation of said single detector, a second collimator comprising an X-ray opaque element, and means for rotating said element through said fanshaped beam about a second axis transverse to the direction of elongation of said single detector, said second collimator having at least one X-ray transparent slit therein whereby, as said element is rotated through said fan-shaped beam about said second axis of rotation, a portion of said fan-shaped beam emerges from said slit in the form of a pencil beam of X-rays that passes through a body on said support means and scans along said single elongated detector.

3. The radiant energy imaging apparatus of claim 2 wherein sad element has a plurality of said X-ray transparent slits angularly spaced from one another about said second axis of rotation.

4. The radiant energy imaging apparatus of claim 3 wherein said element comprises a disc-shaped chopper wheel.

5. The radiant energy imaging apparatus of claim 2 wherein said drive means is operative to effect continuous substantially constant speed rotation of said unit about said firstmentioned axis of rotation.

6. The radiant energy imaging apparatus of claim 5 wherein said X-ray system is operative to expose said body to a total X-ray dosage of substantially 100mR during a complete relative rotation of said unit and said body to be examined.

7. The radiant energy imaging apparatus of claim 5 including means operative prior to operation of said drive means for moving said unit translationally in a direction parallel to said first-mentioned axis of rotation to position said unit adjacent a particular cross section of the body to be examined.

8. The radiant energy imaging apparatus of claim 5 wherein a plurality of said elongated detectors are disposed in side-by-side parallel relation to one another, said single pencil beam of X-rays having a cross sectional shape which is dimensioned to impinge on said plurality of detectors simultaneously, whereby said plurality of detectors simultaneously produce output signals representative respectively of the X-ray response of adjacent cross-sectional slices of the body to be examined as said drive means continuously rotates said unit about said first-mentioned axis of rotation.

9. The radiant energy imaging apparatus of claim 8 wherein said first and second collimators coact to produce a single beam of X-rays whose cross section is elongated in a direction transverse to the directions of elongation of said contiguous detectors, said beam being scanned respectively from a position adjacent first corresponding ends of said elorigated detectors to a position adjacent the opposite corresponding ends of said elongated detectors along a scan path which is transverse to the direction of elongation of said beam.

10. The radiant energy imaging apparatus of claim 8 wherein at least some of said elongated detectors are contiguous with one another, and means for combining the output signals produced by at least two contiguous ones of said detectors for adjusting the width of the cross-sectional slice which is being examined in said body.

11. The radiant energy imaging apparatus of claim 1 wherein said drive means is operative to rotate said unit about said axis of rotation to a desired angular position relative to the body to be examined, and means operative subsequent to operation of said drive means for moving said unit translation ally and at substantially constant speed in a direction parallel to said axis of rotation.

12. The radiant energy imaging apparatus of claim 1 including means for adjusting the position of said X-ray source relative to said axis of rotation in a direction transverse to said axis of rotation thereby to adjust the size of the field being scanned by said apparatus.

13. The radiant energy imaging apparatus of claim 1 including means for adjusting the position of said detector relative to said axis of rotation in a direction transverse to said axis of rotation thereby to adjust the size of the field being scanned by said apparatus

14. The radiant energy imaging apparatus of claim 1 including means for adjusting the position of said unit relative to said axis of rotation in a direction transverse to said axis of rotation thereby to adjust the size of the field being scanned by said apparatus.

15. A method of examining an object by means of penetrating radiation, the method comprising: providing radiant energy imaging apparatus, comprising support means for supporting an object to be examined, and an X-ray system adapted to be moved rotationally as a unit relative to said object, said X-ray system comprising a source of X-rays located on one side of said support means, a single radiant energy detector located on the opposite side of said support means, and a mechanical scanning device located betwen said X-ray source and said support means, and drive means for effecting rotation of said X-ray source and said mechanical scanning device and said single detector as a unit relative to said object to be examined: and the method further comprising the step of causing said drive means to effect rotation of said X-ray source and said mechanical scanning device and said single detctor relative to said object to be examined while causing said source of X-rays to emit X-ray radiation.

16. Radiant energy imaging apparatus for examining a body by means of penetrating radiation substantially as described herein with reference to Fig. 2 of the accompanying drawings, or Fig. 2 as modified by Fig. 3 thereof, or Fig. 2 as modified by Fig. 4 thereof.