FR2482444A1 - X-RAY CALCULATED TOMOGRAPHY APPARATUS USING A FLOATING SPOT MECHANICAL MECHANISM - Google Patents

Abstract

A. APPARATUS FOR FORMING IMAGES BY RADIATION OF ENERGY THROUGH A BODY TO BE EXAMINED. B. APPARATUS CHARACTERIZED IN THAT IT INCLUDES MEANS OF SUPPORT 10 OF THE BODY TO BE EXAMINED; AN X-RAY SYSTEM ROTATING A SINGLE BLOCK IN RELATION TO THE BODY AND INCLUDING A SOURCE 11, A SINGLE EXTENDED DETECTOR 18 AND A MECHANICAL SCAN DEVICE 12 AND 14 MOUNTED BETWEEN SOURCE 11 AND THE SUPPORT MEANS 10 TO FORM A BRUSH SINGLE X-RAY 17 AND TO SWEEP THIS BRUSH 17 ACCORDING TO THE LENGTH OF THE SINGLE DETECTOR 18; AND MEANS INTENDED TO ROTATE THE X-RAY SYSTEM WITH A SINGLE BLOCK. C. THE INVENTION APPLIES TO TOMOGRAPHS CALCULATED IN X-RAYS.

Description

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  The invention relates to a tomography apparatus

  Calculated X-ray, using a scanning mechanism

mechanical floating spot.

  So far, a number of systems have been proposed for obtaining computed tomography

  (abbreviated as TC) for medical applications.

  shims or others. In general, these known systems are structurally

  relatively complex, and they are very expensive and lead to the patient being subjected to relatively large doses of radiation if we want to obtain images

  X-rays of sufficient quality to allow a good diagnosis.

  The invention aims to overcome these disadvantages of the prior art in. creating a device capable, when used in a CT scanning system, of providing comparable X-ray images and even in some cases

  better than those shown by the current CT devices.

  This apparatus according to the invention makes it possible to achieve the above results at much lower costs and by subjecting the patient to much lower radiation doses than in the case of the present conventional apparatus. These advantages are achieved by equipment using a mechanical scanning system of the general type described in U.S.A. Patent No. RE 28,544 to Stein and Co. (U.S.A. Initial Patent No. 3,780,291) allowing

  to get an X-ray brush sweeping a single detector.

  TC equipment using techniques

  Floating spot scanning has been widely proposed so far. One of these devices is described, for example, in an article entitled "Low dose X-ray imaging system using a floating spot X-ray micro-brush (Dynamic Scanner)", by Tateno and Tanaka, Radiology 121s.

October 1976 pages 189-195.

  The Tateno et Cie system, although it is described as capable of giving X-ray images

  of good quality for dosages lower than those

  used in conventional CT equipment, however, uses a special X-ray tube that is not found in

  this tube being characterized by an electronic optic

  very sophisticated analogue similar to that used in

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  high voltage electron microscopes and in electron brush machining equipment. In addition, the Tateno system is based on an electronic scanning technique and assumes

  the use of a two-dimensional detector.

  These characteristics of the system according to the prior art described above make it much more expensive than

  the system according to the invention which uses a balancing device

  Extremely simple mechanical work. In addition, since the Tateno et Cie system uses a two-dimensional detector, this system does not make it possible to eliminate the scattered radiation, unlike the system according to the invention in which the use of a

  single-dimensional detector-allows for automatic

  this elimination of scattered radiation.

  The invention has further advantages

  Compared with the Tateno et al. scanning technique, which employs a device producing a floating spot X-ray brush by projection through a "pinhole" of a scanning focused spot. In order to obtain an X-ray field large enough to cover the entire section of a patient in a CT scan, the brush must diverge a considerable distance from the collimator with a hole in the X-ray tube. needle. The required distance corresponds to a position of the needle hole at the point of the focal point (X-ray source) in the case of the invention. As the cross section of the brush represents in each point a picture

  from the focal spot through the needle hole, the relative distance

  A large gap between the needle-hole collimator and the patient leads to a relatively large brush section degrading the resolution of the device. The close proximity between the collimation system and the patient is a very important advantage of the invention because the size of the brush essentially consists of a projection of the small aperture

  collimator from the remote source thereof.

  Another system heretofore proposed for producing CT images by a floating spot technique is described in U.S. Patent No. 3,866,047 to Hounsdfeld, entitled "Radiation Penetration Examination Apparatus Using a Scanning Collimator". Hounsfield's apparatus uses a mechanical sweeping device comprising a pair of flaps

  lengthened so as to come and go in synchronism.

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  Each shutter element is provided with a number of slots cooperating with each other to produce simultaneously

  a number of radially spaced radiating brushes-

  each brush performing its scanning in a relative angle.

  small on a relatively small associated detector. The flap device comes and goes from

  Hounsfield is much more mechanically complex than colloid

  relatively simple rotary array used in the invention.

  On the other hand, the Hounsfield mechanical scanning device requires very critical alignments of the different slots used. Moreover, since the Hounsfield apparatus provides for the simultaneous production of a certain number of angularly spaced X-ray beams, and the scanning simultaneous of all these brushes on the same number of associated detectors, the arrangement used may pose problems of loss of information at the boundaries between adjacent detectors. Thus, two specific problems of this apparatus can be identified: (1) the limits produce a geometric loss of yield leading to doses of radiation which are lost in the! patient, and (2) the loss of information about the brush trajectories at the location of the boundaries can lead to artifacts in the 3

reconstruction of the CT image.

  Other problems with Hounsfield's multi-brush arrangement are related to the need for perfect adaptation or standardization of

  different detectors throughout the range of dynamic use

  signal, because in the absence of this precaution one obtains

  In addition, a certain number of phenomena such as, for example, variations in cathode resistivity and wear of dynodes can lead, as is well known, to nonlinearities or variations. gain in photomultiplier tubes

  used by the Hounsfield apparatus.

  Similar problems may arise with other, less efficient detectors than the photomultiplier scintillator devices. To reduce

  the dynamic range and thereby reduce the rigor of

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  Hounsfield incorporates a "block of plastic material" (reference 26 in the figure) into the apparatus, and proposes the use of a water pocket filling the space between the plastic block and the patient. The use of these devices leads to additional expense and greater mechanical complexity, leading to lost radiation doses

  by absorption of photons (and consequently to a loss of information

  mation) between the patient and the detector.

  The invention makes it possible to overcome all the above disadvantages of the prior art by using a

  unique detector of excellent performance and a device for

very simple mechanical age.

  To this end, the invention relates to an apparatus for image formation by radiation of energy through a body to be examined, characterized in that it comprises support means intended to support the body to be examined, a system for X-ray capable of rotating in a single block relative to the body to be observed, about an axis of rotation formed by the support means, the X-ray system comprising an X-ray source placed on one side of the means of support, a single elongated detector for detecting radiant energy, said detector being placed opposite the support means and lying in a direction transverse to the axis of rotation; and a mounted mechanical scanning device between the x-ray source and the support means so as to shape the radiation emitted by the source to form a single beam of X-rays, and to scan this single brush at an angle relative to at the source and-following the direction of the length of the single detector, the length of this

  detector and the positions of the detector and the

  mechanical scanning positive being selected so that the X-ray pinch subtends an angle embracing a complete cross section of the body placed on the support means, when the x-ray brush is scanning along the single detector; and training means for doing

  turn the X-ray source, the mechanical scanner

  and the single detector of a single block in relation to the body

  to examine, the rotation being around the axis of rotation.

  The mechanical scanning device is

  of the general type of that described in USA Stein et al.

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  RE 280544 resubmitted on 2 September 1975; based on the principle

  of US Patent No. 3,780,291 filed December 18, 1973. This arrangement

  device comprises a first radiation shaping collimator emitted by an X-ray source, so as to give the X-ray beam a fan shape, and a second collimator constituted by a disc-shaped cutting wheel made of a material X-ray opaque and having one or more transparent slots through which passes an X-ray brush, this brush being scanned according to the

  single linear detector when the second collimator rotates.

  The cutting die can take the form described in the above-mentioned Stein et al. Patent, or, in an alternative embodiment, be in the form of a drum structure of the type described in US Pat. No. 4,031. .401 of Jacob. The representative of each of these patents is the Company

  "Science and Engineering Inc", Cambridge, Massachusetts.

  The x-ray system including the x-ray source, the mechanical stripping device, and a single elongate detector is designed to be movable in multiple directions for different purposes. This system may, for example, move in translation along a line parallel to the axis of the support means, to give a conventional radiographic projection, similar to that obtained by the X-ray system Medical X-ray MICRO-DOSE (Manufactured by Ameridan Science and Engineering, Inc., Cambridge, Massachusetts.) In this mode of operation, as the X-ray system can rotate at any desired angle relative to the body support structure, the images can obtain easily, in any angle, in the form of AP, PA side or oblique images. The mode of operation described above can also be used to obtain location images preparing the TC scanning operation. , that is, the

  X-ray system can be translated from a single block parallel-

  to the body support structure, and conventional images obtained during this mode of operation can be monitored to locate the system in a particular area of the body for which a CT slice is desired, after which the X-ray system takes a rotational movement at substantially constant speed relative to the support structure 40 of the body, so as to obtain a CT scan of the selected slice.

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  This relative rotation between the scanner and the object being examined can be achieved by rotating either the scanning mechanism or the object or both. The relative rotation axis can be further selected for any particular application, and can be located either horizontally or vertically or at an angle

determined between the two parties.

  The system preferably comprises means for adjusting the size of the field of the CT magnet, this setting

  by mechanically manipulating the collision system.

  fan beam and cutting wheel, either in

  moving. the position of the X-ray block or

  of the axis of rotation so as to vary the spacing between this axis of rotation and the source and / or the X-ray detector. The system can also be used to produce simultaneously several CT scans using one or more fan beam collimation slots, all of which slots are traversed simultaneously, e.g.

  by providing a slot cut into a cutting wheel

  nant, and directing a number of parallel floating spot brushes, or a single beam of sufficient size,

  on several adjacent linear detectors, the multi-detector

  ples used in this configuration for which each elongated idetector subtends an area larger than the full field of its TC section, are not subject to the same

  requirements for standardization only in the case of several

  such as those used in the Hounsfield patent above.

  This is because: (a) each CT slice is obtained by means of a single detector, and (b) each detector can be calibrated many times during a single CT scan using the information obtained when the floating spot brush hits the

  detector outside the circle of his TC field.

  The output signals of multiple detectors can be used to simultaneously produce multiple independent CT images, thereby reducing the time that would otherwise be required to produce a series of CT images of a patient. This possibility can be particularly useful for obtaining

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  sagittal and coronal reconstitutions from infor

  multiple tranches9 because obtaining the information

  At the same time, the problems associated with the patient's movements between successive scans are eliminated. In an alternative embodiment of the operating mode, the output signals of two or more contiguous group detectors can be combined to allow an effective adjustment of the width of the same. slice under review., Other features and benefits of

  construction and operation of the apparatus according to the

  will appear more clearly on reading the description

  following which refers to the attached drawings in which:

  FIG. 1 is a schematic illustration

  of a medical X-ray system MICRODOSE According to the prior art,

  FIG. 2 is a schematic illustration

  FIG. 3 illustrates the system of FIG. 2 used in the scanning device of TC9 and FIG.

  FIG. 4 is a schematic illustration

  of an alternative detector arrangement that can be used in the embodiment of FIG.

  obtain multi-slice scans.

  As described above, the invention relates to a radiant energy imaging apparatus for obtaining CT scans and other types of scans for medical and other applications. This apparatus is based on the unique scanning mechanism and detector used in the Medical X-ray MICRODOSE system manufactured by American Science and Engineering, Inc., Cambridge, Massachusetts. This

  The system according to the prior art is illustrated in FIG.

  drawings. The apparatus of FIG. 1 comprises a support table or structure 10 for supporting the body of a patient to be examined by means of penetrating radiation, and an associated X-ray system for producing an X-ray brush. sweeping the patient's body. The X-ray system generally corresponds to the system described in the US patent

., 2482444

  No. RE 28,544 to Stein, incorporated herein by reference, and comprising a conventional rotary anode X-ray tube 11 whose output is collimated into a thin fan-shaped beam by a wedge-shaped collimator 12 formed by example, an alloy of lead and tungsten, with an opening

  relatively elongated elongated form 13 at its upper end.

  The fan beam is also collimated

  by an X-ray opaque cutting wheel 14 made of, for example, a lead-loaded aluminum alloy provided with tungsten jaws, this wheel being provided with a

  number of slots 15 arranged radially inwardly

  The cutting wheel 14 is rotatably mounted on a central axis as indicated by the arrow 169 and is positioned so that one of its edges completely covers the slot 13. collimator 12, except in the overlap area of the slots 13, 15. For purposes of illustration, that is to say to better see the slot 13 in Figures 1 and 2, the complete overlap relationship n ' has not been shown in the figures and so reference will be made to this

  to the drawings of US Patent No. RE 28,544 to Stein et al.

  The lead and tungsten used in the collimators 12, 14 completely attenuate the X-rays except in the slot overlap area, and the movement of the wheel 14 causes the smooth and repetitive movement of the slits 15 in the fan beam thereby giving a single X-ray scanning brush 17 whose section size is determined by the shapes of the slits 13 and 15 in their overlap area. This X-ray brush is attenuated in particular by the subject placed on the table 10, and the attenuated x-ray X is picked up by the elongate photon detector 18 constituted by the single detector of the type described above in the Stein et Cie patent. when the brush 17 performs its

  scanning from one end to the other of the detector 18.

  During this sweep operation the whole

  X-ray system including the X-ray source, the cutting wheel, and the detector moves in a single block in the direction indicated by the arrows 19, i.e. in a transverse direction relative to to the length of the detector 18, to travel the entire length of the patient who remains in a fixed position on the table 10, so as to produce

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  thus a multitude of rows of data similar to those

  of a television scan, these data being taken from the

18 as indicated in 20.

  These output signals provide a radiograph on the television screen (not shown, for example, by intensity modulation of the electron beam of the CRT of a memory oscilloscope, or conventional scan-type convective-heat storage tube In an alternative embodiment, the output signals can be digitized and stored in a computer memory, then

  treated by this calculator to give a digital X-ray

  only on a television screen or any other device deaffi = chage. The single detector 18 is a scintillation crystal coupled to one or more combined output photomultipliers, and substantially 100% of the patient's unmitigated X-rays are thus detected. The electrical signals obtained at the photomultiplier output are pulses. amplitude of each of these pulses being proportional to the energy of a single X-ray photon detected. Since the flow rate of the photons X arriving at the detector is very large, these pulses add up to give an overall signal representing at each instant a value proportional to the incident X-ray flow of the brush.

attenuated X-ray.

  The electrical signal from the detector, during a brush scan from one end to the other of this detector, corresponds to a one-dimensional line of the radiographic image of the object, this line being similar to that of an ordinary television scan. The second dimension of

  the image is obtained by the movement of the source-collimator plane

  detector relative to the patient. The series of lines in the image is stored sequentially in digital form and, when

  X-ray exposure is complete, radiographic data

  phics are read and played back line by line on the TV screen. The restitution is done sequentially in the same order as the reading of the data in the memory, so that the image obtained on the television screen corresponds to the image projected in X-rays of the subject under examination,

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  In the apparatus according to the prior art of

  Figure 1, the X-ray system can only move in trans-

  tion only, that is, in the direction of the arrows 19.

  On the contrary, according to the invention, the X-ray system of FIG. 1, whose same parts as those of FIG. 2 are marked with the same references, is mounted so as to be able to take a large number of positions under the control of various training means known per se and which are therefore not

  not shown in Figure 2 for simplification purposes.

  The lateral movement indicated by the arrow 19 can be blocked

  in FIG. 2 when it is desired that the system according to the invention

  tion has the characteristics already described in FIG.

  and / or when the system of Figure 2 is to perform

  TC situations preceded by the formation of location images.

  However, the system of FIG. 2 is essentially characterized by a provision in which the lateral movement indicated by the arrow 19 is replaced or completed by a rotational movement of the patient relative to the scanning device, as indicated by the arrows 21, around an axis of rotation 22 constituted by the nominal axis of the patient supported by the table 10. In practice it is possible to rotate either the patient or the scanning mechanism or both. When the scanning mechanism rotates about the axis 22, this mechanism rotates in a single block that is to say that the linear detector 18 located on one side of the table 10 is physically connected to the

  mechanism of X-ray production and the colliding structure

  on the other side of the table, the fixing being ensured by an appropriate connecting structure] indicated by the

dotted line 23.

  When the device is used in CT scanning device, TC scanning performed by the system

  Figure 2 is essentially similar to that of the

  TO scanning devices with two movements or translational

  rotat.ion, but does not present the mechanical disadvantages

  and the complexity of these known devices which require

  mechanical translation back and forth from the X-ray source, the collimator and the detector (s), between

  rotational movements step by step of the set. According to the invention

  The two movements (sweep brush and rotation of the sweep assembly) are smooth, continuous, and simultaneously. The number of brush passes with each rotation of the scanner relative to the patient determines the number of "views" of the TCo scan. The data read by the detector 18 is reconstructed by methods well known in the art of T09 algorithms. Examples are, for example, described in the article BKP Horn "Fan Bundle Reconstruction", Proceedings IEEE,

December 19799 pages 1616-1623.

  A passage of the brush along the detector: typically takes about 1 second, and a typical rotation of the object under examination relative to the X-ray scanning system can be done in about 5 to 10 seconds, giving a total of 900 to 1800 views during a full rotation

  of the X-ray scanner relative to the patient.

  These characteristics are only given by way of example and it is also possible, in another embodiment of the invention, to use a rate of 30 sweeps per second and a complete relative rotation of the scanning system 9 by

  to the object to be examined, with a period of 15 seconds, to

thus hold 450 views.

  The general operation of the system according to these features of the invention is described in FIG. 3, where again the same parts are marked with the same references. The important points to note in Figure 3 are that the x-ray source 11 and the mechanical scanner 129 14 cooperate to provide a single scan brush X-ray scanning linearly in the direction of arrow 24 by going from one end to the other of the

  linear detector 18, this scanning subtending an embracing angle

  a full cross-section of the body or object to be inspected generally indicated by the reference 25 and moving in a rotational movement (see arrow 21) relative to the Xo-ray scanner. TC scanning can be adjusted by mechanical manipulation of the fan beam and the collimating wheel system 129 14, for example by changing the size of the collimation slots. We can still adjust the size of the field (we will refer to this in Figure 3) by moving the source 11 to the axis of rotation of the object 25 to obtain a smaller field and a

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  higher resolution, or closer to the detector 18 the axis of rotation of the object to thereby obtain a larger field and a lower resolution. These possible movements of the x-ray source 11 and / or the detector 18 with respect to the table 10, have been identified by the arrow 26 in FIG. 2. Typically the total radiation dose at which the swept area of the body is exposed. , during a CT scan, is about 100 mR. This dose represents between _ and 1 of the dose applied in the devices

'100

  However, it has been found that the image obtained according to the invention, with these very low radiation doses, is quite comparable and even in some respects better than the images provided at the present time. much higher costs and with much higher radiation doses, by the current scanning devices of the trade. In addition to these very important advantages, the invention makes it possible to retain most of the advantages of the systems according to the prior art shown in FIG. 1. More precisely, the invention makes it possible to obtain a spatial resolution of less than one millimeter. virtually all of the scattered radiation, and an operating efficiency of the

radiation approaching 100%.

  Another very important advantage of the system

  Figure 2 is that it constitutes its own system of loca-

  and allows for digital data processing in either of its two modes of operation, ie it achieves both its X-ray goals

  digital and TC system. Moreover, because of its

  relative rotation represented by the arrows 21, the system can be used not only to produce its own

  location images and to perform radiographic processing

  digital image of these images, but still to obtain very

  capping AP, PA, lateral or oblique images in any

what angle would you like

  As indicated above, the relative rotation between the object or patient to be examined, and scanning device, can be achieved by rotating either the scanning mechanism, the object, or both. Moreover the axis of rotation can be chosen and oriented at will for any desired application, and in particular this axis can be ilorUzontal as shown in Figures 1 and 29 or verticalo A vertical orientation of the present scan axis The advantage of facilitating the rotation of the rotating cutting wheel 14 in the earth gravity field. The radiation source used in the invention may be a conventional X-ray tube, a radioisotope source or a synchrotron. However, regardless of the source used, the simplifications provided by the invention largely result from the use of a rotary type collimator which can take the form indicated in the drawings, or the form described in US Pat. No. 4,031,401. from Jacob, or again, if desired, the shape of a cylinder

  rotating with transparent helical slots

  ment. The detector used presents essential

  detection efficiency of 100% and a geometric

  100%, which is not the case with most TO scanning sensors according to the prior art. The resolution

  Spatial image of TC image is very high. The trans-

  Both the versale (in the slice plane) and the axial resolution (in the slice thickness) are both less than one millimeter, and these resolutions are achieved without loss of radiation dose efficiency. In addition, radiographic images and CT images can be obtained by placing the detectors outside the scanning plane and then using the scattered radiation detected to produce an image, as described for example in the Stein patent and Company mentioned above. This image formation by backscattering is possible according to the invention because there is only one known geometric position of the scanning brush at each instant9 and because the diffusion of its trajectory through the object essentially controls the amplitude of the broadcast signal

at this moment.

  The system of FIG. 2 can also be used to produce several CTo scans simultaneously. This result can be obtained by means of an arrangement of the type described in FIG. 4 in which a number of linear detectors such as 18a, 18b and 18c are arranged parallel to each other, and in which the brush

  (shown in section 17a of Figure 4) shows dimensions

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  It is such that it simultaneously hits the various detectors as it sweeps in the direction 24 from one end to the other of the neighboring detectors. The brush 17a may consist of a number of parallel brushes respectively associated with the detectors 18a to 18c, or

  a single brush with an elongated section in a trans-

  versale with respect to the scanning direction 24, these various brush configurations being obtainable by using one or more collimation slots of the fan beam of the mechanical scanner 12, 14, or by increasing the

  width of the slit 13 of the collimator 12, increasing correlatively

  the length of the slit 15 of the collimator 14.

  Using the arrangement of FIG. 4, several output signals 20a can be obtained simultaneously from the various detectors 18a to 18c, and these various simultaneous output signals can be processed in various ways to obtain different results. For example, the various output signals can be individually processed to produce multiple slice images simultaneously. On the contrary, it is possible to combine and process together the output signals of two or more neighboring group detectors to adjust, in fact, the width of a slice

particular being examined.

  The invention also applies to

  even to other techniques such as using

  different filtering or different detection characteristics

  in contiguous planes, or to use a low-energy detector supported by a high-energy detector placed in the same plane, which makes it possible simultaneously to obtain data corresponding to two different energy levels. This type of use can be used for both

  TC only for digital radiography images. The subtraction

  two images obtained at different energy levels

  can be used to exploit iodinated contrast materials.

  The use of this feature combined with the observation of multiple slices, for example allows to obtain a volume image of the blood vessels rather than a picture in a slice.

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  It is obvious that the embodiment of the invention described above is not limiting and that specialists of the question can make many variations. For example, instead of applying to the field of medical diagnostic imaging as described above, the invention can equally well be applied to any other

  type of non-destructive test within the scope of this

this. ap

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Claims (12)

  1. Apparatus for forming energy radiation images through a body to be examined, characterized in that it comprises support means (10) for supporting the body to be examined, an X-ray system capable of to rotate in a single block relative to the body to be observed, about an axis of rotation (22) formed by the support means, the X-ray system comprising an X-ray source (11) placed on one side support means, an elongated detector   a single detector (18) for detecting the radiant energy, this detection   the driver (18) being placed on the opposite side of the support means (10) and lying in a direction transverse to the rotation rate (22); and a mechanical scanning device (12, 14) mounted between the X-ray source (11) and the support means (10) so as to shape the radiation emitted by the source (11) to form a single brush ( 17), and for scanning this single brush at a certain angle with respect to the source (11) and following the direction of the length of the single detector (18), the length of this single detector (18) and that the positions thereof and the mechanical scanning device (12, 14) are selected such that the X-ray brush (17) subtends an angle embracing a complete cross-section of the body on the support means ( 10), when the x-ray brush X (17) performs its   scanning along the single detector (18); and means of   tracing for rotating the x-ray source X (11), the mechanical scanning device (12, 14) and the single detector (18) in a single block with respect to the body to be examined, the   rotating around the axis of rotation (22).   2. Apparatus according to claim 1,   characterized in that the mechanical sweeping device comprises   takes a first collimator (12) for shaping the radiation emitted by the source to form a fan-shaped X-ray beam, the elongated direction of the beam section being parallel to the length of the single detector (18). ); a second collimator comprising an X-ray opaque element (14); and means for rotating the opaque member (14) in the fan-shaped beam, the rotation being about a second axis transverse to the length direction of the single detector (18), the second collimator (14) being pierced with at least one X-ray transparent slit (15), at which point, when the element rotates in the fan-shaped beam about the second axis of rotation, a portion of the fan-shaped beam emerges through the slit ( 15) forming an X-ray brush (17) passing through the body on the support means (10) and scanning along the single elongated detector (18). 3. Apparatus according to any one of   Claims 1 and 2, characterized in that the upaque element   (14) has a number of slots (15) transparent to X-rays, these slots (15) being angularly spaced apart   others around the second axis of rotation.   4. Apparatus according to any one of   Claims 1 to 3, characterized in that the opaque element (14)   consists of a disc-shaped cutting wheel.   5. Apparatus according to any one of   1 to 4, characterized in that the means of   can be used to rotate the assembly block continuously and at a perfectly constant speed around the first rotation axis (22) -   6. Apparatus according to any one of   Claims 1 to 5, characterized in that the spoke system   X is designed to expose the body to be observed at a total x-ray dose of 100 mR during a complete rotation of the block   overall compared to the body to be observed.   7.- Apparatus according to one quebonque   Claims 1 to 6, characterized in that it comprises   means operating before the drive means for driving the assembly block (11i, 12, 14, 18) in translation in a direction parallel to the first axis of rotation, in order to bring this assembly block into a position adjacent to a   particular section of the body to be examined.   8. Apparatus according to any one of   Claims 1 to 7, characterized in that a number   elongate detectors (18a, 18b, 18c) are placed parallel to each other, and in this case the single X-ray brush has a cross-section of dimensions such that it can simultaneously strike all the detectors, whereby these various detectors , simultaneously produce output signals representing respectively the X-ray response of slices 18 2482444   adjacent to the body to be examined, when the drive means   rotate the assembly block (11, 12, 14, 18) continuously   around the first axis of rotation (22).   9. Apparatus according to any one of   Claims 1 to 8, characterized in that the first and the   second collimator (12, 14) cooperate to produce a single X-ray beam (17) whose cross section is elongated in a direction transverse to the longitudinal directions of the contiguous detectors (18a, 18b, 18c), this beam respectively performing its sweeping between a first position close to the corresponding ends of the elongate detectors, and a second position close to the other corresponding ends of the elongated detectors, this sweeping along a path transverse to the direction longitudinal beam (17).   10. Apparatus according to any one of   Claims 1 to 9, characterized in that at least some   elongate detectors are contiguous and means are provided for combining the output signals produced by at least two adjacent detectors so as to adjust the   width of the cross-sectional area of the body to be examined   undermine. 11. Apparatus according to any one of   claims 1 to. 10, characterized in that the means for   processing enable the assembly block (11, 12, 14, 18) to rotate about the axis of rotation to bring it into the desired angular position relative to the body to be examined, and that additional means enter then in play   to train the assembly block in a translational movement   constant speed in a direction parallel to the axis rotation (22).   12. Apparatus according to any one of   Claims 1 to 11, characterized in that it comprises   means for adjusting the position of the x-ray source X (11) relative to the axis of rotation (22) so as to adjust   thus the size of the field scanned by the device.   13. Apparatus according to any one of   Claims 1 to 12, characterized in that it comprises   means for adjusting the position of the detector (18) with respect to the axis of rotation (22) in a transverse direction by 19 2482444   compared to it9 so as to adjust the size of the field swept by the device.   14.- Apparatus according to any one of   Claims 1 to 139, characterized in that it comprises   means for adjusting the position of the assembly block (11, 12, 14, 18) with respect to the rotation coefficient (22), in a direction transverse to the latter, so as to thereby adjust   the size of the field scanned by the device.