FR2551220A1 - System for detecting X-rays at grazing incidence and an essentially rectangular detector cluster included in this system - Google Patents

Abstract

The system is positioned in such a way as to intercept the radiated energy from the source 10 after passing through the object under examination 18. A number of elongated tubular elements 21 are arranged alongside and parallel to each other and lie in a direction roughly parallel to that of the linear scanning. Each element has an internal surface which reflects optical photons. A light-sensitive system produces a composite output signal representative of the energy content of the radiation from the object under examination. Application to an X-ray detector giving as short as possible an exposure time for the object under examination.

Description

Low angle X-ray detector and detector unit
tor entering this essential beam assembly
rectangular. "

The present invention relates to an X-ray detector assembly capable of being used to convert penetrating incident radiation, such as X-rays or gamma rays (hereinafter generically designated by the term X-rays) into light, and this invention relates more particularly to an improved set of on-line detectors of the general type described in the prior pending US patent application mentioned above, No. 304 442, and intended to be used with an X-ray machine with a moving spot, by example of the type described in the US patent of Stein and others no. 3,780,291 (published on December 18, 1973 and published again on September 2, 1975 under the reference RE 28 544 under the title "Radiant Energy Imaging With Scanning
Pencil Beam "), or with other types of ray device
X employees for medical diagnoses.

The apparatus represented in the aforementioned patent of
Stein et al. Includes an X-ray source, the output of which is collimated by a fixed slit in cooperation with a rotating disc having slits, in order to produce a fine beam of X-rays which sweeps in a linear direction an object to be examined. X-rays that pass through this object are detected by an elongated detector which is oriented in the scanning direction and which is capable of generating output signals representative of the x-ray opacity of the object on the object. a plurality of such lines are generated by translation of the source device / X-ray detector and / or of the object to be examined relative to one another in a direction transverse to the direction of scanning, so as to generate groups of 51 o signals which can be processed and used to obtain a two-dimensional image of the x-ray opacity of the object to be examined.

 The first also pending application no. 304 442, the description of which is incorporated in the present text for reference, describes an improved on-line detector which can be used in an X-ray inspection system and which is intended to convert a online beam, a fine beam, or a fine X-ray scanning beam into an electronic signal with 100 percent X-ray detection. The detector has an elongated tubular member made from a material transparent to X-rays, having an inner surface reflective for optical photons and which supports a thin elongated planar scintillator, the plane of which is oriented at an acute angle with respect to the direction of the beam, whereby the path of the X-rays through the scintil - lator is more important than the thickness of this scintillator. The optical photons which are emitted by the scintillator are reflected by ld on the inner face of the tubular organ towards a multiplier tube which is adjacent to at least one end of the detector. scintillation which is an efficient X-ray absorber, which has a very reduced optical phosphorescence and / or which has unique absorption characteristics for a specific X-ray energy but which, at the same time, can be a poor transmitter of visible light , either because it is not really transparent, or because the scintillator material is in the form of a powder, as in a conventional X-ray intensification screen.

 The present invention relates inter alia to a new set of detectors of the general type described in this previous application No. 304,442, which makes it possible to obtain a certain number of advantages.

In particular d) the energy collected from the X-ray source
is increased by a factor equal to the number of pairs of
detectors implemented in the detector assembly,
thus ensuring an increase in the efficiency of
collection which can be used to improve the re
Space solution, since data is obtained
si.nultanenent in each of the detectors, so
that each detector can define a dimension of ima
smaller age, b) alternatively, excess energy can be used
to obtain a higher resolution density by increasing the exposure, c) alternatively, the improved collection efficiency
can be used to decrease exposure time
tion for the subject, that is to say that the exhibition time
sition can be reduced by a factor equal to the number
pairs of detectors that are used in this
together, d) since each of the detectors in the set sees the
the whole subject, the problem of adapting
detectors to each other is eliminated, i.e.
that as opposed to the other systems suggested jus
that here that use a row of small detectors
discrete, there is no need in this
invention of standardizing (i.e. adapting the
response) from each detector to each signal level
to avoid "lines" in the final image, e) since the different detectors in this set
each generate a representative output signal
of the whole subject, the signals coming from
different detectors can be combined according to
selected means to provide various types
information regarding the x-ray opacity of
the object to be examined.

 The aforementioned advantages of the present invention are obtained by using a new detector assembly which is designed to cooperate with a source of radiation energy which, in the preferred embodiment of the invention, generates a beam of radiation energy which provides a scanning in a predetermined linear scanning direction through an object to be examined. The cross section of the beam is of substantially rectangular configuration and its longest cross section dimension oriented transversely to the linear scanning direction of the beam. The detector assembly is positioned to intercept radiation energy from the X-ray source having passed through the object, and this assembly includes a plurality of elongated tubular members which are arranged in parallel juxtaposition with one to the other with the elongation axis of each of these tubular members oriented essentially parallel to the direction of linear scanning.

 As in the case of the previous application also pending No. 304,442, each of the detectors in the detector assembly comprises an elongated tubular member, preferably having a rectangular cross section, which is made of a material transparent to irradiated energy. and which has an internal surface reflected healthily to optical photons. Each of these tubular members has a relatively thin body of scintillator material which has an elongated rectangular planar surface extending in the direction of elongation of the tubular member and which is positioned to intercept the irradiated energy passing through it. tubular member, when the beam is moved in the direction of linear scanning. The length of each of these scintillators is at least equal to the linear extent of the scanning of the beam. The width of the planar surface of each of these scintillators is a fraction of the longest cross-sectional dimension of the rectangular cross-section beam, whereby each of these planar surfaces is intended to intercept only part of this beam when the beam is moved in its scanning direction. In addition, the planar surface of each of these scintillators is oriented so as to intercept the part which is associated with it of the scanning beam at a grazing angle, 'each of these different planar surfaces intercepting respectively different parts of the beam.

 The elongated tubular members constituting the various detectors in this assembly are juxtaposed according to at least one row of tubular members which extends from the source of radiation energy, whereby the beam passes successively through the tubular members in this row. In a preferred embodiment of the invention, the elongated tubular members are juxtaposed in a plurality of these rows which are superimposed on each other and the scintillator material, associated with the different tubular members, comprises respectively a pair of sheets planar of this scintillator material supported on opposite sides of an interposed optically opaque substrate, and disposed in the planar region extending between the superimposed rows of tubular detector members. In this latter preferred embodiment of the invention, the detectors are positioned with respect to the X-ray beam so that this beam falls simultaneously on two rows of detectors, and immediately passes through the detectors in the two rows, thus generating groups of signals from all the detectors, these signals then being able to be added or subtracted from each other to prepare the generation of an image including specific varieties of information.

The aforementioned objects and advantages, the construction and the operation of the present invention, will be clear from the following description and the attached drawings in which
FIG. 1 is a schematic perspective view of an X-ray apparatus comprising a detector assembly constructed in accordance with the present invention,
FIG. 2 is a schematic section of the detector assembly shown in FIG. 1,
FIG. 3 is a section along the line AA in FIG. 2,
FIG. 4 is a section along the line BB in FIG. 2,
FIG. 5 is a perspective view of the detector assembly of the present invention showing the typical dimensions which can be used in an embodiment of the invention,
- Figure 6 is a schematic section of a single detector in the assembly of Figure 5, indicating other dimensional considerations with regard to the operation at a grazing angle of each detector.

 Referring firstly to FIG. 1, the X-ray apparatus with which the detector assembly of the present invention is used, comprises an X-ray source 10 which generates a beam 11, in the conical assembly, X-rays which are collimated into a moving beam 12 of X-rays of rectangular cross section by means of a rotating disc 13 made of an material opaque to X-rays and comprising a plurality of slots 14 in cooperation with a plate 15 opaque to rays X comprising a fixed slot 16. The entire device used to produce the x-ray beam with a moving spot and the operation of this device, are described in patent RE 28 544 of Stein and the like, previously mentioned. But unlike the device described in this prior patent, the height of the fixed slot 16 is such that the X-ray beam 12, emerging from this slot, has a rectangular cross section with its largest dimension p oriented transversely to the r ection of linear scanning of the beam, and the ends of the fixed slot 16 are inclined to danner this slot 16 in a trapezoidal configuration, guaranteeing irisai that the cross-sectional shape of the beam 12 is essentially constant, when each slot 14 passes from one end to the other of the stationary slot 16, during the rotation of the wheel 13.

 When each slot 14 passes from one end to the other of the fixed slot 16, the X-ray beam 12 moves in a direction in the linear assembly designated by the arrow 17, through an object or subject 1.8 to be examined . While the object 18 is repeatedly scanned in the direction 17, the subject 18 (or the X-ray source / collimator / detector assembly) is moved in translation in a direction at right angles to the scanning direction 17 to carry out a scanning of the trdme type of the subject 19 in two dimensions.

The scanning beam falls on the detector assembly which as a whole is designated by 19 and which intervenes to generate the output signals from each of the different detectors of this set at several output points designated as a whole by 20, a such an output being provided for each of the detectors in the set, these signals being able to be combined with one another and / or processed in another way in a manner which will be examined below to produce a visual image representative of the opacity at X-ray of the object 18 examined.

 Referring now more particularly to FIGS. 1 to 6, where the same numbers are used to designate the same parts, the detector assembly 19 comprises a plurality of detectors I, II, III, IV, etc., each of which has a rectangular cross section and each of which is of an elongated configuration extending in the whole parallel to the scanning direction 17. The dimensions of the different detectors are not critical but for the explanation which will be given below, it is assumed that each detector has a depth (in the direction of incidence of the X-ray beam 12), of 2 cm, a height of 4 cm, and a length, according to the scanning direction, of 1.5 meters (see figures 5 and 6). Each detector further comprises a hollow tubular member 21 having a reflective internal surface formed for example by a layer of aluminum sheets, and a wall of this tubular member is limited by a planar sheet 22 of a scintillator material having a thickness for example 0.1 mm (see Figure 6). The different detectors I, II, etc., are arranged face to face and being juxtaposed with each other (see Figures 1, 2 and 5) to form a row of detectors which extends from the X-ray source 10 so that, when the beam 12 scans in the direction 17, the incident beam on the detector assembly 19 passes through the various detectors I, II, III , etc ..., successively and, in doing so, falls on the part of the scintillator screen 22 associated with each of these detectors, to cause by this scintillator screen, the emission of optical photons which are reflected by the surface internal of the tubular detector organ v ers one or more photo-multiplier tubes 23 (see FIG. 3) which are available at one end or at both ends of the elongated detector or which can be coupled to the detector at other suitable locations.

 According to a preferred embodiment of the invention, the assembly 19 comprises a second row, of similar configuration, of detectors I ', II', III ', etc.

which is superimposed on the row of detectors I, II, III, etc., and which is provided with a similar sheet of scintillating material 22a (see FIG. 4) which is separated from the sheet 22 by an optically opaque substrate interposed 22b used to support the two scintill screens teu r. When rows of superimposed detectors are used, the detectors in row I, II,
III, etc ..., are offset respectively from the detectors in the row I ', II', III ', etc ..., all the more since the scintillator 22, 22a, 22b has a finite thickness (see FIG. 2) .

 The assembly 19 as a whole is oriented in such a way that with respect to the direction of incidence of the beam 12, this beam falls on the part of the scintillator screen of each detector at a grazing angle 0 (see FIG. 2) which according to an embodiment of the invention, can be an angle of 20 (see FIG. 6). As a result, the path of the X-rays through the scintillator is greater than the thickness of the scintillator. More particularly with reference to FIG. 6, it is assumed that the width of each rotary slot 14 is 0.7 mm, in which case the smallest dimension of the cross section of the beam 12 is 0.7 min and when the beam falls on a scintillator screen 22 having a thickness of 0.1 mm, the actual penetration of the X-rays into the screen 22 has a path length of 1.5 mm.

 Due to the cross-sectional dimensions of each detector in the detector assembly, and the angular orientation of the scintillator screen associated with each detector, the projection of the sheet, angularly inclined, of the scintillator material in a transverse direction to the scanning direction 17 of the beam; is only a fraction of the largest dimension p of the beam 12. The number of detectors which are employed in the rows of the assembly are however such that the projection of the complete sheet 22 in a direction transverse to the scanning direction 17 of the beam, has a dimension at least equal to p (see Figure 1), whereby all the parts of the beam are intercepted by the scintillator screens in the different detectors. For example, twenty detectors of this kind can be used in each row in the detector assembly, each of them being designed to intercept a part of 0.7 mm of the dimension p of the beam (see FIG. 6), whereby the twenty detectors collectively intercept all the parts of a beam with a larger dimension p of 14 mm (see Figure 5).

 When several rows of detectors are used, as seen for example in FIGS. 1, 2 and 5, the detector assembly is positioned with respect to the beam 12 so that a line parallel to the X-ray beam and cutting the junction of a side wall of I, II, III, etc ..., and of the scintillator, will cut the same junction in I ', II', III ', etc. . More particularly, as previously mentioned with the dimensions indicated in FIG. 6, the spatial resolution of each detector in the detector assembly is approximately 0.7 mm in a direction transverse to the detectors, when the width of the rotary slot is 0.7mm. There is a "crosstalk effect" due to the fact that an X-ray photon falling in the vicinity of the upper edge of the detector I 'for example (see FIG. 2) can be detected, either in the detector I or in the detector TI. This effect can be reduced by using a thinner scintillator screen. When the scintillator screen is 0.1 mm thick, the penetration of X-rays into detector I is 1.5 mm and using pairs of detectors I, I 'in parallel, the total absorption is 3 mm. The edge effect or "crosstalk" is therefore approximately 1 mm outside of 7 nin, which is of acceptable importance.

 To increase collection efficiency, the number of detectors used in the detector set is said to be as large as possible. As previously mentioned, twenty detectors of this kind can be used in each row of the detector assembly, i.e. twenty pairs of detectors Z-I ', II-IL', etc ..., can be used , and this will result in a detector assembly having the dimensions indicated in FIG. 5. Jn such an assembly using twenty pairs of detectors, will in fact be able to process twenty lines at a time, and when the relative portions of the object 18 and of the detector assembly 19 are displaced in a direction transverse to the scanning direction 17, between each of the different movements of the beams, of a dimension equal to the height of each detector, the energy collected from the X-ray source is increased by a factor related to the number of detectors, either the additional energy can be used to achieve higher density resolution by increasing the dose, or the increased collection efficiency can be used to reduce the exposure time of the subject. As an example from this last point of view, when twenty detectors can be used in the detector assembly, the exposure time can be reduced by a factor of twenty, thus allowing the subject to only be exposed to X-rays for a small number of tenths of a second.

 Since each of the detectors is used to record the entire image, it is only necessary to total the signals from the different detectors to obtain these advantages. By way of example, considering the succession of data obtained, during a first beam scan, a data line will be obtained with the detector I. In the second beam scan another data line will be obtained with the detector I, but a data line will also be obtained with the detector II and added to the previous line of the detector I, because these two data lines are at the same level on the object. During a third scan of the beam, since there is had an additional increment of the movement of the object relative to the detector assembly, the first line of data coming from detector III can be obtained from the same location on the object as the second sampling from detector II and the first sampling from detector I, and all these samples can be added up, etc. . . .

This combination of data lines is carried out by means of an appropriate computer program or else by electronic circuits dedicated to this purpose (see FIG. 1), in order to obtain the advantages described above.

 When combining the signals generated by the different detectors in the detector set, one must take into account the delay with which each successive detector "sees" the same surface of the subject while being delayed by a short time interval, and the combination of the signals must also provide for an actual correction phase to correct the faster scanning along the successive detectors of the parts of the X-ray scanning beam corresponding to relatively larger rays along the slots on the rotary wheel 13. In the center of the image or in its vicinity, that is to say when the active slit 14 is perpendicular to the length of the detector assembly 19, no correction phase is necessary. Towards the edges of the image on the other hand, the radiation received by successive detectors at any time (i.e. for each particular data sampling interval) corresponds to projections through the subject which are successively further away born from the central line of the detector assembly. Before adding the successive lines of data to constitute a final image, it is therefore necessary to introduce a phase difference in the successive lines, so that the combined data samples correspond to locations on the subject which are also distant from the central line. This phase difference can be corrected in the electronics of each detector or alternatively in beech variant carried out by an appropriate software interpolation of the uncorrected measurements.

Instead of totaling the signals, the energy of the different signals can be subtracted conveniently by subtracting the signal from the detectors I + II t III, etc., from the signal generated by the detectors I '- Il' t III ', etc ...,. Detectors
I + II - III, etc ..., measure the lowest X-ray energy, while the detectors I '- II' - III ', etc ..., measure the highest X-ray energy.

 The previous description is for illustrative purposes only and is not limitative of the present invention.

and that all variants and modifications in accordance with the principles set out are considered to fall within the scope of the appended claims.

Claims (12)

 10) X-ray detector assembly for use with a radiation energy source (10) intended to produce a beam (11) of radiation energy which is rapidly moved in a predetermined linear scanning direction through an object to be examined (18), the cross section of this beam being essentially of rectangular configuration and the largest dimension of this cross section being oriented transversely to the linear scanning direction, characterized in that it is positioned so as to intercept the radiation energy from the source (10) having passed through the object to be examined (18) comprising a plurality of elongated tubular members (21) arranged by being juxtaposed parallel to one another with the axis d elongation of each of these tubular members (21) oriented substantially parallel to the linear scanning direction, each of these tubular members (21) being made of a material transparent to radiation energy and having an internal surface reflecting for optical photons, each of these tubular members (21) comprising a relatively fine structure of scintillating matte material (22), this structure having an elongated rectangular planar surface extending in the direction of elongation of the tubular member and positioned to intercept the radiation energy passing through this tubular member, when the beam is moved rapidly in the direction of linear scanning, the length of each of these planar surfaces being at least equal to the linear extent of the beam scan, the width of each of these planar surfaces being a fraction of the largest cross-sectional dimension of the beam, whereby each of these surfaces is designed to intercept only part of the beam , when this beam is moved rapidly in the scanning direction, the planar surfaces of each of these structures d e scintillator material being oriented to intercept this part of the beam (11) at a grazing angle (), each of these different planar surfaces intercepting different parts of the beam, a plurality of elements reacting to light being coupled to this plurality of tubular members (21) for actually receiving the optical photons emitted by these structures of scintillator material (22), and means being coupled to this plurality of light-reactive elements for producing a composite output signal representative of the ability to radiation energy of the object to be examined.  20) X-ray detector assembly according to claim 1, in which each of these elongated tubular members (21) has a rectangular cross section, the planar surface of the structure of scintillator material (22) associated with each of these tubular members (21 ), being adjacent to an outer flat wall of this tubular member.  30) An X-ray detector assembly according to claim 1, in which each of these tubular members (21) has an elongated parallelepiped configuration, these tubular members (21) being arranged face to face with one another in a two-dimensional assembly, taking the form of a pair of superimposed rows of these tubular members, the scintillator material structures (22) associated with these tubular members comprising parts of an essentially continuous sheet of this scintillator material which is arranged between these superimposed rows of tubular organs.  40) An X-ray detector assembly according to claim 3, in which the tubular members (21) of one of these rows are arranged offset relative to the dux tubular members of the other of these rows.  50) X-ray detector assembly according to claim 3, in which the continuous sheet of scintillator material (22) is arranged in a plane inclined at an acute angle with respect to the direction of incidence of the beam (11) on the assembly detector, the projection of this angularly inclined sheet of scintillator material (22) having a dimension in the direction transverse to the scanning direction of the beam (11) which is at least equal to the largest dimension of the cross section of this beam (11).  60) X-ray detector assembly according to claim 1, in which the plantar surfaces of the scintillator material structures (22) are essentially co-planar with one another.  70) X-ray detector assembly according to claim 1, in which the dimensions of these elongated rectangular planar surfaces are the same for each of the tubular members (21), whereby each of these planar surfaces is designed to intercept a same fraction of the beam (11).  80) X-ray detector intended for use in a system of the type comprising a radiation energy source (10) intended to produce a beam (11) of penetrating radiation and to rapidly move this beam through an object to be examined ( 17), this detector being designed to intercept the radiation energy having passed through this object, this detector comprising a plurality of elongated tubular members (21) each of which is transparent to this radiation energy and each of which has a fine structure of scintillator material (22) extending in the direction of elongation of this tubular member (21) to emit optical photons in response to the radiation energy arriving on this structure, each of these scintillator material structures (22 ) having a planar surface which, in order to intercept this energy of incident radiation, is oriented at an angle () grazing with respect to the direction of incidence of the beam (11) towards the axis of elongation n of the tubular member (21) with which this structure of scintillator material (22) is associated, the positions of this plurality of tubular members (21) relative to one another, and relative to the source, as well as dimensions, in a direction transverse to the directions of scanning of the beam (11), of the planar surfaces associated with each of these tubular members (21), being such that the planar surfaces associated with each of these different members are respectively provided for intercepting different parts of the beam (11), a plurality of light reacting elements being coupled to this plurality of tubular members (21) to generate output signals in response to the emission of optical photons from the material structures scintillator (22), andmeans (20), responsive to the output signals from this plurality of light-responsive elements, being provided to generate a composite signal representative of the radiation energy capacity ent of the object to be examined (18).  90) X-ray detector according to claim 8, wherein the elongated tubular members (21) are juxtaposed in a row of these members which extends from the source of radiation energy, whereby the beam (11 ) passes successively through the tubular members (21) of this row.  100) X-ray detector according to claim 5. wherein the elongated tubular members (21) are Juxtaposed in a plurality of rows which are superposed on each other, the bundle (11) being designed to arrive essentially on each of the gold tubular gaffles (21) corresponding to each of these different rows.  110) X-ray detector according to claim 10, in which the planar surfaces of scintillator material (22) are arranged coplanar with one another in a plane extending between the superimposed rows.  12) X-ray detector according to claim 10, wherein the tubular members (21) in each of the adjacent superimposed rows are arranged offset from each other.  130) X-ray detector for use with a radiation energy source (10) generating a penetrating beam (11) of radiation, this detector comprising an elongated hollow tubular member (21) made of a material which is transparent at this energy, the internal surface of this tubular member (21) being reflective to optical photons, means being provided for supporting this tubular member in a position such with respect to the source of radiation energy that the beam (11) of penetrating radiation is directed towards the axis of this hollow tubular member (21), along a line extending essentially parallel to this ate, this hollow tubular member (21) having a fine elongated structure of scintillation material (22 ), this structure having a planar face positioned to intercept the radiation energy passing through this tubular member (21) along this line, this planar face extending overall parallel to the axis of the tubular member (21) and being oriented at a small angle () grazing with respect to the direction of the beam (11), whereby the path of energy through this structure of scintillation material (22), has a length which is a large multiple of the thickness of this structure, however light-reacting means are provided adjacent to at least one end of this tubular member for receiving the optical photons emitted by the structure of scintillation material ( 22) and reflected by the internal surface of this tubulaite organ.  140) An X-ray detector according to claim 13, wherein the planar face of the scintillation material structure (22) is oriented at a grazing angle of not more than 20 relative to the direction of the beam (11).  150) An X-ray detector according to claim 1, wherein the length of the path of radiation energy through the structure of scintillation material (22) is at least 15 times the thickness of this structure.  160) An X-ray detector according to claim 13, wherein the elongated structure of scintillation material (22) has substantially the same extension as the elongated hollow tubular member (21).  170) An X-ray detector according to claim 13, wherein the thickness of the scintillation material structure (22) is of the order of 0.1 mm.