FR2459487A1 - APPARATUS FOR TOMOGRAPHY OF POSITRON TRANSAXIAL TRANSMISSION AND RECONSTRUCTION OF COMPUTER IMAGE - Google Patents

Abstract

TRANSAXIAL TRANSAXIAL EMISSION TOMOGRAPHY APPARATUS WITH POSITRONS AND WITH COMPUTER IMAGE RECONSTRUCTION, ESSENTIALLY INCLUDING A SET OF GAMMA RAY DETECTION DEVICES DISTRIBUTED ACCORDING TO A POLYGONAL ARRANGEMENT AROUND THE BODY REGION TO EXAMINE TEMPORALLY AND VALIDATE THE BODY REGIONS. DETECTIONS WHICH ACTUALLY CORRESPOND TO AN ANNIHILATION OF POSITRON. THE DETECTION DEVICES EACH ONE SIDE OF THE POLYGONAL STRUCTURE AND ALLOW CONTINUOUSLY OVER THE ENTIRE SURFACE OF EACH OF THEM TO LOCATE THE EVENTS CONSTITUTED BY THE PHOTON DETECTIONS. APPLICATION: NUCLEAR MEDICINE (STUDIES OF THE METABOLISM OF ORGANS, PHYSIOLOGICAL EXAMINATIONS, AID IN DIAGNOSIS).

Description

The present invention is in the field of

  nuclear medicine and finds its application in the study of

  tabolism of the organs, in the physiological examinations and in the aid to the diagnosis. More specifically, it concerns an improved version of transaxial emission tomography

  positrons used for such applications.

  The methods of medical investigation which proceed by positron transaxial emission tomography and involve the detection of gamma photons make it possible, as we know, to represent the distribution of a radioactive isotope in a body organ with a good contrast and to study biological functions, for example by the measurement, as a function of time, of the fixation rates

  molecules that play a role in the body, such as

  glucose lecules involved in cerebral metabolism and

  which, marked by this isotope, have, however, from the point of view of

  the same selective fixing behavior as a molecule

  The most common positron emitting radioelements for labeling molecules are carbon 11, nitrogen 13, oxygen 15 and fluorine 18). This representation can also lead to a good location of a lesion, or to the location of active brain regions in the example cited.

glucose molecules.

  The physical phenomenon that makes it possible to determine the distribution of the positron-emitting radioactive isotope is that of the positron / + annihilation emitted by a molecule.

  marked, during the interaction of this positron with an e_ electron.

  This annihilation consists of the total disappearance of the two particles A and e and the emission of two photons carrying an energy of 0.511 MeV. As this phenomenon occurs at the point of emission of the positron and in two opposite directions (with small statistical fluctuations, affecting both the position of annihilation and the angle formed by these two directions), the simultaneous emission of two photons can be detected using the known technique of detection by coincidence (described in particular in the US patent

  3,965,353, column 2, line 49, column 3, line 29).

  The direction thus determined by virtue of the presence of a temporal coincidence circuit substantially passes through the emission point of the positron and therefore constitutes information

  partial relative to the location of the emission molecule.

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  The repetition of such detections throughout the slice of

  the region to be examined and the computer

  obtained, using one of the reconstruction algorithms

  usually used, allow reconstruction by

  the image of the slice in question. Transaxial emission tomography

  positrons are for the most part

  caniques: linear displacements, rotations, movements of pre-

  assignment. These sweeps are indispensable for performing a complete sampling of the field of view of the apparatus, since the width at half height of the measurement lines can be up to

  about ten times less than the center distance of the individual detectors.

  duels (by construction, taking into account the thickness of casings, shields, and screens). Such devices using the time coincidence detection method recalled above, are described for example in the following articles of the Journal of Nuclear Medicine: (1) Volume 16, NI 3: Application

  of annihilation coincidence detection to transaxial reconstruc-

  tomography, by Phelps, Hoffman, Mullani and Ter-Pogossian (2) volume 17, NI 6: Design and performance characteristics of a transaxial tomogram positron, by the same authors

  and in the article "PETT IV: Design analysis and performance cha-

  racteristics ", pages 180 to 183 of the journal IEEE Transactions on

  Nuclear Science, volume NS-25, No. 1, February 1978.

  A stationary apparatus using inductive detectors

  The videos distributed in a circular arrangement are described in the article "The Analytical Study of a High-resolution Positron Ring Detector System for Transaxial Reconstruction Tomography", pages 1,166 to 1,173, of the Journal of Nuclear Medicine, Volume 16, NI 12. This type of equipment has the disadvantage of limiting the number of parallel measurement lines, linked

  important dimensions of the detectors, and therefore of a limi-

  geometric resolution. If one chooses on the contrary, to improve this geometric resolution, detectors of small dimensions, they do not have then any more than a weak detection efficiency at 0.511 MeV (energy of each one).

  photons to detect). A compromise between the effectiveness of

  tection and geometric resolution was obtained with the apparatus described in the article "Performance and evaluation of the circular

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  axial transverse ring positron camera ", pages 532 to 543 of the journal" IEEE Transactions on Nuclear Science ", volume NS-24, NI 1, February 1977. But in this apparatus, the detectors are driven by an alternating scanning movement of amplitude equal to half the distance that separates them: we thus find in

  part the disadvantages of non-stationary equipment.

  The object of the invention is to overcome the drawbacks

  inherent to scanning devices, as well as

  mitations noted above which force to adopt, for devices existing until now, features that do not simultaneously achieve high detection efficiency and good spatial resolution; the invention proposes

  a transaxial emission tomography machine with po-

  sitrons in which these two essential qualities are found

met.

  The invention relates more specifically to a transaxial emission tomography apparatus with positrons and reconstruction

  computer image, of the type used in

  nuclear medicine in the study of organ metabolism, in physiological examinations and for diagnostic assistance, the functioning of which is based on the principle of detecting photons emitted during positron annihilation by impact on an electron, this apparatus being consisting mainly of: a) a set of gamma-ray detectors distributed in a polygonal arrangement around the body region to be examined, b) amplification circuits of the signals delivered by the gamma-ray detectors,

  (c) calculators consisting essentially of

  energy integration and discrimination and provided at the output of the detectors for calculating and delivering, from the

  amplified signals, position information and energy re-

  each of the events constituted by the detections of photons, d) temporal coincidence circuits intended to select by emission of detector validation signals, among all the detected events, only those

  actually result from a positron annihilation in the

  interior of the region examined, and

  (e) - a data processing device

  all the information corresponding to the events validated by the temporal coincidence circuits to ensure

  according to a determined image reconstruction algorithm the

  constructing the image of at least one slice of the body region under examination; this apparatus being further characterized in that

  the set of detectors is stationary and composed of n

  gamma-ray detectors each occupying one side of the polygonal structure and in each of which the location of the events formed by the photon detections can be carried out continuously over the entire surface of this device

detection.

  The location-based detection device thus continues

  adopted may be a scintillation camera equipped with a system

  location system which proceeds by weighted combination of the signals provided by the photomultiplier tubes of the camera

  it can also be a son chamber equipped with a conver-

  energy weaver, or a gamma camera with solid detector.

  So that the detection devices between which

  no temporal coincidence has been observed

  As soon as possible available for new detections, it is

  It is interesting to calculate the two addresses cor-

  responding to the detection of positron annihilation only if such coincidence has been observed. For this purpose, the apparatus according to the invention may be provided in such a way that the validation signal possibly present at the output of a temporal coincidence circuit is then directly applied to the position calculators respectively provided at the output of the detection devices set. in coincidence, so that the calculation of the addresses is completed. In the absence of temporal coincidence, the position calculators are thus reduced to a zero state and do not have to wait for the end of the integration of the

  detection pulses to be available again.

  Depending on whether the chosen polygonal structure comprises an even or odd number of sides, the number n of the detection devices is also even or, alternatively, odd, and the temporal coincidence circuits are then provided between each

  detection device occupying any side of the structure

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  considered polygonal aspect and at least the device for de-

  tion occupying the opposite side (the case of an even number), that is,

  on the other hand, at least the two detection devices occu-

  on both sides opposite to any side considered (case of an odd number). Other features and advantages of the invention

  will be better understood by referring to the following description and

  to the accompanying drawings which show, by way of non-limiting example, an embodiment of the invention and in which: - Figure 1 shows the arrangement of the detection devices in a regular hexagonal structure and the circuits associated with them ; FIG. 2 shows in more detail one of the detection devices; and

  - Figure 3 shows the system of treatment by

  associated with the hexagonal structure containing the provisions

detection.

  In the exemplary embodiment shown in these figures, the emission tomography apparatus according to the invention comprises

  essentially a set of six detection devices 1 to 6 oc-

  respectively containing the six sides of a regular hexagonal structure. These six devices 1 to 6, rigorously stationary,

  each comprise (see Figure 2) a scintillating crystal CS.

  coupled via a GO optical guide. to a number

  finished, here eight, photomultiplier tubes TPMij (the index

  i may vary from 1 to 6 depending on the detection device con-

  surrounded and the index j varying from 1 to 8 in the case of eight tubes).

  The outputs of the eight tubes TPMij are connected, via amplification circuits AMij, separator stages ESij and resistors R .., to a computer CA. of position and energy 1J iJ which comprises an integration circuit CIi of the signals delivered by the tubes TPMij, a weighted combination circuit CP. of

  these signals and a CDEi energy discrimination circuit

  signals whose energy is located outside a

  be energy centered on 0.511 MeV.

  Devices 1 to 6 are associated with nine time coincidence circuits CCT13, CCT14, CCT15, CCT24, CTCTCT

  CCT35, CCT36 and CCT46 (see Figure 1, as well as, on the

  2, one of the links L between these time coincident circuits

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  porridge and the detector-calculator assemblies as-

  Socié). The double index which follows the reference CCT indicates between which detection devices (from 1 to 6) these time coincidence circuits are provided: for example, the circuit CCT24 is intended to deliver a validation signal if and only if the detection devices 2 and 4 simultaneously detected a photon. If this condition is observed, the validation signal issued by the circuit CCT24 (in this example), and therefore received by the

  sensing devices 2 and 4 and their respective calculators

  associated CA2 and CA4 via the L-type links, is applied directly to these coincidence-sensing units CA2 and CA4, so that the calculation of the addresses of the detected events is carried out at its location.

  term; otherwise, the output signals of the

  Sensors are not taken into account. The reference ADDi

  means an adder whose inputs are connected through

  ESi. separator stages, at the outputs of the amplifiers

  AM .. and whose output is connected to the circuits of

  temporal dence associated with the detection device under consideration.

  If there is validation, the integration carried out by

  CI circuits. continues to completion; if it is not valid

  the integration is almost immediately interrupted. In both cases, the discharge of the integrator circuits CIi must be

  fast so that the detection devices are as soon as pos-

  available for new detections. This speed

  can be obtained for example by associating with each integrated circuit

  grating a discharge circuit such as those described in

  French Patent Application No. 7,835,600, filed by the Applicant on December 18, 1978, circuits in which the discharge has the advantage of being fast, independent of the amplitude of the signal

  detected, and complete (with no residual charge that would distort

following tegration).

  The knowledge of the two calculated addresses corresponds to

  each detected photon constitutes a pair of useful information transmitted to a buffer memory M via an ECR stage of analog-to-digital conversion and control of the

  information flow. At the end of the entire tomography examination

  graphically, the reading of M makes it possible to take stock of the numbers of strokes occurring in any given direction and

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  to carry out an image reconstruction of the examined body slice. Indeed, all the information thus accumulated in the memory M as events occur

  consisting of photon detections by annihilation of

  then will be used by a signal processing system such as that of Figure 3, to reconstruct the image of the examined body slice, or

  the images of the body slices examined, according to one of the

  usually used reconstruction gorithms and which, well

  known, are not described here.

  This treatment system includes a computer

  21, intended to deal with the information provided by the

  hexagonal circuit 20 comprising the detection devices and all the circuits associated therewith, and the following peripheral devices, namely a disk memory 22, a magnetic strip memory 23, a printer 24, a console of

  command 25, and a display console 26 (allowing

  possible photographic shots).

  In the example described with reference to FIGS. 1 to 3,

  each detection device 1 to 6 is a scintillation camera

  and the energy associated with the events constituted by the detections of photons is thus evaluated by weighted combination of the signals provided by the photomultiplier tubes TPMij of

  the camera, this calculation being carried out for each device of de-

  tection by the CA calculator. associated with it (see the

  2, on which the energy information is available on the connection E, while the position information is

available on connection P).

  Of course, the present invention is not limited to the example here described and shown, from which other modes and other embodiments can be provided without

  to do this depart from the scope of the invention.

  Instead of scintillation cameras, it is possible to use, as continuously locating detection devices, sensors of the son-chamber type equipped with a converter.

  of energy or the type of gamma camera with a solid detector, which

  also come to form the polygonal detection structure (or the polygonal detection structures if several are associated as described above).

far).

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  It will also be noted that the choice of the number of detection devices between which time coincidence circuits are provided depends on several factors. For example, if (as

  in the embodiment described above) the poly-structure

  The most simple embodiment of the invention consists in providing for the possibility of a temporal coincidence only between detection devices belonging to two opposite sides of the polygonal structure (in the case of a hexagonal structure, between devices 1 and 4, 2 and 5, 3 and 6, in the case of an octagonal structure, between the devices

  1 and 5, 2 and 6, 3 and 7, 4 and 8; etc ...). In fact, in the real

  As proposed in the example described above, a complete coverage of the field of view of the apparatus is ensured by also taking into account the positron annihilations detected by temporal coincidence between a detection device occupying any side of the structure. hexagonal chosen and (at least)

  the two detection devices that occupy this structure.

  the two sides on either side of the side opposite to any one considered (more than two can be expected if the number of sides of the polygonal structure is sufficiently high). In the case of the hexagonal structure, time coincidences can occur between the devices (1 and 3, 4,), (2 and 4, 5, 6), etc. In the case of a polygonal structure with odd number of sides <2n + 1), the possibilities of temporal coincidence would for example be provided between the devices (1 and n, n + 1, n + 2, n + 3), (2 and n + 1, n + 2 , n + 3, n + 4), etc .... By the judicious choice of the detection devices between which there are possibilities of temporal coincidence, one thus manages to take into account most of the annihilations of positrons which occur at the within the region or body under review. One can even propose an even more elaborate embodiment, in which account is taken of annihilations

  positrons detected by temporal coincidence between

  adjacent detectors, to remove their effect from those corresponding to the annihilation occurring between opposite detection devices. It can be estimated that the number of these coincidences between adjacent devices, corresponding to

  annihilations that occur, due to the location re-

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  of the devices concerned, outside the region or body examined, is substantially equal to the number of random (and therefore parasitic) temporal coincidences which are observed within the region or organ under examination and which come to distort the final result of the tomographic examination. There is thus a simple way to eliminate these disturbing temporal coincidences. In the embodiment described with reference to FIGS. 1 to 3, this advantageous characteristic would amount to

  provide for the possibility of temporal coincidence between

  positive detection (1 and 2, 6), (2 and 3, 1), (3 and 4, 2), etc.

hexagonal structure.

  The apparatus described above and the embodiments of

  mentioned allow the transaxial examination of a slice

  relatively thin body region or organ. In juxtaposition

  several identical polygonal structures or

  two-dimensional devices for localized detection

  tinue, we realize a device that allows the reconstruction of images

  several parallel tranches, instead of one, of the region

  undermined. In the case of the apparatus with several polygo-

  Similarly, screens may be interposed between the structures to ensure good separation of the distinct region slices examined with each of these structures respectively, and time coincidence circuits may be

  be provided in exactly the same way as previously

  inside the same polygonal structure, between

  tection belonging to opposite or substantially opposite sides of two adjacent structures, or even belonging to adjacent sides, according to whether one simply wishes to take into account all the temporal coincidences observed in the region under examination or, in addition, to eliminate random coincidences parasites like

it has been described previously.

  In the device version with two-dimensional detection devices, it can be expected that the geometric resolution will be different in one direction and in the other, for example more

  fine in the transaxial sense only in the axial direction.

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Claims (10)

  1. Transaxial emission tomography apparatus with positrons and computer-image reconstruction, of the type used in nuclear medicine in the study of organ metabolism, in physiological examinations and for diagnostic assistance and whose operation is based on the principle of the detection of photons emitted during annihilations   positrons by impact on an electron, this device being con-   principally: a) a set of gamma-ray detectors distributed in a polygonal arrangement around the body region to be examined, b) amplification circuits for the signals delivered by the gamma-ray detectors, c) computers essentially comprising energy integration and discrimination circuits and provided at the output of the detectors for calculating and delivering, from the   amplified signals, position information and energy re-   lative at each of the events constituted by the detections of photons, d) temporal coincidence circuits intended to select by emission of detector validation signals, among all the detected events, only those which   actually result from a positron annihilation at the   of the region under examination, and e) a data processing device taking all the information corresponding to the events validated by the temporal coincidence circuits to ensure, according to a determined image reconstruction algorithm, the reconstruction   image of at least one slice of the bodily region   undermined; this apparatus being further characterized in that the set of detectors is stationary and composed of n devices   gamma-ray detectors, each occupying one side of the struc-   polygon and in each of which the location of events   photon detections may be effected by   performed continuously on the entire surface of this device detection.   2. Apparatus according to claim 1, characterized in that it 2459487 that each detection device with continuous localization of events is a scintillation camera equipped with a positioning system by weighted combination of the signals provided by   the photomultiplier tubes of the camera.   3. Apparatus according to claim 1 characterized in that each detection device with continuous location of events is a son chamber equipped with a power converter. 4. Apparatus according to claim 1, characterized in that each detection device with continuous localization of   Events is a solid detector gamma camera.   5. Apparatus according to one of claims 2 to 4, characterized   characterized in that each validation signal present at the output of a temporal coincidence circuit is directly applied to the computers respectively provided at the output of the devices.   detected by this circuit.   6. Apparatus according to one of claims 2 to 5, characterized   in that the number n of the detection devices occu-   each having a side of the polygonal structure is even and in that the temporal coincidence circuits are provided between each detection device occupying any side of this structure and at least the detection device which, in   this structure, occupies the opposite side to any sidered.   7. Apparatus according to one of claims 2 to 5,   characterized in that the number n of the detection devices   each having a side of the polygonal structure is odd and in that the temporal coincidence circuits are provided between each detecting device occupying any side of this structure and at least the two detecting devices which occupy, in this structure, the two sides opposed to the side any considered.   8. Apparatus according to one of claims 1 to 7,   characterized in that the set of detectors is composed of n   two-dimensional detection systems to perform the   reconstruction of images from several slices of the region undermined.   9. Apparatus according to one of claims 1 to 7, characterized   characterized by the fact that it comprises several polygonal structures 12 2459487 juxtaposed followers.   Apparatus according to claim 9, characterized in that   what screens are interposed between the polygovernmental structures   in order to ensure the separation of   examined using each of these structures. i1. Apparatus according to claim 9 if it depends on   claim 6, characterized in that wedge circuits   The temporal relationship is also provided between each sensing device occupying any side of any one of the polygonal structures and at least the sensing device.   which, in the structures located on both sides of the structure,   polygonal structure, occupies the opposite side of the any side considered.   Apparatus according to claim 9 if it depends on   Claim 7, characterized in that wedge circuits   temporal relationship are also provided between each detection device occupying any side of any of the   polygonal structures and at least the two   which, in the structures situated on either side of the polygonal structure in question, occupy the two   opposite to the side considered. -