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EP-4095565-B1 - DEVICE FOR THE DETECTION OF GAMMA RAYS WITH INTERACTION DEPTH AND TIME-OF-FLIGHT ENCODING

EP4095565B1EP 4095565 B1EP4095565 B1EP 4095565B1EP-4095565-B1

Inventors

  • BENLLOCH BAVIERA, Jose María
  • GONZÁLEZ MARTÍNEZ, Antonio Javier
  • Ilisie, Victor
  • BARRIO TOALA, John
  • LAMPROU, Efthymios

Dates

Publication Date
20260506
Application Date
20210120

Claims (15)

  1. A device for the detection of gamma rays, comprising a plurality of scintillation crystal detection blocks (1) disposed on an array (2) of photosensors, wherein said array (2) comprises a plurality of rows and a plurality of columns, and wherein said detection blocks (1): - comprise a plurality of elongated scintillation crystal sheets (3), in the form of rectangular prisms or truncated wedges, which are disposed consecutively on said array (2) of photosensors, wherein said scintillation crystal sheets (3) define a gamma ray input region (7) and a scintillation light output region (4), in such a way that the scintillation light can be detected by the array (2) of photosensors; - are optically isolated, in such a way that the scintillation light can only exit said blocks (1) via the output region (4); wherein the scintillation crystal detection blocks (1) and the array (2) of photosensors are disposed in direct optical coupling at the scintillation light output region (4); wherein the detection device comprises electronic means connected to the array (2) of photosensors, configured to record the reading information from said photosensors, and to process and/or analyse said information; and wherein the array (2) of photosensors is at least partially disposed such that it is shared between said detection blocks (1); said device being characterised in that: the electronic means connected to the array (2) are configured to - determine, along the two parallel directions of the array (2) of photosensors defined by its rows and columns, a plurality of integrated detection signals, and to record said plurality of integrated detection signals, wherein each of the integrated detection signals is formed by a sum of individual signals generated in one row or in one column of said array (2) of photosensors, and to - record a set of timestamps (t 1 ...t N ) associated with each of the individual signals that form the integrated detection signals in the respective rows or columns.
  2. The device according to the preceding claim, wherein the electronic means connected to the array (2) are configured to determine an impact time value associated with a detected gamma ray, from the sum of all of the integrated detection signals and from the sets of timestamps (t 1 ...t N ) of the integrated detection signals.
  3. The device according to the preceding claim, wherein the gamma ray input region (7) is completely covered by a retroreflective sheet (6) or an ESR sheet.
  4. The device according to any of the preceding claims, wherein the array (2) of photosensors comprises a dead zone covered by a reflective grid (2').
  5. The device according to any of the preceding claims, further comprising one or more reflective films (8) disposed between the consecutive scintillation crystal sheets (3).
  6. The device according to the preceding claim, wherein the number of scintillation crystal sheets (3) is substantially equal to 2N-1, N being the number of photosensors in a direction (x) perpendicular to the scintillation crystal sheets (3); and/or the reflective films (8) are prolonged beyond the scintillation crystal block (1), partially or completely going through the array (2) of photosensors.
  7. The device according to any of claims 5-6, wherein one or more of the reflective films (8) comprise optically transparent side windows (9), disposed in regions close to the scintillation light output region (4).
  8. The device according to the preceding claim, comprising a plurality of reflective films (8) equipped with side windows (9), disposed in series between consecutive scintillation crystal sheets (3), in such a way that said side windows (9) form an arc geometry.
  9. The device according to any of the preceding claims, wherein two or more scintillation crystal sheets (3) are joined together by means of a clear adhesive having a refractive index greater than 1.5.
  10. The device according to any of the preceding claims, further comprising one or more auxiliary scintillation crystal elements (10) disposed in the blocks (1) between the scintillation crystal sheets (3) and the array (2) of photosensors, or on the scintillation crystal sheets (3) in the gamma ray input region (7).
  11. The device according to the preceding claim, wherein the auxiliary scintillation crystal elements (10) comprise monolithic blocks, sheets disposed perpendicularly to the scintillation crystal sheets (3) or pixels (11), wherein the main dimension (L z ) of said auxiliary elements (10) is less than the main dimension (L z ) of the scintillation crystal sheets (3).
  12. The device according to any of the preceding claims, wherein the scintillation crystal sheets (3) are sub-divided as a plurality of pixels (11).
  13. The device according to any of the preceding claims, wherein the array (2) of photosensors comprises a plurality of silicon photomultipliers (SiPM), and wherein each element photosensor of the array (2) has a number of microcells of at least twice the number of scintillation optical photons expected by each of said photosensors.
  14. A system for the detection of gamma rays, comprising one or more devices according to the preceding claims, integrated in a ring or facing plane detection structure of a positron emission tomography camera, a gamma camera, of a particle physics and/or astrophysics detector, or of an animal PET scanner.
  15. A method for the detection of gamma rays, where the method comprises performing the following steps by means of a device according to any of the preceding claims: - determining, with the electronic means connected to the array (2) of photosensors along two parallel directions of said array (2) of photosensors defined by its rows and columns, a plurality of integrated detection signals, and recording, with said electronic means, the plurality of integrated detection signals, wherein each of the integrated detection signals is formed by a sum of individual signals generated in one row or in one column of the array (2) of photosensors of said device; - recording, with said electronic means a set of timestamps (t 1 ...t N ) associated with each of the individual signals that form the integrated detection signals in the respective rows or columns; and - determining, with the mentioned electronic means, the impact time of the gamma rays in the detection blocks (1), the impact energy of the gamma rays, the projection of the position of said impact on the array (2) of photosensors and/or the depth of interaction (5) of said gamma rays from the integrated detection signals and their corresponding timestamps (t 1 ...t N ).

Description

FIELD OF THE INVENTION The present invention is comprised in the technical field relative to imaging by means of gamma rays. More specifically, the invention relates to the design of devices for the detection of gamma radiation to obtain information about a source, for example, nuclear imaging medical devices, such as gamma cameras, positron emission tomography (PET) equipment or single photon emission computed tomography (SPECT) equipment, among others. The devices according to the invention allow to be determined with a high resolution both the three-dimensional position (3D) and the impact time of a gamma ray in a detector such as a scintillator crystal. The invention is preferably applicable to the manufacture of scanners, such as PET scanners or PET probes. BACKGROUND OF THE INVENTION Current scanners based on positron emission tomography (PET) are used in multiple clinical applications which include, primarily, the diagnosis and monitoring of cancer. Radiopharmaceuticals, i.e., molecules specific for the diagnosis of a disease, are used in the PET technique (in the case of cancer, glucose is mostly used given its higher absorption by tumours), together with positron-emitting isotopes (fundamentally, fluorine-18 (18F)) acting as radiotracers, for tracking thereof in the body being imaged. Once in the body, the radiopharmaceutical accumulates in the areas of the highest absorption and the isotope emits positrons which are rapidly annihilated when they encounter electrons from the body, simultaneously generating two gamma rays in the same direction, but in opposite ways. Time-coincident detection of the two gamma rays, e.g. by means of a ring of detectors or by means of pairs of facing detection panels (placed on both sides of the organ to be examined), makes it possible to discriminate true events from random background noise. More recently, the most advanced PET scanners make it possible to measure the arrival time of the two gamma rays at these detectors, with sufficient temporal resolution to determine, within a margin of error, the position within the body where the annihilation of the positron emitted with the electron has occurred. This characteristic is essential for the improvement of the signal-to-noise ratio and, accordingly, of the sensitivity and quality of the clinical image. In this respect, PET scanners based on scintillation crystals are currently of great interest because of their potential for improvement due to the determination of the time-of-flight of the gamma rays with a higher resolution. Scintillation crystals can be continuous or pixelated. Most gamma ray detector designs use pixelated crystals with a smaller scintillation crystal size, since these crystals define the spatial resolution both of the detector and of the scanner that may be obtained. These scintillation crystals must always have a significant thickness so as to ensure that a high percentage of gamma particles interacts with said crystal. The required thickness of the scintillation crystals involves an indeterminacy in the depth of interaction (DOI) of the gamma ray along said crystals. Thus, the two directions defining an array of photosensors are usually not sufficient to determine the line of incidence of the gamma ray. Not knowing the position of the gamma ray interaction along the perpendicular to the input face of the scintillation crystal (DOI) prevents distinguishing between possible lines that do not have the same angle of incidence, or that interact at different depths of the crystal, resulting in a parallax error. Accordingly, the greater the thickness of the crystal, the greater the parallax error. To minimise this parallax error, the angle of incidence or depth of interaction of the gamma ray must be known. With current techniques for the detection of gamma rays, it is completely impossible to measure said angle of incidence in any way, so the depth of interaction must necessarily be determined with a certain measurement error. In addition, the parallax error becomes more important the higher the energy of the gamma ray, since thicker scintillation crystals are needed to record a high percentage of gamma radiation. There are detectors based on continuous scintillation crystals (for example, J.M. Benlloch et al., "Gamma Ray Detector with Interaction Depth Coding", US 7,476,864 B2), which use the width of the distribution of scintillation light to determine depth of interaction. To that end, these detectors utilise the fact that the scintillation light is distributed isotropically, which leads to different densities of light along the reading faces where photodetectors are positioned. As a result, a distribution of scintillation light the width of which allows the depth of interaction of the gamma ray to be deduced is obtained. In large scanners (> 50 cm in diameter), the resolution in determining the DOI is not so important, as they do not produce a significant parallax error. However, when detectors ar