Device for detecting ionizing particles

Abstract

The invention relates to an intraoperative probe for guiding an excision tool, the intraoperative probe comprising a detection head configured to detect beta particles and / or gamma radiation, the detection head comprising: • a single continuous scintillator (10) able to interact with beta and / or gamma particles and to emit, in response to the interaction, scintillation photons; • a plurality of photodetectors (30), and wherein the intraoperative probe is associated with a signal processing system configured to analyze the signals delivered by the photodetectors (30), the signal processing system comprising: • means for time-coincidence analysis of the signals delivered by a plurality of photodetectors (30), in order to discriminate actual interaction events from thermal noise of the photodetectors; • processing means configured to reconstruct an interaction position of the particles in the continuous scintillator (10) from the relative spatial distribution of the light signals detected by the plurality of photodetectors (30).

Description

Ionizing particle detection device Scope of the invention

[0001] The present invention relates to the field of ionizing particle detectors, and more particularly to detection systems using scintillators to capture beta and gamma particles. Devices of this type are used in various sectors, including nuclear medicine, particle physics, radiation protection, and industrial radiation monitoring applications.

[0002] The invention relates in particular to the application of such detectors for the creation of a probe capable of guiding surgeons during the surgical treatment of solid tumors. The TRIOP probe (acronym for 'Tumor Resection Intraoperative Probe') integrates the coupling between a detection head and a surgical tool, such as a modular aspirator, an ultrasonic aspirator, or any other excision device, to improve the accuracy of tumor resection by providing real-time feedback on the tumor margins.

[0003] The probe is designed to be placed close to the tumor during surgery. It detects all types of cancerous tissue in real time using specific imaging or detection techniques (e.g., fluorescence or ionizing particle detection). This allows for precise identification of the tumor's boundaries. Associated excision devices are used to precisely cut and aspirate the tumor tissue. By being coupled with the probe, they allow the surgeon to remove only the cancerous tissue, following the probe's guidance.

[0004] The coupling allows for highly precise guidance of the surgeon, improving the quality of the surgical procedure and reducing the risk of leaving residual tumor. By rapidly identifying cancerous tissue, the probe accelerates the surgical process, enabling the surgeon to progress more efficiently. The ability to define tumor resection margins in real time minimizes the risk of damage to surrounding healthy tissue. State of the art

[0005] In the field of ionizing particle detection, devices using scintillators coupled with optical collection systems, such as optical fibers and silicon photomultiplier tubes (SiPMs), are well established. These systems exploit the ability of scintillators to emit light when they interact with ionizing particles, such as beta particles and gamma rays. The emitted light is then captured by optical fibers and guided to photodetectors, which convert this light into electrical signals. These signals are then processed to identify and analyze interaction events. Discrimination between useful signals and noise relies solely on comparing the intensities of active and shielded fibers.

[0006] The prior art is known in the article by CRAIG S LEVIN ET AL: "Annihilation Gamma Ray Background Characterization and Rejection for a Small Beta Camera Used for Tumor Localization During Surgery", IEEE TRANSACTIONS ON NUCLEAR SCIENCE, vol. 44, June 1, 1997, pages 1120-1126. This document describes an intraoperative probe comprising individual scintillating fibers, each acting as a primary detector, with the light signals being transmitted to multichannel photomultipliers.

[0007] The article by VERDIER M.-A. ET AL: "Gamma-background rejection method for a dual scintillator positron probe dedicated to radio-guided surgery", NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION A, vol. 912, December 1, 2018, pages 315-319, describes an intraoperative detection probe comprising several individual small-diameter scintillator fibers, each coupled to a photomultiplier tube (PMT) via transparent optical fibers. The signals from the fibers are processed independently to determine the direction and intensity of the beta radiation. The device is therefore based on a segmented structure, with each scintillator fiber providing both detection and transmission of light. No mention is made of a single continuous scintillator or a time-coincidence analysis system between photodetectors.

[0008] We are also familiar with the article by MOO JOSHUA ET AL: "Real-Time Deep-Learned Reconstruction for a Scanning Intraoperative Probe", IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES, vol. 7, September 26, 2022. The authors propose a real-time reconstruction of the radiotracer distribution measured by a scanned intraoperative probe, to better delineate tumor margins. A miniaturized CMOS probe acquires sensor-on-a-probe (SAO) images composed of clusters of events corresponding to the charges deposited on several pixels. A deep convolutional encoder-decoder (CED) network learns the SAO→activity map transformation by training on synthetic data (ring phantoms, Shepp-Logan and “brainweb”) with low / medium / high counting levels and augmentation (rotation, scaling, shearing).The results compare the CED method to a reference smoothing method (optimized Gaussian filter) and show better structure recovery, but limited generalization between counting levels, requiring adapted training or normalization. A live reconstruction example illustrates a frame rate of approximately 3.5 fps in the operating room.

[0009] Finally, Frédéric Bogalhas et al., in "Physical Performance of an Intraoperative Beta Probe Dedicated to Glioma Radioguided Surgery," published in IEEE Transactions on Nuclear Science, vol. 55, June 1, 2008, describe the performance of an intraoperative beta probe dedicated to radioguided glioma surgery, aimed at detecting residual tumor after resection. The detection head comprises eight elements arranged in a ring, made from scintillating fibers optically coupled to a multi-anode photomultiplier tube; a β-sensitive fiber is paired with a β-shielded fiber to allow subtraction of the gamma background (notably 511 keV). The paper measures the uniformity and detection efficiency, then the beta sensitivity (≈139 cps / kBq) and the gamma rejection efficiency (≈99.5%) using phantoms.A scanning imaging mode provides spatial distribution and improves the tumor-to-noise ratio (TNR), enabling the detection of simulated lesions down to ~5 mm depending on the tracer (FDG, FET, choline) and geometry. Limitations and optimization strategies (geometry, fibers, calibration) are discussed. Disadvantages of prior art

[0010] Current systems have several drawbacks.

[0011] The use of fiber elements that simultaneously detect ionizing particles and transmit scintillation light introduces dead zones between each detection element and therefore limits the sensitivity of the device.

[0012] Furthermore, the use of fiber elements ensuring both the detection of ionizing particles and the transmission of scintillation light imposes a compromise between spatial resolution, sensitivity and number of electronic channels.

[0013] Thermal noise generated by photodetectors (such as Silicon SiPM photomultipliers) introduces significant interference that can distort the detection of real events, especially when it comes to detecting low-energy beta particles.

[0014] In general, there is a need for a system significantly improved in terms of sensitivity and resolution, capable of quantifying the contribution of detected beta and gamma particles, while optimizing light collection and reducing detection limits due to thermal noise from photodetectors. Solution provided by the invention

[0015] To remedy these drawbacks, the present invention relates to an intraoperative probe for guiding an excision tool having the characteristics stated in claim 1 and optionally in the dependent claims, wherein the discrimination of intrinsic thermal noise from photodetectors (SiPM) is attenuated by means of time-coincidence processing of signals from a single continuous scintillator.

[0016] The probe includes, in particular, a detection head associated with a photodetector, for example, by a plurality of optical fibers, each coupled to a photodetector. These optical fibers are transparent and scintillator-free. The proximal end of each transparent fiber is optically coupled to a light guide, itself coupled to a single continuous scintillator, for example, annular in shape, designed to capture beta and / or gamma particles and emit light in response to this interaction. The single continuous scintillator is optically coupled to a light guide. The distal end of each transparent fiber is coupled to a photodetector (for example, a silicon photomultiplier). The intraoperative probe is associated with a signal processing system configured to analyze the signals delivered by the photodetectors.comprising: a means for temporal coincidence analysis of said signals delivered by the photodetectors to discriminate real events from thermal noise; a processing means enabling the reconstruction of the interaction position of particles in the continuous scintillator from the distribution of light transmitted by said optical fibers.

[0017] According to a first variant, this probe further comprises a witness detector, consisting of a transparent optical fiber fused to a section of scintillating fiber, said scintillating section being covered with an absorbing material, preventing beta particles from penetrating the scintillating fiber while allowing the detection of gamma rays; said single continuous scintillator optically coupled to a light guide, having a cutout of a portion of its active surface to make room for the surface associated with the scintillating fiber of the witness detector, said processing means enabling a reference measurement of the gamma noise level in the environment from the signal from the witness detector, which can then be used to estimate by weighted subtraction the count associated only with beta particles in the continuous scintillator.

[0018] Preferably, the probe includes a control detector consisting of a transparent optical fiber fused to a scintillation fiber segment. This scintillation fiber segment is coupled to a light guide and shielded from beta particles by the continuous scintillator and the light guide. Thus, the scintillation fiber segment serves both as a guide for the light from the continuous scintillator and as a detector for gamma rays. The time-coincidence analysis method allows discrimination of the signals from the continuous scintillator and therefore provides a reference measurement of the gamma background noise from the signal from the control detector.

[0019] According to a second variant, this probe includes a witness detector, consisting of a transparent optical fiber fused to a scintillating fiber segment, said scintillating fiber segment being coupled to the light guide, so that said scintillating fiber segment serves both as a guide for the light from the continuous scintillator and as a detector for gamma rays; said time-coincidence analysis means performing an event discrimination system, configured to separately analyze the signals from the continuous scintillator and the scintillating fiber of the witness detector, and thus obtain a reference measurement of the gamma noise level in the environment from the signal from the witness detector.

[0020] Advantageously, said signal processing system is configured to perform time-coincidence analysis of signals captured by multiple photodetectors, so that signals received simultaneously by multiple optical fibers indicate a real event, while isolated signals received by a single photodetector are rejected as thermal noise (except for the signal associated with the control fiber for the first variant).

[0021] Preferably, said continuous scintillator, the light guide and said optical fibers are surrounded by a reflective coating to optimize the collection of light emitted by the scintillator and maximize the transmission of light to the photodetectors.

[0022] According to a particular embodiment, said signal processing system is configured to apply discrimination based on temporal coincidence and comparison of the amplitudes of signals from the different photodetectors, in order to obtain a reference measurement of the gamma background noise.

[0023] Advantageously, said signal processing system includes a neural network or machine learning algorithm configured to analyze the distribution of light captured by the optical fibers and reconstruct the interaction position of particles in the continuous scintillator.

[0024] Detailed description of a non-limiting example of implementation

[0025] The present invention will be better understood upon reading the following description, concerning a non-limiting example of an embodiment illustrated by the accompanying drawings where:

[0026] This represents a three-quarter front perspective view of the detection head according to a first embodiment.

[0027] Figure 1 represents another perspective view of the detection head, rotated 90° relative to the previous figure.

[0028] This represents another side perspective view of the detection head according to said first embodiment

[0029] This represents a three-quarter front perspective view of the detection head according to a second embodiment.

[0030] Figure 1 represents another perspective view of the detection head, rotated 90° relative to the previous figure.

[0031] lare represents another side perspective view of the detection head according to said second embodiment.

[0032] This represents a schematic diagram of the processing of signals delivered by each photodetector.

[0033] : This represents a perspective view of a detection head according to an example embodiment with a continuous ring scintillator

[0034] : the represents a perspective view of a detection head according to an example embodiment with continuous annular scintillator and annular light guide.

[0035] The figure represents a perspective view of a variant with optical fiber sections.

[0036] The figure represents a perspective view illustrating a chamfered geometry of the scintillator.

[0037] The figure represents a cross-sectional view illustrating a chamfered geometry of the scintillator

[0038] The figure represents a cross-sectional view illustrating a second variant of the chamfered scintillator geometry

[0039] The figure represents a perspective view of a detection head according to an example embodiment with a continuous annular scintillator and a plurality of light guide blocks

[0040] The figure represents a schematic view of the optical path in such a block. General principle of the invention

[0041] The general principle of the invention is to produce an intraoperative beta / gamma detection probe with a continuous active surface and multi-channel optical reading, in order to improve both sensitivity, spatial resolution and robustness to noise.

[0042] In practice, the detection head uses a single continuous scintillator (often annular) that scintillates upon interaction with ionizing particles. The emitted light is collected and distributed to a plurality of photodetectors (SiPM / PMT) via an optical coupling element (light guide, possibly transparent fibers). The processing system then uses (i) a time coincidence analysis between several channels to reject isolated triggers due to thermal noise from the photodetectors, and (ii) the relative distribution of the signals measured on the channels to reconstruct the interaction position within the scintillator (and thus provide real-time spatial guidance).

[0043] Description of a first variant using a continuous scintillator (10) in combination with an optical fiber network (20)

[0044] According to this first variant, the detection system uses a continuous scintillator (10) in combination with an optical fiber array (20) to capture the scintillation light emitted during the interaction of ionizing particles with the scintillator (10). The light thus captured is guided to photodetectors, for example silicon photomultiplier tubes (30), which transform the light signals into usable electrical signals.

[0045] Each of the optical fibers (20) in the transmission beam is a transparent fiber, without a doped area interacting by scintillation with the ionizing particles. Each of the optical fibers (20) in the beam extends from the continuous scintillator (10) to a dedicated photodetector (30).

[0046] Optionally, several adjacent fibers (20) can be coupled to the same photodetector, provided however that the head has a plurality of photodetectors (30) each coupled to a limited number of adjacent fibers (20), preferably three adjacent fibers (20) at most.

[0047] This system is optimized to provide accurate detection of ionizing particles (1) while reducing thermal noise and interference from gamma background radiation.

[0048] The invention also relates to the use of a witness detector coupled to the continuous scintillator configuration (10), enabling effective discrimination between beta particles and gamma radiation. The various proposed variants aim to improve the system's sensitivity, optimize light collection, and ensure high accuracy in reconstructing particle interaction events, while minimizing thermal noise.

[0049] The technical field covered by the present invention relates to ionizing particle detection technologies, with applications in radiation detection, environmental monitoring, radiological safety and medical imaging. Description of the single scintillator (10)

[0050] The operation of the continuous detection head relies on an annular scintillator (10), which can be organic or inorganic. This scintillator (10) captures beta (electron or positron) or gamma particles and emits light in response.

[0051] The scintillator (10) is, for example, an annular scintillator designed in the form of a ring (hollow cylinder) that detects ionizing particles (such as gamma rays or beta particles) by emitting light when it interacts with these particles. The annular scintillator (10) is preferably associated with an annular light guide (11) ensuring diffusion of the light towards several optical fibers (20).

[0052] The scintillating part typically has a length of about 500µm and 2mm for the control fiber, and a length of about 15 cm for the transparent fibers.

[0053] The annular scintillator (10) takes the form of a ring or a hollow cylinder with a recess (15), which allows the passage of an instrument or a suction tube or even an additional optical fiber, for example, for visual inspection through the hole (15) formed in the center of the ring. This shape provides 360-degree coverage around the object or area of ​​interest to be detected.

[0054] The annular scintillator (10) can be designed with different radii and thicknesses depending on the application and the type of radiation to be detected.

[0055] When ionizing particles (1), such as beta particles or gamma rays, interact with the ring scintillator (10), the latter emits light photons. The emitted light is then collected by optical fibers (20), preferably arranged perpendicular to the inner or outer surface of the ring scintillator (10). These fibers (20) carry the light to detectors (30) such as silicon photomultiplier tubes (SiPMs).

[0056] The fabrication of an annular scintillator (10) involves several technical steps, which vary depending on the materials used and the application specifications. Scintillators can be made from organic or inorganic materials, each with specific properties in terms of luminous efficacy, scintillation time, and optical transparency.

[0057] Inorganic scintillators (e.g., NaI(Tl), LaBr3, or BGO) are generally preferred for their high density and high light output.

[0058] For an annular scintillator (10) according to the invention, it is important that the material be homogeneous and capable of emitting isotropic light in response to ionizing radiation.

[0059] In the case of organic scintillators, such as plastic scintillators, such an annular scintillator (10) can be manufactured by molding into specific annular shapes using vacuum molding techniques. This allows for the formation of a homogeneous ring without air inclusions, which improves light transmission.

[0060] Plastic scintillators, such as fluorophore-doped polystyrene, can also be extruded into ring shapes. This method facilitates the fabrication of organic scintillators.

[0061] Inorganic scintillators can also be cut or machined from a block to obtain the desired ring shape. Machining scintillators such as NaI(Tl) is delicate because this material is hygroscopic and brittle.

[0062] Once the annular shape is obtained, the scintillator can be coated with a reflective material, such as aluminum or Teflon, to improve the internal reflection of photons and maximize the light guided to the optical fibers.

[0063] The scintillator can be coated with a thin, transparent protective layer to protect against moisture (for hygroscopic scintillators such as NaI(Tl)). The interface with the transparent optical fibers (20) is preferably provided by an annular diffuser (11).

[0064] The optical coupling surfaces (where the optical fibers are connected) are polished to minimize photon loss and optimize coupling with the optical fibers.

[0065] Optical fibers are preferentially arranged perpendicular to the external surface of the diffuser (11) or the annular scintillator (10). They capture the scintillation light produced during the interaction with the ionizing particles and guide it towards photodetectors (such as SiPMs, photodiodes or PMT photomultipliers).

[0066] The optical coupling between the scintillator (10), the diffuser (11) and the optical fibers (20) is optimized by applying optical gels or adhesives to maximize light transmission.

[0067] Once the ring scintillator is manufactured and the optical fibers are coupled, it is integrated into the detection head. The scintillator is mounted in a mechanical structure that ensures the stability and protection of the scintillator ring (10) and the optical fibers (20).

[0068] The optical fibers (20) are then connected to photodetectors (30), for example SiPMs or PMTs, to convert the light into an electrical signal, which is then analyzed to determine the characteristics of the detected ionizing particles (interaction position and energy).

[0069] Transmission of photons emitted by the annular scintillator.

[0070] The ring scintillator (10) emits light isotropically. To capture this light efficiently, several optical fibers (20) are arranged around or near the scintillator. The light is then collected by several optical fibers (20) simultaneously.

[0071] The light emitted by the scintillator (10) is guided towards the optical fiber bundle (20). To improve the amount of light captured, the scintillator, the light guide, and the optical fibers are advantageously coated with a reflective coating that reflects photons back towards the fibers. This maximizes the light available to the detectors.

[0072] The optical fibers (20) are in physical contact with the surface of the scintillator (10) or with the surface of the ring diffuser (11). The light emitted by the scintillator (10) enters the optical fibers through direct optical coupling or a material with a suitable refractive index, such as an optical adhesive, to improve light collection. The optical fibers carry this light to the photodetectors, where the light is converted into an electrical signal.

[0073] By analyzing the light distribution across multiple fibers, the interaction positions of particles within the scintillator can be reconstructed. A neural network can be used for this task.

[0074] At the output of the optical fibers, light is detected by photodetectors (photomultiplier tubes (PMTs) or SiPMs). These devices convert the light photons into an electrical signal proportional to the intensity of the light captured. The SiPM is a very compact, sensitive semiconductor device that can detect very low levels of light, even from just a few photons. Each optical fiber can be coupled to its own photodetector, or several fibers (20) (preferably no more than three) can be directed to a single detector (30) for collective processing.

[0075] If several optical fibers (20) and several photodetectors (30) are used, the distribution of light on the fibers makes it possible to precisely locate where the particle interacted with the scintillator (10). By analyzing the light on several fibers and the temporal coincidences, the system can reconstruct the position of the interaction event and discriminate real particles from thermal noise. Thermal noise reduction

[0076] To improve detection sensitivity, a noise discrimination mechanism is integrated to eliminate thermal noise from the photodetectors.

[0077] Thermal noise is a spurious signal generated by photodetectors (30), even in the absence of radiation. This thermal noise originates from the thermal agitation of charge carriers inside the photodetectors, which generates signals similar to those produced by ionizing particles.

[0078] To partially eliminate thermal noise from SiPMs, a temporal coincidence analysis of optical signals across multiple fibers is performed: scintillation light created by a real detection event (a beta or gamma particle) will simultaneously activate several optical fibers (20) and therefore several photodetectors (30), whereas a thermal noise event will activate only a single photodetector. By using temporal coincidence techniques, it is possible to significantly reduce photodetector noise and thus improve detection sensitivity.

[0079] Temporal coincidence: when several optical fibers (20) capture scintillating light simultaneously, there is a high probability that this event is real (radiation). Conversely, a signal emanating from only one SiPM without activation of the others is most likely due to thermal noise.

[0080] Filtering: By measuring the temporal coincidence between signals from different fibers, we can distinguish real events (where multiple fibers or SiPMs are activated simultaneously) from thermal noise signals that activate only a single SiPM. This allows for effective thermal noise reduction by considering only events where multiple fibers show a signal simultaneously.

[0081] When a beta or gamma particle enters the ring scintillator (10), it interacts with the material and generates scintillation photons. These photons are scattered through the scintillator and collected by several optical fibers (20) strategically placed around or near the scintillator. Each fiber guides the light to a photodetector, where the photons are converted into an electrical signal.

[0082] By using signal processing techniques, such as reconstruction of the interaction position based on the distribution of light on the different fibers and temporal coincidence to eliminate thermal noise, the system can determine the exact position of the detection and ensure high sensitivity with minimal interference from thermal noise of the photodetectors. Gamma background noise reduction

[0083] Gamma noise refers to gamma rays emanating from the accumulation of the radiotracer in regions distant from the area of ​​interest, which can interfere with the detection of beta particles. This type of noise is particularly problematic when attempting to isolate beta events, as gamma rays can activate the scintillator and produce a similar signal. The control detector (40) is used to measure gamma noise in real time. The control detector (40) consists of a scintillating fiber, specially designed to capture gamma rays without being influenced by beta particles.

[0084] Using the signals from the control detector (40) as a reference, the system can estimate the gamma background noise. The main scintillator (10) captures both beta and gamma particles, while the control detector (40) is only sensitive to gamma rays.

[0085] By subtracting the signals measured by the control detector (40) (which only captures gamma rays) from those of the continuous scintillator (10), the signal due only to beta particles can be estimated.

[0086] Based on this principle, several configurations can be implemented to reduce the gamma background noise resulting from the annihilation of positrons in matter, using a witness detector consisting of an additional scintillating fiber (40). First variant of implementation

[0087] In the first embodiment illustrated in Figures 1 and 2, a witness detector (40) is used to estimate the gamma background noise and improve the detection accuracy of events associated with beta particles (electron or positron). The witness detector consists of an optical fiber (41) fused to a thin layer of scintillator fiber (40). This scintillator fiber (41) also captures ionizing radiation, but it has a different function than the main scintillator (10).

[0088] The scintillating fiber (40) of the control detector is coated with an absorbent material (45) forming a shield that blocks beta particles but allows gamma radiation to pass through. Consequently, the control detector (40) is primarily sensitive to gamma radiation.

[0089] The main scintillator (10) is said to have its detection area "truncated" by the scintillator fiber of the control detector. This means that a small portion (12) of the surface of the ring scintillator (10) is not used for particle detection in the main system. This portion of the scintillator is dedicated to the control detector. In other words, the active area of ​​the continuous scintillator (10) is reduced to allow the control detector (41) to operate independently and exclusively capture gamma background noise.

[0090] The continuous scintillator (10) captures beta or gamma particles (1), and the emitted light is transmitted to optical fibers (20) for analysis. However, under certain operating conditions, it is necessary to be able to distinguish beta events from gamma background noise. The control detector (41) plays a crucial role here. As it is primarily sensitive to gamma rays (since beta particles are blocked by the absorbing material), it can provide a reference measurement of the gamma noise level in the environment.

[0091] By subtracting this reference measurement of the gamma background noise from the signal detected by the continuous scintillator (10), it is possible to obtain an estimate of the pure beta signal. This improves the detection specificity of the system.

[0092] This configuration is useful in environments where it is essential to accurately detect beta particle activity without contamination from gamma radiation, for example, in medical or industrial settings where gamma particles can be ubiquitous. The ability to accurately estimate gamma noise allows for a better interpretation of the actual events captured by the main detector.

[0093] Amputating the surface of the continuous scintillator to integrate the witness detector allows for an accurate estimation of gamma noise and more certain discrimination of captured events, which is crucial in applications requiring fine detection of beta particles with a minimum of false detections. Second variant of implementation

[0094] The second embodiment of the continuous detection head illustrated in the figure presents a design where the witness detector consists of an optical fiber (41) fused to a small thickness of scintillating fiber (40) which fulfills two roles: it guides the light from the continuous scintillator and serves as a detector for gamma radiation.

[0095]

[0096] In the first variant, the control detector is covered with an absorbing material (45) to block beta particles, but here the scintillating fiber is made sensitive only to gamma radiation thanks to the continuous scintillator (10) and the light guide (11) which act as shielding for the control detector (40).

[0097] Unlike the first variant, the scintillating fiber (41) serves two functions: Detecting gamma radiation: the scintillating fiber (41) detects gamma radiation and emits light in response. Guiding light: in addition to serving as a detector, the scintillating fiber (41) helps to guide the light emitted by the main continuous scintillator towards the photodetectors.

[0098] In an alternative design, the scintillating portion is coated with a reflective material that prevents light from the continuous scintillator from passing through this fiber. The control fiber is then self-contained, as in the first variant, but without encroaching on the surface of the continuous scintillator.

[0099] The scintillating fiber (41) is coupled to the light guide (11), which diffuses the light emitted by the continuous scintillator (10) and directs it towards the optical fibers (20).

[0100] In this configuration, the scintillating fiber (40) collects light from gamma rays directly via its own scintillation (31), but it also acts as part of the light guiding system for the light emitted by the continuous scintillator (10).

[0101] The scintillating fiber detects gamma rays directly by capturing the photons emitted during the interactions of gamma particles with the fiber. When gamma rays pass through this thin layer of scintillating fiber, it scintillates and emits light. This light is then guided primarily along the fused optical fiber, which carries the light to a photodetector (30), capable of converting the photons into an electrical signal.

[0102] In addition to serving as a detector, the scintillator fiber (40) is also coupled to the light guide (11). The continuous scintillator (10) (which captures both beta and gamma particles) emits light when it interacts with these particles. This light is scattered by the light guide (11) and then transmitted to the optical fiber array (20), which includes the scintillator fiber (41) in the control detector (40). This detector helps guide the light to the associated photodetector, in addition to its own gamma detection role.

[0103] In this variant, when ionizing particles (such as beta or gamma particles) interact with the continuous scintillator, several optical fibers simultaneously collect the emitted light. The photodetectors (30) coupled to these fibers (20) detect this light at the same time, and the signals are recorded in temporal coincidence.

[0104] Conversely, when a gamma ray interacts in the control detector, only the photodetector associated with the fused fiber will be triggered. This allows for the discrimination, by temporal coincidence, of signals from the continuous scintillator and the control scintillator. As with the first variant, this enables obtaining a reference measurement of the gamma noise level in the environment from the signal from the control detector. Comparison between the two variants

[0105] Unlike the first variant, where the control detector (40) is isolated from beta particles using an absorbing material, in this second variant, the scintillation fiber of the control detector (40) is directly integrated into the light guiding system and participates in the collection of scintillation light. In addition to directly detecting gamma rays, the scintillation fiber helps guide the light emitted by the main scintillator, making the system more efficient by optimizing light capture in the optical fibers (20).

[0106] The use of a scintillating fiber integrated into the light guidance system for gamma detection not only allows for the quantification of gamma background noise but also optimizes the collection of light emitted by the continuous scintillator. Another significant advantage is that the surface area of ​​the continuous scintillator is not reduced, resulting in a substantial increase in the detection area and therefore in the device's sensitivity. Improved light collection

[0107] Another key aspect of detection relies on improving the collection and guidance of scintillating light. This optimization notably improves the detection of low-energy beta particles.

[0108] The scintillator, the light guide (11), and the optical fibers (20) are advantageously surrounded by a reflective coating that prevents the emitted light from escaping in unnecessary directions. This coating redirects the emitted photons towards the optical fibers (20), thus improving the efficiency of light collection.

[0109] In the second variant, the scintillating fiber coupled to the light guide also plays a role in improving light transport to the detectors by increasing the number of collection fibers. Better light collection and guidance maximizes the amount of photons directed to the photodetectors while minimizing signal loss due to misdirected or uncaptured photons, thus increasing the signal-to-noise ratio.

[0110] The light guide (11) ensures diffusion of light towards several optical fibers (20) and therefore also optimizes the collection of scintillation light produced by the continuous scintillator (10),

[0111] Digital filtering and signal processing for noise suppression

[0112] Finally, a significant part of noise reduction in these systems relies on digital signal processing techniques. Once the signals are collected by the photodetectors, they can be analyzed and processed by digital algorithms that apply filters to eliminate spurious signals and enhance the reliability of the detected events.

[0113] Thermal noise reduction method by signal shape analysis: In addition to the temporal coincidence mentioned above, algorithms can be used to analyze the shape of signals over time. Thermal noise signals have a different shape than signals from real events, such as an interaction with a beta or gamma particle. Algorithms can filter out signals whose shape does not correspond to that expected for an ionizing particle detection event.

[0114] Gamma noise reduction method by energy filtering of signals: In addition to the use of the control detector mentioned above, energy filtering can be used to discriminate between the signals generated by the interaction of beta and gamma particles in the continuous scintillator. The energy distribution deposited by these two types of radiation is indeed different, and it is therefore possible to eliminate a significant portion of the gamma events without significantly degrading beta particle detection by applying a suitable energy threshold.

[0115] After recording a signal, the digital algorithm compares the signal's shape to a database of typical events. If the signal's shape corresponds to thermal noise, it is rejected, while a signal corresponding to an interaction with a particle is retained.

[0116] Noise reduction in detection systems using a continuous scintillator with optical fibers (20) relies on a combination of techniques: time coincidence to eliminate thermal noise, the use of a witness detector (40) to discriminate between gamma and beta events, improved light collection through a reflective coating and an optimized light guide, and digital filtering methods to refine the quality of the detected signals. Together, these techniques increase the signal-to-noise ratio and enable accurate detection of ionizing particles while minimizing interference.

[0117] Exploitation of the signal delivered by each photodetector

[0118] The exploitation of the signal delivered by each photodetector in a detection system using a scintillator and optical fibers (20) is a crucial step in interpreting the detection events of beta and gamma particles.

[0119] The photodetector converts the light emitted by the scintillator in response to ionizing particles into an electrical signal, which is then processed to determine the characteristics of the detected event.

[0120] Schematic diagram of the signal processing system for signals delivered by each photodetector

[0121] The figure illustrates the processing involved in the exploitation of the signal delivered by each photodetector:

[0122] Photon-to-electron conversion (51): The SiPM photodetector (30, 31) is a semiconductor detector designed to detect very small amounts of light (photons). Each optical fiber (20, 41) is coupled to a SiPM (30, 31) that captures the light from the scintillator. When photons from the scintillation reach the surface of the SiPM (30, 31), they are converted into electrical charges by the photoelectric effect. The SiPM (30, 31) is composed of thousands of microcells, each behaving like an avalanche photodiode. Each incident photon can trigger an electron avalanche in a microcell. The total signal corresponds to the sum of the currents generated in the different microcells by the incident photons and is therefore proportional to the received light intensity.

[0123] Electrical signal amplification: The SiPM (30, 31) delivers an electrical current whose amplitude is proportional to the number of photons detected. This signal is then processed by electronics that integrate, amplify, and digitize the signals. This ensures that even very small amounts of light (such as a few photons) can be detected with high sensitivity.

[0124] Analog signal processing (52): The amplified signal is first processed analogically to determine certain parameters, such as the charge collected at the output of the photodetectors, which is proportional to the energy of the detected event. Measurement of the collected charge (53): The analog signal is integrated to determine the collected charge, which is proportional to the amount of light received by the SiPM (30, 31), which, in turn, is related to the energy deposited in the scintillator by the ionizing particle (beta or gamma). This collected charge allows the energy of the detected event to be quantified, to better distinguish different types of particles or to measure their energy. Time-stamping detection (54): Another important piece of information is the time at which the event occurred. This is crucial for time-coincidence analysis and for discriminating real events from thermal noise (as described above).A precise timestamp of the signal is therefore performed for each SiPM (30, 31).

[0125] Digital Signal Processing (55): Once the analog signals are captured and amplified, they are converted into digital signals for more complex processing. Here are the main steps in this digital processing:

[0126] a. Time analysis and coincidence (56) The signal delivered by each SiPM (30, 31) is continuously analyzed to detect when it receives a signal (i.e., when a packet of photons from the scintillation reaches the surface). The time coincidence between several SiPMs (30, 31) is analyzed. If several SiPMs (i.e., several optical fibers (20)) register a signal simultaneously, this indicates a real event (e.g., a beta or gamma particle). Coincidence is an important criterion for discriminating real events from thermal noise, which generally activates only one SiPM (30, 31) at a time. In the second variant, time coincidence also allows discrimination between signals from the control detector and the continuous scintillator. b.Reconstruction of the Energy and Interaction Position of Detected Events (57) The information from each SiPM (30, 31), including the arrival time and the collected charge, is used to reconstruct the energy and position of the interaction event in the scintillator. The sum of the charge collected by each SiPM in time coincidence is proportional to the energy of the detected particle. This measurement is useful in helping to differentiate between beta and gamma particles, as they generally have different energy signatures. If the system uses several optical fibers (20) (as well as the control detector (40)) placed around the scintillator, the distribution of photons in these different fibers provides information on the position where the ionizing particle interacted with the scintillator.By comparing the amount of light received coincidentally by each SiPM (30, 31), the system can accurately estimate where the interaction occurred within the scintillator. The annular light guide (11) allows diffusion of scintillation light onto several optical fibers (20). Adjusting its thickness and optical coating thus optimizes the distribution of light on the optical fibers (20) to reconstruct the interaction position of the detected particle with greater accuracy. Neural networks or other advanced algorithms: In some systems, sophisticated algorithms, such as neural networks, can be used to analyze the signals from the different SiPMs and perform a precise reconstruction of the interaction position of the event.Thermal Noise Filtering (58) As mentioned previously, digital processing applies filters to eliminate thermal noise and spurious gamma signals. Thermal noise, which typically activates only one SiPM, is rejected through time-coincidence analysis.

[0127] Data communication: Once signal processing is complete, the data (position, energy, time, etc.) is sent to a data collection system for further analysis or for use in specific applications (such as radiation detection, medical imaging, etc.). The results can also be used in real time for certain applications such as image-guided surgery.

[0128] Basic design with continuous ring scintillator and one-piece light guide

[0129] As illustrated in Figure 9, the detection head comprises a single continuous scintillator (10) of annular shape, centered on a longitudinal axis X–X of the probe. The scintillator (10) defines a central recess (15) allowing the passage of a functional component of the excision tool, such as a suction conduit or an ultrasonic tip.

[0130] The scintillator (10) is made of organic scintillating material, for example doped polystyrene, having an optical index of about 1.55 and isotropic emission of photons when interacting with beta particles or gamma radiation.

[0131] Optionally, as shown in the figure, an annular light guide (11) is arranged axially between the scintillator (10) and the photodetector (30), in direct optical contact with the latter. The light guide (11) is configured to capture the scintillation light emitted on the periphery of the scintillator and redistribute it to a plurality of output zones.

[0132] The external surface of the scintillator (10) and / or the light guide (11) is covered with a reflective coating in order to limit photon losses.

[0133] A plurality of photodetectors (30), for example SiPMs, is arranged opposite the light guide (11), each photodetector being optically coupled to a distinct area of ​​the guide.

[0134] The scintillator (10) is made of an organic scintillating material, for example a fluorophore-doped polystyrene, having an optical index close to 1.55 at 430 nm, and an isotropic emission of photons when interacting with beta and / or gamma particles.

[0135] When an ionizing particle interacts with the scintillator (10), the light produced is scattered in the light guide (11) and detected almost simultaneously by several photodetectors (30). The electrical signals from these photodetectors are transmitted to a processing system configured to analyze their temporal coincidence and to reconstruct the interaction position from the relative distribution of the measured amplitudes.

[0136] Implementation without a light guide, with optical fibers directly coupled to the scintillator

[0137] As illustrated in the figure, the light guide is removed. The scintillation light is collected directly from the continuous scintillator (10) by a plurality of transparent optical fibers (20) arranged around the external surface of the scintillator.

[0138] The fibers (20) are coupled to the scintillator by direct optical contact, possibly using a gel or optical adhesive. This configuration reduces the number of optical interfaces while retaining the ability to perform spatial reconstruction by analyzing the signal distribution.

[0139] In this variant illustrated in the figure, the photodetectors (30) are optically coupled directly to the continuous scintillator (10), without intervening light guide or optical fibers.

[0140] An index matching layer can be interposed between the scintillator and the photodetectors to optimize light transmission. This architecture maximizes photon collection and enables rapid event detection, while maintaining a non-segmented scintillator.

[0141] Scintillator with chamfered scintillator geometry

[0142] Figures , et illustrate variants in which the annular scintillator (10) has chamfered edges (13) instead of straight edges.

[0143] These inclined surfaces are configured to redirect scintillation photons outwards from the scintillator, towards the light guide (11) or the photodetectors (30). This geometry improves collection efficiency, particularly for low-energy beta particles. Implementation with remote indicator detector

[0144] Figures 8, 9 and 13 illustrate an embodiment comprising a gamma (40) witness detector spatially offset from the main scintillator.

[0145] The indicator detector (40) is mounted on the rear side of a flexible PCB (50) which also carries the photodetectors (30). The indicator detector comprises a scintillating element (41) associated with a dedicated photodetector (40) and is naturally shielded against beta particles.

[0146] The signal from the control detector is used by the processing system to estimate the gamma background noise level and correct the signal from the main scintillator. Light guide illustrated by figure 14

[0147] The function of the light guide is to better homogenize the light.

[0148] The light guide (11) can be annular or advantageously designed to redirect photons to the photodetectors – in the form of a continuous block (60) of prismatic shape, as shown in or of a plurality of light guides.

[0149] The light guide can be in direct contact with the scintillator and optionally covered with a reflective or diffusing coating to ensure the guidance of the rays within it (and the coupling can be optimized by applying optical gels or adhesives to maximize light transmission).

[0150] The light guide can also be separated from the scintillator by an air hole which allows the photons to be trapped and directed so that they are then routed through the light guide in total internal reflection – possibly covered with a coating (but normally not necessary having total internal reflection) as illustrated by the. Signal processing and advanced reconstruction

[0151] In all the above-mentioned realizations, the signal processing system is configured to detect simultaneous events on several photodetectors in a predetermined time window, reject isolated signals corresponding to thermal noise, reconstruct the interaction position in the continuous scintillator from the relative distribution of measured amplitudes and / or charges, and, according to some variants, apply a machine learning algorithm to improve spatial accuracy. Nomenclature

[0152] (1) Ionizing particles (beta and / or gamma) Detection head / optics

[0153] (10)Single continuous scintillator(11)Optical coupling element / light guide(12)Reflective and / or diffusing optical coating (on the scintillator and / or the guide)(13)Photon redirection surfaces / chamfered edges of the scintillator(14)Air gap between scintillator and guide, promoting total internal reflection(15)Central recess of the scintillator(20)Transparent optical fiber (without scintillator) Photodetection

[0154] (30) Photodetector (e.g. SiPM) (31) Photodetector dedicated to the control detector (optional, if distinct from (30)) Gamma indicator detector (optional)

[0155] (40) Witness detector (dedicated scintillating element) (41) Transparent optical fiber associated with the witness detector (if present) (45) Beta particle blocking absorbing material (witness shielding) Electronic processing chain (optional in dedicated figures) (51) Photodetection module / photon-to-electron conversion (SiPM module) (52) Analog signal processing (preamplification, shaping) (53) Charge measurement / integration (energy) (54) Time-of-arrival detection (timestamp / TDC) (55) Digital signal processing (DSP / FPGA / CPU) (56) Time-of-flight analysis and coincidence (57) Reconstruction of interaction energy and position (58) Thermal noise filtering / rejection

Claims

Intraoperative probe for guiding an excision tool, comprising a detection head configured to detect beta particles and / or gamma radiation, comprising: a single continuous scintillator (10), capable of interacting with beta and / or gamma particles and of emitting, in response to said interaction, scintillation photons, a plurality of photodetectors (30) and in that said intraoperative probe is associated with a signal processing system, configured to analyze the signals delivered by the photodetectors (30), comprising: a means for analyzing in temporal coincidence the signals delivered by several photodetectors (30), in order to discriminate real interaction events from the thermal noise of the photodetectors, a processing means configured to reconstruct an interaction position of the particles in the continuous scintillator (10) from the relative spatial distribution of the light signals detected by said several photodetectors (30). Intraoperative probe according to claim 1, characterized in that it further comprises at least one optical coupling element (11) disposed between the continuous scintillator (10) and said photodetectors (30), configured to collect and distribute the scintillation light from the continuous scintillator to said photodetectors (30), Intraoperative probe according to claim 1, characterized in that said single continuous scintillator (10) is annular in shape and defines a central recess (15) suitable for the passage of an organ of the excision tool. Intraoperative probe according to claim 1, characterized in that it further comprises a plurality of transparent optical fibers (20) without scintillator, arranged between the coupling element (11) and the photodetectors (30), each fiber being coupled to at least one photodetector. Intraoperative probe according to claim 1, characterized in that several of said adjacent optical fibers (20) are coupled to the same photodetector (30), preferably to at most three adjacent fibers. Intraoperative probe according to claim 1, characterized in that at least a part of the photodetectors (30) is optically coupled directly to the scintillator (10) or to the coupling element (11), without interposed optical fiber. Intraoperative probe according to claim 1, characterized in that said scintillator (10) has at least one photon redirection surface, in particular chamfered edges and / or inclined surfaces, configured to promote the transmission of photons to the outside of the scintillator. Intraoperative probe according to claim 1, characterized in that the scintillator (10) and / or the coupling element (11) is surrounded by a reflective and / or diffusing coating configured to increase light collection. Intraoperative probe according to claim 1, characterized in that said optical coupling element (11) is a one-piece annular light guide. Intraoperative probe according to claim 1, characterized in that said optical coupling element (11) comprises a plurality of distinct light guides configured to redirect light to subsets of photodetectors. Intraoperative probe according to claim 1, characterized in that said optical coupling between the scintillator (10) and said coupling element (11) is achieved by optical contact using an optical gel or adhesive. Intraoperative probe according to claim 1, characterized in that said optical coupling between the scintillator (10) and said coupling element (11) comprises a gaseous gap configured to promote total internal reflection and trapping of photons. Intraoperative probe according to claim 1, characterized in that said time coincidence analysis means is configured to reject an event when a signal exceeds a threshold on a single photodetector, and to validate an event when at least two photodetectors present signals in a predetermined time window. Intraoperative probe according to the preceding claim, characterized in that said time window is less than 100 ns, preferably less than 20 ns. Intraoperative probe according to the preceding claim, characterized in that it comprises a control detector (40) configured to provide a representative measurement of gamma background noise, the control detector being associated with a dedicated photodetector. Probe according to the preceding claim characterized in that said witness detector (40) comprises a transparent optical fiber (41) fused to a scintillating segment (40) covered with an absorbing material (45) blocking beta particles while allowing gamma radiation to pass through. Probe according to the preceding claim characterized in that said control detector (40) is disposed under the scintillator (10) and / or under the coupling element (11) so as to be shielded against beta particles. Probe according to the preceding claim characterized in that said witness detector (40) is located at a distance from the area of ​​the main scintillator, in particular on a rear face of a support carrying the photodetectors, and in which the processing system is configured to use the witness signal to compensate for the gamma contribution. Probe according to one of the preceding claims, characterized in that said photodetectors (30) are SiPMs. Probe according to one of the preceding claims, characterized in that the detection head is mechanically and / or functionally coupled to an excision tool comprising a modular aspirator and / or an ultrasonic aspirator.

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