Application of Silicon Photomultipliers to Positron Emission Tomography

Historically, positron emission tomography (PET) systems have been based on scintillation crystals coupled to photomultipliers tubes (PMTs). However, the limited quantum efficiency, bulkiness, and relatively high cost per unit surface area of PMTs, along with the growth of new applications for PET, offers opportunities for other photodetectors. Among these, small-animal scanners, hybrid PET/MRI systems, and incorporation of time-of-flight information are of particular interest and require low-cost, compact, fast, and magnetic field compatible photodetectors. With high quantum efficiency and compact structure, avalanche photodiodes (APDs) overcome several of the drawbacks of PMTs, but this is offset by degraded signal-to-noise and timing properties. Silicon photomultipliers (SiPMs) offer an alternative solution, combining many of the advantages of PMTs and APDs. They have high gain, excellent timing properties and are insensitive to magnetic fields. At the present time, SiPM technology is rapidly developing and therefore an investigation into optimal design and operating conditions is underway together with detailed characterization of SiPM-based PET detectors. Published data are extremely promising and show good energy and timing resolution, as well as the ability to decode small scintillator arrays. SiPMs clearly have the potential to be the photodetector of choice for some, or even perhaps most, PET systems

Development of liquid xenon detectors for medical imaging

In the present paper, we report on our developments of liquid xenon detectors for medical imaging, positron emission tomography and single photon imaging, in particular. The results of the studies of several photon detectors (photomultiplier tubes and large area avalanche photodiode) suitable for detection of xenon scintillation are also briefly described.Comment: 13 pages, 5 figures, presented on the International Workshop on Techniques and Applications of Xenon Detectors (Xenon01), ICRR, Univ. of Tokyo, Kashiwa, Japan, December 3-4, 2001 (submitted to proceedings

Performance of digital silicon photomultipliers for time of flight PET scanners

The performance of Digital Silicon Photomultipliers (dSiPM) coupled to a LYSO array containing 15×15 pixels with a size of 2×2×22 mm3 is evaluated to determinate their potential for whole body Time of Flight (TOF) PET scanners. The detector pixels are smaller in size than the light sensors and therefore light spreading is required to determine the crystal where interaction occurred. A light guide of 1 mm was used to spread the light and neighbor logic (NL) configuration were employed to ensure correct crystals identification. We studied the energy resolution and coincidence resolving time (CRT) for different trigger levels. The measured average energy resolution across detector was 14.5 %. Prior to measurements of time resolution skew time calibration of dSiPM was performed. The average CRT achieved using trigger level 1 option was 376 ps FWHM. Finally, we studied the amount of events that are disregarded due to dark count effects for different trigger levels and temperatures. Our studies show that a trade-off must be made between the detector’s CRT and sensitivity due to its vulnerability to dark counts. To employ dSiPM in TOF PET systems without 1:1 coupling effective cooling is necessary to limit dark count influence

Implementation and characterisation of radiation detectors based on SIPM for medical imaging

In the last decades, medical imaging techniques have revolutionized medicine facilitating the work to the clinicians, favouring the earlier diagnosis of diseases such as cancer, and reducing the time required for surgical procedures. Among these techniques, one of the most promising is Positron Emission Tomography (PET) due to its constant evolution, the functional information it provides and the possibility of combining it with other structural techniques such as CT or MRI. Recently, new generations of PET detectors have been developed leaving behind the conventionally used photomultiplier tubes (PMTs) for the state-of-the-art digital silicone photomultipliers (d-SiPM). In this work, the last generation of radiation detectors, Philips Digital Photon Counting’s (PDPC) d-SiPMs, was studied and characterized. These detectors are used in the commercial Philips Vereos time-of-flight PET/CT scanner, as well as in the Hyperion-IID preclinical PET scanner. The main objective of this work was to learn how to operate this new system in optimum conditions for small-animal imaging, how to design a precise centre of gravity (COG) algorithm for the localization of the scintillator pixels in a scintillator array, and to characterize the energy and spatial resolutions obtained with this PDPC module. Different COG algorithms were tested, and the final one was designed in such a way that only valid events were considered. This algorithm focuses on the main pixel of each event and the eight pixels surrounding it, discarding scatter and noise as much as possible. The energy resolution was measured by studying the full width half maximum (FWHM) of the photopeak, whereas the spatial resolution was measured by computing the valley-to-peak ratio (V/P) and the resolvability index (RI) of a profile taken from the flood field images acquired. In this project, we used a 30×30 scintillator matrix of LYSO crystals of 1.3×1.3×12 mm3, coupled to a 50×50×2 mm3 light guide in order to spread the scintillation photons among 36 of the 64 die sensors integrated in the PDPC DPC 3200-22 module. A study of how the temperature affects the performance of the system and which acquisition parameters, light guide and time window gives better results was performed. As a final check, we compared the initial and final images obtained, considering their spatial and energy resolution.Ingeniería Biomédic

A Promising Future: comparable Imaging Capability of MRI-Compatible Silicon Photomultiplier and Conventional Photosensor Preclinical PET Systems

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Design and Development of an APD algorithm development board for Positron Emission Tomography

Using the PET scanner, three dimensional images of the human body with sufficient detail can be viewed which help physicians to visualize both normal metabolic functions and discover the chemical processes underlying physical abnormalities. Commercial PET scanners employ Photo Multiplier Tubes to detect the anti-matter annihilation photons and amplify the signals to a suitable level for digital sampling. Photomultiplier tubes provide extremely high sensitivity and exceptionally low noise compared to other photosensitive devices currently used to detect radiant energy in the ultraviolet, visible and near infrared regions. A combined magnetic resonance positron emission tomography (MR-PET) modality would require a solid-state photo detector due to the known gain/timing variation of PMTs with variable magnetic field. PET detector block designs have been described and implemented in the literature using APD photo detectors at moderate values of gain. The APD Algorithm Development Board is basically a signal processing board which receives the integrated APD analog signals and outputs a digital event packet composing of position and timing data for each detected photon. These digital event packets are digitally transmitted to a downstream module for comparison with opposing detectors to detect the coincidence photons fundamental to PET. The main functions are to process analog signals from the APDs to determine if an energy qualified gamma ray event has been detected, localize the crystal position and time of the event, and transmit the event information to the control interface, en route to a coincidence processor