Abstract
Positron emission tomography (PET) imaging is an essential tool in clinical applications for the diagnosis of diseases due to its ability to acquire functional images to help differentiate between metabolic and biological activities at the molecular level. One key limiting factor in the development of efficient and accurate PET systems is the sensor technology in the PET detector. There are generally four types of sensor technologies employed: photomultiplier tubes (PMTs), avalanche photodiodes (APDs), silicon photomultipliers (SiPMs), and cadmium zinc telluride (CZT) detectors. PMTs were widely used for PET applications in the early days due to their excellent performance metrics of high gain, low noise, and fast timing. However, the fragility and bulkiness of the PMT glass tubes, high operating voltage, and sensitivity to magnetic fields ultimately limit this technology for future cost-effective and multi-modal systems. As a result, solid-state photodetectors like the APD, SiPM, and CZT detectors, and their applications for PET systems, have attracted lots of research interest, especially owing to the continual advancements in the semiconductor fabrication process. In this review, we study and discuss the operating principles, key performance parameters, and PET applications for each type of sensor technology with an emphasis on SiPM and CZT detectors—the two most promising types of sensors for future PET systems. We also present the sensor technologies used in commercially available state-of-the-art PET systems. Finally, the strengths and weaknesses of these four types of sensors are compared and the research challenges of SiPM and CZT detectors are discussed and summarized.
Highlights
Medical imaging plays a very important role in the clinical analysis and diagnosis of diseases by providing visual representations of the interior structures of a subject and/or the physiological processes hidden underneath the skin
Due to the need for a scintillator to convert gamma rays into visible light, the photosensors Photomultiplier Tubes (PMTs), avalanche photodiodes (APDs), analog silicon photomultipliers (SiPMs), and digital silicon photomultiplier (dSiPM) can be categorized as indirect-type sensors
It is clear that PMTs and APDs have been replaced by single-photon avalanche diode (SPAD)-based sensors—analog SiPM and dSiPM—in positron emission tomography (PET) applications due to their compatibility with magnetic fields, excellent timing resolution, low operating voltage and highly integrated readout and signal processing system
Summary
Medical imaging plays a very important role in the clinical analysis and diagnosis of diseases by providing visual representations of the interior structures of a subject and/or the physiological processes hidden underneath the skin. Medical imaging helps to establish a database with thousands of anatomical and physiological images The emergence of these databases become a powerful tool for training both doctors and emerging machine-based systems to identify abnormalities. PET has been integrated with other techniques like CT and MRI to develop multimodal imaging systems that take the advantages of combining both functional and anatomical images for improved diagnostics. While PMTs were initially selected for the development of PET systems because of their high gain and low noise, their fragility, bulkiness, high operating voltage, and magnetic field sensitivity led to intensive research on solid-state photodetectors like avalanche photodiodes (APDs), silicon photomultipliers (SiPMs), and their potential for PET applications.
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