The development of radiation detectors capable of delivering spatial information about gamma-ray interactions was one of the key enabling technologies for nuclear medicine imaging and, eventually, single-photon emission computed tomography (SPECT). The continuous sodium iodide scintillator crystal coupled to an array of photomultiplier tubes, almost universally referred to as the Anger Camera after its inventor, has long been the dominant SPECT detector system. Nevertheless, many alternative materials and configurations have been investigated over the years. Technological advances as well as the emerging importance of specialized applications, such as cardiac and preclinical imaging, have spurred innovation such that alternatives to the Anger Camera are now part of commercial imaging systems. Increased computing power has made it practical to apply advanced signal processing and estimation schemes to make better use of the information contained in the detector signals. In this review we discuss the key performance properties of SPECT detectors and survey developments in both scintillator and semiconductor detectors and their readouts with an eye toward some of the practical issues at least in part responsible for the continuing prevalence of the Anger Camera in the clinic.

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SPECT detectors: the Anger Camera and beyond.

Secondary radiation emission induced by nuclear reactions is correlated to the path of ions in matter. Therefore, such penetrating radiation can be used for in vivo control of hadrontherapy treatments, for which the primary beam is absorbed inside the patient. Among secondary radiations, prompt-gamma rays were proposed for real-time verification of ion range. Such a verification is a desired condition to reduce uncertainties in treatment planning. For more than a decade, efforts have been undertaken worldwide to promote prompt-gamma-based devices to be used in clinical conditions. Dedicated cameras are necessary to overcome the challenges of a broad- and high-energy distribution, a large background, high instantaneous count rates, and compatibility constraints with patient irradiation. Several types of prompt-gamma imaging devices have been proposed, that are either physically-collimated or electronically collimated (Compton cameras). Clinical tests are now undergoing. Meanwhile, other methods than direct prompt-gamma imaging were proposed, that are based on specific counting using either time-of-flight or photon energy measurements. In the present article, we make a review and discuss the state of the art for all techniques using prompt-gamma detection to improve the quality assurance in hadrontherapy.

Prompt-gamma monitoring in hadrontherapy: A review

This paper reviewed the deep learning-based studies for medical imaging synthesis and its clinical application. Specifically, we summarized the recent developments of deep learning-based methods in inter- and intra-modality image synthesis by listing and highlighting the proposed methods, study designs, and reported performances with related clinical applications on representative studies. The challenges among the reviewed studies were then summarized with discussion.

A review on medical imaging synthesis using deep learning and its clinical applications.

Unmanned aerial vehicle for internet of everything: Opportunities and challenges

Positron emission tomography (PET) is the most sensitive of all medical imaging modalities for quantitatively probing biologic processes at the molecular level. However, spatial resolution in PET is significantly inferior to that of other imaging modalities that can provide exquisite images of the anatomy, such as X-ray computed tomography (CT) or magnetic resonance (MR) imaging. It has been one of the outstanding challenges of the last decade to combine PET with these complementary imaging modalities in order to synergistically exploit the benefits of each modality and to enhance the role of PET in pre-clinical research as well as in clinical routine and research. The simple juxtaposition of tomographs around a common axial bed, such as with current PET/CT technology, is very successful in allowing sequential acquisition of PET and anatomical data. However, novel imaging combinations are being considered that would enable simultaneous, or at least concurrent, dual-modality imaging through combined PET/MR or PET/CT. The development of these new integrated instruments creates new bewildering challenges for PET detection systems, which, in addition to the ability to measure annihilation radiation in PET, must satisfy several other critical requirements.

Novel detector technology for clinical PET

The invention discloses a PET/CT geometric registration method and system. The method includes the steps that conventional imaging scanning and establishment are conducted on geometric body models through a CT machine, so that a CT reestablished image is acquired; a lutetium background conforming event of the geometric body models is scanned and reestablished through a PET instrument, so that a lutetium background conforming image is acquired; the gravity center of each geometric body in the CT reestablished image and the lutetium background conforming image is extracted; according to the gravity centers of the geometric bodies, gravity center mapping data of the CT reestablished image and the lutetium background conforming image are acquired; according to the gravity center mapping data, a rotation matrix and a horizontally-moving vector from the lutetium background conforming image to the CT reestablished image are acquired and serve as registration parameters from a PET image to a CT image. By the adoption of the method, PET/CT geometric registration can be conducted, the method can be used for regular calibration of a machine, a multi-point or multi-line positive electron source does not need to be prepared, the price of the geometric body models is low, the geometric body models can be reused, and an operator is merely irradiated.

PET/CT geometric registration method and system

The invention discloses a method for calibrating gains of photovoltaic conversion modules in a gamma camera. The method is directed at the gamma camera of the following technology: a whole scintillation crystal (non-array or cutting) coupling photovoltaic conversion module array. The calibrating method comprises that the scintillation crystals receive quasi extensive field incident gamma photons to be converted into visible light photons, the photovoltaic conversion modules receive and convert visible light photons into electrical signals to be processed by subsequent electronics to be converted into digital amplitude values, analysis and characteristic extraction are performed on the output signal amplitude spectrum of each photoelectric conversion module to obtain output signal amplitude expectation values of incident gamma photons when the photoelectric effect occurs to the center of the photovoltaic conversion module; gains of each photovoltaic conversion module are calibrated according to the output signal amplitude expected values. By the aid of the method, the calibrating method is not limited by whether a collimator is mounted and is not affected by errors between prior set gains and actual gains. The invention further discloses a method applying the method.

Method and system for calibrating gains of photovoltaic conversion modules in gamma camera

We developed SPECT imaging capability on an animal PET scanner by placing a slit-slat collimator inside the PET detector gantry. To perform in vivo animal imaging with minimal gravity induced animal motion, we investigated the performance of hybrid rotation-translation (HRT) tomographic scan scheme in this paper. Three evaluation indices, i.e. sampling completeness (SC), sensitivity, and directional spatial resolution (DR), were designed and calculated throughout the field-of-view to assess the performance of the HRT and the conventional rotation-only scan scheme. The reconstructed image quality was evaluated through simulated and experimental studies. Ten HRT schemes with different rotation and translation combinations and the conventional rotation-only scheme were tested. General HRT schemes (containing both rotational and translational movements) have comparable sampling completeness (SC), comparable sensitivity and better spatial resolution (in terms of both DR and visual image quality), as compared to the conventional rotation-only scheme We concluded that HRT scan scheme enables in vivo animal SPECT imaging on the stationary scanner and has the advantage of improving image resolution.

A hybrid rotation-translation (HRT) scan scheme for in vivo animal SPECT imaging on a stationary scanner

Photosensitive device inclined arrangement type high energy ray detector

In pixelated PET detector, extraction of timing information is very simple and does not need any complex algorithm. However, in monolithic PET detector, the conventional timing extraction method is not optimal in any sense because it doesn’t incorporate any statistical model. Due to optical photon transport within monolithic crystal, the timing information of each SiPM signal has a correlation with gamma interaction position. Based on this correlation, timing estimation algorithm incorporating spatial position for the monolithic PET detector is studied to improve timing resolution. The whole physical process in monolithic PET detector is analyze carefully and the timing properties of detector signals is modeled. Based on Monte Carlo simulation, the correlation between gamma interaction position and timing information is fully validated. Based on a $21\times 21\times 21 \mathrm {m}\mathrm {m}^{3}$ LYSO crystal and SiPM (SensL MicroFJ-30035), two different monolithic detectors (Single Ended and Dual Ended) are proposed to be evaluated. Based on Maximum Likelihood Estimation (MLE) and Artificial Neural Network (ANN), two different timing estimation algorithm were established. The simulation results shows that the timing resolution of conventional, MLE and ANN timing estimation algorithm are 148. 0ps, 129. 4ps, 112.1ps in Single Ended detector and 121.1ps, 112. 7ps, 97. 3ps in Dual Ended detector. The timing resolution of Dual Ended detector is better than Single Ended detector with any timing estimation algorithms. Compared with conventional timing estimation algorithm, two timing estimation algorithms incorporating spatial position can achieve better timing resolution. In conclusion, incorporating spatial position of gamma interaction into timing estimation algorithm can obviously improve timing resolution. The ANN has the best timing performance in both Single Ended detector and Dual Ended detector.

Tianyu Ma

Papers

PET/CT geometric registration method and system

Method and system for calibrating gains of photovoltaic conversion modules in gamma camera

A hybrid rotation-translation (HRT) scan scheme for in vivo animal SPECT imaging on a stationary scanner

Photosensitive device inclined arrangement type high energy ray detector

Timing Estimation Algorithm Incorporating Spatial Position for Monolithic PET Detector