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

This work is to replace PET ring in human brain PET/MR system with a dedicated wearable PET insert, aimed at improving both patient feasibility and system performance for brain imaging. The designed PET/MR system includes two parts: the inside parts, including a radio frequency (RF) coil and PET ring, are mounted on patient’s head, and the outside part, a MR imager, is dependent of patient. The RF coil is the innermost layer, surrounded by an outer PET-ring layer. They are supported by a MRcompatible structure. And both RF coil and PET detectors are placed inside a standard clinical 3-T MR imager. From the design of the system we can infer that some advantages can be achieved. First, high sensitivity will be achieved with the same amount crystals as the PET ring is more close to region-of-interest area, at a reduced cost. Second, by using a 2-layer depth of interaction (DOI) detector, the parallax effect can be minimized. The resolution will benefit from short positron range caused by magnetic field and smaller ring diameter will also reduce the effect of non-collinearity. Thirdly, as the PET ring is mounted on head, impact of patient motion will be reduced.

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Dedicated brain PET system of PET/MR for brain research.

Fast and accurate lost radioactive source positioning is of critical importance for the prevention of radiation damage in the accident. Traditional instruments with low detection efficiency cost lots pf time and energy, and may lead to harms to the operator's health. A portable detector to directly determine the incident angle of gamma rays is promising for the homeland security applications. In this work, we proposed a collimator-less 4π gamma imaging with 3-D position-sensitive detector. The distribution of photon counts is dependent on the orientation angle of the point gamma source, and the angle is reconstructed with Maximum Likelihood Expectation Maximization (MLEM) algorithm. Angular resolution of this imaging system was calculated by Cramer-Rao lower bound (CRLB). We simplified the 3-D position-sensitive detector to 2-D angular discrimination design. This design is capable of positioning the incident angle of 511 keV gamma rays. Excellent angular discrimination performance can be achieved except some particular angular positions at 0°, 90°, 180° and 270°. And the angular discrimination performance can be improved with more counts. Besides, we performed a preliminary experiment with 4 BGO crystal blocks and for all the tested angular positions ranging from 15° to 75° with an increment of 15°, the maximum error was less than 6.5°. Besides, we are now developing the positioning technology in a monolithic crystal which can be applied to the gamma imaging method. From the analytical calculation and experimental results, we conclude that the proposed 4π gamma imaging method with 3-D position-sensitive detector is effective and capable of searching for radioactive sources with excellent accuracy.

Collimator-less 4π gamma imaging with 3-D position-sensitive detector

Compared to pixelated detector, monolithic detector has better performance in sensitivity, light collection efficiency and cost. In PET detector, photon detector arrangement is of critical importance, which can influence detector performance significantly. In this study, three monolithic PET detector designs with different photon detector arrangement are proposed to improve spatial resolution and resolution uniformity. The PET detector is based on a $21\times 21\times 21 \mathrm {m}\mathrm {m}^{3}$ LYSO crystal and SiPM (SensL MicroFJ-30035). To improve detector performance with a reasonable number of SiPM, we proposed three different photon detector arrangements: Dual Ended (top and bottom: 5x5 array), Flexible Design A (top and bottom: 4x4 array, lateral: 2x2 array) and Flexible Design B (top and bottom: 3x3 array, lateral: 2x4 array). The Single Ended and Six Ended arrangement were also evaluated as reference. The solid angle criterion (SAC) is designed to evaluate spatial performance with less computation amounts, comparing with Cramer-Rao lower bound (CRLB). The Single Ended, Dual Ended and Flexible Design B detectors were realized to be evaluated in the preliminary experiment. The simulation results show that mean CRLB of Dual Ended, Flexible Design A and Flexible Design B are respectively 0.362, 0.363 and 0.325 mm in x/y direction, and 0.316, 0.331 and 0.325 mm in z direction. The SAC shows a strong correlation with CRLB. The preliminary experiment shows the spatial resolution of Flexible Design Bx/y:2.88 mm,z:5.16mm) is best, comparing with Single Ended (x/y:3.21 mm, z:5.88mm) and Dual Ended (x/y:3.05mm, z: 6.23mm). Flexible Design B has best resolution uniformity in both simulation and experiment. In conclusion, the simulation and experiment results proved that spatial performance of monolithic detector can be improved by optimizing the photon detector arrangement. SAC is a good simple evaluation criterion for spatial performance, which need less computation amounts compared with CLRB.

Improved Spatial Resolution and Resolution Uniformity of Monolithic PET Detector by Optimization of Photon detector Arrangement

In this study we proposed a novel design of the stationary multi-pinhole dedicated cardiac SPECT based on clinical dual-head scanner with high sensitivity and low cost for nuclear medicine myocardial perfusion imaging.

Feasibility studies of a high sensitivity, stationary dedicated cardiac SPECT with multi-pinhole collimators on a clinical dual-head scanner

The stability of crystal monochromator is the main technical bottleneck of the overall performance of X-ray beam. Generally, in the field of synchrotron radiation , the stability of double crystal monochromator (DCM) is guaranteed by passive vibration control method. In this paper, we propose a new active vibration control method of DCM based on FuLMS-ADRC hybrid algorithm. The angular stability of DCM in the pitch direction is improved from 352.24 nrad to 3.07 nrad (LN 2 cooling cycle) by the active vibration control method. This new active vibration control method based on FuLMS-ADRC hybrid algorithm not only provides a new technical scheme to improve the overall performance of hard X-ray beam, but also is of great significance to realize the nano-radian stability index of the fourth-generation synchrotron radiation beam optical equipment . 

Tianyu Ma

Papers

Dedicated brain PET system of PET/MR for brain research.

Collimator-less 4π gamma imaging with 3-D position-sensitive detector

Improved Spatial Resolution and Resolution Uniformity of Monolithic PET Detector by Optimization of Photon detector Arrangement

Feasibility studies of a high sensitivity, stationary dedicated cardiac SPECT with multi-pinhole collimators on a clinical dual-head scanner

A new active vibration control method of double crystal monochromator based on FuLMS-ADRC hybrid algorithm