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

Current pharmacokinetic models, such as the linear parametric neurotransmitter PET (lp-ntPET) model have been developed to detect and quantify transient changes in receptor occupancy caused by variations in the concentration of endogenous neurotransmitters. However, it often performs poorly when applied at the voxel level due to high statistical noise. In this paper, we propose a new method to detect transient changes in neurotransmitter concentration in dynamic PET data using deep learning. Activation onset time and response magnitude of neurotransmitter were directly estimated using a convolution neural network (CNN) and compared to the lpntPET model. Computer simulations, as well as realistic GATE simulations were used to generate dynamic PET data, representing a [11C]raclopride study, with a known range of activation onset times and response magnitudes, across a wide range of noise levels. Results showed that the proposed neural network had better quantitative performance in estimating activation onset time and response magnitude than the conventional lp-ntPET method, especially where noise is high.

Direct Estimation of Neurotransmitter Activation Parameters in Dynamic PET Using Regression Neural Networks

YSO block detector of a self-developed animal PET system. The aim of this work is to optimize the optical parameters of the block detector design. Scintillation photons are generated and transported in the L YSO crystal array and finally detected by the 4 PMTs. Based on 2D Anger logic, the position of the crystal from which optical photons originate is calculated from the number of optical photons detected by the 4 PMTs. Different simulation parameters such as crystal side and bottom roughness and optical coupling pattern between crystals and reflecting films are tested in the simulation and 2D-MAPs of the detector are obtained. By comparing the 2D-MAPs acquired, we conclude that crystal side surface roughness has a significant influence on PET detector performance and a relatively rougher crystal side surface is recommended for applications while the detector performance is not sensitive to crystal bottom surface roughness and optical coupling pattern between crystals and reflecting films is key parameter for PET detector design as it determines the amounts of light sharing. The developed method is feasible for facilitating PET detector design and performance prediction.

with PQS Technology using GATE

Study of 99mTc absorption on micro-sized ion exchange resins to achieve high activity for SPECT.

Detectors with thin continuous scintillators and (charge coupled devices) CCDs have been used for animal SPECT imaging for their high intrinsic resolution. Thicker scintillators augment detection efficiency but also increase the light spread and difficulty in identification of gamma events. The objective of this work was to study the characteristics of the detector composed of a continuous CsI(TI) scintillator, a fiber optic taper, a light image intensifier (LII), and a CCD image sensor. Continuous scintillator was chosen for its simple optical propagation model. The large variable gain of the LII enables the detector to work in single photon counting (SPC) mode which may recover the light spread of each scintillation event to improve the detector's spatial resolution. The energy of gamma-rays studied was 140 keV. A linear cascade model was used to quantify the photon propagation through each component of the detector. For a continuous scintillator, its modular transfer function (MTF) was modeled by an analytical function. The MTFs of other detector components were obtained from the results of prior reports. With the cascade model, the detector's overall point spread function was derived and mixed with Poisson noise and CCD read-out noise. A local-maxima based peak detection algorithm was used to identify the photon events in each frame acquired. A simulation study with a limited number of photons showed that when the light-spread distance augmented from 0.8 to 1.0 mm, the fraction of noise equivalent count decreased from 0.73 to 0.06. So the thickness limit for a continuous scintillator with the detector configuration studied was about 0.8 mm.

Signal characteristics study of continuous scintillator CCD-based single photon counting (SPC) detector

In high resolution CT image reconstruction, a proper geometrical model is beneficial for achieving high quality images. This work aimed to improve CT image resolution with OSC (Ordered Subset Convex) reconstruction algorithm by incorporating a geometric model for the finite-size of CT detector pixels.

http://ieeexplore.ieee.org/iel7/7422433/7430744/07430950.pdf

Tianyu Ma

Papers

Direct Estimation of Neurotransmitter Activation Parameters in Dynamic PET Using Regression Neural Networks

with PQS Technology using GATE

Study of 99mTc absorption on micro-sized ion exchange resins to achieve high activity for SPECT.

Signal characteristics study of continuous scintillator CCD-based single photon counting (SPC) detector

CT image resolution improvement by geometric modelling in iterative reconstruction