Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session K08: Physics in Medicine: Imaging and RadiationLive
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Sponsoring Units: GMED Chair: Wojtek Zbijewski, Johns Hopkins Biomedical Engineering |
Sunday, April 18, 2021 1:30PM - 1:42PM Live |
K08.00001: Simulation study of a limited angle PET system with 50 ps CTR panel detectors Gašper Razdevšek, Rok Dolenec, Peter Križan, Stan Majewski, Andrej Studen, Samo Korpar, Rok Pestotnik We present a simulation study of key performance characteristics of a limited angular coverage TOF PET system consisting of 2 or 4 flat-panel detectors. Such devices are of interest, as they enable novel ways of designing adjustable, modular and mobile PET scanners. We have investigated the impact of the coincidence time resolution (CTR) on image quality as it is crucial for obtaining distortion-free and artefact-free images with incomplete angular sampling. Panels consisting of LSO crystals of different lengths (5 mm - 20 mm) and CTR as low as 50 ps are considered. We have evaluated spatial resolution, image quality and count rates following the NEMA NU 2-2018 standard, imaged a Derenzo phantom for a visual inspection of the resolution, and evaluated the performance in a more realistic scenario by imaging a digital human phantom generated with XCAT software. A reference scanner based on the Siemens Biograph Vision was used as comparison. We demonstrate that very good image quality without distortions can be obtained with a simple and robust limited angle system. As expected, CTR is crucial in recovering sensitivity and improving resolution in the two-panel design, while designs with longer crystals are considerably impacted by the parallax error. [Preview Abstract] |
Sunday, April 18, 2021 1:42PM - 1:54PM Live |
K08.00002: Xenon-Doped Liquid Argon Scintillation for Positron Emission Tomography Alejandro Ramirez, Xinran Li, Andrew Renshaw Positron Emission Tomography (PET) is used to observe metabolic processes within patients. It works by reconstructing the annihilation origin of incident gamma rays produced by a positron emitting tracer. However, inefficiencies of current PET technology, such photomultiplier tubes, can result in poor imaging. We propose 3Dπ: a full body, Time of Flight (TOF) PET scanner using Silicon Photomultipliers (SiPM) coupled with a xenon-doped Liquid Argon (Lar+Xe) scintillator. We simulated this design using Geant4 while following the National Electrical Manufacturers Association’s evaluation tests for performance assessment. We will present results that highlight a 200-fold increase in sensitivity, spatial resolutions comparable to commercial PET scanners and produce PET images from 15-30 second scans faster than traditional 30-35-minute scans. Further studies will involve optimizing the layer thickness of Lar+Xe. Moreover, scintillation induced ionization electrons can produce Cherenkov radiation along with the Lar+Xe scintillation light. We will discuss strategies to characterize this other signal in Geant4 to improve the timing resolution of our scanner. With the Lar+Xe scintillator and SiPMs of 3Dπ, we can use the precise TOF info of gamma rays to improve the localization of individual positron annihilations and provide low-dose PET scans for patients who may be at high risk for exposure to radiation. [Preview Abstract] |
Sunday, April 18, 2021 1:54PM - 2:06PM Live |
K08.00003: Deep-learning-based Image Segmentation of Small Volumes in CT Images of the Brain Jianxin Zhou, Massimiliano Salvatori, Daniele Della Latta, Angela Di Fulvio Treatment planning in external radiation therapy is based on the acquisition of planning images, such as CT scans, which are used to outline the target volumes and organs at risk. This process is called "segmentation" and can be aided by deep learning (DL) algorithms to improve the segmentation accuracy and streamline the workflow in radiation therapy. In this work, we have developed a general-purpose V-Net algorithm to segment 3-D CT brain images. Although the segmentation of most organs is satisfactory, the segmentation of small volumes remains challenging. We used three different approaches to improve the segmentation accuracy of small volumes, the lens of the eye as relevant case studies. We found that the optimization of the image pre-processing parameter and the V-Net segmentation parameter significantly improved segmentation accuracy of the lens of the eye. After the optimization of these parameters, we used an additional DL algorithm to predict tight bounding boxes surrounding the eyes before segmentation and used the V-Net to segment the lens of the eye in the bounding boxes. This approach yielded the best small-volume segmentation results, which are improved by approximately 20{\%} compared to the general-purpose V-Net results. [Preview Abstract] |
Sunday, April 18, 2021 2:06PM - 2:18PM Live |
K08.00004: High-resolution Quantitative Bone Imaging Using Cone-beam Ct with Scintillator-based Cmos and Amorphous Silicon Flat-panel Detectors Gengxin Shi, Fernando Quevedo Gonzalez, Ryan Breighner, Wojciech Zbijewski We compare quantitative imaging of bone microstructure using two high-resolution orthopedic Cone-Beam CT (CBCT) systems: (i) a prototype CMOS-based scanner with 99 um pixel size, custom 400 um thick CsI scintillator, 140 e- electronic noise, and 17 sec scan time vs. (ii) a conventional aSi flat-panel-based scanner with 137 um pixel size, 700 um thick CsI, 2000 e- electronic noise, and 60 sec scan time. Based on these specifications, CMOS-CBCT is anticipated to provide improved performance in in vivo high-resolution imaging tasks, such as structural and topological assessment of trabecular bone. 26 bone cores from human proximal and distal cadaveric tibias were imaged with both CBCT systems (100 um voxels) and with gold standard micro-CT (30 um voxels). Bernsen segmentation was used for trabecular binarization in CBCT. We investigated the sensitivity of trabecular metrics to CBCT spatial resolution and to the settings of the Bernsen algorithm. Initial results indicate that for a segmentation setting where both CBCT systems achieved similar correlations in bone volume fraction against gold-standard micro-CT, the CMOS-CBCT yields slightly better correlations than aSi-CBCT for trabecular spacing (TbSp), thickness, and number (e.g. TbSp$=$0.76 for CMOS-CBCT vs 0.7 for aSi-CBCT). [Preview Abstract] |
Sunday, April 18, 2021 2:18PM - 2:30PM Live |
K08.00005: A novel calibration for L-shell x-ray fluorescence measurements of bone lead concentration Mihai Gherase, Sarah Kroeker, Blaz Serna Lead (Pb) is a well-known neurotoxin which accumulates in the bone. Recent blood and bone Pb surveys indicate a significant reduction of Pb exposure. However, health concerns persist. In particular, low levels of Pb exposures in children were linked with cognitive developmental problems. Long-term Pb exposures are best assessed by x-ray fluorescence (XRF) \textit{in vivo} bone Pb concentration measurements. These measurements are typically done at the mid-tibia bone site to minimize the soft tissue (ST) x-ray attenuation. Bone Pb L-shell XRF (LXRF) method could use practical compact XRF systems as survey tools. Quantification of bone Pb requires knowledge of the ST x-ray attenuation. Past studies employing ultrasound ST thickness measurements gave inaccurate results. Using a model of bone and ST attenuation of incident and emergent XRF photons, measured K$\beta $/K$\alpha $ ratio of strontium (Sr) (an essential trace element in the bone) was used to estimate the ST attenuation of the Pb x-rays. The calibration method was validated using six Pb-doped plaster-of-Paris (poP) bone phantoms containing 1 mg/g of Sr and four overlying ST phantoms of 1 to 4 mm thickness made of three different materials: polyoxymethylene (POM), resin, and wax. [Preview Abstract] |
Sunday, April 18, 2021 2:30PM - 2:42PM Live |
K08.00006: Detecting COVID-19 via Cherenkov Luminescence Imaging on a cellphone Arbaaz Mahmood COVID-19's rampant rise has had a chilling effect on mankind's daily regimen worldwide. Millions have been lost to the pandemic, tens of millions are infected, while billions are caught in a standstill by this dolorous state of affairs. Developing a fast, cheap and reliable testing method is the linchpin for eradicating this evil for good, which, we sadly don't have at the moment. Here, I propose a revolutionary new technology for clinical testing via Cherenkov Luminescence Imaging (CLI), using a smartphone, which, if implemented will accelerate our diagnostic work-flow by many orders of magnitude and in turn disease eradication. In the first half of the paper, it is tentatively proven, that CR can be detected using a mobile phone, while, in the latter half feasibility of CLI in clinic-grade diagnosis is discussed. Moreover, a proposal for further research required to practically use the technology, employing chromophores, fluorescence, and, CLI-CT for detection of diagnostically significant variables is developed. It hypothesized that those variables can be detected with reasonable accuracy and that, they can be of diagnostic value in detection of COVID. [Preview Abstract] |
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