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Medical Physics

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https://read.qxmd.com/read/30768796/quality-assurance-tasks-and-tools-the-many-roles-of-machine-learning
#1
Alan M Kalet, Samuel M H Luk, Mark H Phillips
The recent explosion in machine learning efforts in the quality assurance (QA) space has produced a variety of proofs-of-concept many with promising results. Expected outcomes of model implementation include improvements in planning time, plan quality, advanced dosimetric QA, predictive machine maintenance, increased safety checks,and developments key for new QA paradigms driven by adaptive planning. In this article, we outline several areas of research and discuss some of the unique challenges each area presents...
February 15, 2019: Medical Physics
https://read.qxmd.com/read/30762875/indirect-methods-for-improving-parameter-estimation-of-pet-kinetic-models
#2
Hsuan-Ming Huang, Chih-Chieh Liu, Chieh Lin
PURPOSE: Parametric images obtained from kinetic modeling of dynamic positron emission tomography (PET) data provide a new way of visualizing quantitative parameters of the tracer kinetics. However, due to the high noise level in pixel-wise image-driven time-activity curves, parametric images often suffer from poor quality and accuracy. In this study, we propose an indirect parameter estimation framework which aims to improve the quality and quantitative accuracy of parametric images...
February 14, 2019: Medical Physics
https://read.qxmd.com/read/30761545/technical-note-simplified-and-practical-pretherapy-tumor-dosimetry-a-feasibility-study-for-131-i-mibg-therapy-of-neuroblastoma-using-124-i-mibg-pet-ct
#3
Youngho Seo, Yoonsuk Huh, Shih-Ying Huang, J Miguel Hernandez-Pampaloni, Randall A Hawkins, W Clay Gustafson, Kieuhoa T Vo, Katherine K Matthay
PURPOSE: Radiation dose calculated on tumors for radiopharmaceutical therapy varies significantly from tumor to tumor and from patient to patient. Accurate estimation of radiation dose requires multiple time-point measurements using radionuclide imaging modalities such as SPECT or PET. In this report, we show our technical development of reducing the number of scans needed for reasonable estimation of tumor and normal organ dose in our pretherapy imaging and dosimetry platform of 124 I-metaiodobenzylguanidine (MIBG) PET/CT for 131 I-MIBG therapy of neuroblastoma...
February 13, 2019: Medical Physics
https://read.qxmd.com/read/30748029/technical-note-a-comparison-of-point-set-registration-methods-for-electromagnetic-tracking
#4
Th I Götz, H Wankerl, A M Tomé, A Meyer-Baese, Ch Bert, B Hensel, E W Lang
PURPOSE: High dose rate brachytherapy applies intense and destruc-tive radiation. A treatment plan defines radiation source dwell positions to avoid irradiating healthy tissue. The study discusses methods to quan-tify any positional changes of source locations along the various treat-ment sessions. METHODS: Electromagnetic tracking (EMT) localizes the radiation source during the treatment sessions. But in each session the relative position of the patient relative to the filed generator is changed...
February 12, 2019: Medical Physics
https://read.qxmd.com/read/30746722/a-linear-programming-approach-to-inverse-planning-in-gamma-knife-radiosurgery
#5
J Sjölund, S Riad, M Hennix, H Nordström
PURPOSE: Leksell Gamma Knife® is a stereotactic radiosurgery system that allows fine-grained control of the delivered dose distribution. We describe a new inverse planning approach that both resolves shortcomings of earlier approaches and unlocks new capabilities. METHODS: We fix the isocenter positions and perform sector-duration optimization using linear programming, and study the effect of beam-on time penalization on the trade-off between beam-on time and plan quality...
February 12, 2019: Medical Physics
https://read.qxmd.com/read/30742714/validation-of-post-treatment-pet-based-dosimetry-software-for-hepatic-radioembolization-of-yttrium-90-microspheres
#6
Nichole M Maughan, Jose Garcia-Ramirez, Matt Arpidone, Amy Swallen, Richard Laforest, S Murty Goddu, Parag J Parikh, Jacqueline E Zoberi
PURPOSE: Yttrium-90 (90 Y) microsphere radioembolization enables selective internal radiotherapy for hepatic malignancies. Currently, there is no standard post-delivery imaging and dosimetry of the microsphere distribution to verify treatment. Recent studies have reported utilizing the small positron yield of 90 Y (32 ppm) with PET to perform treatment verification and dosimetry analysis. In this study, we validated a commercial dosimetry software, MIM SurePlan™ LiverY90 (MIM Software Inc...
February 11, 2019: Medical Physics
https://read.qxmd.com/read/30740709/technical-note-optimization-of-spot-and-trimmer-position-during-dynamically-collimated-proton-therapy
#7
Blake R Smith, Daniel E Hyer, Ryan T Flynn, Wesley S Culberson
PURPOSE: To demonstrate a novel theoretical optimization design which considers beam spot and trimmer positioning in addition to beamlet weighting for dynamically collimated proton therapy treatments. Prior to this, the previous methods of plan optimization used to study this emerging technology relied upon an intuitive selection criterion to fix the trimmers blades for a uniform grid of beam spots before determining the individual beamlet weights. To evaluate the potential benefit from this new optimization design, a treatment planning optimization study was performed in order to compare the algorithm's functionality against the existing methods of plan optimization...
February 10, 2019: Medical Physics
https://read.qxmd.com/read/30740701/development-of-a-simple-numerical-model-for-trabecular-bone-structures
#8
Carlos A Peña-Solórzano, David W Albrecht, David M Paganin, Peter C Harris, Chris J Hall, Richard B Bassed, Matthew R Dimmock
PURPOSE: Advances in additive manufacturing processes are enabling the fabrication of surrogate bone structures for applications including use in high-resolution anthropomorphic phantoms. In this research a simple numerical model is proposed that enables the generation of microarchitecture with similar statistical distribution to trabecular bone. METHODS: A human humerus, radius, ulna, and several vertebrae were scanned on the Imaging and Medical beamline at the Australian Synchrotron and the proposed numerical model was developed through the definition of two complex functions that encode the trabecular thickness and position-dependant spacing to generate volumetric surrogate trabecular structures...
February 10, 2019: Medical Physics
https://read.qxmd.com/read/30740699/let-response-variability-of-gafchromic-tm-ebt3-film-from-a-60-co-calibration-in-clinical-proton-beam-qualities
#9
Blake R Smith, Mark Pankuch, Clifford G Hammer, Larry A DeWerd, Wesley S Culberson
PURPOSE: To establish a method of accurate dosimetry required to quantify the expected LET quenching effect of EBT3 film used to benchmark the dose distribution for a given treatment field and specified measurement depth. In order to facilitate this technique, a full analysis of film calibration which considers LET variability at the plane of measurement and as a function of proton beam quality is demonstrated. Additionally, the corresponding uncertainty from the process was quantified for several measurement scenarios...
February 10, 2019: Medical Physics
https://read.qxmd.com/read/30737803/microwave-induced-thermoacoustic-tomography-through-an-adult-human-skull
#10
An Yan, Li Lin, Changjun Liu, Junhui Shi, Shuai Na, Lihong V Wang
PURPOSE: To demonstrate the feasibility of microwave-induced thermoacoustic tomography of adult human brain. METHODS: We analyzed the electric field distribution radiated from an antenna to acquire homogeneous illumination. We first imaged the anatomical structures in a rat's trunk to validate the thermoacoustic contrast in vivo. We then imaged an agar cylinder through an adult human skull ex vivo to demonstrate transcranial penetration of both microwave and ultrasound...
February 8, 2019: Medical Physics
https://read.qxmd.com/read/30734937/convolutional-neural-network-based-approach-for-segmentation-of-left-ventricle-myocardial-scar-from-3d-late-gadolinium-enhancement-mr-images
#11
Fatemeh Zabihollahy, James A White, Eranga Ukwatta
PURPOSE: Accurate 3-dimensional (3D) segmentation of myocardial replacement fibrosis (i.e. scar) is emerging as a potentially valuable tool for risk stratification and procedural planning in patients with ischemic cardiomyopathy. The main purpose of this study was to develop a semi-automated method using a 3D convolutional neural network (CNN)-based for the segmentation of left ventricle (LV) myocardial scar from 3D late gadolinium enhancement magnetic resonance (LGE-MR) images. METHODS: Our proposed CNN is built upon several convolutional and pooling layers aimed at choosing appropriate features from LGE MR images to distinguish between myocardial scar and healthy tissues of the left ventricle...
February 8, 2019: Medical Physics
https://read.qxmd.com/read/30734932/u-net-based-deep-learning-bladder-segmentation-in-ct-urography
#12
Xiangyuan Ma, Lubomir M Hadjiiski, Jun Wei, Heang-Ping Chan, Kenny H Cha, Richard H Cohan, Elaine M Caoili, Ravi Samala, Chuan Zhou, Yao Lu
OBJECTIVES: To develop a U-Net based deep learning approach (U-DL) for bladder segmentation in computed tomography urography (CTU) as a part of a computer-assisted bladder cancer detection and treatment response assessment pipeline. MATERIALS AND METHODS: A dataset of 173 cases including 81 cases in training/validation set (42 masses, 21 with wall thickening, 18 normal bladders), and 92 cases in the test set (43 masses, 36 with wall thickening, 13 normal bladders) were used with Institutional Review Board (IRB) approval...
February 8, 2019: Medical Physics
https://read.qxmd.com/read/30734923/high-frame-rate-doppler-ultrasound-bandwidth-imaging-for-flow-instability-mapping
#13
Billy Y S Yiu, Adrian J Y Chee, Guo Tang, Wenbo Luo, Alfred C H Yu
PURPOSE: Flow instability has been shown to contribute to the risk of future cardiovascular and cerebrovascular events. Nonetheless, it is challenging to non-invasively detect and identify flow instability in blood vessels. Here, we present a new framework called Doppler ultrasound bandwidth imaging (DUBI) that uses high-frame-rate ultrasound and Doppler bandwidth analysis principles to assess flow instability within an image view. METHODS: DUBI seeks to estimate the instantaneous Doppler bandwidth based on autoregressive modeling at every pixel position of data frames acquired from high frame rate plane wave pulsing...
February 8, 2019: Medical Physics
https://read.qxmd.com/read/30734318/application-of-a-directional-palladium-103-brachytherapy-device-on-a-curved-surface
#14
I Veltchev, R Price, X Chen, K Howell, J Meyer, C-M Ma
PURPOSE: The directional planar palladium-103 LDR device (CivaSheet™ ) may be used for intra-operative implantation at the interface between the tumor site and healthy tissue. Its dosimetric properties have been studied in the ideal case of application on a at surface. The dosimetric impact of implanting this highly directional device on a curved surface that may be encountered in clinical treatments is analyzed. METHODS: CivaSheet is designed as an array of directional palladium-103 sources (CivaDots)...
February 8, 2019: Medical Physics
https://read.qxmd.com/read/30734324/machine-learning-for-automated-quality-assurance-in-radiotherapy-a-proof-of-principle-using-epid-data-description
#15
Issam El Naqa, Jim Irrer, Tim A Ritter, John DeMarco, Hania Al-Hallaq, Jeremy Booth, Grace Kim, Ahmad Alkhatib, Richard Popple, Mario Perez, Karl Farrey, Jean M Moran
PURPOSE: Developing automated methods to identify task-driven quality assurance (QA) procedures is key towards increasing safety, efficacy, and efficiency. We investigate the use of machine learning (ML) methods for possible visualization, automation and targeting of QA, and assess its performance using multi-institutional data. METHODS: To enable automated analysis of QA data given its higher dimensional nature, we used nonlinear kernel mapping with Support Vector Data Description (SVDD) driven approaches...
February 7, 2019: Medical Physics
https://read.qxmd.com/read/30730058/a-preliminary-study-of-the-local-biomechanical-environment-of-liver-tumors-in-vivo
#16
Shengyuan Ma, Mo Zhu, Xiaolong Xia, Liang Guo, Guy M Genin, Michael S Sacks, Mingyuan Gao, Sasa Mutic, Yanle Hu, Chun-Hong Hu, Yuan Feng
PURPOSE: Biomechanical properties can be used as biomarkers to diagnose tumors, monitor tumor development, and evaluate treatment efficacy. The purpose of this preliminary study is to characterize the biomechanical environment of two typical liver tumors, hemangiomas (HEMs) and hepatocellular carcinomas (HCCs), and to investigate the potential of using strain metrics as biomarkers for tumor diagnosis, based on a limited clinical dataset. METHODS: Magnetic resonance (MR) tagging was used to quantify the motion and deformation of the two types of liver tumors...
February 7, 2019: Medical Physics
https://read.qxmd.com/read/30729543/density-effects-of-silica-aerogel-insulation-on-the-performance-of-a-graphite-probe-calorimeter
#17
Julien Bancheri, Jan Seuntjens, Arman Sarfehnia, James Renaud
PURPOSE: With the introduction of a novel graphite probe calorimeter, called the Aerrow, various thermal insulating materials are being explored to further improve the device. Silica-based aerogels are proving to be an optimal material due to their low densities, small thermal conductivities, rigidity and machinability. The aim of this work is to determine how various silica aerogel densities affect the Aerrow's performance. METHODS: Performance concerns three areas; heat transfer from the core, the Aerrow's beam quality dependence and the effects of an applied magnetic field on its measurement of absorbed dose to water...
February 6, 2019: Medical Physics
https://read.qxmd.com/read/30723944/a-data-efficient-method-for-local-noise-power-spectrum-nps-estimation-in-fdk-reconstructed-3d-cone-beam-ct
#18
Rongping Zeng, Mahsa Torkaman, Holly Ning, Ying Zhuge, Robert Miller, Kyle J Myers
PURPOSE: For CT systems in which noise is nonstationary, a local NPS is often needed to characterize its noise property. We have previously developed a data-efficient radial NPS method to estimate the two-dimensional (2D) local NPS for FBP reconstructed fan-beam CT utilizing the polar separability of CT NPS[1]. In this work we extend this method to estimate three-dimensional (3D) local NPS for FDK-reconstructed cone-beam CT (CBCT) volumes. METHODS: Starting from the 2D polar separability, we analyze the CBCT geometry and FDK image reconstruction process to derive the 3D expression of the polar separability for CBCT local NPS...
February 5, 2019: Medical Physics
https://read.qxmd.com/read/30723939/removing-ring-artifacts-in-cone-beam-ct-via-tv-stokes-and-unidirectional-total-variation-model
#19
Huantang Wu, JianWu Li, Hong Wang
PURPOSE: It often happens that cone-beam corrupted tomography (CBCT) images have some ring artifacts due to the inconsistent response of detector pixels. Removing ring artifacts in CBCT images without impairing the image quality is critical. The purpose of this study is to implement a whole new method of removing ring artifacts in CBCT images based on TV-Stokes denoising equation and unidirectional total variation (UTV). METHODS: This method is based on the polar coordinates, where the ring artifacts are shown as horizontal parallel stripes...
February 5, 2019: Medical Physics
https://read.qxmd.com/read/30723934/exam-level-dose-monitoring-in-ct-quality-metric-consideration-for-multiple-series-acquisitions
#20
Xinhua Li, Kai Yang, Bob Liu
PURPOSE: Multi-series CT examination is common in the clinic, but no metric is agreed upon to report the overall dose from such an examination. This work proposes a relevant metric for tracking patient dose from multi-series examinations and illustrates the evaluation method through explanatory examples. MATERIALS AND METHODS: In each acquisition series, a previously reported method was used to evaluate the cross-sectional average dose along the z-axis of a water phantom, with inputs of CTDIvol , scan length, tube current, and patient water-equivalent diameter...
February 5, 2019: Medical Physics
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