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Physics in Medicine and Biology

Malwina Jaszczak, Radosław Wach, Piotr Maras, Mariusz Dudek, Marek Kozicki
This work discusses the substitution of a gelatine physical gel matrix with a matrix made of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F-127) in five 3D radiotherapy polymer gel dosimeters: MAGAT, PAGAT, NIPAM, VIPARnd (VIP) and VIPARCT (VIC). The current research outcomes showed that not each polymer gel dosimeter could be manufactured with Pluronic F-127. Two of the polymer gel dosimeters (PAGAT and VIP) containing the Pluronic F-127 matrix allowed for some proper dose response for radiotherapy dosimetry (a response to a dose range of e...
August 13, 2018: Physics in Medicine and Biology
Mengke Ge, Hejun Jiang, Xiaoyan Huang, Yufu Zhou, Debo Zhi, Gang Zhao, Yuping Chen, Lulu Wang, Bensheng Qiu
This paper presents a multi-slot coaxial antenna with a pi impedance matching network for liver tumor ablation. In order to reduce damage to surrounding healthy tissues during ablation, a multi-slot radiating part was designed to produce a near-spherical heating zone with greatly increased possibility of conformal treatment. A pi impedance matching network part was designed to match the feeding transmission line and antenna without increasing antenna size. The reflection coefficient, ablation zone shape, specific absorption rate, and temperature were determined by using a finite element electromagnetic simulation COMSOL...
August 13, 2018: Physics in Medicine and Biology
Eivind Rørvik, Lars Fredrik Fjæra, Tordis J Dahle, Jon Espen Dale, Grete May Engeseth, Camilla Hanqvuist Stokkevåg, Sara Thörnqvist, Kristian Smeland Ytre-Hauge
The relative biological effectiveness (RBE) of protons varies with multiple physical and biological factors. Phenomenological RBE models have been developed to include such factors in the estimation of a variable RBE, in contrast to the clinically applied constant RBE of 1.1. In this study, eleven published phenomenological RBE models and two plan-based models were explored and applied to simulated patient cases.
 Method and Materials: All models were analysed with respect to the distribution and range of linear energy transfer (LET) and reference radiation fractionation sensitivity ((α/β)<sub>x</sub>) of their respective experimental databases...
August 13, 2018: Physics in Medicine and Biology
Thalat Theresa Monajemi, Ethan Avila Ruiz
This work investigated the application of plastic scintillation detectors (PSDs) in dosimetry measurements on the surface of a phantom in megavoltage photon and electron beams. Emission spectra associated with fluorescence in the PMMA optical fibre, Cerenkov in the optical fibre, and the signal from the scintillator were characterized with a spectrophotometer. The angular dependence of the PSD response was studied with the PSD both in the plane and perpendicular to the plane of gantry rotation. Two methods of stem correction were investigated: stem subtraction and full spectral correction...
August 13, 2018: Physics in Medicine and Biology
Marie-Ève Delage, Marie-Ève Lecavalier, Dominic Larivière, Caudine Ni Allen, Luc Beaulieu
Scintillation dosimetry has evolved towards utilizing 3D liquid dosimeters to perform quality assurance verification of complex treatment configuration for photon, electron and proton beams. However, most of the fluorophores utilized in these dosimeters are alike and present limitations. This study aims to establish the profile of CdSe colloidal quantum dots (cQDs) that were given the role of the fluorophore in a binary liquid scintillation system. We chose to investigate the cQDs because of their wide absorption spectrum, the tunability of their absorption and emission spectra with respect to their size and composition, and their ability to function as an effective energy transfer intermediate...
August 13, 2018: Physics in Medicine and Biology
Qin Li, Benjamin P Berman, Tomoe Hagio, Marios A Gavrielides, Rongping Zeng, Berkman Sahiner, Qi Gong, Yuan Fang, Songtao Liu, Nicholas P Petrick
Extracting coronary artery calcium (CAC) scores from contrast-enhanced computed tomography (CT) images using dual-energy (DE) based material decomposition has been shown feasible, mainly through patient studies. However, the quantitative performance of such DE-based CAC scores, particularly per-stenosis, is underexamined due to lack of reference standard and repeated scans. In this work we conducted a comprehensive quantitative comparative analysis of CAC scores obtained with DE and compare to conventional unenhanced single-energy (SE) CT scans through phantom studies...
August 13, 2018: Physics in Medicine and Biology
Ignasi Mendez, Aljosa Polsak, Rihard Hudej, Bozidar Casar
The main objective of multichannel radiochromic film dosimetry methods is to correct, or at least mitigate, spatial heterogeneities in the film-scanner response, especially variations in the active layer thickness. To this end, films can also be scanned prior to irradiation. In this study, the abilities of various single channel and multichannel methods to reduce spatial heterogeneities, with and without scanning before irradiation, were tested. Red, green and blue single channel models, two additive channel independent perturbation (CHIP) models and two multiplicative CHIP models were compared with the Multigaussian method...
August 13, 2018: Physics in Medicine and Biology
Fujio Araki, Takeshi Ohno, Suzuna Umeno
The purpose of this study was to develop a new ionization chamber dosimetry formalism for diagnostic kilovoltage x-ray beams based on a 60Co absorbed dose-to-water calibration coefficient . To validate the new chamber dosimetry, 39 fluence spectra of kilovoltage x-rays were calculated, using a SpekCalc program, for Al half-value-layer (Al-HVL) values of 1.4 8.5 mm and tube voltages of 50 137.6 kVp. We used these spectra to calculate the beam quality conversion factor for kilovoltage x-ray beams Qx to a 60Co beam for a PTW 30013 Farmer ionization chamber in a reference geometrical setup (depth = 1 cm in water, field size = 20 × 20 cm2)...
August 13, 2018: Physics in Medicine and Biology
Justine Robin, Alverède Simon, Bastien Arnal, Mickael Tanter, Mathieu Pernot
Ultrasound shock wave therapy is increasingly used for non-invasive surgery. It requires the focusing of very high pressure amplitude in precisely controlled focal spots. In transcostal therapy of the heart or the liver the high impedance mismatch between the bones and surrounding tissues gives rise to strong aberrations and attenuation of the therapeutic wavefront, with potential risks of injury at the tissue - bone interface. An adaptive propagation of the ultrasonic beam through the intercostal spaces would be required...
August 13, 2018: Physics in Medicine and Biology
Nicolas Garraud, Rohan Dhavalikar, Mythreyi Unni, Shehaab Savliwala, Carlos Rinaldi, David P Arnold
This paper presents the design, construction, and testing of a magnetic particle relaxometer (MPR) to assess magnetic nanoparticle response to dynamic magnetic fields while subjected to a bias field. The designed MPR can characterize magnetic particles for use as tracers in magnetic particle imaging (MPI), with the variation of an applied bias field emulating the scan of the MPI field free point. The system applies a high-frequency time-varying excitation field (up to 45 mT at 30 kHz), while slowly ramping a bias field (± 100 mT in 1 s)...
August 10, 2018: Physics in Medicine and Biology
Qing Ye, Jing Wu, Yihuan Lu, Mika Naganawa, Jean-Dominique Gallezot, Tianyu Ma, Yaqiang Liu, Lynn Tanoue, Frank Detterbeck, Justin Blasberg, Ming-Kai Chen, Michael Casey, Richard E Carson, Chi Liu
Lung cancer mortality rate can be significantly reduced by up to 20% through routine low-dose computed tomography (LDCT) screening, which, however, has high sensitivity but low specificity, resulting in a high rate of false-positive nodules. Combining PET with CT may provide more accurate diagnosis for indeterminate screening-detected nodules. In this work, we investigated low-dose dynamic <sup>18</sup>F-FDG PET in discrimination between benign and malignant nodules using a virtual clinical trial based on patient study with ground truth...
August 10, 2018: Physics in Medicine and Biology
Gabriel Famulari, Marc-André Renaud, Christopher M Poole, Michael D C Evans, Jan Seuntjens, Shirin A Enger
Despite being considered the gold standard for brachytherapy dosimetry, Monte Carlo (MC) has yet to be implemented into a software for brachytherapy treatment planning. The purpose of this work is to present RapidBrachyMCTPS, a novel treatment planning system (TPS) for brachytherapy applications equipped with a graphical user interface (GUI), optimization tools and a Geant4-based MC dose calculation engine, RapidBrachyMC. Brachytherapy sources and applicators were implemented in RapidBrachyMC and made available to the user via a source and applicator library in the GUI...
August 10, 2018: Physics in Medicine and Biology
Mailyn Pérez-Liva, Thomas Viel, Thulaciga Yoganathan, Anikitos Garofalakis, Joevin Sourdon, Caterina Facchin, Mickael Tanter, Jean Provost, Bertrand Tavitian
We recently introduced a hybrid imaging instrument, PETRUS, based on a combination of Positron Emission Tomography (PET) for molecular imaging, X-ray Computed Tomography (CT) for anatomical imaging, co-registration and attenuation correction, and Ultrafast Ultrasound Imaging (UUI) for motion-correction, hemodynamic and biomechanical imaging. In order to ensure a fine co-registration of simultaneous PET-UUI acquisitions, ultrasound probes attached to an ultrafast ultrasound scanner are operated in the field of view (FOV) of a small animal PET/CT scanner using a remote-controlled micro-positioner...
August 9, 2018: Physics in Medicine and Biology
Chieh Lin, Chih-Chieh Liu, Hsuan-Ming Huang
In this study, we present an image denoising method for diffusion-weighted magnetic resonance imaging (DW-MRI) data. Our aim is to improve the estimation of intravoxel incoherent motion (IVIM) parameters using denoised DW-MRI data. A general-threshold filtering (GTF) reconstruction via total variation minimization has been proposed to improve image quality in few-view computed tomography. Here, we applied the combination of GTF and total difference to image denoising. Voxel-wise IVIM analysis was performed using both real and simulated DW-MRI data...
August 9, 2018: Physics in Medicine and Biology
Gaoyu Chen, Fenghua Weng, Xiang Hong, Weijie Tao, Zhixiang Zhao, Qiyu Peng, Qiu Huang
This work modified the commonly used Monte Carlo tool package GATE by developing a new "multiPatchPET" system so that GATE users will be able to easily simulate PET systems with irregular geometries. The motivation was to design a brain PET scanner with high sensitivity. It is known that the compact PET scanner with a large solid coverage angle achieves high sensitivity, and thus is potential to provide better image quality in brain PET imaging than the conventional ring PET, even with fewer scintillation detectors...
August 8, 2018: Physics in Medicine and Biology
Anders Garpebring, Patrik Brynolfsson, Peter Kuess, Dietmar Georg, Thomas H Helbich, Tufve Nyholm, Tommy Löfstedt
The Haralick texture features are common in the image analysis literature, partly because of their simplicity and because their values can be interpreted. It was recently observed that the Haralick texture features are very sensitive to the size of the GLCM that was used to compute them, which led to a new formulation that is invariant to the GLCM size. However, these new features still depend on the sample size used to compute the GLCM, i.e. the size of the input image region-of-interest (ROI).
 The purpose of this work was to investigate the performance of density estimation methods for approximating the GLCM and subsequently the corresponding invariant features...
August 8, 2018: Physics in Medicine and Biology
Mingxin Jin, Dongdong Hao, Song Ding, Binjie Qin
This letter proposes to extract contrast-filled vessels from the overlapped noisy complex backgrounds in X-ray coronary angiogram image sequence using low-rank and sparse decomposition. A refined vessel segmentation is finally achieved by implementing Radon-like feature filtering plus local-to-global adaptive thresholding to tackle the spatially varying noisy residuals in the extracted vessels. Based on real and synthetic XCA data, experiment results show the superiority of the proposed method over the state-of-the-art methods...
August 8, 2018: Physics in Medicine and Biology
Aimee Louise McNamara, Jose Ramos-Mendez, Joseph Perl, Kathryn Held, Naoki Dominguez, Eduardo Barbosa Moreno, Nicholas T Henthorn, Karen J Kirkby, Sylvain Meylan, Carmen Villagrasa, Sebastien Incerti, Bruce Faddegon, Harald Paganetti, Jan Schuemann
Computational simulations, such as Monte Carlo track structure simulations, offer a powerful tool for quantitatively investigating radiation interactions within cells. The modelling of the spatial distribution of energy deposition events as well as diffusion of chemical free radical species, within realistic biological geometries, can help provide a comprehensive understanding of the effects of radiation on cells. Track structure simulations, however, generally require advanced computing skills to implement...
August 8, 2018: Physics in Medicine and Biology
Xinhui Wang, Bao Yang, Matthew Paul Adams, Xiangzhen Gao, Nicolas A Karakatsanis, Jing Tang
Myocardial perfusion (MP) PET imaging plays an important role in risk assessment and stratification of patients with coronary artery disease. In this work, we developed an anatomy-assisted maximum a posteriori (MAP) reconstruction method incorporating a wavelet-based joint entropy (WJE) prior for MP PET imaging. Using the XCAT phantom, we first simulated three MP PET datasets, one with normal perfusion and the other two with non-transmural and transmural regionally reduced perfusion of the left ventricular myocardium...
August 8, 2018: Physics in Medicine and Biology
Tabea Pfuhl, Felix Horst, Christoph Schuy, Uli Weber
Dose build-up effects in the entrance channel of proton Bragg curves were investigated in detail by means of simulations and experiments. There are two relevant dose build-up effects. Firstly, the δ-electron build-up effect which takes place in the first few millimeters of the tissue until an equilibrium state of the forwards scattered δ-electrons is reached. Secondly, the target fragment build-up effect that covers the first centimeters in the entrance channel of the proton Bragg curve. These target fragments are created in inelastic interactions of the beam protons with the target nuclei and partially have low kinetic energies and/or high atomic numbers compared to the incident beam protons...
August 8, 2018: Physics in Medicine and Biology
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