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Physics in Medicine and Biology

Amir Borna, Tony R Carter, Josh D Goldberg, Anthony P Colombo, Yuan-Yu Jau, Christopher Berry, Jim McKay, Julia Stephen, Michael Weisend, Peter D D Schwindt
We describe a multichannel magnetoencephalography (MEG) system that uses optically pumped magnetometers (OPMs) to sense the magnetic fields of the human brain. The system consists of an array of 20 OPM channels conforming to the human subject's head, a person-sized magnetic shield containing the array and the human subject, a laser system to drive the OPM array, and various control and data acquisitions systems. We conducted two MEG experiments: auditory evoked magnetic field (AEF) and somatosensory evoked magnetic field (SEF), on three healthy male subjects, using both our OPM array and a 306-channel Elekta-Neuromag superconducting quantum interference device (SQUID) MEG system...
October 16, 2017: Physics in Medicine and Biology
Manasavee Lohvithee, Ander Biguri, Manuchehr Soleimani
There are a number of powerful total variation (TV) regularization methods with great promises in limited data cone-beam CT reconstruction with an enhancement of image quality. These promising TV methods require careful selection of image reconstruction parameters for which there is no well established criteria. This pa- per presents a comprehensive valuation of parameter selection in a number of major TV-based reconstruction algorithms. The appropriate way of selecting the values for each individual parameter has been suggested...
October 16, 2017: Physics in Medicine and Biology
Ravi K Samala, Heang-Ping Chan, Lubomir M Hadjiiski, Mark A Helvie, Kenny Cha, Caleb Richter
Transfer learning in deep convolutional neural networks (DCNNs) is an important step in its application to medical imaging tasks. We propose a multi-task transfer learning DCNN with the aims of translating the 'knowledge' learned from non-medical images to medical diagnostic tasks through supervised training and increasing the generalization capabilities of DCNNs by simultaneously learning auxiliary tasks. We studied this approach in an important application: classification of malignant and benign breast masses...
October 16, 2017: Physics in Medicine and Biology
Soha Bazyar, Christina R Inscoe, E Timothy O'Brien Iii, Otto Z Zhou, Yueh Z Lee
Minibeam radiation therapy (MBRT) delivers ultrahigh dose of X-ray (≥100 Gy) in 200-1000 μm beams (peaks), separated by wider non-irradiated regions (valleys) usually as a single temporal fraction. Preclinical studies performed at synchrotron facilities revealed that MBRT is able to ablate tumors while maintaining normal tissue integrity. The main purpose of present study was to develop an efficient and accessible method to perform MBRT using a conventional X-ray irradiator. We then tested this new method both in-vitro and in-vivo...
October 10, 2017: Physics in Medicine and Biology
Sarah Ouadah, Matthew W Jacobson, Joseph Webster Stayman, Tina Ehtiati, Clifford Raabe Weiss, Jeffrey H Siewerdsen
Cone-beam CT (CBCT) is increasingly common in guidance of interventional procedures but can be subject to artifacts arising from patient motion during fairly long (~5-60s) scan times. We present a fiducial-free method to mitigate motion artifacts using 3D-2D image registration that simultaneously corrects residual errors in the intrinsic and extrinsic parameters of geometric calibration. The 3D-2D registration process registers each projection to a prior 3D image by maximizing gradient orientation using the covariance matrix adaptation-evolution strategy (CMA-ES) optimizer...
October 10, 2017: Physics in Medicine and Biology
Monica Hernandez
This paper proposes a method for primal-dual convex optimization in variational Large Deformation Diffeomorphic Metric Mapping problems formulated with robust regularizers and robust image similarity metrics. The method is based on Chambolle and Pock primal-dual algorithm for solving general convex optimization problems. Diagonal preconditioning is used to ensure the convergence of the algorithm to the global minimum. We consider three robust regularizers liable to provide acceptable results in diffeomorphic registration: Huber, V-Huber and Total Generalized Variation...
October 10, 2017: Physics in Medicine and Biology
Bulat Ibragimov, Diego Toesca, Daniel Chang, Albert Koong, Lei Xing
Automated segmentation of portal vein (PV) for liver radiotherapy planning is a challenging task due to potentially low vasculature contrast, complex PV anatomy and image artifacts originated from fiducial markers and vasculature stents. In this paper, we propose a novel framework for automated PV segmentation from computed tomography (CT) images. We apply convolutional neural networks (CNN) to learn consistent appearance patterns of PV using a training set of CT images with reference annotations and then enhance PV in previously unseen CT images...
October 10, 2017: Physics in Medicine and Biology
Mattia Fontana, Denis Dauvergne, Jean Michel Letang, Jean-Luc Ley, Etienne Testa
Single Photon Emission Computed Tomography (SPECT) is at present one of the major techniques for non-invasive diagnostics in nuclear medicine. The clinical routine is mostly based on collimated cameras, originally proposed by Hal Anger. Due to the presence of mechanical collimation, detection eciency and energy acceptance are limited and xed by the system's geometrical features. In order to overcome these limitations, the application of Compton cameras for SPECT has been investigated for several years...
October 10, 2017: Physics in Medicine and Biology
Jarno van Roosmalen, Freek J Beekman, Marlies C Goorden
Imaging of Tc-99m labelled tracers is gaining popularity for detecting breast tumours. Recently, we proposed a novel design for molecular breast tomosynthesis (MBT) based on two sliding focusing multi-pinhole collimators that scan a modestly compressed breast. Simulation studies indicate that MBT has the potential to improve the tumour-to-background contrast-to-noise ratio significantly over state-of-the-art planar molecular breast imaging. The aim of the present paper is to optimize the collimator-detector geometry of MBT...
October 10, 2017: Physics in Medicine and Biology
Patrik Nowik, Robert Bujila, Love Kull, Jonas Andersson, Gavin Poludniowski
The purpose of this study was to evaluate the dosimetric impact of including the patient table in Monte Carlo CT dose estimates for both spiral scans and scan projection radiographs (SPR). CT scan acquisitions were simulated for a Siemens SOMATOM Force scanner (Siemens Healthineers, Forchheim, Germany) with and without a patient table present. An adult male, an adult female and a pediatric female voxelized phantom were simulated. The simulated scans included tube voltages of 80 and 120 kVp. Spiral scans simulated without a patient table resulted in effective doses that were overestimated by approximately 5 % compared to the same simulations performed with the patient table present...
October 10, 2017: Physics in Medicine and Biology
Patricia Diez, Edwin G A Aird, Thorsten Sander, Clare A Gouldstone, Peter H G Sharpe, Christopher D Lee, Gerry Lowe, Russell A S Thomas, Tania Simnor, Peter Bownes, A Margaret Bidmead, Laura Gandon, David J Eaton, Antony L Palmer
A UK multicentre audit to evaluate HDR and PDR brachytherapy has been performed using alanine absolute dosimetry. This is the first national UK audit performing an absolute dose measurement at a clinically relevant distance (20 mm) from the source. It was performed in both INTERLACE (a phase III multicentre trial in cervical cancer) and non-INTERLACE brachytherapy centres treating gynaecological tumours. Forty-seven UK centres (including the National Physical Laboratory) were visited. A simulated line source was generated within each centre's treatment planning system and dwell times calculated to deliver 10 Gy at 20 mm from the midpoint of the central dwell (representative of Point A of the Manchester system)...
October 6, 2017: Physics in Medicine and Biology
Weishan Chang, Yusuke Koba, Tetsurou Katayose, Keisuke Yasui, Chihiro Omachi, Masatsugu Hariu, Hidetoshi Saitoh
To measure the absorbed dose to water <i>D</i><sub>w</sub> in proton beams by radiophotoluminescent glass dosimeter (RGD), a method with the correction for the change of the mass stopping power ratio (SPR) and the linear energy transfer (LET) dependence of radiophotoluminescent (RPL) efficiency ε<sup>RGD</sup><sub>LET</sub> has been proposed. The calibration coefficient in terms of <i>D</i><sub>w</sub> for RGDs (GD-302M, Asahi Techno Glass) was obtained using a <sup>60</sup>Co γ-ray...
October 5, 2017: Physics in Medicine and Biology
Jin Long Yue, Marion Tardieu, Felicia Julea, Tanguy Boucneau, Ralph Sinkus, Claire Pellot-Barakat, Xavier Maître
Magnetic Resonance Elastography (MRE) is a non invasive imaging modality, which holds the promise of absolute quantification of the mechanical properties of human tissues <i>in vivo</i>. MRE reconstruction with algebraic inversion of the Helmholtz equation upon the curl of the shear displacement field may theoretically be flawless. However, its performances are challenged by multiple experimental parameters, especially the frequency and the amplitude of the mechanical wave, the voxel size and the signal-to-noise ratio of the MRE acquisition...
October 5, 2017: Physics in Medicine and Biology
Jonathan Hugh Mason, Alessandro Perelli, William H Nailon, Michael E Davies
Quantifying material mass and electron density from computed tomography (CT) reconstructions can be highly valuable in certain medical practices, such as radiation therapy planning. However, uniquely parameterising the X-ray attenuation in terms of mass or electron density is an ill-posed problem when a single polyenergetic source is used with a spectrally indiscriminate detector. Existing approaches to single source polyenergetic modelling often impose consistency with a physical model, such as water--bone or photoelectric--Compton decompositions, which will either require detailed prior segmentation or restrictive energy dependencies, and may require further calibration to the quantity of interest...
October 5, 2017: Physics in Medicine and Biology
Daniel Maneval, Hugo Bouchard, Benoît Ozell, Philippe Després
The equivalent restricted stopping power formalism is introduced for proton mean energy loss calculations under the continuous slowing down approximation. The objective is the acceleration of Monte Carlo dose calculations by allowing larger steps while preserving accuracy. The fractional energy loss per step length ε was obtained with a secant method and a Gauss-Kronrod quadrature estimation of the integral equation relating the mean energy loss to the step length. The midpoint rule of the Newton-Cotes formulae was then used to solve this equation, allowing the creation of a lookup table linking ε to the equivalent restricted stopping power L<sub>eq</sub>, used here as a key physical quantity...
October 5, 2017: Physics in Medicine and Biology
Hans-Peter Wieser, Philipp Hennig, Niklas Wahl, Mark Bangert
Particle therapy is especially prone to uncertainties. This issue is usually being addressed with uncertainty quantification and minimization techniques based on scenario sampling. For proton therapy, however, it was recently shown that it is also possible to use closed-form computations based on Analytical Probabilistic Modeling (APM) for this purpose. APM yields unique features compared to sampling-based approaches motivating further research in this context. This paper demonstrates the application of APM for intensity-modulated carbon ion therapy to quantify the influence of setup and range uncertainties on the RBE-weighted dose...
October 5, 2017: Physics in Medicine and Biology
Syed Salman Shahid, Robert Gaul, Christian M Kerskens, Vittoria Flamini, Caitriona Lally
Diffusion magnetic resonance imaging (dMRI) can provide insights into the microstructure of intact arterial tissue. The current study employed high magnetic field MRI to obtain ultra-high resolution dMRI at an isotropic voxel resolution of 117 µm<sup>3</sup> in less than 2 hours of scan time. A parameter selective single shell (128 directions) diffusion-encoding scheme based on Stejskel-Tanner sequence with echo-planar imaging (EPI) readout was used. EPI segmentation was used to reduce the echo time (TE) and to minimise the susceptibility-induced artefacts...
October 5, 2017: Physics in Medicine and Biology
Stefan Bartzsch, Uwe Oelfke
Currently hard coherent x-ray radiation at high photon fluxes can only be produced with large and expensive radiation sources, such as 3rd generation synchrotrons. Especially in medicine, this limitation prevents various promising developments in imaging and therapy, such as microbeam radiation therapy from being translated into clinical practice. Here we present a new concept of highly brilliant x-ray sources, line focus x-ray tubes (LFXTs), which may serve as a powerful and cheap alternative to synchrotrons and a range of other existing technologies...
October 4, 2017: Physics in Medicine and Biology
Priscilla Lai, Zhongli Cai, Jean-Philippe Pignol, Eli Lechtman, Shahram Mashouf, Yijie Lu, Mitchell A Winnik, David A Jaffray, Raymond M Reilly
Permanent seed implantation (PSI) brachytherapy is a highly conformal form of radiation therapy but is challenged with dose inhomogeneity due to its utilization of low energy radiation sources. Gold nanoparticles (AuNP) conjugated with electron emitting radionuclides have recently been developed as a novel form of brachytherapy and can aid in homogenizing dose through physical distribution of radiolabeled AuNP when injected intratumorally (i.t.) in suspension. However, the distribution is unpredictable and precise placement of many injections would be difficult...
October 4, 2017: Physics in Medicine and Biology
Negar Omidvari, Jorge Cabello, Geoffrey Topping, Florian Roland Schneider, Stephan Paul, Markus Schwaiger, Sibylle I Ziegler
MADPET4 is the first small animal PET insert with two layers of individually read out crystals in combination with silicon photomultiplier technology. It has a novel detector arrangement, in which all crystals face the center of field of view transaxially. In this work, the PET performance of MADPET4 was evaluated and compared to other preclinical PET scanners using the NEMA NU 4 measurements, followed by imaging a mouse-size hot-rod resolution phantom and two in vivo simultaneous PET/MRI scans in a 7-T MRI scanner...
October 4, 2017: Physics in Medicine and Biology
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