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Physics in Medicine and Biology

Annette Caenen, Mathieu Pernot, Mathias Peirlinck, Luc Mertens, Abigail Swillens, Patrick Segers
Shear wave elastography (SWE) is a potential tool to non-invasively assess cardiac muscle stiffness. This study focused on the effect of the orthotropic material properties and mechanical loading on the performance of cardiac SWE, as it is known that these factors contribute to complex 3D anisotropic shear wave propagation. To investigate the specific impact of these complexities, we constructed a finite element model with an orthotropic material law subjected to different uniaxial stretches to simulate SWE in the stressed cardiac wall...
February 16, 2018: Physics in Medicine and Biology
Jeppe Brage Christensen, Erik Almhagen, Håkan Nyström, Claus E Andersen
Photons emitted in optical fibres under proton irradiations have been attributed to be both entirely Čerenkov radiation or to be light consisting of fluorescence with a substantial amount of Čerenkov radiation. The source of the light emission is assessed in order to understand why the signal from optical fibres irradiated with protons reportedly is quenching-free. 
 The present study uses the directional emittance of Čerenkov photons in 12 MeV and 20 MeV electron beams to validate a Monte Carlo model for simulating the emittance and transmission of Čerenkov radiation in optical fibres...
February 15, 2018: Physics in Medicine and Biology
Shu-Ju Tu, Chih-Wei Wang, Kuang-Tse Pan, Yi-Cheng Wu, Chen-Te Wu
Lung cancer screening aims to detect small pulmonary nodules and decrease the mortality rate. However, studies from large-scale clinical trials of lung cancer screening showed false-positive rate is high and positive predictive value is low. To address these problems, it is highly needed to have a technical approach for accurate malignancy differentiation among these early-detected nodules. We studied the clinical feasibility of an additional protocol of localized thin-section CT for further assessment on these recalled patients from lung cancer screening tests...
February 15, 2018: Physics in Medicine and Biology
Wilco J C Koppert, Sandra van der Velden, J H Leo Steenbergen, Hugo W A M de Jong
In SPECT/CT systems X-ray and -ray imaging is performed sequentially. Simultaneous acquisition may have advantages, for instance in interventional settings. However, this may expose a gamma camera to relatively high X-ray doses and deteriorate its functioning. We studied the NaI(Tl) response to X-ray pulses with a photodiode, PMT and gamma camera, respectively. Method: First, we exposed a NaI(Tl)-photodiode assembly to X-ray pulses to investigate potential crystal afterglow. Next, we exposed a NaI(Tl)-PMT assembly to 10 ms LED pulses (mimicking X-ray pulses) and measured the response to flashing LED probepulses (mimicking -pulses)...
February 13, 2018: Physics in Medicine and Biology
John Civale, Ian Rivens, Adam Shaw, Gail R Ter Haar
Characterisation of the spatial peak intensity at the focus of high intensity focused ultrasound (HIFU) transducers is difficult because of the risk of damage to hydrophone sensors at the high focal pressures generated. Hill et al (1994) provided a simple equation for estimating spatial-peak intensity for solid spherical bowl transducers using measured acoustic power and focal beamwidth. This paper demonstrates theoretically and experimentally that this expression is only strictly valid for spherical bowl transducers without a central (imaging) aperture...
February 13, 2018: Physics in Medicine and Biology
Jonathan Jenner Macoskey, Sang Won Choi, Timothy L Hall, Eli Vlaisavljevich, Jonathan Erik Lundt, Fred T Lee, Eric Johnsen, Charles A Cain, Zhen Xu
Histotripsy is an ultrasonic tissue ablation method based on acoustic cavitation. It has been shown that cavitation dynamics change depending on the mechanical properties of the host medium. During histotripsy treatment, the target-tissue is gradually fractionated and eventually liquefied to acellular homogenate. In this study, the change in the collapse time (t<sub>col</sub>) of the cavitation bubble cloud over the course of histotripsy treatment is investigated as an indicator for progression of the tissue fractionation process throughout treatment...
February 9, 2018: Physics in Medicine and Biology
Gilmer Valdes, Yannet Interian
In this comment the authors address some concerns they have about the paper: "Deep convolutional neural network with transfer learning for rectum toxicity prediction in cervical cancer radiotherapy: a feasibility study."
February 9, 2018: Physics in Medicine and Biology
Yoshinori Miyahara, Yuki Hara, Hiroto Nakashima, Tomonori Nishimura, Kanae Itakura, Taisuke Inomata, Hajime Kitagaki
In high-dose-rate (HDR) brachytherapy, a direct-conversion flat-panel detector (d-FPD) clearly depicts a 192Ir source without image halation, even under the emission of high-energy gamma-rays. However, it has been unknown why iridium is visible using a d-FPD. The purpose of this study was to clarify reasons for visibility of the source core based on physical imaging characteristics, including the modulation transfer functions (MTF), noise power spectral (NPS), contrast transfer functions (CTF), and linearity of d-FPD to high-energy gamma-rays...
February 9, 2018: Physics in Medicine and Biology
Oleg N Vassiliev, Stephen F Kry, David R Grosshans, Radhe Mohan
This study concerns calculation of the average electronic stopping power for photon and electron sources. It addresses two problems that have not yet been fully resolved. The first is defining the electron spectrum used for averaging in a way that is most suitable for radiobiological modeling. We define it as the spectrum of electrons entering the sensitive to radiation volume (SV) within the cell nucleus, at the moment they enter the SV. For this spectrum we derive a formula that combines linearly the fluence spectrum and the source spectrum...
February 7, 2018: Physics in Medicine and Biology
Suleman Surti, Joel S Karp
The advent of silicon photomultipliers (SiPMs) has introduced the possibility of increased detector performance in commercial whole-body PET scanners. The primary advantage of these photodetectors is the ability to couple a single SiPM channel directly to a single pixel of PET scintillator that is typically 4 mm wide (one-to-one coupled detector design). We performed simulation studies to evaluate the impact of three different event positioning algorithms in such detectors: i) a weighted energy centroid positioning (Anger logic), ii) identifying the crystal with maximum energy deposition (1<sup>st</sup> max crystal), and iii) identifying the crystal with second highest energy deposition (2<sup>nd</sup> max crystal)...
February 7, 2018: Physics in Medicine and Biology
Emily L Marshall, David Borrego, Trung Tran, James C Fudge, Wesley E Bolch
Epidemiologic data demonstrate that pediatric patients face a higher relative risk of radiation induced cancers than their adult counterparts at equivalent exposures. Infants and children with congenital heart defects are a critical patient population exposed to ionizing radiation during life-saving procedures. These patients will likely incur numerous procedures throughout their lifespan, each time increasing their cumulative radiation absorbed dose. As continued improvements in long-term prognosis of congenital heart defect patients is achieved, a better understanding of organ radiation dose following treatment becomes increasingly vital...
February 6, 2018: Physics in Medicine and Biology
Seungeun Lee, Min Sun Lee, Jun Yeon Won, Jae Sung Lee
In this study, we measured the performance of a newly developed Hamamatsu Photonics R13478 photomultiplier tube (PMT) and compared the results with those for an existing R9800 PMT. In R13478, an accelerating electrode is placed between the focusing electrode and first dynode for time resolution improvement through reduced transit time jitter. We investigated the time resolution dependence on the supply voltage and time pickoff method for R13478 and R9800 PMTs, each coupled with a 2.9 × 2.9 × 20 mm3 fast LGSO:Ce (0...
February 6, 2018: Physics in Medicine and Biology
Tsuicheng D Chiu, David Parsons, Yue Zhang, Brian Hrycushko, Bo Zhao, Rajiv Chopra, Nathan Kim, Ann Spangler, Asal Rahimi, Robert D Timmerman, Steve B Jiang, Weiguo Lu, Xuejun Gu
Accurate dose delivery in Stereotactic partial breast irradiation (S-PBI) is challenging because of the target position uncertainty caused by breast deformation, the target volume changes caused by lumpectomy cavity shrinkage, and target delineation uncertainty on simulation computed tomography (CT) images caused by poor soft tissue contrast. We have developed a volumetric ultrasound tomography (UST) image guidance system for prone position S-PBI. The system is composed of a novel 3D printed rotation water tank, a patient-specific resin breast immobilization cup, and a 1D array ultrasound transducer...
February 6, 2018: Physics in Medicine and Biology
Miriam Krieger, Grischa Klimpki, Giovanni F Fattori, Jan Hrbacek, David Oxley, Sairos Safai, Damien Charles Weber, Antony John Lomax, Ye Zhang
The aim of this study was to verify the temporal accuracy of the estimated dose distribution by a 4D dose calculation (4DDC) in comparison to measurements. A single-field plan (0.6Gy), optimised for a liver patient case (CTV volume: 403cc), was delivered to a homogeneous PMMA phantom and measured by a high resolution scintillating-CCD system at two water equivalent depths. Various motion scenarios (no motion and motions with amplitude of 10mm and two periods: 3.7s and 4.4s) were simulated using a 4D Quasar phantom and logged by an optical tracking system in real-time...
February 6, 2018: Physics in Medicine and Biology
Reko Kemppainen, Teuvo Vaara, Timo Joensuu, Timo Kiljunen
Background and Purpose Magnetic resonance imaging (MRI) has in recent years emerged as an imaging modality to drive precise contouring of targets and organs at risk in external beam radiation therapy. Moreover, recent advances in MRI enable treatment of cancer without computed tomography (CT) simulation. A commercially available MR-only solution, MRCAT, offers a single-modality approach that provides density information for dose calculation and generation of positioning reference images. We evaluated the accuracy of patient positioning based on MRCAT digitally reconstructed radiographs (DRRs) by comparing to standard CT based workflow...
February 6, 2018: Physics in Medicine and Biology
Yi Zheng, Robert Speller, Jennifer Griffiths
The first step that is required to extract the correct information from a two-dimensional (2D) diffraction signature is to remove the background accurately. However, direct background subtraction inevitably overcorrects the signal as it does not take into account the attenuation by the sample. Other traditional background removal methods, such as the rolling ball technique, can separate sharp diffraction peaks of crystalline materials from their background. These methods are unsuitable for biological tissue, which is amorphous and does not have sharp diffraction peaks...
February 2, 2018: Physics in Medicine and Biology
Amir M Owrangi, Peter B Greer, Carri K Glide-Hurst
Over the past decade, the application of magnetic resonance imaging (MRI) has increased, and there is growing evidence to suggest that improvements in the accuracy of target delineation in MRI-guided radiation therapy may improve clinical outcomes in a variety of cancer types. However, some considerations should be recognized including patient motion during image acquisition and geometric accuracy of images. Moreover, MR-compatible immobilization devices need to be used when acquiring images in the treatment position while minimizing patient motion during the scan time...
February 2, 2018: Physics in Medicine and Biology
Filipa Costa, Simon J Doran, Ian Maddock Hanson, Simeon Nill, Ilias Billas, David R Shipley, Simon Duane, John Adamovics, Uwe Oelfke
Dosimetric quality assurance (QA) of the new Elekta Unity (MR-linac) will differ from the QA performed of a conventional linac due to the constant magnetic field, which creates an electron return effect (ERE). In this work we aim to validate PRESAGE(R) dosimetry in a transverse magnetic field, and assess its use to validate the research version of the Monaco TPS of the MR-linac. Cylindrical samples of PRESAGE(R) 3D dosimeter separated by an air gap were irradiated with a cobalt-60 unit, while placed between the poles of an electromagnet at 0...
February 2, 2018: Physics in Medicine and Biology
Tae-Ho Kim, Siyong Kim, Dong-Su Kim, Seong-Hee Kang, Min-Seok Cho, Kyeong-Hyun Kim, Dong-Seok Shin, Tae-Suk Suh
In this study, we developed and evaluated a system that could monitor abdominal compression force (ACF) in real time and provide a surrogating signal, even under abdominal compression. The system could also provide visual-biofeedback (VBF). The real-time ACF monitoring system developed consists of an abdominal compression device, an ACF monitoring unit and a control system including an in-house ACF management program. We anticipated that ACF variation information caused by respiratory abdominal motion could be used as a respiratory surrogate signal...
February 2, 2018: Physics in Medicine and Biology
Hannah Jungeun Lee, Mo Kadbi, Gary Bosco, Geoffrey S Ibbott
The integration of magnetic resonance imaging (MRI) with linear accelerators (linac) has enabled the use of 3D MR-visible gel dosimeters for real-time verification of volumetric dose distributions. Several iron-based radiochromic 3D gels were created in-house then imaged and irradiated in a pre-clinical 1.5 T - 7 MV MR-Linac. MR images were acquired using a range of balanced-fast field echo (b-FFE) sequences during irradiation to assess the contrast and dose response in irradiated regions and to minimize the presence of MR artifacts...
January 31, 2018: Physics in Medicine and Biology
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