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Physics in Medicine and Biology

Mustafa Ege Babadagli, Ron Sloboda, John Doucette
Low dose rate (LDR) brachytherapy is a minimally invasive form of radiation therapy, used to treat prostate cancer, and it involves permanent implantation of radioactive sources (seeds) inside of the prostate gland. Treatment planning in brachytherapy involves a decision making process for the placement of the sources in order to deliver an effective dose of radiation to cancerous tissue in the prostate while sparing the surrounding healthy tissue. Such a decision making process can be modeled as a mixed-integer linear programming (MILP) problem...
February 15, 2019: Physics in Medicine and Biology
Benjamin J Cooper, Ricky T O'Brien, Chun-Chien Shieh, Paul J Keall
Four dimensional cone-beam computed tomography (4D CBCT) improves patient positioning and the accuracy of radiation therapy for patients with mobile tumours. Generally, 4D CBCT requires many hundreds of x-ray projections to measure target trajectories and the imaging frequency is not adapted to the patient's respiratory signal resulting in over-sampling. In contrast, respiratory triggered 4D CBCT (RT 4D CBCT) is an acquisition technique that has been experimentally implemented and has shown to reduce the number of x-ray projections and thus 4D CBCT dose with minimal impact on image quality...
February 12, 2019: Physics in Medicine and Biology
Giuseppina Esposito, Giovanni Mettivier, Kristina Bliznakova, Zhivko Bliznakov, Hilde Bosmans, Alberto Bravin, Ivan Buliev, Francesca Di Lillo, Danail Ivanov, Martina Minutillo, Antonio Sarno, Janne Vignero, Paolo Russo
3D breast modelling for 2D and 3D breast X-ray imaging would benefit from the availability of digital and physical phantoms that reproduce accurately the complexity of the breast anatomy. While a number of groups have produced digital phantoms with increasing level of complexity, physical phantoms reproducing that software approach have been scarcely developed. One possibility is offered by 3D printing technology. This implies the assessment of the energy dependent absorption index β of 3D printing materials for absorption based imaging, as well as the assessment of the refractive index decrement, δ, of the material, for phase contrast imaging studies, at the energies of interest for breast imaging...
February 12, 2019: Physics in Medicine and Biology
Simon R Cherry
Not applicable.
February 12, 2019: Physics in Medicine and Biology
Jaewon Yang, Dookun Park, Grant T Gullberg, Youngho Seo
Dedicated brain positron emission tomography (PET) devices can provide higher-resolution images with much lower dose, compared to conventional whole-body PET systems, which is important to support PET neuroimaging particularly useful for the diagnosis of neurodegenerative diseases. However, when a dedicated brain PET scanner does not come with a combined CT or transmission source, there is no direct solution for accurate attenuation and scatter correction, both of which are critical for quantitative PET. To address this problem, we propose joint attenuation and scatter correction (ASC) in image space for non-corrected PET (PET<sub>NC</sub>) using deep convolutional neural networks (DCNN)...
February 11, 2019: Physics in Medicine and Biology
Weixing Cai, Hakan Oesten, Benjamin Clasie, Brian Winey, Kyung-Wook Jee
To promote accurate image-guided radiotherapy (IGRT) for a proton pencil beam scanning (PBS) system, a new QA procedure employing a cone-shaped scintillator detector has been developed for multiple QA tasks in a semi-automatic manner. 
 The cone-shaped scintillator detector (XRV-124, Logos Systems, CA) is sensitive to both x-ray and proton beams. It records scintillation on the cone surface as a 2D image, from which the geometry of the radiation field that enters and exits the cone can be extracted...
February 8, 2019: Physics in Medicine and Biology
Miguel Bernal, Indrani Sen, Matthew W Urban
Cardiovascular disease is the leading cause of mortality in the United States. Peripheral artery disease (PAD) affects a substantial portion of the elderly population (> 70 years). PAD can be symptomatic or asymptomatic, and treatment is directed towards improving functional vessel patency and limb salvage. Revascularization surgical treatments are needed in some cases, and it is not always possible to use autologous veins for vascular grafting. In this case, synthetic materials may be used. Synthetic materials such as expanded polytetrafluoroethylene (ePTFE) and poly (ethylene terephthalate) (Dacron) have been used...
February 8, 2019: Physics in Medicine and Biology
Kun Li, Kensuke Sasaki, Soichi Watanabe, Hiroshi Shirai
This study presents an investigation of human skin exposure to obliquely incident electromagnetic waves at frequencies from 6 GHz to 1 THz. We aim to clarify the relationship between the power density and the skin surface temperature elevation under various exposure conditions. A Monte Carlo simulation was conducted to assess the transmittance and surface temperature elevation considering the variation of skin tissue thickness. For the case of TM wave injection, transmittance increases with increasing incidence angle from the normal incidence because of the Brewster effect...
February 8, 2019: Physics in Medicine and Biology
Young-Bin Cho, Hamideh Alasti, Vickie Kong, Charles Catton, Alejandro Berlin, Peter Chung, Andrew Bayley, David A Jaffray
The aim of the study is to determine PTV margin for inter-observer variability in the volumetric modulated arc therapy (VMAT) prostate radiotherapy with high-dose volumetric CT (HDVCT) and conventional helical CT (CCT) for planning. Secondly to investigate the impact of geometric (PTV expansion) and dosimetric (conformity) imperfection of planning process on the PTV margin analysis. Prostate gland of ten patients were scanned with CCT and HDVCT techniques consecutively on a 320 slice volumetric CT scanner with wide field detector of 16 cm...
February 7, 2019: Physics in Medicine and Biology
Veronika Ludwig, Maria Seifert, Christian Hauke, Katharina Hellbach, Florian Horn, Georg Pelzer, Marcus Radicke, Jens Rieger, Sven-Martin Sutter, Thilo Michel, Gisela Anton
X-ray dark-field imaging is a promising technique for lung diagnosis. Due to the alveolar structure of lung tissue, a higher contrast is obtained by the dark-field image compared to the attenuation image. Animal studies indicate an enhancement regarding the detection of lung diseases in early stages. In this publication, we focus on the influence of different Talbot-Lau interferometer specifications while maintaining the X-ray source, sample magnification and detector system. By imaging the same porcine lung with three different grating sets, we analyze the contrast-to-noise ratio of the obtained dark-field images with respect to visibility and correlation length...
February 7, 2019: Physics in Medicine and Biology
Ilias Billas, Hugo Bouchard, Uwe Oelfke, Simon Duane
With the advent of MRI-guided radiotherapy, the suitability of commercially available radiation dose detectors needs to be assessed. The aim of this study was to investigate the effect of the magnetic field (B-field) on the response of the Gafchromic EBT-3 films. Moreover, as an independent study, we contribute to clarifying the inconsistency of the results of recent published studies, on the effect of B-field on the sensitivity of Gafchromic films. 
 A <sup>60</sup>Co beam was used to irradiate film samples in an electromagnet...
February 7, 2019: Physics in Medicine and Biology
Félicien Hespeels, Stephane Lucas, Tijani Tabarrant, Emanuele Scifoni, Michael Kraemer, Gregoire Chêne, David Strivay, Hoang N Tran, Anne-Catherine Heuskin
In protontherapy, it has been suggested that nanoparticles of high-Z material like gold (GNP) be used as radiosensitizers. The origin of this enhancement phenomenon for proton radiation is not yet well understood and additional mechanistic insights are required. Previous works have highlighted the good capabilities of TRAX to reproduce secondary electron emission from gold material. Therefore, TRAX cross sections obtained with the binary encounter approximation (BEA) model for proton ionization were implemented within Geant4 for gold material...
February 7, 2019: Physics in Medicine and Biology
Paul Edimo, Angelika Kroshko, Luc Beaulieu, Louis Archambault
The purpose of the present study is to develop patient specific unbiased quality control (QC) models for high dose rate (HDR) brachytherapy plans. The proposed models are based on the stochastic frontier analysis formalism, a method of economic modeling. They act as a QC tool by predicting before the treatment planning process starts, the dosimetric coverage achievable for a HDR brachytherapy prostate plan. The geometric parameters considered in developing the models were: patient clinical target volume (CTV), organs at risk (OAR) volume, the bidirectional Hausdorff distance between CTV and OARs, and a fourth parameter measuring the catheters degree of non-parallelism within the target volume...
February 7, 2019: Physics in Medicine and Biology
Jing Wu, Chi Liu
Cardiac SPECT continues to play a critical role in detecting and managing cardiovascular disease, in particularly coronary artery disease (CAD) (Jaarsma et al., 2012; Agostini et al., 2016). While conventional dual-head SPECT scanners using parallel-hole collimators and scintillation crystals with photomultiplier tubes are still the workhorse of cardiac SPECT, they have the limitations of low photon sensitivity (~130 count s-1 MBq-1), poor image resolution (~15 mm) (Imbert et al., 2012), relatively long acquisition time, inefficient use of the detector, high radiation dose, etc...
February 6, 2019: Physics in Medicine and Biology
Lindsay C Johnson, Marie A Guerraty, Stephen C Moore, Scott D Metzler
Myocardial blood flow and myocardial blood flow reserve (MBFR) measurements are often used clinically to quantify coronary microvascular function. Developing imaging-based methods to measure MBFR for research in mice would be advantageous for evaluating new treatment methods for coronary microvascular disease, yet this is more challenging in mice than in humans. This work investigates microSPECT's quantitative capabilities of cardiac imaging by utilizing a multi-part cardiac phantom and applying a known kinetic model to synthesize kinetic data from static data, allowing for assessment of kinetic modeling accuracy...
February 5, 2019: Physics in Medicine and Biology
Linxi Shi, Adam S Wang, Jikun Wei, Lei Zhu
The quantitative use of cone beam computed tomography (CBCT) in radiation therapy is limited by severe shading artifacts, even with system embedded correction. We recently proposed effective shading correction methods, using planning CT (pCT) as prior information to estimate low-frequency errors in either the projection domain or the image domain. In this work, we further improve the clinical practicality of our previous methods by removing the requirement of prior pCT images. 
 Clinical CBCT images are typically composed of a limited number of tissue types...
February 5, 2019: Physics in Medicine and Biology
Marko Mikkonen, Ilkka Laakso
The brain moves when the orientation of the head changes. This inter-postural motion has been shown to affect the distribution of cerebrospinal fluid (CSF). As CSF layer thickness affects the distribution of electric fields (EF) in non-invasive brain stimulation methods such as transcranial direct current (TDCS) and magnetic (TMS) stimulation, possible differences in body position between sessions could affect the stimulation efficacy. Additionally, inter-postural differences might distort the modeling results of TDCS and TMS, as the models are usually built based on magnetic resonance images (MRI) obtained while the subject is in the supine position, whereas the actual stimulation is given while the subject is in an upright position...
February 1, 2019: Physics in Medicine and Biology
Nils Krah, Vincenzo Patera, Simon Rit, Angelo Schiavi, Ilaria Rinaldi
Proton transmission imaging has been proposed and investigated as imaging modality complementary to X-ray based techniques in proton beam therapy. In particular, it addresses the issue of range uncertainties due to the conversion of an X-ray patient computed tomography (CT) image expressed in Hounsfield Units (HU) to relative stopping power (RSP) needed as input to the treatment planning system. One approach to exploit a single proton radiographic projection is to perform a patient-specific calibration of the CT to RSP conversion curve by optimising the match between a measured and a numerically integrated proton radiography...
February 1, 2019: Physics in Medicine and Biology
Anthony J Deegan, Ruikang Ricky Wang
Despite our understanding that the microvasculature plays a multifaceted role in the development and progression of various conditions, we know little about the extent of this involvement. A need exists for non-invasive, clinically meaningful imaging modalities capable of elucidating microvascular information to aid in our understanding of disease, and to aid in the diagnosis/monitoring of disease for more patient-specific care. In this review article, a number of imaging techniques are summarized that have been utilized to investigate the microvasculature of skin, along with their advantages, disadvantages and future perspectives in preclinical and clinical settings...
February 1, 2019: Physics in Medicine and Biology
Cristian T Badea, Darin P Clark, Matthew Holbrook, Mayank Srivastava, Yvonne Mowery, Ketan B Ghaghada
Advances in computed tomography (CT) hardware have propelled the development of novel CT contrast agents. In particular, the spectral capabilities of X-ray CT can facilitate simultaneous imaging of multiple contrast agents. This approach is particularly useful for functional imaging of solid tumors by simultaneous visualization of multiple targets or architectural features that govern cancer development and progression. Nanoparticles are a promising platform for contrast agent development. While several novel imaging moieties based on high atomic number elements are being explored, iodine (I) and gadolinium (Gd) are particularly attractive because of their existing approval for clinical use...
February 1, 2019: Physics in Medicine and Biology
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