Read by QxMD icon Read

Physics in Medicine and Biology

Antonio Gonzalez-Lopez
Portal images have a unique feature among the imaging modalities used in radiotherapy: they provide direct visualization of the irradiated volumes. However, contrast and spatial resolution are strongly limited due to the high energy of the radiation sources. Because of this, imaging modalities using x-ray energy beams have gained importance in the verification of patient positioning, replacing portal imaging.
 The purpose of this work was to develop a method for the enhancement of local contrast in portal images...
June 18, 2018: Physics in Medicine and Biology
Sadegh Riyahi, Wookjin Choi, Chia-Ju Liu, Hualiang Zhong, Abraham J Wu, James G Mechalakos, Wei Lu
We proposed a framework to detect and quantify local tumor morphological changes due to chemo-radiotherapy (CRT) using Jacobian map and to extract quantitative radiomic features from the Jacobian map to predict the pathologic tumor response in locally advanced esophageal cancer patients. In 20 patients who underwent CRT, a multi-resolution BSpline deformable registration was performed to register the follow-up (post-CRT) CT to the baseline CT image. Jacobian map (J) was computed as the determinant of the gradient of the Deformation Vector Field...
June 18, 2018: Physics in Medicine and Biology
Grischa Klimpki, Ye Zhang, Giovanni F Fattori, Serena Psoroulas, Damien Charles Weber, Antony John Lomax, David Meer
Therapeutic pencil beams are typically scanned using one of the following three techniques: spot scanning, raster scanning or line scanning. While providing similar dose distributions to the target, these three techniques can differ significantly in their delivery time sequence. Thus, we can expect differences in effectiveness and time efficiency when trying to mitigate interplay effects using rescanning. At the Paul Scherrer Institute, we are able to irradiate treatment plans using either of the three delivery techniques...
June 18, 2018: Physics in Medicine and Biology
Chengxi Wu, Carolyn L Bayer
The function of the placenta is challenging to characterize and as a result is understudied, despite the growing awareness of the impact of the placental environment on human health and development. Medical imaging has the potential to improve our ability to screen for diseases associated with placental insufficiency, and improve the monitoring and treatment of complex obstetric patients. This review provides an overview of clinical and preclinical imaging modalities currently available for assessing placental function, with an emphasis on emerging preclinical imaging modalities; as a group, these emerging modalities provide exceptional contrast and sensitivity for multimodal functional and molecular imaging of the placenta...
June 14, 2018: Physics in Medicine and Biology
Anne T Davis, James Earley, Sue Edyvean, Una Findlay, Rebecca Lindsay, Andrew Nisbet, Antony L Palmer, Rosaleen Plaistow, Matthew Geraint Joseph Williams, Tim J Wood
CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for dose calculations in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance on dose levels in radiotherapy CT imaging either within the UK or internationally...
June 14, 2018: Physics in Medicine and Biology
Bernard Gottschalk
To find a deterministic pencil beam algorithm that computes, from first principles, the dose in some region of interest when a known heterogeneous terrain is irradiated by known proton beams.
 Methods: The terrain is discretized into slabs perpendicular to the nominal beam direction. Pencil beams (PBs) are transported through each slab using generalized Fermi-Eyges theory with the correct stopping and scattering powers for each material (no water-like assumption).
 At transverse heterogeneities PBs are divided into smaller ones using either redefinition (all PBs divided) or dynamic splitting (PBs divided one at a time as needed)...
June 14, 2018: Physics in Medicine and Biology
Jakob Meineke, Fabian Wenzel, Matteo de Marco, Annalena Venneri, Daniel J Blackburn, Kevin Teh, Iain D Wilkinson, Ulrich Katscher
As Quantitative Susceptibility Mapping (QSM) is maturing, more clinical applications are being explored. With this comes the question whether QSM is sufficiently robust and reproducible to be directly used in a clinical setting where patients are possibly not cooperative and/or unable to suppress involuntary movements sufficiently.
 Subjects and Methods: Twenty-nine patients with Alzheimer's Disease (AD), 31 patients with Mild Cognitive Impairment (MCI) and 41 healthy controls (HC) were scanned on a 3T scanner, including a multi-echo gradient-echo sequence for QSM and an inversion-prepared segmented gradient-echo sequence (T1-TFE, MPRAGE)...
June 13, 2018: Physics in Medicine and Biology
James L B Robertson, Jillian Urban, Joel Stitzel, Bradley E Treeby
Transcranial transmission of ultrasound is increasingly used in a variety of clinical and research applications, including high intensity ablation, opening the blood brain barrier, and neural stimulation. Numerical simulations of ultrasound propagation in the head are used to enable effective transcranial focusing and predict intracranial fields. Such simulations require maps of the acoustic properties of the head, which can be derived from clinical CT images. However, the spatial resolution of these images is typically coarser than the scale of heterogeneities within the skull bone, which are known to exert a major influence on ultrasound propagation...
June 13, 2018: Physics in Medicine and Biology
Chunyi Liu, Jin Jin, Lei Guo, Mingyan Li, Yasvir Tesiram, Haiwei Chen, Feng Liu, Xuegang Xin, Stuart Crozier
Magnetic resonance electrical properties tomography (MR-EPT) reconstructs electrical properties (EPs) from measured magnetic fields in Magnetic Resonance Imaging (MRI) systems. In this study, a MR-EPT method was proposed that utilized a new finite difference approximation of the involved differential wave equation. Compared with existing MR-EPT approaches, the construction of the system matrix involves applying first derivative twice based on a larger number of neighbouring finite-difference grids, which is different from standard Laplacian operator on a regular grid structure, leading to a better conditioned linear inverse problem...
June 13, 2018: Physics in Medicine and Biology
Xiaochun Lai, Yoann Petibon, Georges El Fakhri, Jinsong Ouyang
Myocardial perfusion imaging (MPI) using rest/stress single photon emission computed tomography (SPECT) allows non-invasive assessment of reversible cardiac perfusion defects. Conventionally, reversible defects are identified using a difference image, called reversible map, obtained by subtracting the stress image from the rest image after registration and normalization of the two images. The identification of reversible defects using the conventional subtraction method is however limited by noise. We propose to jointly reconstruct rest and stress projection data to directly obtain the reversible map in a single reconstruction framework to improve the detectability of reversible defects...
June 13, 2018: Physics in Medicine and Biology
Yazid Touileb, Hamid Ladjal, Michael Beuve, Behzad Shariat
The use of tetrahedral-based phantoms in conjunction with Monte Carlo dose calculation techniques has shown high capabilities in radiation therapy. However, the generation of a precise dose distribution can be very time-consuming since a fine tetrahedral mesh is required. In this work, we propose a new method that defines the density distribution of patient-specific tetrahedral phantoms, based upon the CT-scans and the direction of the particle beam. The final purpose is to coarsen the tetrahedral mesh to improve computational performance in Monte Carlo simulations while guaranteeing a precise dose distribution in the target volume...
June 12, 2018: Physics in Medicine and Biology
Ye Li, Shannon E O'Reilly, Donika Plyku, S Ted Treves, Yong Du, Frederic H Fahey, Xinhua Cao, Abhinav K Jha, George Sgouros, Wesley E Bolch, Eric C Frey
Please see abstract in the final version of the manuscript.
June 12, 2018: Physics in Medicine and Biology
Qi Zeng, Qingyan Wang, Jianfeng Jason Zheng, Wolfgang Kainz, Ji Chen
A typical cochlear implant system under Magnetic Resonance Imaging (MRI) procedures may couple with the radio frequency (RF) electromagnetic field (EMF) and results in an intensified electric field at the lead tip. As a result, the RF energy deposited in human tissues around the lead tip may induce heating and cause tissue damage concerns. The purpose of this work is to evaluate the RF-EMF-induced heating for cochlear implant system in 1.5T MRI coil and highlight the factors that have significant effects on the heating...
June 12, 2018: Physics in Medicine and Biology
Tianye Niu, Pengfei Yang, Xiaonan Sun, Tingyu Mao, Lei Xu, Ning Jeff Yue, Yu Kuang, Liming Shi, Ke Nie
Tumor angiogenesis is considered as an important prognostic factor. With an increasing emphasis on imaging evaluation of the tumor microenvironment, dynamic contrast enhanced (DCE) CT has evolved as an important functional technique in this setting. Yet many questions remain as how and when these functional measurements should be performed for each agent and tumor type, and what quantitative models should be used in the fitting process. In this study, we evaluated the variations of perfusion measurement on DCE-CT for rectal cancer patients from (1) different tracer kinetic models, (2) different scan acquisition lengths and (3) different scan intervals...
June 11, 2018: Physics in Medicine and Biology
Hendrik Paysen, James Wells, Olaf Kosch, Uwe Steinhoff, Jochen Franke, Lutz Trahms, Tobias Schaeffter, Frank Wiekhorst
Magnetic Particle Imaging (MPI) is an imaging modality capable of quantitatively determining the 3D distribution of a magnetic nanoparticle (MNP) ensemble. In this work, we present a method for reducing the MNP limit of detection by employing a new receive-only coil (Rx-coil) for signal acquisition. The new signal detector is designed to improve the sensitivity and thus quality of reconstructed images. We present characterization measurements conducted with the prototype Rx-coil installed in a preclinical MPI scanner...
June 11, 2018: Physics in Medicine and Biology
Jennifer Petra Kieselmann, Cornelis Philippus Kamerling, Ninon Burgos, Martin J Menten, Clifton David Fuller, Simeon Nill, M Jorge Cardoso, Uwe Oelfke
Owing to its excellent soft-tissue contrast, magnetic resonance (MR) imaging has found an increased application in radiation therapy (RT). Harnessing these properties for treatment planning, automated segmentation methods can alleviate the manual workload burden to the clinical workflow. 
 We investigated atlas-based segmentation methods of organs at risk (OARs) in the head and neck (H&N) region: one approach selecting the most similar atlas from a library of segmented images and two multi-atlas approaches...
June 8, 2018: Physics in Medicine and Biology
Lucas Paixão, Margarita Chevalier, Antonio E Hurtado-Romero, Julia Garayoa
The aim of this work is to study the radiation doses delivered to a group of patients that underwent a stereotactic breast biopsy (SBB) procedure. Mean glandular doses (MGD) were estimated from the air-kerma measured at the breast surface entrance multiplying by specific conversion coefficients (DgN) that were estimated using Monte Carlo simulations. DgN were calculated for the 0º and ±15º projections used in SBB and for the particular beam quality. Data on 61 patients were collected showing that a typical SBB procedure is composed by 10 images...
June 7, 2018: Physics in Medicine and Biology
Ligin M Solamen, Matthew D J McGarry, Likun Tan, John B Weaver, Keith D Paulsen
This study evaluated non-linear inversion MRE (NLI-MRE) based on viscoelastic governing equations to determine its sensitivity to small, low contrast inclusions and interface changes in shear storage modulus and damping ratio. Reconstruction parameters identical to those used in recent in vivo MRE studies of mechanical property variations in small brain structures were applied. NLI-MRE was evaluated on four phantoms with contrast in stiffness and damping ratio. Image contrast to noise ratio was assessed as a function of inclusion diameter and property contrast, and edge and line spread functions were calculated as measures of imaging resolution...
June 7, 2018: Physics in Medicine and Biology
Leonard Che Fru, Erin Beth Adamson, David Daniel Campos, Sean B Fain, Steven L Jacques, Albert J van der Kogel, Kwang Park Nickel, Chihwa Song, Randall J Kimple, Michael W Kissick
At the time of publication, our group had performed short tandem repeat (STR) testing on the SCC22B cell line and believed that had been correctly identified. As part of a recent comprehensive process to confirm the identity of cell lines in use in our lab, we repeated STR testing on all cell lines. These results were compared to the ExPASy Cellosaurus database ( One cell line used in this manuscript was a near perfect match for T24 (CVCL_0554), a bladder carcinoma cell line commonly found as a cellular contaminant...
June 6, 2018: Physics in Medicine and Biology
Wonmo Sung, Jan Schuemann
Gold nanoparticles (GNPs) have been demonstrated as radiation dose enhancing agents. Kilovoltage external photon beams have been shown to yield the largest enhancement due to the high interaction probability with gold. While orthovoltage irradiations are feasible and promising, they suffer from a reduced tissue penetrating power. This study quantifies the effect of varying photon beam energies on various beam arrangements, body, tumour and cellular GNP uptake geometries. Cell survival was modeled based on our previously developed GNP-Local Effect Model (LEM) with radial doses calculated using the TOPAS-nBio Monte Carlo code...
June 6, 2018: Physics in Medicine and Biology
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"