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Physics in Medicine and Biology

Markus A de Jong, Atilla Gül, Jan Pieter de Gijt, Maarten J Koudstaal, Manfred Kayser, Eppo B Wolvius, Stefan Böhringer
Landmarking of CT scans is an important step in the alignment of skulls that is key in surgery planning, pre-/post-surgery comparisons, and morphometric studies. We present a novel method for automatically locating anatomical landmarks on the surface of cone beam CT-based image models of human skulls using 2D Gabor wavelets and ensemble learning. The algorithm is validated via human inter- and intra-rater comparisons on a set of 39 scans and a skull superimposition experiment with an established surgery planning software (Maxilim)...
April 20, 2018: Physics in Medicine and Biology
Jarno van Roosmalen, Freek J Beekman, Marlies C Goorden
Recently, we proposed and optimized dedicated multi-pinhole molecular breast tomosynthesis (MBT) that images a lightly compressed breast. As MBT may also be performed with other types of collimators, the aim of this paper is to optimize MBT with fan beam and slit-slat collimators and to compare its performance to that of multi-pinhole MBT to arrive at a truly optimized design. Using analytical expressions, we first optimized fan beam and slit-slat collimator parameters to reach maximum sensitivity at a series of given system resolutions...
April 20, 2018: Physics in Medicine and Biology
Mark Tseytlin, Alexander V Stolin, Priyaankadevi Guggilapu, Andrey A Bobko, Valery V Khramtsov, Oxana Tseytlin, Raymond R Raylman
The advent of hybrid scanners, combining complementary modalities, has revolutionized imaging; enhancing clinical practice and biomedical research. In this project, we investigated the melding of two complementary, functional imaging methods: positron emission tomography (PET) and electron paramagnetic resonance imaging (EPRI). The PET radiotracers can provide important information about cellular parameters, such as glucose metabolism. While EPR probes can provide assessment of tissue microenvironment, measuring parameters such as oxygenation and pH, for example...
April 20, 2018: Physics in Medicine and Biology
Jeffrey Barber, Chun-Chien Shieh, William Counter, Jonathan R Sykes, Peter Bennett, Verity Ahern, Stéphanie Corde, Soo-Min Heng, Paul White, Michael Jackson, Paul Liu, Paul J Keall, Ilana Feain
Fixed-beam radiotherapy systems with subjects rotating about a longitudinal (horizontal) axis are subject to gravity-induced motion. Limited reports on the degree of this motion, and any deformation, has been reported previously. The purpose of this study is to quantify the degree of anatomical motion caused by rotating a subject around a longitudinal axis, using cone-beam CT (CBCT). 
 In the current study, a purpose-made longitudinal rotating was aligned to a Varian TrueBeam kV imaging system...
April 18, 2018: Physics in Medicine and Biology
Seyedehnafiseh Mirniaharikandehei, Alan B Hollingsworth, Bhavika Patel, Morteza Heidari, Hong Liu, Bin Zheng
This study aims to investigate the feasibility of identifying a new quantitative imaging marker based on false-positives generated by computer-aided detection (CAD) scheme to help predict short-term breast cancer risk. An image dataset including four view mammograms acquired from 1,044 women was retrospectively assembled. All mammograms were originally interpreted as negative by radiologists. In the next subsequent mammography screening, 402 women were diagnosed with breast cancer and 642 remained negative...
April 18, 2018: Physics in Medicine and Biology
Vandiver Chaplin, Marshal A Phipps, Charles F Caskey
Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650 kHz. The array is randomized with 128 elements 6.6 mm in diameter, radius of curvature 7.2 cm, opening diameter 10.3 cm (focal ratio 0.7), and 46% coverage. Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity...
April 18, 2018: Physics in Medicine and Biology
Michel Defrise, Ahmadreza Rezaei, Johan Nuyts
This paper presents new data driven methods for the time of flight (TOF) calibration of positron emission tomography (PET) scanners. 
 These methods are derived from the consistency condition for TOF PET, they can be applied to data measured with an arbitrary tracer distribution and are numerically efficient because they do not require a preliminary image reconstruction from the non-TOF data. 
 Two-dimensional simulations are presented for one of the methods, which only involves the two first moments of the data with respect to the TOF variable...
April 17, 2018: Physics in Medicine and Biology
Pierre Nauleau, Iason Zacharias Apostolakis, Matthew McGarry, Elisa E Konofagou
The stiffness of the arteries is known to be an indicator of the progression of various cardiovascular diseases. Clinically, the pulse wave velocity (PWV) is used as a surrogate for the arterial stiffness. Pulse Wave Imaging (PWI) is a non-invasive, ultrasound-based imaging technique capable of mapping the motion of the vessel walls allowing local assessment of the arterial properties. Conventionally, a distinctive feature of the displacement wave (e.g. the 50% upstroke) is tracked across the map to estimate the PWV...
April 16, 2018: Physics in Medicine and Biology
Kyungho Yoon, Wonhye Lee, Phillip Croce, Amanda Cammalleri, Seung-Schik Yoo
Transcranial focused ultrasound (tFUS) is emerging as a non-invasive brain stimulation modality. Complicated interactions between acoustic pressure waves and osseous tissue introduce many challenges in the accurate targeting of an acoustic focus through the cranium. Image-guidance accompanied by a numerical simulation is desired to predict the intracranial acoustic propagation through the skull; however, such simulations typically demand sophisticated computation, which warrants an expedited processing method to provide on-site feedback for the user in guiding the acoustic focus to a particular brain region...
April 16, 2018: Physics in Medicine and Biology
Min Sun Lee, Seung Kwan Kang, Jae Sung Lee
Here, we proposed a novel method to identify inter-crystal scattering (ICS) events from a PET detector that is even applicable to light sharing designs. In the proposed method, the detector observation was considered as a linear problem and ICS events were identified by solving the linear problem. Three ICS identification methods were suggested to solve the linear problem 1) maximum peak detection, 2) pseudoinverse matrix calculation, and 3) convex constrained optimization. The proposed method was evaluated based on simulation and experimental studies...
April 16, 2018: Physics in Medicine and Biology
Yiqun Yang, Matthew W Urban, Robert J McGough
Shear wave calculations induced by an acoustic radiation force are very time-consuming on desktop computers, and high-performance graphics processing units (GPUs) achieve dramatic reductions in the computation time for these simulations. The acoustic radiation force is calculated using the fast near field method (FNM) and the angular spectrum approach (ASA), and then the shear waves are calculated in parallel with Green's functions on a GPU. This combination enables rapid evaluation of shear waves for push beams with different spatial samplings and for apertures with different f/#...
April 16, 2018: Physics in Medicine and Biology
Marios E Myronakis, Yue-Houng Hu, Rony Fueglistaller, Adam Wang, Paul Baturin, Pascal Huber, Daniel Morf, Josh M Star-Lack, Ross I Berbeco
The architecture of multi-layer imagers (MLIs) can be exploited to provide megavoltage spectral imaging (MVSPI) for specific imaging tasks. In the current work, we investigated bone suppression and gold fiducial contrast enhancement as two clinical tasks which could be improved with spectral imaging. A method based on analytical calculations that enables rapid investigation of MLI component materials and thicknesses was developed and validated against Monte Carlo computations. The figure of merit for task-specific imaging performance was the contrast-to-noise ratio (CNR) of the gold fiducial when the CNR of bone was equal to zero after a weighted subtraction of the signals obtained from each MLI layer...
April 13, 2018: Physics in Medicine and Biology
Yuting Lin, El Hassane Bentefour, Jacob B Flanz, Hanne M Kooy, Benjamin M Clasie
Pencil beam scanning (PBS) periodic quality assurance (QA) programs ensure the beam delivered to patients is within technical specifications. Two critical specifications for PBS delivery are the beam width and position. The aim of this study is to investigate whether a 2-dimensional ionization chamber array, such as the MatriXX detector (IBA Dosimetry, Schwarzenbruck, Germany), can be used to characterize submillimeter-sized PBS beam properties. The motivation is to use standard equipment, which may have pixel spacing coarser than the pencil beam size, and simplify QA workflow...
April 12, 2018: Physics in Medicine and Biology
Premkumar Elangovan, Alistair Mackenzie, David R Dance, Kenneth C Young, Kevin Wells
This work investigates the detection performance of specialist and non-specialist observers for different targets in 2D-mammography and digital breast tomosynthesis (DBT) using the OPTIMAM Virtual Clinical Trials (VCT) Toolbox and a 4-alternative forced choice (4AFC) assessment paradigm.
 Using 2D-mammography and DBT images of virtual breast phantoms, we compare the detection limits of simple uniform spherical targets and irregular solid masses. Target diameters of 4mm and 6mm have been chosen to represent target sizes close to the minimum detectable size found in breast screening, across a range of controlled contrast levels...
April 11, 2018: Physics in Medicine and Biology
Bastien Guerin, Peter Serano, Maria Ida Iacono, Todd M Herrington, Alik S Widge, Darin D Dougherty, Giorgio Bonmassar, Leonardo M Angelone, Lawrence L Wald
We propose a framework for electromagnetic (EM) simulation of deep brain stimulation (DBS) patients in radiofrequency (RF) coils. We generated a model of a DBS patient using post-operative head and neck computed tomography (CT) images stitched together into a "virtual CT" image covering the entire length of the implant. The body was modeled as homogeneous. The implant path extracted from the CT data contained self-intersections, which we corrected automatically using an optimization procedure. Using the CT-derived DBS path, we built a model of the implant including electrodes, helicoidal internal conductor wires, loops, extension cables, and the implanted pulse generator...
April 11, 2018: Physics in Medicine and Biology
Gregory B Moffitt, Robert D Stewart, George A Sandison, John T Goorley, David C Argento, Tatjana Jevremovic, Robert Emery, Landon Scott Wootton, Upendra Parvathaneni, George E Laramore
The University of Washington (UW) Clinical Neutron Therapy System (CNTS), which generates high linear energy transfer (LET) fast neutrons through interactions of 50.5 MeV protons incident on a Be target, has depth-dose characteristics similar to 6 MV x-rays. In contrast to the fixed beam angles and primitive blocking used in early clinical trials of neutron therapy, the CNTS has a gantry with a full 360<sup>○</sup> of rotation, internal wedges, and a multi-leaf collimator (MLC)...
April 11, 2018: Physics in Medicine and Biology
Andre Z Kyme, Stephen Se, Steven R Meikle, Roger R Fulton
Motion-compensated brain imaging can dramatically reduce the artifacts and quantitative degradation associated with voluntary and involuntary subject head motion during positron emission tomography (PET), single photon emission computed tomography (SPECT) and computed tomography (CT). However, motion-compensated imaging protocols are not in widespread clinical use for these modalities. A key reason for this seems to be the lack of a practical motion tracking technology allowing for smooth and reliable integration of motion-compensated imaging protocols in the clinical setting...
April 11, 2018: Physics in Medicine and Biology
Cornelia Hoehr, Clayton Lindsay, Joel Beaudry, Crystal Penner, Vince Strgar, Richard Lee, Cheryl Duzenli
Accurate dosimetry in small field proton therapy is challenging, particularly for applications such as ocular therapy, and suitable detectors for this purpose are sought. The Exradin W1 plastic scintillating fibre detector is known to out-perform most other detectors for determining relative dose factors for small megavoltage photon beams used in radiotherapy but its potential in small proton beams has not yet been explored. The 1 mm diameter cylindrical geometry and near water equivalence of the W1 makes it an attractive alternative to other detectors...
April 10, 2018: Physics in Medicine and Biology
Jessica Goya-Outi, Fanny Orlhac, Raphael Calmon, Agusti Alentorn, Christophe Nioche, Cathy Philippe, Stéphanie Puget, Nathalie Boddaert, Irene Buvat, Jacques Grill, Vincent Frouin, Frédérique Frouin
Few methodological studies regarding widely used textural indices robustness in MRI have been reported. In this context, this study aims at proposing some rules to compute reliable textural indices from multimodal 3D brain MRI. Diagnosis and post-biopsy MR scans including T1, post-contrast T1, T2 and FLAIR images from thirty children with diffuse intrinsic pontine glioma (DIPG) were considered. The Hybrid White Stripe method was adapted to standardize MR intensities. Sixty textural indices were then computed for each modality in different regions of interest, including tumor and white matter (WM)...
April 10, 2018: Physics in Medicine and Biology
Wenjian Qin, Jia Wu, Fei Han, Yixuan Yuan, Wei Zhao, Bulat Ibragimov, Jia Gu, Lei Xing
Segmentation of liver in abdominal computed tomography (CT) is an important step for radiation therapy planning of hepatocellular carcinoma. Practically, a fully automatic segmentation of liver remains challenging because of low soft tissue contrast between liver and its surrounding organs, and its highly deformable shape. The purpose of this work is to develop a novel superpixel-based and boundary sensitive convolutional neural network (SBBS-CNN) pipeline for automated liver segmentation. 
 Method: The entire CT images were first partitioned into superpixel regions, where nearby pixels with similar CT number were aggregated...
April 10, 2018: Physics in Medicine and Biology
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