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Physics in Medicine and Biology

Shiyu Xu, Ali Uneri, Akhil Khanna, Jeffrey Siewerdsen, Joseph Webster Stayman
Metal artifacts can cause substantial image quality issues in computed tomography. This is particularly true in interventional imaging where surgical tools or metal implants are in the field-of-view. Moreover, the region-of-interest is often near such devices which is exactly where image quality degradations are largest. Previous work on known-component reconstruction (KCR) has shown the incorporation of a physical model (e.g. shape, material composition, etc.) of the metal component into the reconstruction algorithm can significantly reduce artifacts even near the edge of a metal component...
February 23, 2017: Physics in Medicine and Biology
Katharina Holland, Albert Gubern-Merida, Ritse Mann, Nico Karssemeijer
Fibroglandular tissue volume and percent density can be estimated in unprocessed mammograms using a physics-based method, which relies on an internal reference value representing the projection of fat only. However, pixels representing fat only may not be present in dense breasts, causing an underestimation of density measurements. In this work, we investigate alternative approaches for obtaining a tissue reference value to improve density estimations, particularly in dense breasts. Two of three investigated reference values (F1, F2) are percentiles of the pixel value distribution in the breast interior (the contact area of breast and compression paddle)...
February 23, 2017: Physics in Medicine and Biology
Imbault Marion, Alex Faccinetto, Bruno-Felix Osmanski, Antoine Tissier, Thomas Deffieux, Jean-Luc Gennisson, Valerie Vilgrain, Mickael Tanter
Hepatic steatosis is a common condition, the prevalence of which is increasing along with non-alcoholic fatty liver disease (NAFLD). Currently, the most accurate noninvasive imaging method for diagnosing and quantifying hepatic steatosis is MRI, which estimates the Proton-Density Fat Fraction (PDFF) as a measure of fractional fat content. However, MRI suffers several limitations including cost, contra-indications and poor availability. Although conventional ultrasound is widely used by radiologists for hepatic steatosis assessment, it remains qualitative and operator dependent...
February 22, 2017: Physics in Medicine and Biology
Oliver Taubmann, Viktor Haase, Guenter Lauritsch, Yefeng Zheng, Gregor Krings, Joachim Hornegger, Andreas Maier
Time-resolved tomographic cardiac imaging using an angiographic C-arm device may support clinicians during minimally invasive therapy by enabling a thorough analysis of the heart function directly in the catheter laboratory. However, clinically feasible acquisition protocols entail a highly challenging reconstruction problem which suffers from sparse angular sampling of the trajectory. Compressed sensing theory promises that useful images can be recovered despite massive undersampling by means of sparsity-based regularization...
February 22, 2017: Physics in Medicine and Biology
Hilary L Byrne, Yaser Gholami, Zdenka Kuncic
The addition of gold nanoparticles within target tissue (i.e. a tumour) to enhance the delivered radiation dose is a well studied radiotherapy treatment strategy, despite not yet having been translated into standard clinical practice. While several studies have used Monte Carlo simulations to investigate radiation dose enhancement by Auger electrons emitted from irradiated gold nanoparticles, none have yet considered the effects due to escaping fluorescence photons. Geant4 was used to simulate a water phantom containing 10 mg/mL uniformly dispersed gold (1% by mass) at 5cm depth...
February 22, 2017: Physics in Medicine and Biology
Masahiro Iwahashi, Jose Gomez-Tames, Ilkka Laakso, Akimasa Hirata
This study proposes a method to evaluate the electric field induced in the brain by transcranial magnetic stimulation (TMS) to realize focal stimulation in the target area considering the inter-subject difference of the brain anatomy. The TMS is a non-invasive technique used for treatment/diagnosis, and it works by inducing an electric field in a specific area of the brain via a coil-induced magnetic field. Recent studies that report on the electric field distribution in the brain induced by TMS coils have been limited to simplified human brain models or a small number of detailed human brain models...
February 21, 2017: Physics in Medicine and Biology
Xinyi Yedda Zhou, Kenneth Jeffris, Elaine Yu, Bo Zheng, Patrick Goodwill, Payam Nahid, Steven Conolly
Pulmonary embolism (PE), along with the closely related condition of deep vein thrombosis, affect an estimated 600,000 patients in the US per year. Untreated, PE carries a mortality rate of 30%. Because many patients experience mild or non-specific symptoms, imaging studies are necessary for definitive diagnosis of PE. Iodinated CT pulmonary angiography (CTPA) is recommended for most patients, while nuclear medicine-based ventilation/perfusion (V/Q) scans are reserved for patients in whom the use of iodine is contraindicated...
February 20, 2017: Physics in Medicine and Biology
Franziska Werner, Nadine Gdaniec, Tobias Knopp
Magnetic Particle Imaging (MPI) is a quantitative imaging modality that allows to determine the distribution of superparamagnetic nanoparticles. Sampling is achieved by moving a field-free point (FFP) along a specific trajectory through the volume of interest. The magnetic material that lies along the path or in the close vicinity of the FFP changes its magnetization and induces a voltage in surrounding receive coils. Various trajectories for the FFP are conceivable, but most experimental MPI scanners either use a Cartesian or a Lissajous sampling trajectory...
February 20, 2017: Physics in Medicine and Biology
Yang Chen, Jin Liu, Yining Hu, Jian Yang, Luyao Shi, Huazhong Shu, Zhiguo Gui, Gouenou Coatrieux, Limin Luo
This paper proposes a concise and effective approach termed discriminative feature representation (DFR) for low dose computerized tomography (LDCT) image processing, which is currently a challenging problem in medical imaging field. This DFR method assumes LDCT images as the superposition of desirable high dose CT (HDCT) 3D features and undesirable noise-artifact 3D features (the combined term of noise and artifact features induced by low dose scan protocols), and the decomposed HDCT features are used to provide the processed LDCT images with higher quality...
February 17, 2017: Physics in Medicine and Biology
J-M Osinga-Blättermann, S Brons, S Greilich, O Jäkel, A Krauss
Until now, the dosimetry of carbon ions with ionization chambers has not reached the same level of accuracy as that of high-energy photons. This is mainly caused by the approximately threefold larger uncertainty of the k Q factor of ionization chambers, which, due to the lack of experimental data, is still derived by calculations. Measurements of absorbed dose to water, D w, by means of water calorimetry have now been performed in the entrance channel of a scanned 6 cm  ×  6 cm radiation field of 429 MeV/u carbon ions, allowing the direct calibration of ionization chambers and thus the experimental determination of k Q...
February 17, 2017: Physics in Medicine and Biology
Ana Lourenco, Russell Thomas, Michael Homer, Hugo Bouchard, Severine Rossomme, James Renaud, Tatsuaki Kanai, Gary Royle, Hugo Palmans
The aim of this work is to develop and adapt a formalism to determine absorbed dose to water from graphite calorimetry measurements in carbon-ion beams. Fluence correction factors, <i>k</i><sub>fl</sub>, needed when using a graphite calorimeter to derive dose to water, were determined in a clinical high-energy carbon-ion beam. Measurements were performed in a 290 MeV/n carbon-ion beam with a field size of 11 x 11 cm<sup>2</sup>, without modulation. In order to sample the beam, a plane-parallel Roos ionization chamber was chosen for its small collecting volume in comparison with the field size...
February 17, 2017: Physics in Medicine and Biology
Hua Zhang, Jianhua Ma, Zhaoying Bian, Dong Zeng, Qianjin Feng, Wufan Chen
Four dimensional cone-beam computed tomography (4D-CBCT) has great potential clinical value because its ability to describe tumor and organ motion. But the challenge in 4D-CBCT reconstruction is the limited number of projections at each phase, which resulting in the reconstruction full of noise and streak artifacts with the conventional analytical algorithms. To address this problem, in this paper, we propose a motion compensated total variation regularization approach which tries to maximum explore the temporal coherence of the spatial structures among 4D-CBCT phases...
February 17, 2017: Physics in Medicine and Biology
John Muryn, Ashraf Morgan, Chris Liptak, Frank Dong, Paul Segars, Andrew Primak, Xiang Li
In Monte Carlo simulation of CT dose, many input parameters are required (e.g., bowtie filter properties and scan start/end location). Our goal was to examine the uncertainties in patient dose when input parameters were inaccurate. Using a validated Monte Carlo program, organ dose from a chest CT scan was simulated for an average-size female phantom using a reference set of input parameter values (treated as the truth). Additional simulations were performed in which errors were purposely introduced into the input parameter values...
February 16, 2017: Physics in Medicine and Biology
Jamie R McClelland, Marc Modat, Simon Arridge, Helen Grimes, Derek D'Souza, David Thomas, Dylan O'Connell, Daniel Low, Evangelia Kaza, David Collins, Martin Leach, David Hawkes
Surrogate-driven respiratory motion models relate the motion of the internal anatomy to easily acquired respiratory surrogate signals, such as the motion of the skin surface. They are usually built by first using image registration to determine the motion from a number of dynamic images, and then fitting a correspondence model relating the motion to the surrogate signals. In this paper we present a generalized framework that unifies the image registration and correspondence model fitting into a single optimization...
February 14, 2017: Physics in Medicine and Biology
Heide Rohling, Marlen Priegnitz, Sebastian Schoene, Andreas Schumann, Wolfgang Enghardt, Fernando Hueso-González, Guntram Pausch, Fine Fiedler
To ensure the optimal outcome of proton therapy, in-vivo range verification is highly desired. Prompt γ-ray imaging (PGI) is a possible approach for in-vivo range monitoring. For PGI, dedicated detection systems, e.g. Compton cameras, are currently under investigation. The presented paper deals with substantial requirements regarding hardware and software that a Compton camera used in clinical routine has to meet. By means of GEANT4 simulations, we investigate the load on the detectors and the percentage of background expected in a realistic irradiation and we simulate γ-ray detections subsequently used as input data for the reconstruction...
February 14, 2017: Physics in Medicine and Biology
Yabo Fu, Shi Liu, Hui Harold Li, Deshan Yang
Accurate segmentation of each bone in human skeleton is useful in many medical disciplines. Results of bone segmentation could facilitate bone disease diagnosis and post-treatment assessment, and support planning and image guidance for many treatment modalities including surgery and radiation therapy. As a medium level medical image processing task, accurate bone segmentation can facilitate automatic internal organ segmentation by providing stable structural reference for inter- or intra-patient registration and internal organ localization...
February 14, 2017: Physics in Medicine and Biology
Valerio Tabacchini, Suleman Surti, Giacomo Borghi, Joel S Karp, Dennis R Schaart
We have recently built and characterized the performance of a monolithic scintillator detector based on a 32 mm  ×  32 mm  ×  22 mm LYSO:Ce crystal read out by digital silicon photomultiplier (dSiPM) arrays coupled to the crystal front and back surfaces in a dual-sided readout (DSR) configuration. The detector spatial resolution appeared to be markedly better than that of a detector consisting of the same crystal with conventional back-sided readout (BSR). Here, we aim to evaluate the influence of this difference in the detector spatial response on the quality of reconstructed images, so as to quantify the potential benefit of the DSR approach for high-resolution, whole-body time-of-flight (TOF) positron emission tomography (PET) applications...
February 13, 2017: Physics in Medicine and Biology
Peter Homolka, Michael Figl, Andreas Wartak, Mathias Glanzer, Martina Duenkelmeyer, Azadeh Hojreh, Johann Hummel
An anthropomorphic head phantom including eye inserts allowing placement of TLDs 3 mm below the cornea has been produced on a 3D printer using photo-cured-acrylic resin to best allow tissue equivalence. Thus Hp(3) can be determined in radiological and interventional photon radiation fields. Eye doses and doses to the forehead have been compared to an Alderson RANDO head and a 3M Lucite skull phantom in terms of surface dose per incident air kerma for frontal irradiation since the commercial phantoms do not allow placement of TLDs 3 mm below the corneal surface...
February 13, 2017: Physics in Medicine and Biology
Andrey Morozov, Francisco Alves, Joao Marcos, Raimundo Martins, Luis Pereira, Vladimir Solovov, Vitaly Chepel
Compact gamma cameras with a square-shaped monolithic scintillator crystal and an array of silicon photomultipliers (SiPMs) are actively being developed for applications in areas such as small animal imaging, cancer diagnostics and radiotracer guided surgery. Statistical methods of position reconstruction, which are potentially superior to the traditional centroid method, require accurate knowledge of the spatial response of each photomultiplier. Using both Monte Carlo simulations and experimental data obtained with a camera prototype, we show that the spatial response of all photomultipliers (light response functions) can be parameterized with axially symmetric functions obtained iteratively from flood field irradiation data...
February 13, 2017: Physics in Medicine and Biology
Kristen A Wangerin, Mark Muzi, Lanell Peterson, Hannah Linden, Alena Novakova, David Mankoff, Paul Kinahan
OBJECTIVE: We developed a method to evaluate variations in the PET imaging process in order to characterize the relative ability of static and dynamic metrics to measure breast cancer response to therapy in a clinical trial setting. METHODS: We performed a virtual clinical trial by generating 540 i.i.d. PET imaging study realizations for each of 22 original dynamic fluorodeoxyglucose (18F-FDG) breast cancer patient studies pre- and post-therapy. Each noise realization accounted for known sources of uncertainty in the imaging process, such as biological variability and SUV uptake time...
February 13, 2017: Physics in Medicine and Biology
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