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Physics in Medicine and Biology

Xi Chen, Zhiguo Zhou, Raquibul Hannan, Kimberly Thomas, Ivan Pedrosa, Payal Kapur, James Brugarolas, Xuanqin Mou, Jing Wang
Genetic studies have identified associations between gene mutations and clear cell renal cell carcinoma (ccRCC). Since the complete gene mutational landscape cannot be characterized through biopsy and sequencing assays for each patient, non-invasive tools are needed to determine the mutation status for tumors. Radiogenomics may be an attractive alternative tool to identify disease genomics by analyzing amounts of features extracted from medical images. Most current radiogenomics predictive models are built based on a single classifier and trained through a single objective...
October 2, 2018: Physics in Medicine and Biology
Martin Rädler, Guillaume Landry, Simon Rit, Reinhard W Schulte, Katia Parodi, Georgios Dedes
We present a formalism for two dimensional (2D) noise reconstruction in proton computed tomography (pCT). This is necessary for the application of fluence modulated pCT (FMpCT) since it permits image noise prescription and the corresponding proton fuence optimization. We aimed at extending previously published formalisms to account for the impact of multiple Coulomb scattering (MCS) on projection noise, and the use of filtered back projection (FBP) reconstruction along \hl{curved paths} with distance driven binning (DDB)...
October 2, 2018: Physics in Medicine and Biology
Bjorn Stemkens, Eric S Paulson, Rob H N Tijssen
Magnetic Resonance Imaging (MRI) is increasingly being used in the radiotherapy workflow because of its superior soft tissue contrast and high flexibility in contrast. In addition to anatomical and functional imaging, MRI can also be used to characterize the physiologically induced motion of both the tumor and organs-at-risk. Respiratory-correlated 4D-MRI has gained large interest as an alternative to 4D-CT for the characterization of respiratory motion throughout the thorax and abdomen. Over the last 15 years numerous methods have been presented in literature...
October 1, 2018: Physics in Medicine and Biology
Carly Pellow, Christopher N Acconcia, Gang Zheng, David E Goertz
Nanobubbles hold potential for expanding utility of ultrasound contrast-based applications to extravascular targets, but their acoustic response and the effects of the surrounding environment remain relatively unexplored. Here we investigate the dynamics of porphyrin-encapsulated nanobubbles (diameter <0.4 µm; 10^6 mL-1) at clinically relevant frequencies (2.5 MHz and 8 MHz) as a function of pressure (0.2 - 1.0 MPa) in vessel- and tissue-mimicking phantoms to gain an understanding of nanobubble behaviour in intra- and extravascular compartments...
October 1, 2018: Physics in Medicine and Biology
Kyle Lafata, Jing Cai, Chunhao Wang, Julian Hong, Christopher R Kelsey, Fang-Fang Yin
The purpose of this research was to study the sensitivity of Computed Tomography (CT) radiomic features to motion blurring and signal-to-noise ratios (SNR), and investigate its downstream effect regarding the classification of non-small cell lung cancer (NSCLC) histology.
 Methods: Forty-three radiomic features were considered and classified into one of four categories: Morphological, Intensity, Fine Texture, and Coarse Texture. First, a series of simulations were used to study feature-sensitivity to changes in spatial-temporal resolution...
October 1, 2018: Physics in Medicine and Biology
Chemseddine Fatnassi, Habib Zaidi
In 3D gradient echo (GRE) and echo planar imaging (EPI), strong macroscopic field gradients are observed at air/tissue interfaces. The respective field gradients lead to an apparent increase in intravoxel dephasing, and, subsequently, to signal loss or image distortion. We propose an analytical approximation and a consequent method to compute low and high resolution field maps over all field map regimes (small and large echo spacing). A number of approaches which compute field maps from reconstructed phase data rely upon optimized linear least square fit and complex division approaches owing to the simplicity of their implementation...
October 1, 2018: Physics in Medicine and Biology
Hossein Arabi, Habib Zaidi
PET images commonly suffer from the high noise level and poor signal-to-noise ratio (SNR), thus adversely impacting lesion detectability and quantitative accuracy. In this work, a novel hybrid dual-domain PET denoising approach is proposed, which combines the advantages of both spatial and transform domain filtering to preserve image textures while minimizing quantification uncertainty. Spatial domain denoising techniques excel at preserving high-contrast patterns compared to transform domain filters, which perform well in recovering low-contrast details normally smoothed out by spatial domain filters...
October 1, 2018: Physics in Medicine and Biology
Feng Yang, Yue-Min Zhu, Gabrielle Michalowicz, Pierre-Simon Jouk, Laurent Fanton, Magalie Viallon, Patrick Clarysse, Pierre Croisille, Yves Usson
Diffusion tensor imaging (DTI) is a non-invasive technique used to obtain the three-dimensional fiber structure of whole human hearts, for both in vivo and ex vivo cases. However, by essence, DTI does not measure directly the orientations of myocardial fibers. In contrast, polarized light imaging (PLI) allows for physical measurements of fiber orientations, but only for ex vivo case. This work aims at quantitatively comparing the myocardial fiber orientations of whole human hearts obtained from cardiac DTI with those measured by PLI...
September 28, 2018: Physics in Medicine and Biology
Yongbo Wang, Dong Zeng, Yuanke Zhang, Ji He, Sui Li, Yuting Liao, Zhaoying Bian, Hao Zhang, Yuanyuan Gao, Deyu Meng, Wangmeng Zuo, Jianhua Ma
Radiation exposure and the associated risk of cancer for patients in computed tomography (CT) scans have been major clinical concerns. The radiation exposure can be reduced effectively via lowering X-ray tube current (mA). However, this strategy may lead to excessive noise and streak artifacts in the conventional filtered back-projection reconstructed images. To address this issue, some deep convolutional neural network (ConvNet) based approaches have been developed for low-dose CT imaging inspired by the recent development of machine learning...
September 28, 2018: Physics in Medicine and Biology
Evan McNabb, Raimond Wong, Michael D Noseworthy
Magnetic resonance imaging (MRI) has superior soft tissue contrast and lower interobserver variability compared to computed tomography and advances in equipment and pseudo-CT estimation have allowed for MR-only radiation therapy planning. Dedicated MR sequences have been used to localize paramagnetic structures with positive contrast, and most implanted seeds are gold fiducial markers (GFMs). We used a fast, dual-plane co-RASOR sequence to localize implanted GFMs with positive contrast in phantom and tissue to
 assess their resolution and registration accuracy of registration to CT...
September 27, 2018: Physics in Medicine and Biology
Ricardo S Augusto, Akram Mohammadi, Hideaki Tashima, Eiji Yoshida, Taiga Yamaya, Alfredo Ferrari, Katia Parodi
In the context of hadrontherapy, whilst ions are capable of effectively destroying radio resistant, deep seated tumors, their treatment localization must be well assessed to ensure the sparing of surrounding healthy tissue and treatment effectiveness. Thus, range verification techniques, such as online positron-emission-tomography (PET) imaging, hold great potential in clinical practice, providing information on the in vivo beam range and consequent tumor targeting. Furthermore, β<sup>+</sup> emitting radioactive ions can be an asset in online PET imaging, depending on their half-life, compared to their stable counterparts...
September 25, 2018: Physics in Medicine and Biology
Jack Sauvage, Martin Flesch, Guillaume Ferin, An Nguyen-Dinh, Jonathan Poree, Mickael Tanter, Mathieu Pernot, Thomas Deffieux
4D Ultrafast ultrasound imaging was recently proposed to image and quantify blood flow with high sensitivity in 3D (Provost et al., 2014) as well as anatomical, mechanical or functional information. In 4D Ultrafast imaging, coherent compounding of tilted planes waves emitted by a 2-D matrix array are used to image the medium at high volume rate. 4D ultrafast imaging, however, requires high count electronics (>1000) to drive those probes. Alternatives approaches have been proposed and investigated to efficiently reduce the density of elements such as sparse or under-sampled arrays while maintaining a decent image quality and high volume rate...
September 25, 2018: Physics in Medicine and Biology
Michael Matter, Lena Nenoff, Gabriel Meier, Damien Charles Weber, Antony John Lomax, Francesca Albertini
Patient specific verification (PSV) measurements for pencil beam scanning (PBS) proton therapy are resource-consuming and necessitate substantial beam time outside of clinical hours. As such, efforts to safely reduce the PSV-bottleneck in the clinical work-flow are of great interest. Here, capabilities of current PSV methods to ensure the treatment integrity were investigated and compared to an alternative approach of reconstructing the dose distribution directly from the machine control- or delivery log files with the help of an independent dose calculation (IDC)...
September 20, 2018: Physics in Medicine and Biology
Mallory C Glenn, Victor Hernandez, Jordi Saez, David S Followill, Rebecca M Howell, Julianne M Pollard, Shouhao Zhou, Stephen F Kry
Previous works indicate that intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans that are highly complex may produce more errors in dose calculation and treatment delivery. Multiple complexity metrics have been proposed and associated with IMRT QA results, but their relationships with plan performance using in situ dose measurements have not been thoroughly investigated. This study aimed to evaluate the relationships between IMRT treatment plan complexity and anthropomorphic phantom performance in order to assess the extent to which plan complexity is related to dosimetric performance in the IROC phantom credentialing program...
September 19, 2018: Physics in Medicine and Biology
Lokesh Basavarajappa, Arun Kumar Thittai
Rotation Elastogram (RE) is a 2D spatial distribution map of the estimated local rigid-body rotation undergone by a target when subjected to an external compression, which is one of the recent variants in elastographic imaging. A recent study has shown that inclusion-contrast in RE is independent of inclusion-background modulus contrast and thus may be helpful in distinguishing between barely-stiff benign and malignant lesions. However, estimation of quality RE requires not only precise axial displacement estimates but also lateral displacement estimates...
September 17, 2018: Physics in Medicine and Biology
Pavel Stavrev, Nadejda Stavreva, Dimitar Penev, Alan E Nahum, Ruggero Ruggieri, Dobromir Pressyanov
The aim of the work is to investigate the impact of radiation-independent (natural or spontaneous) tumor cell death on tumor control probability (TCP) during and following fractionated external-beam radiotherapy employing both analytical and numerical methods. The analytical method solves a TCP model accounting for tumor repopulation and non-radiation tumor cell death during fractionated external-beam radiotherapy. The numerical method is based on a Monte Carlo simulation of the processes of radiation-induced cell kill, as well as cell division and natural cell death randomly taking place in the time interval between fractions...
September 11, 2018: Physics in Medicine and Biology
Nils Krah, Ludovic De Marzi, Annalisa Patriarca, Giuseppe Pittá, Ilaria Rinaldi
Proton transmission imaging uses protons with high enough energy to fully traverse the phantom/patient and to be captured in a suitable detector placed behind it. The measured residual energy or residual range provide a direct estimate of the water equivalent thickness (WET) of the image volume. Requirements for proton imaging to be exploitable in clinical practice include: sufficient WET accuracy and integrability into the treatment room and the clinical workflow, as well as an acceptably low dose to the patient and a sufficient spatial resolution...
September 11, 2018: Physics in Medicine and Biology
Abdelkhalek Hammi, Stefan Koenig, Damien Charles Weber, Bjoern Poppe, Antony John Lomax
We present a proof of principle, experimental validation of the potential of proton 'Range Probes' (RP) for patient positioning verification in proton therapy. In this work, we have evaluated experimentally the accuracy of RP by using tissue-like samples and an in-house developed multilayer ionization chamber (MLIC). In addition we build on our previous, simulation based work to present first experimental measurements of RP through anthropomorphic phantoms to detect either rotational or translational positioning errors...
September 6, 2018: Physics in Medicine and Biology
Doan Trang Nguyen, Jeremy Todd Booth, Vincent Caillet, Nicholas Hardcastle, Adam Briggs, Carol Haddad, Thomas Eade, Ricky T O'Brien, Paul J Keall
Increasing evidence shows that intrafraction tumour motion monitoring must include both six degrees of freedom (6DoF): 3D translations and 3D rotations. Existing real- time algorithms for 6DoF target motion estimation requires continuous intrafraction fluoroscopic imaging at high frequency, thereby exposing patients to additional high imaging dose. This paper presents the first method capable of 6DoF motion monitoring using intermittent 2D kV imaging and a continuous external respiratory signal.
 Method: Our approach is to optimise a state-augmented linear correlation model between an external signal and internal 6DoF motion...
September 5, 2018: Physics in Medicine and Biology
Meriem Outtas, Lu Zhang, Olivier Deforges, Amina Serir, Wassim Hamidouche, Yang Chen
Ultrasonographic examination, either as visual inspection or quantitative
 analysis, is the most widely diagnostic resource. However, speckle noise is
 one of the drawbacks that makes it less effective than other medical imaging
 systems. Several speckle reduction methods often offer effective speckle reduction
 but generally suffer from oversmoothing, a blurring effect and a man-made
 appearance. In this paper, we propose a Multi-Output Filter based on the Multiplicative
 Multiresolution Decomposition (MOF-MMD)...
August 21, 2018: Physics in Medicine and Biology
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