Iterative optimization of relative stopping power by single detector based multi-projection proton radiography.
This study demonstrates the concept of optimizing RSPs of individual CT voxels with multi-projection pRGs acquired by a single flat panel imager, which could be further explored and implemented in proton therapy to reduce range uncertainties. PMID: 30561373 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Zhang R, Sharp GC, Jee KW, Cascio EW, Harms JM, Flanz JB, Lu HM Tags: Phys Med Biol Source Type: research

TomoTherapy treatments of multiple brain lesions: an in-phantom accuracy evaluation.
Conclusions These results demonstrate that multiple brain lesion HT treatments are feasible with an accuracy at least comparable to frameless linac-based delivery, when a set-up capable to assure angular corrections and a reliable patient immobilization is employed. . PMID: 30561374 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Zani M, Marrazzo L, Calusi S, Talamonti C, Scoccianti S, Greto D, Desideri I, Fusi F, Pallotta S Tags: Phys Med Biol Source Type: research

A single detector energy-resolved proton radiography system: a proof of principle study by Monte Carlo simulations.
In this study, we followed a newly proposed proton beam radiography technique based on energy resolved dose functions (ERDF) to construct a Monte Carlo model for a single detector energy-resolved proton radiography system (SDPRS). This SDPRS model was constructed in the Monte Carlo software package TOPAS (TOol for PArticle Simulation) and it includes the Mevion HYPERSCANTM pencil beam scanning treatment head and a 2D dose detector positioned downstream as the imager. A calibration phantom containing a number of tissue equivalent materials was simulated to evaluate the accuracy in WEPL measurement by SDPRS. The mean deviati...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Huo W, Zwart T, Cooley JE, Huang K, Finley C, Jee KW, Sharp GC, Rosenthal S, Xu XG, Lu HM Tags: Phys Med Biol Source Type: research

The impact of inter-unit variations on small field dosimetry correction factors, with application to the CyberKnife system.
Abstract Small field dosimetry correction factors are usually determined from calculations or measurements using one specific example of a treatment system. The sensitivity of the corrections to inter-unit variation is therefore not evaluated. We propose two methods for this evaluation that could be applied to any system. We use them to assess the variability in k_(Q_msr,Q_0)^(f_msr,f_ref ) for the CyberKnife System caused by design changes between pre-M6 and M6 versions, and to the variability in k_(Q_msr,Q_0)^(f_msr,f_ref )and k_(Q_clin,Q_msr)^(f_clin,f_msr ) resulting from measured beam-data variations across 1...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Francescon P, Kilby W, Satariano N, Orlandi C, Elshamndy SK Tags: Phys Med Biol Source Type: research

Commissioning of a water calorimeter as a primary standard for absorbed dose to water in magnetic fields.
This study confirmed that the uncertainty for measurement of <i>D</i><sub>w</sub> with a water calorimeter in a 1.5 T magnetic field is estimated to be the same as under conventional reference conditions. The VSL water calorimeter can be applied as a primary standard for <i>D</i><sub>w</sub> in magnetic fields and is currently the only primary standard operable in a magnetic field that provides direct access to the international traceability framework. . PMID: 30561378 [PubMed - as supplied by publisher] ...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: de Prez LA, de Pooter JA, Jansen BJ, Woodings SJ, Wolthaus JWH, van Asselen B, van Soest TL, Kok JGM, Raaymakers BW Tags: Phys Med Biol Source Type: research

A thermo-sensitive fluorescent agent based method for excitation light leakage rejection for fluorescence molecular tomography.
Abstract Fluorescence molecular tomography (FMT) is widely used in preclinical oncology research. FMT is the only imaging technique able to provide three-dimensional distribution of fluorescent probes within thick highly scattering media. However, its integration into clinical medicine has been hampered by its low spatial resolution caused by the undetermined and ill-posed nature of its reconstruction algorithm. Another major factor degrading the quality of FMT images is the large backscattered excitation light component leaking through the rejection filters and coinciding with the weak fluorescent signal arising ...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Nouizi F, Kwong TC, Ruiz J, Cho J, Chan YW, Ikemura K, Erkol H, Sampathkumaran U, Gulsen G Tags: Phys Med Biol Source Type: research

Model-based material decomposition with a penalized nonlinear least-squares CT reconstruction algorithm.
Abstract Spectral information in CT may be used for material decomposition to produce accurate reconstructions of material density and to separate materials with similar overall attenuation. Traditional methods separate the reconstruction and decomposition steps, often resulting in undesirable trade-offs (e.g., sampling constraints, a simplified spectral model). In this work, we present a model-based material decomposition algorithm which performs the reconstruction and decomposition simultaneously using a multienergy forward model. In a kV-switching simulation study, the presented method is capable of reconstruct...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Tilley Ii SW, Zbijewski W, Stayman JW Tags: Phys Med Biol Source Type: research

Predicting tumour response to anti-PD-1 immunotherapy with computational modelling.
Abstract Cancer immunotherapy is a rapidly developing field, with numerous drugs and therapy combinations waiting to be tested in pre-clinical and clinical settings. However, the costly and time-consuming trial-and-error approach to development of new treatment paradigms creates a research bottleneck, motivating the development of complementary approaches. Computational modelling is a compelling candidate for this task, however, difficulties associated with the validation of such models limits their use in pre-clinical and clinical settings. Here we propose a bottom-up deterministic computational model to simulate...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Valentinuzzi D, Simoncic U, Ursic K, Vrankar M, Turk M, Jeraj R Tags: Phys Med Biol Source Type: research

MR image corrections for PET-induced gradient distortions.
Abstract The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) by using PET inserts in existing MRI scanners is an attractive approach. When designing the PET insert, mutual influences of both imaging modalities need to be minimized. The gradient magnetic fields induce eddy currents in all conductive components of the PET insert. Eddy currents produce superimposing magnetic fields distorting the gradient magnetic field. However, the gradient magnetic fields determine how the MRI data is acquired in the k-space. A distorted gradient shape produces a distorted k-space trajectory ...
Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Gross-Weege N, Nolte T, Schulz V Tags: Phys Med Biol Source Type: research

A recursive ensemble organ segmentation (REOS) framework: application in brain radiotherapy.
In this study, the developed ROES framework is applied for brain radiotherapy on segmenting six OARs including the eyes, the brainstem, the optical nerves and the chiasm. Eighty T1-weighted magnetic resonance images (MRI) from 80 brain cancer patients' cases with OARs' gold standard contours were collected for training and testing REOS. On 20 testing cases, the REOS achieve a high segmentation accuracy with Dice similarity coefficient (DSC) mean and standard deviation of 93.9±1.4%, 94.5±2.0%, 90.6±2.7%, on the left and right eyes and the brainstem, respectively. On small and segmentation-challenging or...
Source: Physics in Medicine and Biology - December 12, 2018 Category: Physics Authors: Chen H, Lu W, Chen M, Zhou L, Timmerman RD, Tu D, Nedzi L, Wardak Z, Jiang SB, Zhen X, Gu X Tags: Phys Med Biol Source Type: research

Development and evaluation of an arterial spin-labeling digital reference object for quality control and comparison of data analysis applications.
Abstract Longitudinal assessment of quantitative imaging biomarkers (QIBs) requires a comprehensive quality control (QC) program to minimize bias and variance in measurement results. In addition, the availability of data analysis software from multiple vendors emphasizes the need for a means of quantitatively comparing the computed QIB measures produced by the applications. The purpose of this work is to describe a digital reference object (DRO) that has been developed for the evaluation of arterial spin-labeling (ASL) measurement results. The ASL DRO is a synthetic data set consisting of 10x10 voxel square blocks...
Source: Physics in Medicine and Biology - December 12, 2018 Category: Physics Authors: Antolak AG, Jackson EF Tags: Phys Med Biol Source Type: research

Interior X-ray diffraction tomography with low-resolution exterior information.
Abstract X-ray diffraction tomography (XDT) resolves spatially-variant XRD profiles within macroscopic objects, and provides improved material contrast compared to the conventional transmission-based computed tomography (CT). However, due to the small diffraction cross-section, XDT suffers from long imaging acquisition time, which could take tens of hours for a full scan using a table-top X-ray tube. In medical and industrial imaging applications, oftentimes only the XRD measurement within a region-of-interest (ROI) is required, which, together with the demand to reduce imaging time and radiation dose to the sampl...
Source: Physics in Medicine and Biology - December 12, 2018 Category: Physics Authors: Zhu Z, Katsevich A, Pang S Tags: Phys Med Biol Source Type: research

Log file based Monte Carlo calculations for proton pencil beam scanning therapy.
Abstract Patient specific quality assurance is crucial to guarantee safety in proton pencil beam scanning. In current clinical practice, this requires extensive, time consuming measurements. Additionally, these measurements do not consider the influence of density heterogeneities in the patient and are insensitive to delivery errors. In this work, we investigate the use of log file based Monte Carlo calculations for dose reconstructions in the patient CT, which takes the combined influence of calculational and delivery errors into account. For one example field, 86%/90% of the voxels agree within &plusm...
Source: Physics in Medicine and Biology - December 12, 2018 Category: Physics Authors: Winterhalter C, Meier G, Oxley D, Weber DC, Lomax AJ, Safai S Tags: Phys Med Biol Source Type: research

B < sub > 1 < /sub > < sup > + < /sup > phase retrieval for non-quadrature radio frequency excitation and its preliminary application in MR-EPT.
In this study, we propose a simple method to acquire the absolute transmit phase in non-quadrature excitation with an eight channel transceiver TEM array for 3 T. The proposed method requires the application of a single additional quadrature drive in order to get the receive phases of the individual channels of the transceiver coil. These receive phases are then subtracted from the transceive phase of the non-quadrature drive experiment to acquire its transmit phase. The developed ideas are tested in the framework of simulations and MRI experiments with the use of four different non-quadrature drive configurations. It has ...
Source: Physics in Medicine and Biology - December 11, 2018 Category: Physics Authors: Ariturk G, Ider YZ Tags: Phys Med Biol Source Type: research

Study of Sensitivity and Resolution for Full Ring PET Prototypes based on Continuous Crystals and analytical modeling of the light distribution.
, Oliver JF Abstract Sensitivity and spatial resolution are the main parameters to maximize in the performance of a PET scanner. For this purpose, detectors consisting of a combination of continuous crystals optically coupled to segmented photodetectors have been employed. With the use of continuous crystals the sensitivity is increased with respect to the pixelated crystals. In addition, spatial resolution is no longer limited to the crystal size. The main drawback is the difficulty in determining the interaction position. In this work, we present the characterization of the per...
Source: Physics in Medicine and Biology - December 11, 2018 Category: Physics Authors: Etxebeste A, Barrio J, Bernabéu Alberola J, Lacasta C, Llosa G, Muñoz E, Ros A, Oliver JF Tags: Phys Med Biol Source Type: research

Simultaneous optimization of isocenter locations and sector duration in radiosurgery.
Abstract Stereotactic radiosurgery is an effective technique to treat brain tumors for which several inverse planning methods may be appropriate. We propose an integer programming model to simultaneous sector duration and isocenter optimization (SDIO) problem for Leksell Gamma Knife{\textregistered} Icon{\texttrademark} (Elekta, Stockholm, Sweden) to tractably incorporate treatment time. We devise a Benders decomposition scheme to solve the SDIO problem to optimality. The performances of our approaches are assessed using anonymized data from eight previously treated cases, and obtained treatment plans are compared...
Source: Physics in Medicine and Biology - December 11, 2018 Category: Physics Authors: Cevik M, Aleman DM, Lee Y, Berdyshev A, Nordstrom H, Riad S, Sahgal A, Ruschin M Tags: Phys Med Biol Source Type: research

Dose response and stability of water equivalent PRESAGE ® dosimeters for synchrotron radiation therapy dosimetry.
Dose response and stability of water equivalent PRESAGE® dosimeters for synchrotron radiation therapy dosimetry. Phys Med Biol. 2018 Dec 06;63(23):235027 Authors: Gagliardi FM, Franich RD, Geso M Abstract This research investigated the dose response and post-irradiation stability of water-equivalent PRESAGE® dosimeters exposed to synchrotron radiation. Water-equivalent PRESAGE® dosimeters were irradiated up to 1000 Gy in a synchrotron x-ray beam with a mean energy of 95.3 keV. The change in optical density was measured using UV/visible spectrophotometry pre- and post-irradiation usi...
Source: Physics in Medicine and Biology - December 6, 2018 Category: Physics Authors: Gagliardi FM, Franich RD, Geso M Tags: Phys Med Biol Source Type: research

Feasibility of closed-MLC tracking using high sensitivity and multi-layer electronic portal imagers.
Abstract In radiation therapy, improvements in treatment conformality are often limited by movement of target tissue. To better treat the target, tumor tracking strategies involving beam's-eye-view (BEV) have been explored. However, localization surrogates like implanted fiducial markers may sometimes leave the field-of-view (FOV), as defined by the linear accelerator (LINAC) multi-leaf collimator (MLC). Radiation leakage through the MLC has been measured previously at approximately 1%-2%. High sensitivity prototype detectors imagers may improve the ability to visualize objects outside of the MLC FOV during treatm...
Source: Physics in Medicine and Biology - December 6, 2018 Category: Physics Authors: Hu YH, Jacobson MW, Shi M, Myronakis M, Wang A, Baturin P, Huber P, Fueglistaller R, Morf D, Star-Lack J, Berbeco RI Tags: Phys Med Biol Source Type: research

Dual SPECT imaging of 111In and 67Ga to simultaneously determine in vivo the pharmacokinetics of different radiopharmaceuticals: a quantitative tool in pre-clinical research.
Häfeli UO Abstract Dual-isotope (DI) studies offer a number of advantages in pre-clinical imaging. These include: reducing study times when compared with sequential scans, reducing the number of animals required for any given study, and most importantly, producing images perfectly registered in space and time that provide simultaneous information about two distinct body functions. The ability of single photon emission computed tomography (SPECT) to measure and differentiate energies of the emitted photons makes it well suited for DI imaging. However, since scattered photons originating from one radioisotope ...
Source: Physics in Medicine and Biology - December 6, 2018 Category: Physics Authors: Esquinas PL, Rodríguez-Rodríguez C, Esposito TVF, Harboe J, Bergamo M, Celler A, Saatchi K, Sossi V, Häfeli UO Tags: Phys Med Biol Source Type: research

2D and 3D real-time passive cavitation imaging of pulsed cavitation ultrasound therapy in moving tissues.
Abstract Pulsed cavitation ultrasound therapy (PCUT) is an effective non-invasive therapeutic approach in various medical indications that relies on the mechanical effects generated by cavitation bubbles. Even though limited by the poor contrast, conventional ultrasound B-Mode imaging has been widely used for the guidance and monitoring of the therapeutic procedure, allowing the visualization of the cavitation bubble cloud. However, the visualization of the bubble cloud is often limited in deep organs such as the liver and the heart and remains moreover completely subjective for the operator. Our goal is to develo...
Source: Physics in Medicine and Biology - December 6, 2018 Category: Physics Authors: Suarez Escudero D, Goudot G, Vion M, Tanter M, Pernot M Tags: Phys Med Biol Source Type: research

Optimization of a depth of interaction encoding PET block detector for a PET/MRI insert.
Abstract Preclinical positron emission tomography, combined with magnetic resonance imaging (PET/MRI), is increasingly used as a tool to simultaneously characterize functional processes in vivo. Many emerging preclinical applications, however, are limited by PET detection sensitivity, especially when generating short imaging frames for quantitative studies. One such application is dynamic multifunctional imaging, which probes multiple aspects of a biological process, using relationships between the datasets to quantify interactions. These studies have limited accuracy due to the relatively low sensitivity of moder...
Source: Physics in Medicine and Biology - December 6, 2018 Category: Physics Authors: Selfridge AR, Cherry SR, Judenhofer MS Tags: Phys Med Biol Source Type: research

An analytical solution for temperature distributions in hepatic radiofrequency ablation incorporating the heat-sink effect of large vessels.
Abstract Fast prediction of the local thermal field induced by radiofrequency ablation (RFA) plays a critical role in hepatic RFA therapy. At present, it is still a challenging task to calculate and visualize the temperature distribution of RFA in real-time, especially when the heat-sink effect of adjacent large vessels is taken into account. To achieve this, the current investigation presented an analytical solution to calculate the temperature in RFA with an execution time of 0.05 s for three dimensional thermal field reconstruction. The presented temperature distribution is a combination of temperatures in homo...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Chen R, Lu F, Wu F, Jiang T, Xie L, Kong D Tags: Phys Med Biol Source Type: research

Mechanical decellularization of tissue volumes using boiling histotripsy.
Abstract High intensity focused ultrasound (HIFU) is rapidly advancing as an alternative therapy for non-invasively treating specific cancers and other pathological tissues through thermal ablation. A new type of HIFU therapy-boiling histotripsy (BH)-aims at mechanical fractionation of into subcellular fragments, with a range of accompanying thermal effects that can be tuned from none to substantial depending on the requirements of the application. The degree of mechanical tissue damage induced by BH has been shown to depend on the tissue type, with collagenous structures being most resistant, and cellular structu...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Wang YN, Khokhlova TD, Buravkov S, Chernikov V, Kreider W, Partanen A, Farr N, Maxwell A, Schade GR, Khokhlova VA Tags: Phys Med Biol Source Type: research

Visually interpretable deep network for diagnosis of breast masses on mammograms.
Abstract Recently, deep learning technology has achieved various successes in medical image analysis studies including computer-aided diagnosis (CADx). However, current CADx approaches based on deep learning have a limitation in interpreting diagnostic decisions. The limited interpretability is a major challenge for practical use of current deep learning approaches. In this paper, a novel visually interpretable deep network framework is proposed to provide diagnostic decisions with visual interpretation. The proposed method is motivated by the fact that the radiologists characterize breast masses according to the ...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Kim ST, Lee JH, Lee H, Ro YM Tags: Phys Med Biol Source Type: research

Modeling the interference between shear and longitudinal waves under high intensity focused ultrasound propagation in bone.
r HMM Abstract Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) is a noninvasive thermal technique that enables rapid heating of a specific area in the human body. Its clinical relevance has been proven for the treatments of soft tissue tumors, like uterine fibroids, and for the treatments of solid tumors in bone. In MR-HIFU treatment, MR-thermometry is used to monitor the temperature evolution in soft tissue. However, this technique is currently unavailable for bone tissue. Computer models can play a key role in the accurate prediction and monitoring of temperature. Here, we present a compute...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Modena D, Baragona M, Bošnački D, Breuer BJT, Elevelt A, Maessen RTH, Hilbers PAJ, Ten Eikelder HMM Tags: Phys Med Biol Source Type: research

Effects of CT FOV displacement and acquisition parameters variation on texture analysis features.
Abstract Texture analysis (TA) applied to CT imaging is an intensely studied topic and many studies suggested TA potential value in imaging characterisation for diagnostic purposes in different fields. However, often authors do not consider the reproducibility and the robustness versus variations in acquisition parameters; in this work, we wanted to explore the robustness of the TA features extracted from CT images. We scanned a commercial phantom (CIRS model 062M) containing plugs with nine different tissue equivalent electron densities using two different CT scanners of the same vendor and changing tube current ...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Biondi M, Vanzi E, De Otto G, Carbone SF, Nardone V, Banci Buonamici F Tags: Phys Med Biol Source Type: research

DoseNet: a volumetric dose prediction algorithm using 3D fully-convolutional neural networks.
In conclusion, DoseNet is capable of making accurate volumetric dose predictions for non-coplanar SBRT prostate patients, while simultaneously preserving computational efficiency. PMID: 30511663 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Kearney V, Chan JW, Haaf S, Descovich M, Solberg TD Tags: Phys Med Biol Source Type: research

Three-dimensional texture analysis of optical coherence tomography images of ovarian tissue.
Abstract Ovarian cancer has the lowest survival rate among all gynecologic cancers due to predominantly late diagnosis. Optical coherence tomography (OCT) has been applied successfully to experimentally image the ovaries in vivo; however, a robust method for analysis is still required to provide quantitative diagnostic information. Recently, texture analysis has proved to be a useful tool for tissue characterization; unfortunately, existing work in the scope of OCT ovarian imaging is limited to only analyzing 2D sub-regions of the image data, discarding information encoded in the full image area, as well as in the...
Source: Physics in Medicine and Biology - December 4, 2018 Category: Physics Authors: Sawyer TW, Chandra S, Rice PFS, Koevary JW, Barton JK Tags: Phys Med Biol Source Type: research

Fast calculation of nanodosimetric quantities in treatment planning of proton and ion therapy.
gon B Abstract Details of the pattern of ionization formed by particle tracks extends knowledge of dose effects on the nanometer scale. Ionization detail (ID), frequently characterized by ionization cluster size distributions (ICSD), is obtained through time-consuming Monte Carlo (MC) track-structure simulations. In this work, TOPAS-nBio was used to generate a highly precise database of biologically significant ID quantities, sampled with randomly oriented 2.3 nm diameter cylinders, 3.4 nm (10 base pairs) long, inside a chromatin-size cylinder, irradiated by 1-1000 MeV/u ions of Z  =&th...
Source: Physics in Medicine and Biology - November 28, 2018 Category: Physics Authors: Ramos-Méndez J, Burigo LN, Schulte R, Chuang C, Faddegon B Tags: Phys Med Biol Source Type: research

Sparsity-induced dynamic guided filtering approach for sparse-view data toward low-dose x-ray computed tomography.
Abstract Iterative reconstruction (IR) methods that can incorporate filtering or regularization techniques have received widespread attention in many situations. Total variation (TV) regularization has proven to be a powerful tool to suppress streak artifacts and noise for sparse-view computed tomography (CT) reconstruction over 360°. However, with under-sampled projection data from limited-view (e.g. half-view) CT scanning, where the projections are further reduced, the edge structures are partly blurred, and some artifacts (such as blocky artifacts) are not effectively suppressed in TV-based results. To furt...
Source: Physics in Medicine and Biology - November 28, 2018 Category: Physics Authors: Yu W, Wang C, Nie X, Zeng D Tags: Phys Med Biol Source Type: research

Hypo-fractionated boost in locally advanced non-small cell lung cancer: temporal distribution of boost fractions.
Abstract To propose new schemas for radiation boosting of primary tumors, in locally advanced non-small cell lung cancers (NSCLC), in conjunction with standard chemoradiotherapy. To investigate the effect of temporal distributions of the boost fractions on tumor control. NSCLC cases, previously treated with 60 Gy in 30 fractions, were retrospectively planned by adding a radiation boost (25 Gy in 5 fractions) to the primary tumor. Several integrated and sequential boosting schedules were considered. Biological doses were calculated for targets and organs at risk (OAR). Tumor control probabilities (TCP) were calcula...
Source: Physics in Medicine and Biology - November 28, 2018 Category: Physics Authors: Fakir H, Chen J, Sachs RK Tags: Phys Med Biol Source Type: research

Receiver array design for sonothrombolysis treatment monitoring in deep vein thrombosis.
Abstract High intensity focused ultrasound (HIFU) can disintegrate blood clots through the generation and stimulation of bubble clouds within thrombi. This work examined the design of a device to image bubble clouds for monitoring cavitation-based HIFU treatments of deep vein thrombosis (DVT). Acoustic propagation simulations were carried out on multi-layered models of the human thigh using two patient data sets from the Visible Human Project. The design considerations included the number of receivers (32, 64, 128, 256, and 512), their spatial positioning, and the effective angular array aperture (100° and 180...
Source: Physics in Medicine and Biology - November 28, 2018 Category: Physics Authors: Acconcia CN, Jones RM, Hynynen K Tags: Phys Med Biol Source Type: research

Viscoelasticity measurement of ex vivo bovine cartilage using Lamb wave method.
This study validates the use of the LWM for measuring the viscoelasticity of ex vivo cartilage and provides a critical step toward the ultimate goal of measuring the viscoelasticity of cartilage in vivo. PMID: 30484437 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 28, 2018 Category: Physics Authors: Xu H, Shi L, Chen S, Zhang X, An KN, Luo ZP Tags: Phys Med Biol Source Type: research

Simultaneous motion monitoring and truth-in-delivery analysis imaging framework for MR-guided radiotherapy.
Abstract Intrafraction motion (i.e. motion occurring during a treatment session) can play a pivotal role in the success of abdominal and thoracic radiation therapy. Hybrid magnetic resonance-guided radiotherapy (MR-gRT) systems have the potential to control for intrafraction motion. Recently, we introduced an MRI sequence capable of acquiring real-time cine imaging in two orthogonal planes (SOPI). We extend SOPI here to permit dynamic updating of slice positions in one-plane while keeping the other plane position fixed. In this implementation, cine images from the static plane are used for motion monitoring and as...
Source: Physics in Medicine and Biology - November 26, 2018 Category: Physics Authors: Mickevicius NJ, Chen X, Boyd Z, Lee HJ, Ibbott GS, Paulson ES Tags: Phys Med Biol Source Type: research

On the accuracy and efficiency of condensed history transport in magnetic fields in GEANT4.
Abstract The purpose of this work was to investigate the accuracy and efficiency of electron transport in GEANT4 with and without a magnetic field present. Fano cavity simulations were performed in GEANT4 version 10.02 and 10.04.p01 using two multiple scattering (MSC) algorithms for two slab and one pseudo-ion chamber geometries. An iterative approach was used to optimize the transport parameters to obtain agreement with theory. Similar to previous works, the step lengths had to be severely restricted to obtain agreement with theory when using the Urban MSC model in GEANT4 v10.02. Using the Goudsmit-Saunderson MSC...
Source: Physics in Medicine and Biology - November 26, 2018 Category: Physics Authors: Simiele E, DeWerd L Tags: Phys Med Biol Source Type: research

Revisiting the single-energy CT calibration for proton therapy treatment planning: a critical look at the stoichiometric method.
In conclusion, the stoichiometric method for SECT calibration seems to depend on the tissue-substitutes used for calibration-which could be regarded as an additional source of uncertainty in proton range for bone tissues. Furthermore, Gammex tissue-substitutes appear to be a good representative of biological tissues within the energy range relevant to computed tomography-making the stoichiometric method unnecessary. PMID: 30474618 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 26, 2018 Category: Physics Authors: Gomà C, Almeida IP, Verhaegen F Tags: Phys Med Biol Source Type: research

How to harmonize SUVs obtained by hybrid PET/CT scanners with and without point spread function correction.
Abstract State of the art point-spread function (PSF) corrections implemented in positron emission tomography/computed tomography (PET/CT) reconstruction improved image quality and diagnostic performance but caused an increase in the standardized uptake value (SUV) compared to a conventional OSEM reconstruction system. The EANM suggested one produce two reconstructions, one optimised for maximum lesion detection and one for semi-quantitative analysis. In this work we investigated an alternative methodology, using a single reconstruction data set together with a post-reconstruction algorithm for SUV harmonization. ...
Source: Physics in Medicine and Biology - November 26, 2018 Category: Physics Authors: Ferretti A, Chondrogiannis S, Rampin L, Bellan E, Marzola MC, Grassetto G, Gusella S, Maffione AM, Gava M, Rubello D Tags: Phys Med Biol Source Type: research

Optimization of a table-top x-ray fluorescence computed tomography (XFCT) system.
Abstract Pencil beam x-ray fluorescence computed tomography (XFCT) has typically used a single spectrometer and prohibitively long scan times. However, detecting backscattered fluorescent x-rays from gold nanoparticles (AuNPs) using multiple spectrometers greatly reduces image noise and scan time. The arrangement of eight spectrometers for combined K-shell and L-shell XFCT was investigated along with a variety of conditions. A 2.5 cm-diameter cylindrical water phantom containing 4 mm-diameter vials with 0.1%-2% AuNP concentrations by weight was modeled by TOPAS, a GEANT4-based Monte Carlo software. The phantom was...
Source: Physics in Medicine and Biology - November 26, 2018 Category: Physics Authors: Dunning CAS, Bazalova-Carter M Tags: Phys Med Biol Source Type: research

SOI microdosimetry and modified MKM for evaluation of relative biological effectiveness for a passive proton therapy radiation field.
In this study the RBE for the CHO-K1 cell line in a passively delivered clinical proton spread out Bragg peak (SOBP) is determined both in vitro and using a silicon-on-insulator (SOI) microdosimetry method paired with the modified microdosimetric kinetic model. The RBE along the central axis of a SOBP with 2 Gy delivered at the middle of the treatment field was found to vary between 1.11-1.98 and the RBE for 10% cell survival between 1.07-1.58 with a 250 kVp x-ray reference radiation and between 1.19-2.34 and 0.95-1.41, respectively, for a Co60 reference. Good agreement was found between RBE values calculated from the SOI-...
Source: Physics in Medicine and Biology - November 23, 2018 Category: Physics Authors: Debrot E, Tran L, Chartier L, Bolst D, Guatelli S, Vandevoorde C, de Kock E, Beukes P, Symons J, Nieto-Camero J, Prokopovich DA, Chiriotti S, Parisi A, De Saint-Hubert M, Vanhavere F, Slabbert J, Rosenfeld AB Tags: Phys Med Biol Source Type: research

Plaque characterization using shear wave elastography-evaluation of differentiability and accuracy using a combined ex vivo and in vitro setup.
Abstract Ultrasound elastography has shown potential for improved plaque risk stratification. However, no clear consensus exists on what output metric to use, or what imaging parameters would render optimal plaque differentiation. For this reason we developed a combined ex vivo and in vitro setup, in which the ability to differentiate phantom plaques of varying stiffness was evaluated as a function of plaque geometry, push location, imaging plane, and analysed wave speed metric. The results indicate that group velocity or phase velocity  ⩾1 kHz showed the highest ability to significantly dif...
Source: Physics in Medicine and Biology - November 23, 2018 Category: Physics Authors: Marlevi D, Maksuti E, Urban MW, Winter R, Larsson M Tags: Phys Med Biol Source Type: research

Accelerating multi-modal image registration using a supervoxel-based variational framework.
Abstract For the successful completion of medical interventional procedures, several concepts, such as daily positioning compensation, dose accumulation or delineation propagation, rely on establishing a spatial coherence between planning images and images acquired at different time instants over the course of the therapy. To meet this need, image-based motion estimation and compensation relies on fast, automatic, accurate and precise registration algorithms. However, image registration quickly becomes a challenging and computationally intensive task, especially when multiple imaging modalities are involved. In th...
Source: Physics in Medicine and Biology - November 23, 2018 Category: Physics Authors: Lafitte L, Zachiu C, Kerkmeijer LGW, Ries M, Denis de Senneville B Tags: Phys Med Biol Source Type: research

Motion effects in proton treatments of hepatocellular carcinoma-4D robustly optimised pencil beam scanning plans versus double scattering plans.
This study investigates the potential use of 4D robust optimisation to maintain sufficient target coverage in the presence of organ motion, while sparing surrounding healthy tissue, for hepatocellular carcinoma (HCC). The liver is particularly suited to study motion interplay effects since the treatment region exhibits smaller density gradients and more homogeneous tissue than targets in the thorax, making it less prone to range errors. A facility-specific beam time model, developed and experimentally validated previously, was used for the clinical evaluation. 4DDD analyses of eleven target volumes did not show a significa...
Source: Physics in Medicine and Biology - November 23, 2018 Category: Physics Authors: Pfeiler T, Ahmad Khalil D, Ayadi M, Bäumer C, Blanck O, Chan M, Engwall E, Geismar D, Peters S, Plaude S, Spaan B, Timmermann B, Wulff J Tags: Phys Med Biol Source Type: research

Comparison of five one-step reconstruction algorithms for spectral CT.
Abstract Over the last decade, dual-energy CT scanners have gone from prototypes to clinically available machines, and spectral photon counting CT scanners are following. They require a specific reconstruction process, consisting of two steps: material decomposition and tomographic reconstruction. Image-based methods perform reconstruction, then decomposition, while projection-based methods perform decomposition first, and then reconstruction. As an alternative, 'one-step inversion' methods have been proposed, which perform decomposition and reconstruction simultaneously. Unfortunately, one-step methods are typica...
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Mory C, Sixou B, Si-Mohamed S, Boussel L, Rit S Tags: Phys Med Biol Source Type: research

The impact of 2D cine MR imaging parameters on automated tumor and organ localization for MR-guided real-time adaptive radiotherapy.
This study systematically investigates the impact of geometric imaging parameters on the ability of 2D cine MR imaging to guide template-matching-driven autocontouring of lung tumors and abdominal organs. Abdominal 4D MR images were acquired of six healthy volunteers and thoracic 4D MR images were obtained of eight lung cancer patients. At each breathing phase of the images, the left kidney and gallbladder or lung tumor, respectively, were outlined as volumes of interest. These images and contours were used to create artificial 2D cine MR images, while simultaneously serving as 3D ground truth. We explored the impact of fi...
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Menten MJ, Fast MF, Wetscherek A, Rank CM, Kachelrieß M, Collins DJ, Nill S, Oelfke U Tags: Phys Med Biol Source Type: research

Autosegmentation of prostate anatomy for radiation treatment planning using deep decision forests of radiomic features.
Abstract Machine learning for image segmentation could provide expedited clinic workflow and better standardization of contour delineation. We evaluated a new model using deep decision forests of image features in order to contour pelvic anatomy on treatment planning CTs. 193 CT scans from one UK and two US institutions for patients undergoing radiotherapy treatment for prostate cancer from 2012-2016 were anonymized. A decision forest autosegmentation model was trained on a random selection of 94 images from Institution 1 and tested on 99 scans from Institution 1, 2, and 3. The accuracy of model contours was measu...
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Macomber MW, Phillips M, Tarapov I, Jena R, Nori A, Carter D, Folgoc LL, Criminisi A, Nyflot MJ Tags: Phys Med Biol Source Type: research

Shearlet-based compressed sensing for fast 3D cardiac MR imaging using iterative reweighting.
h C Abstract High-resolution three-dimensional (3D) cardiovascular magnetic resonance (CMR) is a valuable medical imaging technique, but its widespread application in clinical practice is hampered by long acquisition times. Here we present a novel compressed sensing (CS) reconstruction approach using shearlets as a sparsifying transform allowing for fast 3D CMR (3DShearCS) using 3D radial phase encoding (RPE). An iterative reweighting scheme was applied during image reconstruction to ensure fast convergence and high image quality. Shearlets are mathematically optimal for a simplified model of natural images and ha...
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Ma J, März M, Funk S, Schulz-Menger J, Kutyniok G, Schaeffter T, Kolbitsch C Tags: Phys Med Biol Source Type: research

Measurement of breast-tissue x-ray attenuation by spectral imaging: fresh and fixed normal and malignant tissue.
Abstract Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. In mammography, measurement of breast density, dose estimation, and differentiation between cysts and solid tumours are example applications requiring accurate data on tissue attenuation. Published attenuation data are, however, sparse and cover a relatively wide range. To supplement available data we have previously measured the attenuation of cyst fluid and solid lesions using photon-counting spectral mammography. The present study aims to measure the attenuation of normal adipose and glandular tissue, ...
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Fredenberg E, Willsher P, Moa E, Dance DR, Young KC, Wallis MG Tags: Phys Med Biol Source Type: research

Integrating a low-field open MR scanner with a static proton research beam line: proof of concept.
This study proves that simultaneous irradiation and in-beam MR imaging is technically feasible with a low-field MR scanner integrated with a static proton research beam line. PMID: 30465549 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 22, 2018 Category: Physics Authors: Schellhammer SM, Hoffmann AL, Gantz S, Smeets J, van der Kraaij E, Quets S, Pieck S, Karsch L, Pawelke J Tags: Phys Med Biol Source Type: research

Statistical CT reconstruction using region-aware texture preserving regularization learning from prior normal-dose CT image.
This study aims to learn texture information from the NdCT images and leverage it for follow-up LdCT image reconstruction to preserve textures and structure features. Specifically, the proposed reconstruction method first learns the texture information from those patches with similar structures in NdCT image, and the similar patches can be clustered by searching context features efficiently from the surroundings of the current patch. Then it utilizes redundant texture information from the similar patches as a priori knowledge to describe specific regions in the LdCT image. The advanced region-aware texture preserving prior...
Source: Physics in Medicine and Biology - November 20, 2018 Category: Physics Authors: Jia X, Liao Y, Zeng D, Zhang H, Zhang Y, He J, Bian Z, Wang Y, Tao X, Liang Z, Huang J, Ma J Tags: Phys Med Biol Source Type: research

A statistically optimized regional thresholding method (SORT) for bone lesion detection in 18F-NaF PET/CT imaging.
This study assessed 18F-NaF PET/CT scans of 37 bone metastatic prostate cancer patients. Each PET image was divided into 19 skeletal regions. Areas of disease in each skeletal region were identified by an experienced nuclear medicine physician. A region of interest (ROI) was placed at each disease location and local maxima were extracted for both healthy and diseased ROIs. Secondary physician review was performed after identification of suspicious local maxima. Region-specific SUV thresholds were determined based on receiver operating characteristic (ROC) analysis optimized for detection of malignant disease. The detection...
Source: Physics in Medicine and Biology - November 20, 2018 Category: Physics Authors: Perk T, Chen S, Harmon S, Lin C, Bradshaw T, Perlman S, Liu G, Jeraj R Tags: Phys Med Biol Source Type: research