Fano cavity test for electron Monte Carlo transport algorithms in magnetic fields: comparison between EGSnrc, PENELOPE, MCNP6 and Geant4.
Abstract A Fano cavity test was performed for four general-purpose Monte Carlo codes, EGSnrc, PENELOPE, MCNP6 and Geant4 to evaluate the accuracy of their electron transport algorithms in magnetic fields. In the simulations, a plane-parallel ionization chamber was modelled as a circular gas disk sandwiched between two circular solid wall disks. It was assumed that an isotropic and uniform line source per unit mass along the central axis of the gas and solid emits mono-energetic electrons with energies 0.01, 0.1, 1.0 and 3.0 MeV at different magnetic field strengths 0, 0.35, 1.0, 1.5 and 3.0 T in the electron trans...
Source: Physics in Medicine and Biology - September 5, 2018 Category: Physics Authors: Lee J, Lee J, Ryu D, Lee H, Ye SJ Tags: Phys Med Biol Source Type: research

Method for optimizing planning target volume margin for patients receiving lung stereotactic body radiotherapy.
Abstract Lung stereotactic-body radiotherapy (SBRT) places additional requirements on targeting accuracy over standard approaches. In treatment planning, a tumour volume is geometrically expanded and the resulting planning target volume (PTV) is covered with full dose. This ensures full dose delivery despite various uncertainties encountered during treatment. We developed a retrospective technique for optimizing the PTV expansion for a patient population. The method relies on deformable image registration (DIR) of the planning CT to a treatment cone-beam CT (CBCT). The resulting transformation is used ...
Source: Physics in Medicine and Biology - September 5, 2018 Category: Physics Authors: Wierzbicki M, Mathew L, Swaminath A Tags: Phys Med Biol Source Type: research

Fabrication of an anthropomorphic heterogeneous mouse phantom for multimodality medical imaging.
Abstract This work is to present a comprehensive methodology for constructing a tissue equivalent mouse phantom using image modeling and 3D printing technology. The phantom can be used in multimodality imaging and irradiation experiments, quality control, and management. Computed Tomography (CT) images of a mouse were acquired and imported into 3D modeling software. A skeleton and a skin shell models were segmented in the modeling software and manufactured using 3D printing technology. The bone model was constructed with VERO-WHITE printing material with additional ingredients, including a photosensitive resin, po...
Source: Physics in Medicine and Biology - September 5, 2018 Category: Physics Authors: Zhang H, Hou K, Chen J, Dyer BA, Chen JC, Liu X, Zhang F, Rong Y, Qiu J Tags: Phys Med Biol Source Type: research

Relating ionization quenching in organic plastic scintillators to basic material properties by modelling excitation density transport and amorphous track structure during proton irradiation.
Abstract Ionization quenching in organic scintillators is usually corrected with methods that require careful assessment of the response relative to that of an ionization chamber. Here, we present a framework to compute ionization quenching correction factors (QCFs) from first principles for organic plastic scintillators exposed to ions. The tool solves the kinetic Blanc equation, of which the Birks model is a simplified solution, based on amorphous track structures models. As a consequence, ionization quenching correction factors can be calculated relying only on standard, tabulated scintillator material properti...
Source: Physics in Medicine and Biology - September 5, 2018 Category: Physics Authors: Christensen JB, Andersen CE Tags: Phys Med Biol Source Type: research

Evaluating TOPAS for the calculation of backscatter factors for low energy x-ray beams.
This study evaluated the Monte Carlo code TOPAS as a tool for dose calculations for kilovoltage x-rays, and for calculating BSFs for energies ranging from 50 to 280 kVp. BSFs were also measured experimentally for comparison using Gafchromic EBT3 film and optically stimulated luminescence dosimeters (OSLs). The BSFs calculated using TOPAS were found to be consistent within 2% of the values published in the AAPM TG-61 protocol. The TOPAS BSF calculations were also found to be consistent with film measurements, typically within 2%. The largest discrepancy measured was 5% for the 3 cm field size and 180 kVp beam. OSLs were fou...
Source: Physics in Medicine and Biology - September 5, 2018 Category: Physics Authors: Hewson EA, Butson MJ, Hill R Tags: Phys Med Biol Source Type: research

The one-dimensional lateral dose response functions of photon-dosimetry detectors in magnetic fields - measurement and Monte-Carlo simulation.
Abstract The present study is concerned with clinical photon-beam dosimetry at radiotherapy units combined with magnetic resonance imaging devices. Due to the superposed constant magnetic field, the deflections of the secondary electron trajectories by the Lorentz force not only influence the 2D dose distribution, D(x,y), in water phantoms, but furthermore modify the secondary electron transport within the detectors and thereby the detectors' signal profiles, M(x,y), across the photon beams. This second effect can be represented by the lateral dose response function, K(x,y), the convolution kernel transforming D(x...
Source: Physics in Medicine and Biology - August 28, 2018 Category: Physics Authors: Delfs B, Poppinga D, Ulrichs AB, Kapsch RP, Harder D, Poppe B, Looe HK Tags: Phys Med Biol Source Type: research

Multiple sources array controls shear-wave field in soft tissue using time reversal.
Abstract In most elastography experiments, shear waves are generated using a single source on the surface with a shaker, or in the bulk with radiation pressure of ultrasound. However, emitting controlled shear waves from multiple sources is a good way to improve the signal to-noise-ratio for shear-wave elastography. The experiments are conducted using six shakers with independent driving electronics in gelatin-graphite to mimic the tissue. Based on time reversal, our approach shows the feasibility of controlling shear-wave field in space with multiple focal spots at chosen locations, and in time with a chosen dela...
Source: Physics in Medicine and Biology - August 28, 2018 Category: Physics Authors: Zemzemi C, Aichele J, Catheline S Tags: Phys Med Biol Source Type: research

Characterization of PTW-31015 PinPoint ionization chambers in photon and proton beams.
In this study, 48 PTW-TM31015 PinPoint-type micro-ionization chambers that are used in the commissioning and patient specific QA of a proton pencil beam scanning (PBS) delivery system have been characterized in proton and high-energy photon beams. In both beam modalities, the entire set of PinPoint chambers was characterized by imaging them, by evaluating their stability using check source measurements, by experimentally determining the ion recombination, polarity effect and by cross calibrating them in terms of absorbed dose to water against Farmer-type ionization chambers. Beam quality correction factors were ...
Source: Physics in Medicine and Biology - August 28, 2018 Category: Physics Authors: Carlino A, Stock M, Zagler N, Marrale M, Osorio J, Vatnitsky S, Palmans H Tags: Phys Med Biol Source Type: research

Performance assessment of a software-based coincidence processor for the EXPLORER total-body PET scanner.
Abstract Coincidence processing in positron emission tomography (PET) is typically done during acquisition of the data. However, on the EXPLORER total-body PET scanner we plan, in addition, to store unpaired single events (i.e. singles) for post-acquisition coincidence processing. A software-based coincidence processor was developed for EXPLORER and its performance was assessed. Our results showed that the performance of the coincidence processor could be significantly impacted by the type of data storage (Peripheral Component Interconnect Express (PCIe)-attached solid state drive (SSD) vs RAID 6 hard disk drives ...
Source: Physics in Medicine and Biology - August 28, 2018 Category: Physics Authors: Leung EK, Judenhofer MS, Cherry SR, Badawi RD Tags: Phys Med Biol Source Type: research

Study of the reliability of quantification methods of dynamic contrast-enhanced ultrasonography: numerical modeling of blood flow in tumor microvascularization.
This study is hopeful and may be extended to the treatment of more complex vascular networks, to approach clinical conditions, and to the evaluation of quantification methods in contrast imaging. PMID: 30136651 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 23, 2018 Category: Physics Authors: Boyer L, Leguerney I, Randall Thomas S, Grand-Perret V, Lassau N, Pitre-Champagnat S Tags: Phys Med Biol Source Type: research

Material decomposition with prior knowledge aware iterative denoising (MD-PKAID).
Abstract Dual- or multi-energy CT, also known as spectral CT, obtains X-ray attenuation measurements at two or more energy spectra, allowing quantification of materials with different compositions. This process is known as material decomposition, which is the basis for a number of spectral CT applications. The conventional image-domain basis material decomposition is based on a least-squares fitting between the underlying material-specific images and the measured source spectral CT images (i.e., energy-bin or energy-threshold CT images), and a non-iterative solution based on matrix inversion can be derived for thi...
Source: Physics in Medicine and Biology - August 23, 2018 Category: Physics Authors: Tao S, Rajendran K, McCollough CH, Leng S Tags: Phys Med Biol Source Type: research

Improved single photon time resolution for analog SiPMs with front end readout that reduces influence of electronic noise.
Abstract A key step to improving the coincidence time resolution of positron emission tomography detectors that exploit populations of prompt photon emissions is improving the single photon time resolution (SPTR) of silicon photomultipliers (SiPMs). The influence of electronic noise has previously been identified as the dominant factor affecting SPTR for large area, analog SiPMs. In this work, we measure the achievable SPTR with front end electronic readout that minimizes the influence of electronic noise. With this new readout circuit, the SPTR measured for one FBK NUV single avalanche photodiode (SPAD) was also ...
Source: Physics in Medicine and Biology - August 21, 2018 Category: Physics Authors: Cates JW, Gundacker S, Auffray E, Lecoq P, Levin CS Tags: Phys Med Biol Source Type: research

Subjective and objective evaluations of feature selected multi output filter for speckle reduction on ultrasound images.
Abstract 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). This multi-scale based method enables the enhancement of the ori...
Source: Physics in Medicine and Biology - August 21, 2018 Category: Physics Authors: Outtas M, Zhang L, Deforges O, Serir A, Hamidouche W, Chen Y Tags: Phys Med Biol Source Type: research

Suitability of EBT3 GafChromic film for quality assurance in MR-guided radiotherapy at 0.35 T with and without real-time MR imaging.
Abstract The 0.35 T 60Co MRIdian system (ViewRay Inc., Mountain View) has been in clinical use in our institution since May 2016. For quality assurance (QA) of dose delivery and end-to-end testing for this machine, a reliable dosimeter is required. However, it is possible that a magnetic field may cause perturbations to dosimetry measurements. For static magnetic fields, there is conflicting information in the literature concerning EBT film behaviour, while for real-time MR imaging such information is not available at all. The purpose of this study was to investigate the suitability of EBT3 GafChromic film for MRI...
Source: Physics in Medicine and Biology - August 20, 2018 Category: Physics Authors: Barten DLJ, Hoffmans D, Palacios MA, Heukelom S, van Battum LJ Tags: Phys Med Biol Source Type: research

SCOPE: signal compensation for low-rank plus sparse matrix decomposition for fast parameter mapping.
Abstract Magnetic resonance (MR) parameter mapping is useful for many clinical applications. However, its practical utility is limited by the long scan time. To address this problem, this paper developed a novel image reconstruction method for fast MR parameter mapping. The proposed method (SCOPE) used a low-rank plus sparse model to reconstruct the parameter-weighted images from highly undersampled acquisitions. A signal compensation strategy was introduced to promote low rankness along the parametric direction and thus improve the reconstruction accuracy. Specifically, compensation was performed by multiplying t...
Source: Physics in Medicine and Biology - August 17, 2018 Category: Physics Authors: Zhu Y, Liu Y, Ying L, Peng X, Wang YJ, Yuan J, Liu X, Liang D Tags: Phys Med Biol Source Type: research

Single-shot Talbot-Lau X-ray dark-field imaging of a porcine lung applying the moir é imaging approach.
Single-shot Talbot-Lau X-ray dark-field imaging of a porcine lung applying the moiré imaging approach. Phys Med Biol. 2018 Aug 17;: Authors: Seifert M, Ludwig V, Gallersdoerfer M, Hauke C, Hellbach K, Horn F, Pelzer G, Radicke M, Rieger J, Sutter SM, Michel T, Anton G Abstract Talbot-Lau X-ray imaging provides additionally to the conventional attenuation image, two further images: the differential phase-contrast image which is especially sensitive to differences in refractive properties and the dark-field image which is showing the X-ray scattering properties of the object. Thus, in the dark-fi...
Source: Physics in Medicine and Biology - August 17, 2018 Category: Physics Authors: Seifert M, Ludwig V, Gallersdoerfer M, Hauke C, Hellbach K, Horn F, Pelzer G, Radicke M, Rieger J, Sutter SM, Michel T, Anton G Tags: Phys Med Biol Source Type: research

A new inverse planning formalism with explicit DVH constraints and kurtosis-based dosimetric criteria.
Abstract In inverse planning processes of radiotherapy, dose-volume histograms (DVH) have been commonly used as a measure of plan quality. The exact mathematical formulation of DVHs involves binary variables and is therefore intrinsically nonconvex. In view of the resulting computational intractability, existing treatment planning systems adopt convex surrogate models that involve many tweaking parameters. Manual parameter tweaking is then required to determine reasonable values for those parameters in order to generate plans that meet the target DVHs. However, conventional convex formulations for inverse planning...
Source: Physics in Medicine and Biology - August 17, 2018 Category: Physics Authors: Liu H, Chen Y, Lu B Tags: Phys Med Biol Source Type: research

Design and performance of the micro-dose calibrator.
Abstract A new class of dose calibrator called a micro-dose calibrator, designed to measure radioactivity rates in the range between 1 kBq up to 370 kBq, has been designed and an 8 NaI(Tl)/photo multiplier tube (PMT) module prototype built to evaluate its performance. The design of the micro-dose calibrator is based on the concept of a segmented well counter. By segmenting a single crystal well counter into multiple crystals or segments, with each segment operated and read out independently, one can extend the operational range of a standard single crystal well counter while maintaining its accuracy and spectrogra...
Source: Physics in Medicine and Biology - August 17, 2018 Category: Physics Authors: Adler SS, Choyke P Tags: Phys Med Biol Source Type: research

Deep learning with cinematic rendering: fine-tuning deep neural networks using photorealistic medical images.
Abstract Deep learning has emerged as a powerful artificial intelligence tool to interpret medical images for a growing variety of applications. However, the paucity of medical imaging data with high-quality annotations that is necessary for training such methods ultimately limits their performance. Medical data is challenging to acquire due to privacy issues, shortage of experts available for annotation, limited representation of rare conditions and cost. This problem has previously been addressed by using synthetically generated data. However, networks trained on synthetic data often fail to generalize to real d...
Source: Physics in Medicine and Biology - August 16, 2018 Category: Physics Authors: Mahmood F, Chen R, Sudarsky S, Yu D, Durr NJ Tags: Phys Med Biol Source Type: research

Linear energy transfer (LET) spectra and survival fraction distribution based on the CR-39 plastic charged-particle detector in a spread-out Bragg peak irradiation by a < sup > 12 < /sup > C beam.
Linear energy transfer (LET) spectra and survival fraction distribution based on the CR-39 plastic charged-particle detector in a spread-out Bragg peak irradiation by a 12C beam. Phys Med Biol. 2018 Aug 16;: Authors: Hirano Y, Kodaira S, Souda H, Matsumura A, Torikoshi M Abstract Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose...
Source: Physics in Medicine and Biology - August 16, 2018 Category: Physics Authors: Hirano Y, Kodaira S, Souda H, Matsumura A, Torikoshi M Tags: Phys Med Biol Source Type: research

The role of acquisition and quantification methods in myocardial blood flow estimability for myocardial perfusion imaging CT.
Abstract In this work, we clarified the role of acquisition parameters and quantification methods in myocardial blood flow (MBF) estimability for myocardial perfusion imaging using CT (MPI-CT). We used a physiologic model with a CT simulator to generate time-attenuation curves across a range of imaging conditions, i.e. tube current-time product, imaging duration, and temporal sampling, and physiologic conditions, i.e. MBF and arterial input function width. We assessed MBF estimability by precision (interquartile range of MBF estimates) and bias (difference between median MBF estimate and reference MBF) for multipl...
Source: Physics in Medicine and Biology - August 16, 2018 Category: Physics Authors: Eck BL, Muzic RF, Levi J, Wu H, Fahmi R, Li Y, Fares A, Vembar M, Dhanantwari A, Bezerra HG, Wilson DL Tags: Phys Med Biol Source Type: research

CASToR: a generic data organization and processing code framework for multi-modal and multi-dimensional tomographic reconstruction.
In conclusion, the proposed framework offers a substantial flexibility for the integration of new reconstruction algorithms while maintaining computation efficiency. PMID: 30113313 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 16, 2018 Category: Physics Authors: Merlin T, Stute S, Benoit D, Bert J, Carlier T, Comtat C, Filipovic M, Lamare F, Visvikis D Tags: Phys Med Biol Source Type: research

Cascaded atrous convolution and spatial pyramid pooling for more accurate tumor target segmentation for rectal cancer radiotherapy.
In conclusion, the proposed CAC-SPP which could extract high-resolution features with large receptive fields and capture multi-scale context yields improve the accuracy of segmentation performance for rectal tumors. PMID: 30109986 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 15, 2018 Category: Physics Authors: Men K, Boimel P, Janopaul-Naylor J, Zhong H, Huang M, Geng H, Cheng C, Fan Y, Plastaras JP, Ben-Josef E, Xiao Y Tags: Phys Med Biol Source Type: research

Dose evaluation of fast synthetic-CT generation using a generative adversarial network for general pelvis MR-only radiotherapy.
Abstract To enable magnetic resonance (MR)-only radiotherapy and facilitate modelling of radiation attenuation in humans, synthetic-CT (sCT) images need to be generated. Considering the application of MR-guided radiotherapy and online adaptive replanning, sCT generation should occur within minutes. This work aims at assessing whether an existing deep learning network can rapidly generate sCT images to be used for accurate MR-based dose calculations in the entire pelvis. A study was conducted on data of 91 patients with prostate (59), rectal (18) and cervical (14) cancer who underwent external beam radio...
Source: Physics in Medicine and Biology - August 15, 2018 Category: Physics Authors: Maspero M, Savenije MHF, Dinkla AM, Seevinck PR, Intven MPW, Juergenliemk-Schulz IM, Kerkmeijer LGW, Van den Berg CAT Tags: Phys Med Biol Source Type: research

A key-point based real-time tracking of lung tumor in X-ray image sequence by using difference of Gaussians filtering and optical flow.
In this study, a new key point-based tumor tracking method, which is sufficiently fast and accurate, is presented. Given an X-ray image sequence, the proposed method employs a difference of Gaussians filtering technique to detect key points, which are robust against noise and outliers in the subsequent frames, in the tumor region of the first frame. In the subsequent frames, the key points are tracked by using a fast optical flow technique, and the tumor motion is estimated by the key points movements. To evaluate the performance, the proposed method was tested on several clinical kV and MV X-ray image sequences. The e...
Source: Physics in Medicine and Biology - August 15, 2018 Category: Physics Authors: Ichiji K, Yoshida Y, Homma N, Zhang X, Bukovsky I, Takai Y, Yoshizawa M Tags: Phys Med Biol Source Type: research

An unsupervised convolutional neural network-based algorithm for deformable image registration.
In conclusion, DCIGN is able to maintain high accuracy in the presence of CBCT noise contamination, while simultaneously preserving high computational efficiency. PMID: 30109996 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 15, 2018 Category: Physics Authors: Kearney VP, Haaf S, Sudhyadhom A, Valdes G, Solberg TD Tags: Phys Med Biol Source Type: research

Developing an efficient phase-matched attenuation correction method for quiescent period PET in abdominal PET/MRI.
In conclusion, we demonstrated that a data acquisition of 30 seconds achieved phase-matched &lt;i&gt;μ&lt;/i&gt;-maps when using specialized CIRCUS data sampling and phase-matched &lt;i&gt;μ&lt;/i&gt;-maps improved PET&lt;sub&gt;Q&lt;/sub&gt; quantification significantly. PMID: 30106008 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 14, 2018 Category: Physics Authors: Yang J, Liu J, Wiesinger F, Menini A, Zhu X, Hope TA, Seo Y, Larson PEZ Tags: Phys Med Biol Source Type: research

Self-adaptive ultrasonic beam amplifiers: application to transcostal shock wave therapy.
Abstract Ultrasound shock wave therapy is increasingly used for non-invasive surgery. It requires the focusing of very high pressure amplitude in precisely controlled focal spots. In transcostal therapy of the heart or the liver the high impedance mismatch between the bones and surrounding tissues gives rise to strong aberrations and attenuation of the therapeutic wavefront, with potential risks of injury at the tissue - bone interface. An adaptive propagation of the ultrasonic beam through the intercostal spaces would be required. Several solutions have been developed so far, but they require a prior knowledge of...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Robin J, Simon A, Arnal B, Tanter M, Pernot M Tags: Phys Med Biol Source Type: research

Ionization chamber dosimetry based on < sup > 60 < /sup > Co absorbed dose to water calibration for diagnostic kilovoltage x-ray beams.
Ionization chamber dosimetry based on 60Co absorbed dose to water calibration for diagnostic kilovoltage x-ray beams. Phys Med Biol. 2018 Aug 13;: Authors: Araki F, Ohno T, Umeno S Abstract The purpose of this study was to develop a new ionization chamber dosimetry formalism for diagnostic kilovoltage x-ray beams based on a 60Co absorbed dose-to-water calibration coefficient . To validate the new chamber dosimetry, 39 fluence spectra of kilovoltage x-rays were calculated, using a SpekCalc program, for Al half-value-layer (Al-HVL) values of 1.4 8.5 mm and tube voltages of 50 137.6 kVp. We used these sp...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Araki F, Ohno T, Umeno S Tags: Phys Med Biol Source Type: research

The multigaussian method: a new approach to mitigating spatial heterogeneities with multichannel radiochromic film dosimetry.
In this study, the abilities of various single channel and multichannel methods to reduce spatial heterogeneities, with and without scanning before irradiation, were tested. Red, green and blue single channel models, two additive channel independent perturbation (CHIP) models and two multiplicative CHIP models were compared with the Multigaussian method. The Multigaussian method is a new approach to multichannel dosimetry, based on experimental findings. It assumes that the probability density function of the response vector formed by the pixel values of the different color channels, including irradiated and non-irradiated...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Mendez I, Polsak A, Hudej R, Casar B Tags: Phys Med Biol Source Type: research

Coronary artery calcium quantification using contrast-enhanced dual-energy computed tomography scans in comparison with unenhanced single-energy scans.
Abstract Extracting coronary artery calcium (CAC) scores from contrast-enhanced computed tomography (CT) images using dual-energy (DE) based material decomposition has been shown feasible, mainly through patient studies. However, the quantitative performance of such DE-based CAC scores, particularly per-stenosis, is underexamined due to lack of reference standard and repeated scans. In this work we conducted a comprehensive quantitative comparative analysis of CAC scores obtained with DE and compare to conventional unenhanced single-energy (SE) CT scans through phantom studies. Synthetic vessels filled with ...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Li Q, Berman BP, Hagio T, Gavrielides MA, Zeng R, Sahiner B, Gong Q, Fang Y, Liu S, Petrick NP Tags: Phys Med Biol Source Type: research

Characterization of a binary system composed of luminescent quantum dots for liquid scintillation.
This study aims to establish the profile of CdSe colloidal quantum dots (cQDs) that were given the role of the fluorophore in a binary liquid scintillation system. We chose to investigate the cQDs because of their wide absorption spectrum, the tunability of their absorption and emission spectra with respect to their size and composition, and their ability to function as an effective energy transfer intermediate. The scintillation intensity and spectral response of three organic solvent-based liquid cQD dispersions have been investigated upon irradiation with kV and MV photon beams. The solvents used to disperse the cQDs we...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Delage MÈ, Lecavalier MÈ, Larivière D, Allen CN, Beaulieu L Tags: Phys Med Biol Source Type: research

Application of plastic scintillating fibres to surface dosimetry in megavoltage photon and electron beams: considerations for Cerenkov correction.
In this study a maximum error of 12% was observed for 16 MeV with a gantry angle of 45°. It was shown that the cause of this error was a non-negligible emission of Cerenkov radiation from the scintillator itself. This error was not observed when the PSD was oriented perpendicular to the plane of rotation. Similarly, the full spectral method was effective in isolating the scintillation-only signal regardless of PSD orientation. PMID: 30101759 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Monajemi TT, Avila Ruiz E Tags: Phys Med Biol Source Type: research

Exploration and application of phenomenological RBE models for proton therapy.
Conclusion: There were considerable variations between the estimations of RBE and RBE-weighted doses from the different RBE models. These variations were a consequence of fundamental differences in experimental databases, model assumptions and regression techniques. The results from implementation of RBE models in dose planning studies should be evaluated in light of these deviations. PMID: 30102240 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Rørvik E, Fjæra LF, Dahle TJ, Dale JE, Engeseth GM, Stokkevåg CH, Thörnqvist S, Ytre-Hauge KS Tags: Phys Med Biol Source Type: research

A multi-slot coaxial microwave antenna for liver tumor ablation.
Abstract This paper presents a multi-slot coaxial antenna with a pi impedance matching network for liver tumor ablation. In order to reduce damage to surrounding healthy tissues during ablation, a multi-slot radiating part was designed to produce a near-spherical heating zone with greatly increased possibility of conformal treatment. A pi impedance matching network part was designed to match the feeding transmission line and antenna without increasing antenna size. The reflection coefficient, ablation zone shape, specific absorption rate, and temperature were determined by using a finite element electromagnetic si...
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Ge M, Jiang H, Huang X, Zhou Y, Zhi D, Zhao G, Chen Y, Wang L, Qiu B Tags: Phys Med Biol Source Type: research

Substituting gelatine with Pluronic F-127 matrix in 3D polymer gel dosimeters can improve nuclear magnetic resonance, thermal and optical properties.
In conclusion, Pluronic F-127 is an attractive co-polymer to serve as a substitute for the gelatine matrix in some 3D polymer gel dosimeters. PMID: 30102250 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 13, 2018 Category: Physics Authors: Jaszczak M, Wach R, Maras P, Dudek M, Kozicki M Tags: Phys Med Biol Source Type: research

RapidBrachyMCTPS: a Monte Carlo-based treatment planning system for brachytherapy applications.
Abstract Despite being considered the gold standard for brachytherapy dosimetry, Monte Carlo (MC) has yet to be implemented into a software for brachytherapy treatment planning. The purpose of this work is to present RapidBrachyMCTPS, a novel treatment planning system (TPS) for brachytherapy applications equipped with a graphical user interface (GUI), optimization tools and a Geant4-based MC dose calculation engine, RapidBrachyMC. Brachytherapy sources and applicators were implemented in RapidBrachyMC and made available to the user via a source and applicator library in the GUI. To benchmark RapidBrachyMC, TG-43 p...
Source: Physics in Medicine and Biology - August 10, 2018 Category: Physics Authors: Famulari G, Renaud MA, Poole CM, Evans MDC, Seuntjens J, Enger SA Tags: Phys Med Biol Source Type: research

Improved discrimination between benign and malignant LDCT screening-detected lung nodules with dynamic over static < sup > 18 < /sup > F-FDG PET as a function of injected dose.
Improved discrimination between benign and malignant LDCT screening-detected lung nodules with dynamic over static 18F-FDG PET as a function of injected dose. Phys Med Biol. 2018 Aug 10;: Authors: Ye Q, Wu J, Lu Y, Naganawa M, Gallezot JD, Ma T, Liu Y, Tanoue L, Detterbeck F, Blasberg J, Chen MK, Casey M, Carson RE, Liu C Abstract Lung cancer mortality rate can be significantly reduced by up to 20% through routine low-dose computed tomography (LDCT) screening, which, however, has high sensitivity but low specificity, resulting in a high rate of false-positive nodules. Combining PET with CT may provide...
Source: Physics in Medicine and Biology - August 10, 2018 Category: Physics Authors: Ye Q, Wu J, Lu Y, Naganawa M, Gallezot JD, Ma T, Liu Y, Tanoue L, Detterbeck F, Blasberg J, Chen MK, Casey M, Carson RE, Liu C Tags: Phys Med Biol Source Type: research

Benchtop magnetic particle relaxometer for detection, characterization and analysis of magnetic nanoparticles.
Abstract This paper presents the design, construction, and testing of a magnetic particle relaxometer (MPR) to assess magnetic nanoparticle response to dynamic magnetic fields while subjected to a bias field. The designed MPR can characterize magnetic particles for use as tracers in magnetic particle imaging (MPI), with the variation of an applied bias field emulating the scan of the MPI field free point. The system applies a high-frequency time-varying excitation field (up to 45 mT at 30 kHz), while slowly ramping a bias field (± 100 mT in 1 s). The time-resolved response of the sample is measured using an...
Source: Physics in Medicine and Biology - August 10, 2018 Category: Physics Authors: Garraud N, Dhavalikar R, Unni M, Savliwala S, Rinaldi C, Arnold DP Tags: Phys Med Biol Source Type: research

A general-threshold filtering method for improving intravoxel incoherent motion parameter estimates.
In this study, we present an image denoising method for diffusion-weighted magnetic resonance imaging (DW-MRI) data. Our aim is to improve the estimation of intravoxel incoherent motion (IVIM) parameters using denoised DW-MRI data. A general-threshold filtering (GTF) reconstruction via total variation minimization has been proposed to improve image quality in few-view computed tomography. Here, we applied the combination of GTF and total difference to image denoising. Voxel-wise IVIM analysis was performed using both real and simulated DW-MRI data. Using an institutional review board-approved protocol with written informed...
Source: Physics in Medicine and Biology - August 9, 2018 Category: Physics Authors: Lin C, Liu CC, Huang HM Tags: Phys Med Biol Source Type: research

Performance evaluation of the PET component of a hybrid PET/CT-ultrafast ultrasound imaging instrument.
ian B Abstract We recently introduced a hybrid imaging instrument, PETRUS, based on a combination of Positron Emission Tomography (PET) for molecular imaging, X-ray Computed Tomography (CT) for anatomical imaging, co-registration and attenuation correction, and Ultrafast Ultrasound Imaging (UUI) for motion-correction, hemodynamic and biomechanical imaging. In order to ensure a fine co-registration of simultaneous PET-UUI acquisitions, ultrasound probes attached to an ultrafast ultrasound scanner are operated in the field of view (FOV) of a small animal PET/CT scanner using a remote-controlled micro-positioner. Her...
Source: Physics in Medicine and Biology - August 9, 2018 Category: Physics Authors: Pérez-Liva M, Viel T, Yoganathan T, Garofalakis A, Sourdon J, Facchin C, Tanter M, Provost J, Tavitian B Tags: Phys Med Biol Source Type: research

Transducer impulse response correction for a deconvolution derived ultrasound transit time spectrum.
Abstract Propagation of ultrasound through a complex composite sample may exhibit phase interference between two or more sonic-rays if differences in transit time are less than the pulse length. The transit time spectrum of a test sample, equivalent to its impulse response, was derived through active-set deconvolution of ultrasound signals with, and without, the test sample. The aim of this study was to test the hypothesis that in cases where only the transmit ultrasound transducer's digitally-coded excitation signal is available, hence not the input ultrasound signal without the test sample, incorporation of the ...
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Al-Qahtani SM, Wille ML, Langton CM Tags: Phys Med Biol Source Type: research

Dose build-up effects induced by delta electrons and target fragments in proton Bragg curves - measurements and simulations.
Abstract Dose build-up effects in the entrance channel of proton Bragg curves were investigated in detail by means of simulations and experiments. There are two relevant dose build-up effects. Firstly, the δ-electron build-up effect which takes place in the first few millimeters of the tissue until an equilibrium state of the forwards scattered δ-electrons is reached. Secondly, the target fragment build-up effect that covers the first centimeters in the entrance channel of the proton Bragg curve. These target fragments are created in inelastic interactions of the beam protons with the target nuclei and...
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Pfuhl T, Horst F, Schuy C, Weber U Tags: Phys Med Biol Source Type: research

Improved myocardial perfusion PET imaging with MRI assisted reconstruction incorporating multi-resolution joint entropy.
Abstract Myocardial perfusion (MP) PET imaging plays an important role in risk assessment and stratification of patients with coronary artery disease. In this work, we developed an anatomy-assisted maximum a posteriori (MAP) reconstruction method incorporating a wavelet-based joint entropy (WJE) prior for MP PET imaging. Using the XCAT phantom, we first simulated three MP PET datasets, one with normal perfusion and the other two with non-transmural and transmural regionally reduced perfusion of the left ventricular myocardium. Moreover, we simulated MP PET datasets of the three cases with respiratory and cardiac (...
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Wang X, Yang B, Adams MP, Gao X, Karakatsanis NA, Tang J Tags: Phys Med Biol Source Type: research

Geometrical structures for radiation biology research as implemented in the TOPAS-nBio toolkit.
Abstract Computational simulations, such as Monte Carlo track structure simulations, offer a powerful tool for quantitatively investigating radiation interactions within cells. The modelling of the spatial distribution of energy deposition events as well as diffusion of chemical free radical species, within realistic biological geometries, can help provide a comprehensive understanding of the effects of radiation on cells. Track structure simulations, however, generally require advanced computing skills to implement. The TOPAS-nBio toolkit, an extension to TOPAS (TOol for PArticle Simulation), aims to provide user...
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: McNamara AL, Ramos-Mendez J, Perl J, Held K, Dominguez N, Moreno EB, Henthorn NT, Kirkby KJ, Meylan S, Villagrasa C, Incerti S, Faddegon B, Paganetti H, Schuemann J Tags: Phys Med Biol Source Type: research

Low-rank and sparse decomposition with spatially adaptive filtering for sequential segmentation of 2D+t vessels.
Abstract This letter proposes to extract contrast-filled vessels from the overlapped noisy complex backgrounds in X-ray coronary angiogram image sequence using low-rank and sparse decomposition. A refined vessel segmentation is finally achieved by implementing Radon-like feature filtering plus local-to-global adaptive thresholding to tackle the spatially varying noisy residuals in the extracted vessels. Based on real and synthetic XCA data, experiment results show the superiority of the proposed method over the state-of-the-art methods. PMID: 30088812 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Jin M, Hao D, Ding S, Qin B Tags: Phys Med Biol Source Type: research

Density estimation of grey-level co-occurrence matrices for image texture analysis.
In conclusion, the Gaussian mixture model is the preferred method for the first type of features (in particular for small ROIs). For the second type of features, simply using a large GLCM size is preferred. PMID: 30088815 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Garpebring A, Brynolfsson P, Kuess P, Georg D, Helbich TH, Nyholm T, Löfstedt T Tags: Phys Med Biol Source Type: research

Developing a & quot;multiPatchPET & quot; system in GATE for the PET system design with irregular geometries.
Developing a &quot;multiPatchPET&quot; system in GATE for the PET system design with irregular geometries. Phys Med Biol. 2018 Aug 08;: Authors: Chen G, Weng F, Hong X, Tao W, Zhao Z, Peng Q, Huang Q Abstract This work modified the commonly used Monte Carlo tool package GATE by developing a new "multiPatchPET" system so that GATE users will be able to easily simulate PET systems with irregular geometries. The motivation was to design a brain PET scanner with high sensitivity. It is known that the compact PET scanner with a large solid coverage angle achieves high sensitivity, and thu...
Source: Physics in Medicine and Biology - August 8, 2018 Category: Physics Authors: Chen G, Weng F, Hong X, Tao W, Zhao Z, Peng Q, Huang Q Tags: Phys Med Biol Source Type: research

Monte Carlo optimization of a microbeam collimator design for use on the small animal radiation research platform (SARRP).
Abstract Microbeam radiation therapy (MRT) is a pre-clinical, spatially-fractionated treatment modality noted for its ability to achieve a large differential response between normal and tumoral tissues. In the present study, TOPAS Monte Carlo (MC) simulations were used to optimize the design of a compact, affordable multi-slit collimator (MSC) suitable for use with the small animal radiation research platform (SARRP). MRT dose distributions in a (1×1×3)cm&lt;sup&gt;3&lt;/sup&gt; water phantom were simulated for a tungsten MSC using different focal spot sizes (0.4,3mm), beam energies (40...
Source: Physics in Medicine and Biology - August 3, 2018 Category: Physics Authors: Esplen NM, Chergui L, Johnstone CD, Bazalova-Carter M Tags: Phys Med Biol Source Type: research

A simulation approach for determining the spectrum of DNA damage induced by protons.
Abstract In order to study the molecular damage induced in the form of single-strand and double-strand breaks by the ionizing radiation at the DNA level, Geant4-DNA Monte Carlo simulation code for complete transportation of primary protons and other secondary particles in liquid water have been employed in this work. To this aim, a B-DNA model and a thorough classification of DNA damage concerning their complexity were used. Strand breaks were assumed to have been primarily originated by direct physical interactions via energy depositions, assuming a threshold energy of 17.5 eV, or indirect chemical reactions of h...
Source: Physics in Medicine and Biology - August 3, 2018 Category: Physics Authors: Mokari M, Alamatsaz MH, Moeini H, Taleei R Tags: Phys Med Biol Source Type: research