Evaluation of materials used for vascular anastomoses using shear wave elastography.
In this study we used shear wave elastography (SWE) techniques to compare the mechanical behavior of excised aortas and anastomoses formed between the aortas and the Dacron, ePTFE, and PRAM materials. Different initial longitudinal strains (0-40%) and transmural pressures (20-180 mmHg) were used to test a wide range of parameters that are within physiological ranges. We found that the PRAM materials had similar mechanical behavior in terms of group velocity measured in the vessel wall with respect to the excised aortas compared to the Dacron and ePTFE that had higher values of group velocity. The ratios of the group veloci...
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Bernal M, Sen I, Urban MW Tags: Phys Med Biol Source Type: research

Semi-automated IGRT QA using a cone-shaped scintillator screen detector for proton pencil beam scanning treatments.
This study presents an alternative and more efficient approach for IGRT QA for PBS and potentially for linear accelerators. . PMID: 30736026 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Cai W, Oesten H, Clasie B, Winey B, Jee KW Tags: Phys Med Biol Source Type: research

A stochastic frontier analysis for enhanced treatment quality of high-dose-rate brachytherapy plans.
Abstract The purpose of the present study is to develop patient specific unbiased quality control (QC) models for high dose rate (HDR) brachytherapy plans. The proposed models are based on the stochastic frontier analysis formalism, a method of economic modeling. They act as a QC tool by predicting before the treatment planning process starts, the dosimetric coverage achievable for a HDR brachytherapy prostate plan. The geometric parameters considered in developing the models were: patient clinical target volume (CTV), organs at risk (OAR) volume, the bidirectional Hausdorff distance between CTV and OARs, and a f...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Edimo P, Kroshko A, Beaulieu L, Archambault L Tags: Phys Med Biol Source Type: research

Experimental measurements validate the use of the binary encounter approximation model to accurately compute proton induced dose and radiolysis enhancement from gold nanoparticles.
n AC Abstract In protontherapy, it has been suggested that nanoparticles of high-Z material like gold (GNP) be used as radiosensitizers. The origin of this enhancement phenomenon for proton radiation is not yet well understood and additional mechanistic insights are required. Previous works have highlighted the good capabilities of TRAX to reproduce secondary electron emission from gold material. Therefore, TRAX cross sections obtained with the binary encounter approximation (BEA) model for proton ionization were implemented within Geant4 for gold material. Based on the TRAX cross sections, improved Geant4 si...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Hespeels F, Lucas S, Tabarrant T, Scifoni E, Kraemer M, Chêne G, Strivay D, Tran HN, Heuskin AC Tags: Phys Med Biol Source Type: research

The effect of magnetic field strength on the response of Gafchromic EBT-3 film.
This study finds that there is at most a small effect of the magnetic field on the response of EBT-3 film. In terms of netOD (red channel) the change in response varied from ‒0.0011 at 0.5 T to 0.0045 at 2.0 T, with a standard uncertainty of 0.0030. If uncorrected, this would lead to an error in film-measured dose, for the red channel, of 2.4% at 2 T, with a standard uncertainty on dose of 1.4%. Results are also presented for B-field strengths of 0.5 T, 1 T and 1.5 T, which are all zero within the measurement uncertainty. Comparison between other studies is also presented. Considering the small change on dose deter...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Billas I, Bouchard H, Oelfke U, Duane S Tags: Phys Med Biol Source Type: research

Exploration of different X-ray Talbot-Lau setups for dark-field lung imaging examined in a porcine lung.
Abstract X-ray dark-field imaging is a promising technique for lung diagnosis. Due to the alveolar structure of lung tissue, a higher contrast is obtained by the dark-field image compared to the attenuation image. Animal studies indicate an enhancement regarding the detection of lung diseases in early stages. In this publication, we focus on the influence of different Talbot-Lau interferometer specifications while maintaining the X-ray source, sample magnification and detector system. By imaging the same porcine lung with three different grating sets, we analyze the contrast-to-noise ratio of the obtained dark-fie...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Ludwig V, Seifert 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

Impact of high dose volumetric CT on PTV margin reduction in VMAT prostate radiotherapy.
Abstract The aim of the study is to determine PTV margin for inter-observer variability in the volumetric modulated arc therapy (VMAT) prostate radiotherapy with high-dose volumetric CT (HDVCT) and conventional helical CT (CCT) for planning. Secondly to investigate the impact of geometric (PTV expansion) and dosimetric (conformity) imperfection of planning process on the PTV margin analysis. Prostate gland of ten patients were scanned with CCT and HDVCT techniques consecutively on a 320 slice volumetric CT scanner with wide field detector of 16 cm. Five radiation oncologists delineated CTV of the prostate. VMAT pl...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Cho YB, Alasti H, Kong V, Catton C, Berlin A, Chung P, Bayley A, Jaffray DA Tags: Phys Med Biol Source Type: research

Recent advances in cardiac SPECT instrumentation and imaging methods.
Abstract Cardiac SPECT continues to play a critical role in detecting and managing cardiovascular disease, in particularly coronary artery disease (CAD) (Jaarsma et al., 2012; Agostini et al., 2016). While conventional dual-head SPECT scanners using parallel-hole collimators and scintillation crystals with photomultiplier tubes are still the workhorse of cardiac SPECT, they have the limitations of low photon sensitivity (~130 count s-1 MBq-1), poor image resolution (~15 mm) (Imbert et al., 2012), relatively long acquisition time, inefficient use of the detector, high radiation dose, etc. Recently our field observe...
Source: Physics in Medicine and Biology - February 6, 2019 Category: Physics Authors: Wu J, Liu C Tags: Phys Med Biol Source Type: research

Brain SAR of average male Korean child to adult models for mobile phone exposure assessment.
Abstract This paper aims to implement average head models of Korean males and investigate age-related differences in the brain for exposure from radiation from mobile phones. Four male head models composed of a total of 69 structures were developed through a statistical investigation of the anatomical morphology for the age groups of 6, 9, 15 and 20-24 years in age, which are named KR-6, KR-9, KR-15, and KR-22 herein. Three numerical bar phone models with a dual-band built-in antenna were applied to calculate the specific absorption rate (SAR) in the brain; the body lengths of models M avg and M long have the mean...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Lee AK, Park JS, Hong SE, Taki M, Wake K, Wiart J, Choi HD Tags: Phys Med Biol Source Type: research

Fast shading correction for cone-beam CT via partitioned tissue classification.
Abstract The quantitative use of cone beam computed tomography (CBCT) in radiation therapy is limited by severe shading artifacts, even with system embedded correction. We recently proposed effective shading correction methods, using planning CT (pCT) as prior information to estimate low-frequency errors in either the projection domain or the image domain. In this work, we further improve the clinical practicality of our previous methods by removing the requirement of prior pCT images. Clinical CBCT images are typically composed of a limited number of tissue types. By utilizing the low-frequency characterist...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Shi L, Wang AS, Wei J, Zhu L Tags: Phys Med Biol Source Type: research

Quantification of myocardial uptake rate constants in dynamic small-animal SPECT using a cardiac phantom.
Abstract Myocardial blood flow and myocardial blood flow reserve (MBFR) measurements are often used clinically to quantify coronary microvascular function. Developing imaging-based methods to measure MBFR for research in mice would be advantageous for evaluating new treatment methods for coronary microvascular disease, yet this is more challenging in mice than in humans. This work investigates microSPECT's quantitative capabilities of cardiac imaging by utilizing a multi-part cardiac phantom and applying a known kinetic model to synthesize kinetic data from static data, allowing for assessment of kinetic modeling ...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Johnson LC, Guerraty MA, Moore SC, Metzler SD Tags: Phys Med Biol Source Type: research

Fast optimized Monte Carlo phase-space generation and dose prediction for low energy X-ray intra-operative radiation therapy.
, Udías JM Abstract Low energy X-ray Intra-Operative Radiation Therapy (IORT) is used mostly for breast cancer treatment with spherical applicators. X-ray IORT treatment delivered during surgery (ex: INTRABEAM®, Carl Zeiss) can benefit from accurate and fast dose prediction in a patient 3D volume. However, full Monte Carlo (MC) simulations are time-consuming and no commercial treatment planning system was available for this treatment delivery technique. Therefore, the aim of this work is to develop a dose computation tool based on MC phase space information, which computes fast and accurate dose distrib...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Vidal M, Ibáñez P, Guerra P, Valdivieso-Casique MF, Rodriguez R, Illana C, Udías JM Tags: Phys Med Biol Source Type: research

Towards patient connected imaging with ACROBEAT: Adaptive CaRdiac cOne BEAm computed Tomography.
Abstract Robotic C-arm Cone Beam Computed Tomography (CBCT) systems are playing an increasingly pivotal role in interventional cardiac procedures and high precision radiotherapy treatments. One of the main challenges in any form of cardiac imaging is mitigating the intrinsic motion of the heart, which causes blurring and artefacts in the 3D reconstructed image. Most conventional 3D cardiac CBCT acquisition techniques attempt to combat heart motion through retrospective gating techniques, whereby acquired projections are sorted into the desired cardiac phase after the completion of the scan. However, this results i...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Reynolds T, Shieh CC, Keall PJ, O'Brien RT Tags: Phys Med Biol Source Type: research

Functional imaging of tumor vasculature using iodine and gadolinium-based nanoparticle contrast agents: a comparison of spectral micro-CT using energy integrating and photon counting detectors.
Abstract Advances in computed tomography (CT) hardware have propelled the development of novel CT contrast agents. In particular, the spectral capabilities of X-ray CT can facilitate simultaneous imaging of multiple contrast agents. This approach is particularly useful for functional imaging of solid tumors by simultaneous visualization of multiple targets or architectural features that govern cancer development and progression. Nanoparticles are a promising platform for contrast agent development. While several novel imaging moieties based on high atomic number elements are being explored, iodine (I) and gadolini...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Badea CT, Clark DP, Holbrook M, Srivastava M, Mowery Y, Ghaghada KB Tags: Phys Med Biol Source Type: research

Microvascular imaging of the skin.
Abstract Despite our understanding that the microvasculature plays a multifaceted role in the development and progression of various conditions, we know little about the extent of this involvement. A need exists for non-invasive, clinically meaningful imaging modalities capable of elucidating microvascular information to aid in our understanding of disease, and to aid in the diagnosis/monitoring of disease for more patient-specific care. In this review article, a number of imaging techniques are summarized that have been utilized to investigate the microvasculature of skin, along with their advantages, disadvantag...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Deegan AJ, Wang RR Tags: Phys Med Biol Source Type: research

Regularised patient-specific stopping power calibration for proton therapy planning based on proton radiographic images.
Abstract Proton transmission imaging has been proposed and investigated as imaging modality complementary to X-ray based techniques in proton beam therapy. In particular, it addresses the issue of range uncertainties due to the conversion of an X-ray patient computed tomography (CT) image expressed in Hounsfield Units (HU) to relative stopping power (RSP) needed as input to the treatment planning system. One approach to exploit a single proton radiographic projection is to perform a patient-specific calibration of the CT to RSP conversion curve by optimising the match between a measured and a numerically integrate...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Krah N, Patera V, Rit S, Schiavi A, Rinaldi I Tags: Phys Med Biol Source Type: research

Effects of posture on electric fields of non-invasive brain stimulation.
This study aimed to determine whether small inter-postural changes in the shape of the brain can affect TDCS and TMS EFs as hypothesized. We obtained MRI from five subjects in each position and used them to build anatomically realistic models for use in finite element simulations of the EFs. Position was found to affect EFs, with them being approximately 10% stronger and more diffuse while subjects were in the prone and left lateral than in the supine positions for TDCS. In TMS, a similar trend was observed, but the effect was smaller, approximately 2%, than that observed for TDCS. Thus, the effect of posture should be con...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Mikkonen M, Laakso I Tags: Phys Med Biol Source Type: research

Malignant-benign classification of pulmonary nodules based on random forest aided by clustering analysis.
Abstract To help the radiologists better differentiate the benign from malignant pulmonary nodules on CT images, a novel classification scheme was proposed to improve the performance of benign and malignant classifier of pulmonary nodules. First, the pulmonary nodules were segmented with the references to the results from four radiologists. Then, some basic features of the segmented nodules such as the shape, gray and texture are given by calculation. Finally, malignant-benign classification of pulmonary nodules is performed by using random forest (RF) with the aid of clustering analysis. The data with a set of 95...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Wu W, Hu H, Gong J, Li X, Huang G, Nie S Tags: Phys Med Biol Source Type: research

Analytical model of DOI-induced time bias in ultra-fast scintillation detectors for TOF-PET.
Abstract In Positron Emission Tomography (PET), long crystals (≥20 mm) are used to enhance detection efficiency and increase scanner sensitivity. However, for fast time-of-flight (TOF) scanners, this may affect the achievable coincidence time resolution (CTR) due to depth-of-interaction (DOI) induced blur on timing. Currently, the effect of DOI on CTR evaluation with analytical modeling is incorporated using the probability density function (PDF) for attenuation of the annihilation photons with the PDFs of the other scintillation processes. However, we show that the resulting PDF would not describe accurately t...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Toussaint M, Loignon-Houle F, Dussault JP, Lecomte R Tags: Phys Med Biol Source Type: research

Three-dimensional radiotherapy dose prediction on head and neck cancer patients with a hierarchically densely connected U-net deep learning architecture.
Abstract The treatment planning process for patients with head and neck (H&N) cancer is regarded as one of the most complicated due to large target volume, multiple prescription dose levels, and many radiation-sensitive critical structures near the target. Treatment planning for this site requires a high level of human expertise and a tremendous amount of effort to produce personalized high quality plans, taking as long as a week, which deteriorates the chances of tumor control and patient survival. To solve this problem, we propose to investigate a deep learning-based dose prediction model, Hierarchically Den...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Nguyen D, Jia X, Sher D, Lin MH, Iqbal Z, Liu H, Jiang SB Tags: Phys Med Biol Source Type: research

Effects of transverse heterogeneities on the most likely path of protons.
Rit S Abstract The use of a most likely path (MLP) formalism for protons to account for the effects of multiple Coulomb scattering has improved the spatial resolution in proton computed tomography (pCT). However, this formalism assumes a homogeneous medium and a continuous scattering of protons. In this paper, we quantify the path prediction error induced by transverse heterogeneities to assess whether correcting for such errors might improve the spatial resolution of pCT. To this end, we have tracked protons trajectories using Monte Carlo simulations in several phantoms with different heterogeneities. Our results...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Khellaf F, Krah N, Rinaldi I, Létang JM, Rit S Tags: Phys Med Biol Source Type: research

Phantom evaluations of low frequency MR elastography.
This study explores low frequency actuation (1 Hz) MR elastography in phantoms and analyzes performance of non-linear inversion (NLI) of viscoelastic and poroelastic mechanical models as a framework for assessing clinical results from IA-MRE. We present results from four gelatin phantoms and report stiffness resolution of 6 mm (two measurement voxels) with a stiffness contrast ratio of 4.21 relative to the background and 9 mm (three measurement voxels) with a lower stiffness contrast ratio of near 1.77. Stiffness edge resolution was also evaluated using edge spread and line spread functions and yielded a stiffness edge res...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Solamen LM, Gordon-Wylie SW, McGarry MDJ, Weaver JB, Paulsen KD Tags: Phys Med Biol Source Type: research

A dual-purpose MRI acquisition to combine 4D-MRI and dynamic contrast-enhanced imaging for abdominal radiotherapy planning.
Abstract For successful abdominal radiotherapy it is crucial to have a clear tumor definition and an accurate characterization of the motion. While dynamic contrast-enhanced (DCE) MRI aids tumor visualization, it is often hampered by motion artifacts. 4D-MRI characterizes this motion, but often lacks the contrast to clearly visualize the tumor. This dual requirement is challenging due to time constraints. Here, we propose combining both into a single acquisition by reconstructing the data in various ways in order to achieve both high spatio-temporal resolution DCE-MRI and accurate 4D-MRI motion estimates....
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Stemkens B, Prins FM, Bruijnen T, Kerkmeijer LGW, Lagendijk JJW, Van den Berg CAT, Tijssen RHN Tags: Phys Med Biol Source Type: research

Unsupervised respiratory signal extraction from ungated cardiac magnetic resonance imaging at rest and during exercise.
Abstract We propose and evaluate a method to estimate a respiratory signal from ungated cardiac magnetic resonance (CMR) images. Ungated CMR images were acquired in 5 subjects who performed exercise at different intensity levels under different physiological conditions while breathing freely. The respiratory motion was estimated by applying principal components analysis (PCA). A sign correction procedure was developed to correctly define inspiration and expiration, based on either tracking of the diaphragmatic motion or estimation of the lung volume or a combination of both. Evaluation was done using a pleth...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Novillo F, Van Eyndhoven S, Moeyersons J, Bogaert J, Claessen G, La Gerche A, Van Huffel S, Claus P Tags: Phys Med Biol Source Type: research

FLUKA particle therapy tool for Monte Carlo independent calculation of scanned proton and carbon ion beam therapy.
s V Abstract While Monte Carlo (MC) codes are considered as the gold standard for dosimetric calculations, the availability of user friendly MC codes suited for particle therapy is limited. Based on the FLUKA MC code and its graphical user interface (GUI) Flair, we developed an easy-to-use tool which enables simple and reliable simulations for particle therapy. In this paper we provide an overview of functionalities of the tool and with the presented clinical, proton and carbon ion therapy examples we demonstrate its reliability and the usability in the clinical environment and show its flexibility for research pu...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Kozłowska WS, Böhlen TT, Cuccagna C, Ferrari A, Fracchiolla F, Georg D, Magro G, Mairani A, Schwarz M, Vlachoudis V Tags: Phys Med Biol Source Type: research

Data-driven voluntary body motion detection and non-rigid event-by-event correction for static and dynamic PET.
Abstract PET has the potential to perform absolute in vivo radiotracer quantitation. This potential can be compromised by voluntary body motion, which degrades image resolution, alters apparent tracer uptakes, introduces CT-based attenuation correction mismatch artifacts and causes inaccurate parameter estimates in dynamic studies. Existing body motion correction methods include frame-based image-registration (FIR) approaches and real-time motion tracking using external measurement devices. FIR does not correct for motion occurring within a pre-defined frame and the device-based method is generally not practical i...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Lu Y, Gallezot JD, Naganawa M, Ren S, Fontaine K, Wu J, Onofrey JA, Toyonaga T, Boutagy NE, Mulnix T, Panin VY, Casey ME, Carson RE, Liu C Tags: Phys Med Biol Source Type: research

Studying the effects of metallic components of PET-insert on PET and MRI performance due to gradient switching.
Abstract Inserting Positron Emission Tomography (PET) detection modules inside an MRI bore imposes extra challenges owing to the behavior of metallic materials in a strong magnetic field. The metallic parts even when placed outside an MRI field of view may not only disturb MRI performance, but could also increase temperature and vibrations, leading to premature failure of PET electronics. To investigate the compatibility of detection modules inside 3 T, 7 T and 9.4 T MRI bore, a theoretical study of the metal induced artifacts originating from component materials of electronic circuit is presented. The LabPET II d...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Moghadam N, Espagnet R, Bouchard J, Lecomte R, Fontaine R Tags: Phys Med Biol Source Type: research

Geometric discrepancy of image-guided radiation therapy in patients with prostate cancer without implanted fiducial markers using a commercial pseudo-CT generation method.
Abstract MR-only simulations provide pseudo-CT images which are segmented into 5 kinds of tissues from DIXON-based images. However, it is difficult to register pseudo-CT images to cone-beam CT (CBCT) images collected for image-guided radiation therapy (IGRT), because of the lack of contrasts among tissues. We validated gaps of IGRT between pseudo-CT or planning CT and CBCT for patients without implanted markers. We also propose calcification-assisted registration for MR-only simulation. We conducted retrospective analyses to verify the registration accuracy in 15 patients who underwent volumetric modulated ar...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Kan H, Eguchi Y, Tsuchiya T, Kondo T, Kitagawa Y, Mekata Y, Fukuma H, Yoshida R, Kasai H, Kunitomo H, Hirose Y, Shibamoto Y Tags: Phys Med Biol Source Type: research

Gender, Professional Experiences, and Personal Characteristics of Academic Radiation Oncology Chairs: Data to Inform the Pipeline for the 21st Century.
Abstract PURPOSE: Understanding the pathways and gateways to leadership and challenges faced by individuals in such roles can inform efforts to promote diversity and equity. We sought to describe the professional experiences and personal characteristics of academic Radiation Oncology (RO) Chairs, and to evaluate whether differences exist by gender. MATERIALS/METHODS: Anonymous surveys were distributed to 95 Chairs of RO departments during the 2016 annual meeting of the Society of Chairs of Academic Radiation Oncology Programs (SCAROP). The surveys included 28 closed-ended questions and the Leadership Practice...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Beeler WH, Griffith KA, Jones RD, Chapman CH, Holliday EB, Lalani N, Wilson E, Bonner JA, Formenti SC, Hahn SM, Kalnicki S, Liu FF, Movsas B, Thomas CR, Jagsi R Tags: Int J Radiat Oncol Biol Phys Source Type: research

Comparison of CT ventilation imaging and hyperpolarised gas MRI: effects of breathing manoeuvre.
Abstract Image registration of lung CT images acquired at different inflation levels has been proposed as a surrogate method to map lung 'ventilation'. Prior to clinical use, it is important to understand how this technique compares with direct ventilation imaging modalities such as hyperpolarised gas MRI. However, variations in lung inflation level have been shown to affect regional ventilation distributions. Therefore, the aim of this study was to evaluate the impact of lung inflation levels when comparing CT ventilation imaging to ventilation from 3He-MRI. 7 asthma patients underwent breath-hold CT a...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Tahir BA, Marshall H, Hughes PJC, Brightling CE, Collier G, Ireland RH, Wild JM Tags: Phys Med Biol Source Type: research

Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research.
Abstract The orthovoltage x-Ray energy frequently used in radiation research is prone to dosimetry errors due to insufficient backscatter conditions. In many radiobiology studies, especially for cell irradiations, precise dose calculation algorithms such as Convolution-Superposition or Monte Carlo are impractical and as such, less accurate hand calculation methods are used for dose estimation. These dose estimation methods typically assume full backscatter conditions. The purpose of this study is to demonstrate the magnitude of the dose error that results from insufficient backscatter, and to provide lookup tables...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Chen Q, Molloy J, Izumi T, Sterpin E Tags: Phys Med Biol Source Type: research

A comparison of hyperelastic constitutive models applicable to shear wave elastography (SWE) data in tissue-mimicking materials.
Abstract Shear wave elastography (SWE) techniques have received substantial attention in recent years. Strong experimental data in SWE suggest that shear wave speed changes significantly due to the known acoustoelastic effect (AE). This presents both challenges and opportunities toward in vivo characterization of biological soft tissues. In this work, under the framework of continuum mechanics, we model a tissue-mimicking material as a homogeneous, isotropic, incompressible, hyperelastic material. Our primary objective is to quantitatively and qualitatively compare experimentally measured acoustoelastic data wit...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Rosen DP, Jiang J Tags: Phys Med Biol Source Type: research

Development and application of a simple method for calculating breast dose from radio-guided occult lesion localisation using iodine-125 seeds (ROLLIS).
This study aims to provide a simple technique to estimate the mean absorbed dose to the breast in patients undergoing the ROLLIS procedure. The transverse plane dose rates as a function of distance for the I-125 seed were used to calculate the dose rate to voxels in a breast modelled as a hemisphere. The dose rate to each voxel was assumed to arise from an isotropic point source, and calculated using a linear interpolation of the dose rate data and the radial distance of each voxel from the seed position. Two scenarios were simulated: (i) One seed at the centre of the lesion; and (ii) Two seeds bracketing the lesion. ...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Reed AJ, Kim JH, Burrage JW Tags: Phys Med Biol Source Type: research

Optical elastography: tracking surface waves with digital image correlation.
Abstract Elastography consists in evaluating the propagation speed of waves into a tissue to estimate its stiffness. Usually this method is based on Ultrasounds, Magnetic Resonance Imaging or Optical coherent tomography. This paper proposes a simple optic method using ultrafast cameras. Based on Digital Image Correlation (DIC), the tracking of elastic surface wave from white light intensity pattern, allows estimating the propagation speed as an indicator of the tissue local stiffness. Two configurations are presented: (1) 2D imaging of a flat phantom surface with a single camera and (2) 3D imaging of a curved phan...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Zorgani A, Abdul Ghafour T, Lescanne M, Catheline S, Bel-Brunon A Tags: Phys Med Biol Source Type: research

First prototyping of a dedicated PET system with the hemisphere detector arrangement.
In this study, we developed the first prototype system for proof-of-concept using 4-layer depth-of-interaction detectors, each of which consisted of 16×16×4 Zr-doped GSO crystals with dimensions of 2.8×2.8×7.5 mm3 and a high-sensitivity 64-channel flat-panel photomultiplier tube. We used 47 detectors to form a hemisphere detector with a hemisphere shape of 25 cm inner diameter and 50 cm outer diameter, and we used seven detectors for each of the add-on detectors. The total detector number of 54 was about one-fourth that of a typical whole-body PET scanner. The hemisphere detector for the prototype s...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Tashima H, Yoshida E, Iwao Y, Wakizaka H, Maeda T, Seki C, Kimura Y, Takado Y, Higuchi M, Suhara T, Yamashita T, Yamaya T Tags: Phys Med Biol Source Type: research

A linear relationship for the LET-dependence of Gafchromic EBT3 film in spot-scanning proton therapy.
Abstract Radiochromic film is a valuable dosimetric tool, primarily due to its sub-millimeter spatial resolution. For accurate proton dosimetry, the dependence of film response on linear energy transfer must be characterized and calibrated. In this work, we characterized film under-response, or "quenching," as a function of dose-weighted linear energy transfer (LETd) in several proton fields and established a simple, linear relationship with LETd. We performed measurements as a function of depth in a PMMA phantom irradiated by a spot-scanning proton beam. The fields had energies of 71.3 MeV, ...
Source: Physics in Medicine and Biology - January 23, 2019 Category: Physics Authors: Anderson SE, Grams MP, Wan Chan Tseung H, Furutani KM, Beltran CJ Tags: Phys Med Biol Source Type: research

Numerical workflow of irreversible electroporation for deep-seated tumor.
Abstract The paper provides a numerical workflow, based on the ``real-life" clinical workflow of irreversible electroporation (IRE) performed for the treatment of deep-seated liver tumors. Thanks to a combination of numerical modeling, image registration algorithm and clinical data, our numerical workflow enables to provide the distribution of the electric field as effectively delivered by the clinical IRE procedure. As a proof of concept, we show on a specific clinical case of IRE ablation of liver tumor that clinical data could be advantageously combined to numerical simulations in a near future, in order t...
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Gallinato O, Denis de Senneville B, Seror O, Poignard C Tags: Phys Med Biol Source Type: research

Annihilation gamma imaging for carbon ion beam range monitoring using Si/CdTe Compton camera.
In this study, we performed on-beam monitoring of 511-keV annihilation gamma emissions using a Compton camera. Beam monitoring experiments were conducted using carbon ion beams of 290 MeV/u irradiated on a polymethyl methacrylate (PMMA) phantom. The intensity of the beams was 3e9 particles per pulse, with 20 pulses per minute. A Compton camera based on a silicon/cadmium telluride (Si/CdTe) detector was used to monitor the annihilation gamma rays emitted from the phantom. We successfully reconstructed the energy events of 511-keV annihilation gamma rays and developed Compton images using a simple back-projection method. The...
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Parajuli RK, Sakai M, Kada W, Torikai K, Kikuchi M, Arakawa K, Torikoshi M, Nakano T Tags: Phys Med Biol Source Type: research

Quantitative analysis of regional endocardial geometry dynamics from 4D cardiac CT images: endocardial tracking based on the iterative closest point with an integrated scale estimation.
Abstract Regional cardiac function analysis is important for the diagnosis and treatment planning of ischemic heart disease, but has not been sufficiently developed in the field of computed tomography (CT). Therefore, we propose a three-dimensional endocardial tracking framework for cardiac CT using local point cloud registration based on the iterative closest point with an integrated scale estimation algorithm. We also introduce regional function descriptors that express the curvature and stretching of the endocardium: Surface distortion (E) and Scaling rate (S). For a region-to-region comparison, we propose endo...
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Kobayashi K, Wakasa S, Sato K, Kanai S, Date H, Kimura S, Oyama-Manabe N, Matsui Y Tags: Phys Med Biol Source Type: research

Automatic 3D cephalometric annotation system using shadowed 2D image-based machine learning.
Abstract This paper presents a new approach to automatic three-dimensional (3D) cephalometric annotation for diagnosis, surgical planning, and treatment evaluation. There has long been considerable demand for automated cephalometric landmarking, since manual landmarking requires considerable time and experience as well as objectivity and scrupulous error avoidance. Due to the inherent limitation of two-dimensional (2D) cephalometry and the 3D nature of surgical simulation, there is a trend away from current 2D to 3D cephalometry. Deep learning approaches to cephalometric landmarking seem highly promising, but ther...
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Lee SM, Kim HP, Jeon K, Lee SH, Seo JK Tags: Phys Med Biol Source Type: research

Analysis of radioactive waste generated during the cyclotron production of < sup > 99m < /sup > Tc.
In conclusion, it was determined that the waste generated during cyclotron-based &lt;sup&gt;99m&lt;/sup&gt;Tc production was acceptably low for routine clinical production. PMID: 30669132 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Stothers LA, Hou X, Vuckovic M, Buckley KR, Bénard F, Schaffer P, Celler A Tags: Phys Med Biol Source Type: research

Feasibility of MRI-only photon and proton dose calculations for pediatric patients with abdominal tumors.
Abstract The purpose of this study was to develop a method enabling synthetic computed tomography (sCT) generation of the whole abdomen using magnetic resonance imaging (MRI) images of pediatric patients with abdominal tumors. The proposed method relies on an automatic atlas-based segmentation of bone and lungs followed by an MRI intensity to synthetic Hounsfield unit conversion. Separate conversion algorithms were used for bone, lungs and soft-tissue. Rigidly registered CT and T2-weighted MR images of 30 patients in treatment position and with the same field of view were used for the evaluation of the atlas and t...
Source: Physics in Medicine and Biology - January 22, 2019 Category: Physics Authors: Guerreiro F, Koivula L, Seravalli E, Janssens GO, Maduro JH, Brouwer CL, Korevaar EW, Knopf AC, Korhonen J, Raaymakers BW Tags: Phys Med Biol Source Type: research

Dual layer doI detector modules for a dedicated mouse brain PET/MRI.
Abstract The outcome of preclinical imaging studies are enhanced by simultaneous, high-resolution anatomical and molecular data, which advanced PET/MRI systems provide. Nevertheless, mapping of neuroreceptors and accurate quantification of PET tracer distribution in mouse brains is not trivial. The restricted spatial resolution and sensitivity in commercial animal PET systems limits the image quality and the quantification accuracy. We are currently developing a PET/MRI system dedicated for mouse brain studies. The PET system will offer system dimensions of approx. 30 mm in diameter and an axial length of more tha...
Source: Physics in Medicine and Biology - January 17, 2019 Category: Physics Authors: Parl C, Kolb A, Stricker-Shaver D, Pichler BJ Tags: Phys Med Biol Source Type: research

Modeling the binding and diffusion of receptor-targeted nanoparticles topically applied on fresh tissue specimens.
Abstract Nanoparticle (NP) contrast agents targeted to cancer biomarkers are increasingly being engineered for the early detection of cancer, guidance of therapy, and monitoring of response. There have been recent efforts to topically apply biomarker-targeted NPs on tissue surfaces to image the expression of cell-surface receptors over large surface areas as a means of evaluating tumor margins to guide wide local excision surgeries. However, diffusion and nonspecific binding of the NPs present challenges for relating NP retention on the tissue surface with the expression of cancer cell receptors. Paired-agent meth...
Source: Physics in Medicine and Biology - January 17, 2019 Category: Physics Authors: Kang S, Xu X, Navarro E, Wang Y, Liu JTC, Tichauer KM Tags: Phys Med Biol Source Type: research

Pulmonary blood mass dynamics on 4DCT during tidal breathing.
In this study, we characterize and quantify the respiratory induced variation in pulmonary blood mass (∆PBM) on 89 patients treated with stereotactic body radiotherapy. ∆PBM was computed from the treatment planning helical 4DCT images of each patient. Conversion from Hounsfield Units (HU) to density and mass per voxel was made using the density calibration curve, applied to the lung parenchyma volume within each phase. A difference in the lung mass with breathing was found for all cases, as was a substantial individual variation in lung volume. We found that the ∆PBM increased during inhalation, and decreased during ...
Source: Physics in Medicine and Biology - January 17, 2019 Category: Physics Authors: Myziuk NK, Guerrero TM, Sakthivel G, Solis DE, Nair GB, Guerra R, Castillo E Tags: Phys Med Biol Source Type: research

Tissue-mimicking materials for breast phantoms up to 50 GHz.
Abstract Millimeter (mm)-wave imaging has been recently proposed as a new technique for breast cancer detection, based on the significant dielectric contrast between healthy and tumor tissues. Here we propose a procedure to fabricate, electromagnetically characterize and preserve realistic breast tissue-mimicking phantoms for testing mm-wave imaging prototypes. Low-cost, non-toxic and easy-to-produce mixtures made of sunflower oil, water and gelatin were prepared and their dielectric properties were for the first time measured in the [0.5-50] GHz frequency range using a coaxial probe kit. Different oil and gelatin...
Source: Physics in Medicine and Biology - January 16, 2019 Category: Physics Authors: Di Meo S, Pasotti L, Iliopoulos I, Pasian M, Ettore M, Zhadobov M, Matrone G Tags: Phys Med Biol Source Type: research

Introducing the concept of spiral microbeam radiation therapy (spiralMRT).
Conclusions SpiralMRT is a promising approach to delivering homogeneous dose distributions with spatially fractionated entrance beams, possibly decreasing normal tissue side effects in hypofractionated RT. PMID: 30650386 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - January 16, 2019 Category: Physics Authors: Donzelli M, Oelfke U, Brauer-Krisch E Tags: Phys Med Biol Source Type: research

Cardiac motion correction for improving perfusion defect detection in cardiac SPECT at standard and reduced doses of activity.
In this study, we investigated the potential benefit of cardiac motion correction for improving the detectability of perfusion defects. We considered a post-reconstruction motion correction (PMC) approach in which the image motion between two cardiac gates is obtained with optical flow estimation (OFE). In the experiments, we demonstrated the proposed PMC-OFE approach on a set of clinical acquisitions from 194 subjects. We quantified the detectability of perfusion defects in the reconstructed images by using the total perfusion deficit (TPD) scores, calculated by the clinical software tool QPS, and conducted a ...
Source: Physics in Medicine and Biology - January 16, 2019 Category: Physics Authors: Song C, Yang Y, Wernick MN, Pretorius PH, Slomka PJ, King MA Tags: Phys Med Biol Source Type: research

Performance evaluation of a small animal PET scanner a high level of multiplexing and charge-signal transmission.
Abstract Small animal positron emission tomography (PET) is a noninvasive imaging modality that enables in vivo imaging and quantification of the biological processes of small experimental animals. We have developed a small animal PET that utilizes a high-resolution multiplexed readout and charge signal transmission method. The small animal PET was composed of 6 detector blocks consisting of SiPMs and LYSO arrays. Six detector blocks were mounted on a PET gantry having an inner diameter of 76 mm, outer diameter of 112 mm, and axial length of 40.8 mm. The charge signals of SiPM output were transmitted to the input ...
Source: Physics in Medicine and Biology - January 16, 2019 Category: Physics Authors: Lee S, Choi Y, Jung JH, Jung J, Kim KB, Choe HJ, Leem HT, Lee H, Huh YM Tags: Phys Med Biol Source Type: research

A novel methodology to assess linear energy transfer and relative biological effectiveness in proton therapy using pairs of differently doped thermoluminescent detectors.
Abstract A new methodology for assessing linear energy transfer (LET) and relative biological effectiveness (RBE) in proton therapy beams using thermoluminescent detectors is presented. The method is based on the different LET response of two different lithium fluoride thermoluminescent detectors (LiF:Mg,Ti and LiF:Mg,Cu,P) for measuring charged particles. The relative efficiency of the two detector types was predicted using the recently developed Microdosimetric d(z) Model in combination with the Monte Carlo code PHITS. Afterwards, the calculated ratio of the expected response of the two detector types was correl...
Source: Physics in Medicine and Biology - January 16, 2019 Category: Physics Authors: Parisi A, Chiriotti S, De Saint-Hubert M, Van Hoey O, Vandevoorde C, Beukes P, de Kock EA, Symons J, Nieto-Camero J, Slabbert J, Megret P, Debrot E, Bolst D, Rozenfeld AB, Vanhavere F Tags: Phys Med Biol Source Type: research