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

Automated classification of benign and malignant lesions in 18F-NaF PET/CT images using machine learning.
CONCLUSION: We have developed the first whole-body automatic disease classification tool for NaF PET using RF, and demonstrated its ability to replicate different physicians' classification tendencies. This enables fully-automated analysis of whole-body NaF PET/CT images. PMID: 30457118 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 20, 2018 Category: Physics Authors: Perk T, Bradshaw T, Chen S, Im HJ, Cho S, Perlman S, Liu G, Jeraj R Tags: Phys Med Biol Source Type: research

Validation of fast motion-including dose reconstruction for proton scanning therapy in the liver.
This study validates a method of fast motion-including dose reconstruction for proton pencil beam scanning in the liver. The method utilizes a commercial treatment planning system (TPS) and calculates the delivered dose for any translational 3D target motion. Data from ten liver patients previously treated with photon radiotherapy with intrafraction tumour motion monitoring were used. The dose reconstruction method utilises an in-house developed program to incorporate beam's-eye-view tumour motion by shifting each spot in the opposite direction of the tumour and in-depth motion as beam energy changes for each spot. The dos...
Source: Physics in Medicine and Biology - November 20, 2018 Category: Physics Authors: Colvill E, Petersen JBB, Hansen R, Worm E, Skouboe S, Høyer M, Poulsen PR Tags: Phys Med Biol Source Type: research

MRI-guidance for motion management in external beam radiotherapy: current status and future challenges.
Abstract High precision conformal radiotherapy requires sophisticated imaging techniques to aid in target localisation for planning and treatment, particularly when organ motion due to respiration is involved. X-ray based imaging is a well-established standard for radiotherapy treatments. Over the last few years, the ability of magnetic resonance imaging (MRI) to provide radiation-free images with high-resolution and superb soft tissue contrast has highlighted the potential of this imaging modality for radiotherapy treatment planning and motion management. In addition, these advantageous properties motivated sever...
Source: Physics in Medicine and Biology - November 20, 2018 Category: Physics Authors: Paganelli C, Whelan B, Peroni M, Summers P, Fast M, van de Lindt T, McClelland J, Eiben B, Keall P, Lomax T, Riboldi M, Baroni G Tags: Phys Med Biol Source Type: research

Radiation Therapy Outcomes Models in the Era of  Radiomics and Radiogenomics: Uncertainties and Validation.
Radiation Therapy Outcomes Models in the Era of Radiomics and Radiogenomics: Uncertainties and Validation. Int J Radiat Oncol Biol Phys. 2018 Nov 15;102(4):1070-1073 Authors: El Naqa I, Pandey G, Aerts H, Chien JT, Andreassen CN, Niemierko A, Ten Haken RK PMID: 30353869 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 27, 2018 Category: Physics Authors: El Naqa I, Pandey G, Aerts H, Chien JT, Andreassen CN, Niemierko A, Ten Haken RK Tags: Int J Radiat Oncol Biol Phys Source Type: research

"Wisest Is He Who Knows What He Does Not Know."
"Wisest Is He Who Knows What He Does Not Know." Int J Radiat Oncol Biol Phys. 2018 Nov 15;102(4):687-690 Authors: Marks LB, Tepper JE PMID: 30353877 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 27, 2018 Category: Physics Authors: Marks LB, Tepper JE Tags: Int J Radiat Oncol Biol Phys Source Type: research

Ultrasonic fat fraction quantification using in vivo adaptive sound speed estimation.
Abstract The non-invasive quantification of human tissue fat fraction using easily scalable and accessible imaging technologies is crucial for the diagnosis of many diseases including liver steatosis. Here, we propose a non-invasive quantification of fat content using a highly accessible ultrasonic imaging technology. Ultrasonic echoes backscattered from human liver tissues are recombined to synthetize echoes of a virtual point-like reflector within the organs. This virtual point-like reflector is an ultrasonic analogue of artificial stars generated by laser beams in the field of astronomy, which are used to estim...
Source: Physics in Medicine and Biology - October 26, 2018 Category: Physics Authors: Imbault M, Burgio MD, Faccinetto A, Ronot M, Bendjador H, Deffieux T, Triquet EO, Rautou PE, Castera L, Gennisson JL, Vilgrain V, Tanter M Tags: Phys Med Biol Source Type: research

Continuous aperture dose calculation and optimization for volumetric modulated arc therapy.
Abstract Although VMAT delivery features continuous gantry rotation and leaf motion, dose calculation is often performed under the dual assumption of discrete apertures changing instantaneously from one discrete angle to the next. In this work, the validity of these two approximations is determined, as well as their impact on the quality of optimized plans. Further, an accurate method of fluence calculation is derived which does not use the discrete aperture approximation, but instead calculates the fluence as the multi-leaf collimator leaves sweep from one position to another. This continuous aperture fluence cal...
Source: Physics in Medicine and Biology - October 26, 2018 Category: Physics Authors: Christiansen E, Heath E, Xu T Tags: Phys Med Biol Source Type: research

Clinical applications of in vivo magnetic resonance spectroscopy in oncology.
Abstract Magnetic resonance spectroscopy (MRS) can be performed in vivo using commercial MRI systems to obtain biochemical information about tissues and cancers. Applications in brain, prostate and breast aid lesion detection and characterisation (differential diagnosis), treatment planning and response assessment. Multi-centre clinical trials have been performed in all these tissues. Single centre studies have been performed in many other tissues including cervix, uterus, musculoskeletal and liver. While generally MRS is used to study endogenous metabolites it has also been used in drug studies, for example those...
Source: Physics in Medicine and Biology - October 26, 2018 Category: Physics Authors: Payne GS Tags: Phys Med Biol Source Type: research

Spatial domain reconstruction for imaging speed-of-sound with pulse-echo ultrasound: simulation and in vivo study.
Abstract Despite many uses of ultrasound, some pathologies such as breast cancer still cannot reliably be diagnosed in either conventional B-mode ultrasound imaging nor with more recent ultrasound elastography methods. Speed-of-sound (SoS) is a quantitative imaging biomarker, which is sensitive to structural changes due to pathology, and hence could facilitate diagnosis. Full-angle ultrasound computed tomography (USCT) was proposed to obtain spatially-resolved SoS images, however, its water-bath setup involves practical limitations. To increase clinical utility and for widespread use, recently, a limited-angle Fou...
Source: Physics in Medicine and Biology - October 26, 2018 Category: Physics Authors: Sanabria SJ, Ozkan E, Rominger M, Goksel O Tags: Phys Med Biol Source Type: research

A momentum-based diffeomorphic demons framework for deformable MR-CT image registration.
We report a multi-modality, diffeomorphic, deformable registration method using momentum-based acceleration of the Demons algorithm to solve the transformation relating preoperative MRI and intraoperative CT as a basis for high-precision guidance. The registration method (pMI-Demons) extends the mono-modality, diffeomorphic form of the Demons algorithm to multi-modality registration using pointwise mutual information (pMI) as a similarity metric. The method incorporates a preprocessing step to nonlinearly stretch CT image values and incorporates a momentum-based approach to accelerate convergence. Registration performance ...
Source: Physics in Medicine and Biology - October 24, 2018 Category: Physics Authors: Han R, De Silva T, Ketcha M, Uneri A, Siewerdsen JH Tags: Phys Med Biol Source Type: research

Optimisation of the design of SOI microdosimeters for hadron therapy quality assurance.
Abstract Silicon-on-insulator (SOI) microdosimeters offer a promising method for routine quality assurance (QA) for hadron therapy due to their ease of operation and high spatial resolution. However, one complication which has been shown previously is that the traditional use of the mean chord length, [Formula: see text], calculated using Cauchy's formula, for SOI devices in clinical carbon ion fields is not appropriate due to the strong directionality of the radiation field. In a previous study, we demonstrated that the mean path length, [Formula: see text], which is the mean path of charged particles in the sens...
Source: Physics in Medicine and Biology - October 24, 2018 Category: Physics Authors: Bolst D, Guatelli S, Tran LT, Rosenfeld AB Tags: Phys Med Biol Source Type: research

A large aperture row column addressed probe for in vivo 4D ultrafast doppler ultrasound imaging.
In this study, we investigate the row and column addressed (RCA) approach with the orthogonal plane wave (OPW) compounding strategy using real hardware limitations. We designed and built a large 7 MHz 128  +  128 probe dedicated to vascular imaging and connected to a 256-channel scanner to implement the OPW imaging scheme. Using this strategy, we demonstrate that 4D ultrafast Power Doppler imaging of a large volume of [Formula: see text] up to [Formula: see text] depth, both in vitro on flow phantoms and in vivo on the carotid artery of a healthy volunteer at a volume rate of 834 Hz. PMID: ...
Source: Physics in Medicine and Biology - October 24, 2018 Category: Physics Authors: Sauvage J, Flesch M, Férin G, Nguyen-Dinh A, Porée J, Tanter M, Pernot M, Deffieux T Tags: Phys Med Biol Source Type: research

A model-based approach to investigate the effect of elevated interstitial fluid pressure on strain elastography.
Abstract Finite element (FE) modeling provides a useful tool to understand the mechanical behavior of complex tissues, such as cancers, in a variety of testing conditions. Although a number of numerical and analytical models for cancerous tumors are retrievable in the literature, none of these models is capable of completely describing the behavior of a cancer embedded in a normal tissue in the conditions typical for an ultrasound elastography experiment. In this paper, we first design and implement a realistic FE model of the mechanical behavior of a cancer embedded in a normal tissue under ultrasound elastograph...
Source: Physics in Medicine and Biology - October 24, 2018 Category: Physics Authors: Islam MT, Reddy JN, Righetti R Tags: Phys Med Biol Source Type: research

Two dimensional noise reconstruction in proton computed tomography using distance-driven filtered back-projection of simulated projections.
We present a formalism for two dimensional (2D) noise reconstruction in proton computed tomography (pCT). This is necessary for the application of fluence modulated pCT (FMpCT) since it permits image noise prescription and the corresponding proton fuence optimization. We aimed at extending previously published formalisms to account for the impact of multiple Coulomb scattering (MCS) on projection noise, and the use of filtered back projection (FBP) reconstruction along \hl{curved paths} with distance driven binning (DDB). 2D noise reconstruction for a beam of protons with parallel initial momentum vectors, and ...
Source: Physics in Medicine and Biology - October 2, 2018 Category: Physics Authors: Rädler M, Landry G, Rit S, Schulte RW, Parodi K, Dedes G Tags: Phys Med Biol Source Type: research

Reliable gene mutation prediction in clear cell renal cell carcinoma through multi-classifier multi-objective radiogenomics model.
Abstract Genetic studies have identified associations between gene mutations and clear cell renal cell carcinoma (ccRCC). Since the complete gene mutational landscape cannot be characterized through biopsy and sequencing assays for each patient, non-invasive tools are needed to determine the mutation status for tumors. Radiogenomics may be an attractive alternative tool to identify disease genomics by analyzing amounts of features extracted from medical images. Most current radiogenomics predictive models are built based on a single classifier and trained through a single objective. However, since many classifiers...
Source: Physics in Medicine and Biology - October 2, 2018 Category: Physics Authors: Chen X, Zhou Z, Hannan R, Thomas K, Pedrosa I, Kapur P, Brugarolas J, Mou X, Wang J Tags: Phys Med Biol Source Type: research

Improvement of image quality in PET imaging using post-reconstruction hybrid spatial-frequency domain filtering.
Abstract PET images commonly suffer from the high noise level and poor signal-to-noise ratio (SNR), thus adversely impacting lesion detectability and quantitative accuracy. In this work, a novel hybrid dual-domain PET denoising approach is proposed, which combines the advantages of both spatial and transform domain filtering to preserve image textures while minimizing quantification uncertainty. Spatial domain denoising techniques excel at preserving high-contrast patterns compared to transform domain filters, which perform well in recovering low-contrast details normally smoothed out by spatial domain filters. Fo...
Source: Physics in Medicine and Biology - October 1, 2018 Category: Physics Authors: Arabi H, Zaidi H Tags: Phys Med Biol Source Type: research

Robust selective weighted field mapping using multi-echo gradient echo-based MRI.
Abstract In 3D gradient echo (GRE) and echo planar imaging (EPI), strong macroscopic field gradients are observed at air/tissue interfaces. The respective field gradients lead to an apparent increase in intravoxel dephasing, and, subsequently, to signal loss or image distortion. We propose an analytical approximation and a consequent method to compute low and high resolution field maps over all field map regimes (small and large echo spacing). A number of approaches which compute field maps from reconstructed phase data rely upon optimized linear least square fit and complex division approaches owing to the simpli...
Source: Physics in Medicine and Biology - October 1, 2018 Category: Physics Authors: Fatnassi C, Zaidi H Tags: Phys Med Biol Source Type: research

Spatial-temporal variability of radiomic features and its effect on the classification of lung cancer histology.
Conclusions: Several radiomic features have been identified as being relatively robust to spatial-temporal variations based on both simulation data and patient data. In general, features that were sensitive to motion blurring were not necessarily the same features that were sensitive to changes in SNR. Our modeling results suggest that the EoE phase of a 4DCT acquisition may provide useful radiomic information, particularly for features that are highly sensitive to respiratory motion. . PMID: 30272571 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 1, 2018 Category: Physics Authors: Lafata K, Cai J, Wang C, Hong J, Kelsey CR, Yin FF Tags: Phys Med Biol Source Type: research

Threshold-dependent nonlinear scattering from porphyrin nanobubbles for vascular and extravascular applications.
Abstract Nanobubbles hold potential for expanding utility of ultrasound contrast-based applications to extravascular targets, but their acoustic response and the effects of the surrounding environment remain relatively unexplored. Here we investigate the dynamics of porphyrin-encapsulated nanobubbles (diameter <0.4 µm; 10^6 mL-1) at clinically relevant frequencies (2.5 MHz and 8 MHz) as a function of pressure (0.2 - 1.0 MPa) in vessel- and tissue-mimicking phantoms to gain an understanding of nanobubble behaviour in intra- and extravascular compartments. The results provide the first direct observatio...
Source: Physics in Medicine and Biology - October 1, 2018 Category: Physics Authors: Pellow C, Acconcia CN, Zheng G, Goertz DE Tags: Phys Med Biol Source Type: research

Nuts and bolts of 4D-MRI for radiotherapy.
Abstract Magnetic Resonance Imaging (MRI) is increasingly being used in the radiotherapy workflow because of its superior soft tissue contrast and high flexibility in contrast. In addition to anatomical and functional imaging, MRI can also be used to characterize the physiologically induced motion of both the tumor and organs-at-risk. Respiratory-correlated 4D-MRI has gained large interest as an alternative to 4D-CT for the characterization of respiratory motion throughout the thorax and abdomen. Over the last 15 years numerous methods have been presented in literature. This review article provides a comprehensive...
Source: Physics in Medicine and Biology - October 1, 2018 Category: Physics Authors: Stemkens B, Paulson ES, Tijssen RHN Tags: Phys Med Biol Source Type: research

Iterative quality enhancement via residual-artifacts learning networks for low-dose CT.
Abstract Radiation exposure and the associated risk of cancer for patients in computed tomography (CT) scans have been major clinical concerns. The radiation exposure can be reduced effectively via lowering X-ray tube current (mA). However, this strategy may lead to excessive noise and streak artifacts in the conventional filtered back-projection reconstructed images. To address this issue, some deep convolutional neural network (ConvNet) based approaches have been developed for low-dose CT imaging inspired by the recent development of machine learning. Nevertheless, some of the image textures reconstructed by the...
Source: Physics in Medicine and Biology - September 28, 2018 Category: Physics Authors: Wang Y, Zeng D, Zhang Y, He J, Li S, Liao Y, Bian Z, Zhang H, Gao Y, Meng D, Zuo W, Ma J Tags: Phys Med Biol Source Type: research

Quantitative comparison of human myocardial fiber orientations derived from DTI and polarized light imaging.
Abstract Diffusion tensor imaging (DTI) is a non-invasive technique used to obtain the three-dimensional fiber structure of whole human hearts, for both in vivo and ex vivo cases. However, by essence, DTI does not measure directly the orientations of myocardial fibers. In contrast, polarized light imaging (PLI) allows for physical measurements of fiber orientations, but only for ex vivo case. This work aims at quantitatively comparing the myocardial fiber orientations of whole human hearts obtained from cardiac DTI with those measured by PLI. Whole human neonatal and infant hearts were first imaged using DTI. The ...
Source: Physics in Medicine and Biology - September 28, 2018 Category: Physics Authors: Yang F, Zhu YM, Michalowicz G, Jouk PS, Fanton L, Viallon M, Clarysse P, Croisille P, Usson Y Tags: Phys Med Biol Source Type: research

Resolution and registration in dual-plane co-RASOR MR.
Abstract Magnetic resonance imaging (MRI) has superior soft tissue contrast and lower interobserver variability compared to computed tomography and advances in equipment and pseudo-CT estimation have allowed for MR-only radiation therapy planning. Dedicated MR sequences have been used to localize paramagnetic structures with positive contrast, and most implanted seeds are gold fiducial markers (GFMs). We used a fast, dual-plane co-RASOR sequence to localize implanted GFMs with positive contrast in phantom and tissue to assess their resolution and registration accuracy of registration to CT. Off-resonant recon...
Source: Physics in Medicine and Biology - September 27, 2018 Category: Physics Authors: McNabb E, Wong R, Noseworthy MD Tags: Phys Med Biol Source Type: research

Inter-institutional variability of small-field-dosimetry beams among HD120 < sup > TM < /sup > multileaf collimators: a multi-institutional analysis.
In conclusion, this multi-institutional investigation of small field dosimetry for HD120 multileaf collimators demonstrated some large variations in the dosimetric parameters, especially for a 5-mm square field size. Most differences were detector-dependent, and the variation was reduced when output correction factors were applied. However, variations probably due to measurement errors were also observed, indicating that careful management is needed for small-field dosimetry. PMID: 30255847 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 26, 2018 Category: Physics Authors: Akino Y, Mizuno H, Tanaka Y, Isono M, Masai N, Yamamoto T Tags: Phys Med Biol Source Type: research

Applying a new maximum local asymmetry feature analysis method to improve near-term breast cancer risk prediction.
Conclusions - The study demonstrated that near-term breast cancer risk prediction could be improved by using the proposed feature extraction method. . PMID: 30255850 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 26, 2018 Category: Physics Authors: Yan S, Zhang L, Song C Tags: Phys Med Biol Source Type: research

Delivery efficiency and susceptibility to setup uncertainties of flattening filter free lung SBRT: influence of isocentre geometry and treatment modality.
This study used a cohort of ten patients to investigate the sensitivity of OAG SBRT lung plans to offsets in the isocentre position and compared it to those where the isocentre is placed at the centre of the target volume, i.e. central axis geometry (CAG). Comparisons were made for SBRT treatment plans using 3D conformal radiotherapy (3DCRT) and volumetric modulated arc therapy (VMAT). No statistically significant difference was found between OAG and CAG for SBRT treatments delivered with either 3DCRT or VMAT techniques in terms of plan quality metrics. Planned monitor units for 3DCRT plans were significantly less (p&l...
Source: Physics in Medicine and Biology - September 26, 2018 Category: Physics Authors: Tyler M, Dowdell S Tags: Phys Med Biol Source Type: research

A single-optical kernel for a phosphor-screen-based geometric QA system (RavenQA < sup > TM < /sup > ) as a tool for patient-specific IMRT/VMAT QA.
Conclusions: It is feasible to perform the patient-specific IMRT/VMAT verification with a single kernel using a commercially available phosphor-screen-based mechanical QA device in accordance with AAPM TG-142. It is also practical to implement since it only requires to measure the optical intensities of the field centers of several square fields, in order to obtain the OSK. . PMID: 30255855 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 26, 2018 Category: Physics Authors: Lee M, Ding K, Yi BY Tags: Phys Med Biol Source Type: research

A large aperture row column addressed probe for < i > in vivo < /i > 4D ultrafast doppler ultrasound imaging.
In this study, we designed and built a new Row and Column Adressed (RCA) probe dedicated to vascular imaging and investigated it with a specific Orthogonal Plane Wave (OPW) compounding strategy (Flesch et al., 2017). Using this prototype, 4D ultrafast Power Doppler imaging of a large volume of 25.6×25.6 mm² up to 40 mm depth is demonstrated in vitro on flow phantoms and vivo on the carotid artery of a healthy volunteer at a volume rate of 834 Hz. PMID: 30251966 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 25, 2018 Category: Physics Authors: Sauvage J, Flesch M, Ferin G, Nguyen-Dinh A, Poree J, Tanter M, Pernot M, Deffieux T Tags: Phys Med Biol Source Type: research

Experimental validation of the FLUKA Monte Carlo code for dose and β < sup > + < /sup > -emitter predictions of radioactive ion beams.
Experimental validation of the FLUKA Monte Carlo code for dose and β+-emitter predictions of radioactive ion beams. Phys Med Biol. 2018 Sep 25;: Authors: Augusto RS, Mohammadi A, Tashima H, Yoshida E, Yamaya T, Ferrari A, Parodi K Abstract In the context of hadrontherapy, whilst ions are capable of effectively destroying radio resistant, deep seated tumors, their treatment localization must be well assessed to ensure the sparing of surrounding healthy tissue and treatment effectiveness. Thus, range verification techniques, such as online positron-emission-tomography (PET) imaging, hold great pote...
Source: Physics in Medicine and Biology - September 25, 2018 Category: Physics Authors: Augusto RS, Mohammadi A, Tashima H, Yoshida E, Yamaya T, Ferrari A, Parodi K Tags: Phys Med Biol Source Type: research

Meshfree simulations of ultrasound vector flow imaging using smoothed particle hydrodynamics.
Abstract Before embarking on a series of &lt;i&gt;in vivo&lt;/i&gt; tests, design of ultrasound-flow-imaging modalities are generally more efficient through computational models as multiple configurations can be tested methodically. To that end, simulation models must generate realistic blood flow dynamics and Doppler signals. The current &lt;i&gt;in silico&lt;/i&gt; ultrasound simulation techniques suffer mainly from uncertainty in providing accurate trajectories of moving ultrasound scatterers. In mesh-based Eulerian methods, numerical truncation errors from the interpolated veloc...
Source: Physics in Medicine and Biology - September 24, 2018 Category: Physics Authors: Shahriari S, Garcia D Tags: Phys Med Biol Source Type: research

Learning SPECT detector angular response function with neural network for accelerating Monte-Carlo simulations.
Abstract A method to speed-up Monte-Carlo simulations of Single Photon Emission Computed Tomography (SPECT) imaging is proposed. It uses an artificial neural network (ANN) to learn the Angular Response Function (ARF) of a collimator-detector system. The ANN is trained once from a complete simulation including the complete detector head with collimator, crystal, and digitization process. During the simulation, particle tracking inside the SPECT head is replaced by a plane. Photons are stopped at the plane and the energy and direction are used as input to the ANN that provide detection probabilities in each energy w...
Source: Physics in Medicine and Biology - September 21, 2018 Category: Physics Authors: Sarrut D, Krah N, Badel JN, Letang JM Tags: Phys Med Biol Source Type: research

Should dose from small fields be limited for dose verification procedures?: uncertainty vs. small field dose in VMAT treatments.
Abstract Over the years, radiotherapy treatments have become more complex and conformal, leading to an increased use of small field segments in VMAT arcs. The impact of small field dose inaccuracy on dose verification methods has not been studied yet. The aim of this work is therefore to quantify the relationship between the uncertainty of a 2D pre-treatment dose prediction model and the proportion of dose coming from small fields in VMAT arcs for a range of clinical plans. The model evaluated in this work predicts 2D portal dose images (PDIs) without a patient or phantom in the beam. The uncertainty of the m...
Source: Physics in Medicine and Biology - September 21, 2018 Category: Physics Authors: Wolfs CJA, Swinnen ACC, Nijsten SMJJG, Verhaegen F Tags: Phys Med Biol Source Type: research