Assessment of 3D motion modeling performance for dose accumulation mapping on the MR-linac by simultaneous multislice MRI.
In this study we used 2D Simultaneous MultiSlice (SMS) imaging to improve the PCA-based motion modeling method developed previously (Stemkens et al. 2016). From the additional simultaneously acquired slices, several independent motion models could be generated, which allowed for an assessment of the sensitivity of the motion model to the location of the time-resolved 2D slices. Additionally, the best model could be chosen at every time-point, increasing the method's robustness. Imaging experiments were performed in six healthy volunteers using three simultaneous slices, which generated three independent models ...
Source: Physics in Medicine and Biology - March 26, 2019 Category: Physics Authors: Borman PTS, Bos C, Stemkens B, Moonen CTW, Raaymakers BW, Tijssen RHN Tags: Phys Med Biol Source Type: research

Plane wave versus focused transmissions for contrast enhanced ultrasound imaging: the role of parameter settings and the effects of flow rate on contrast measurements.
In conclusion, if higher frame rate imaging is not required, a benefit of PW, FI appears to be a better choice of imaging mode for CEUS, providing greater image quality over PW for similar rates of contrast reduction. PMID: 30917360 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 26, 2019 Category: Physics Authors: Moghimirad E, Bamber JC, Harris EJ Tags: Phys Med Biol Source Type: research

Deformable image registration for dose mapping between external beam radiotherapy and brachytherapy images of cervical cancer.
This study proposed and evaluated different deformable image registration (DIR) methods for this application. Twenty patients who underwent EBRT and BT for LACC were retrospectively analyzed. Each patient had a pre-BT CT at EBRT boost (without applicator) and a CT and MRI at BT (with applicator). The evaluated DIR methods were the diffeomorphic Demons, commercial intensity and hybrid methods, and three different biomechanical models. The biomechanical models considered different boundary conditions. The impact of the BT devices insertion on the anatomy was quantified. DIR method performances were quantified using geom...
Source: Physics in Medicine and Biology - March 25, 2019 Category: Physics Authors: Rigaud B, Klopp A, Vedam S, Venkatesan A, Taku N, Simon A, Haigron P, de Crevoisier R, Brock KK, Cazoulat G Tags: Phys Med Biol Source Type: research

Preclinical voxel-based dosimetry through GATE Monte Carlo simulation using PET/CT imaging of mice.
In this study, we used PET/CT images of real mice to estimate the absorbed doses in sensitive organs at voxel-level to evaluate the suitability of GATE MC simulation for preclinical dosimetry. Thirteen normal C57BL/6 mice (male, body weight: 27.71 ± 4.25 g) were used to acquire dynamic positron emission tomography/computed tomography (PET/CT) images after IV injection of 18F-FDG. GATE MC toolkit was applied to estimate the absorbed doses in various organs of mice at voxel-level using CT and PET images as voxelized phantom and voxelized source, respectively. In addition, mean absorbed dose at organ-level was calculat...
Source: Physics in Medicine and Biology - March 25, 2019 Category: Physics Authors: Gupta A, Lee MS, Kim JH, Park S, Park HS, Kim SE, Lee DS, Lee JS Tags: Phys Med Biol Source Type: research

Dosimetric and chemical characteristics of Fricke gels based on PVA matrices cross-linked with glutaraldehyde.
Abstract Fricke gel radiochemical sensors based on various matrices have been studied for decades as 3D dosimeters for radiotherapy. Despite their many appealing features, progressive aging and blurring of the signal have prevented the widespread use of these dosimeters, so far. We have addressed these shortcomings and hereby present our development of a Fricke gel based on a chemically cross-linked PVA matrix. We investigated the influence of several parameters of the polymeric matrix on sensitivity, diffusion coefficient and spontaneous oxidation of the proposed gel dosimeter. Based on these findings, we optimiz...
Source: Physics in Medicine and Biology - March 25, 2019 Category: Physics Authors: Lazzeri L, Marini A, Cascone MG, d'Errico F Tags: Phys Med Biol Source Type: research

Ionization quenching in scintillators used for dosimetry of mixed particle fields.
Abstract Ionization quenching in ion beam dosimetry is often related to the fluence- or dose-averaged linear energy transfer (LET). Both quantities are however averaged over a wide LET range and a mixed field of primary and secondary ions. We propose a novel method to correct the quenched luminescence in scintillators exposed to ion beams. The method uses the energy spectrum of the primaries and accounts for the varying quenched luminescence in heavy, secondary ion tracks through amorphous track structure theory. The new method is assessed against more traditional approaches by correcting the quenched luminescence...
Source: Physics in Medicine and Biology - March 24, 2019 Category: Physics Authors: Christensen JB, Almhagen E, Stolarczyk L, Vestergaard A, Bassler N, Andersen CE Tags: Phys Med Biol Source Type: research

Feasibility of ultrashort echo time images using full-wave acoustic and thermal modeling for transcranial MRI-guided focused ultrasound (tcMRgFUS) planning.
Abstract Transcranial MRI-guided focused ultrasound (tcMRgFUS) is increasingly used to non-invasively treat a wide variety of neurological disorders including essential tremors, Parkinson disease and neuropathic pain. Although this treatment is an MRI-guided procedure, the current pre-treatment screening and planning involve a CT of the head to obtain three-dimensional skull images. These images are necessary for estimating the proportion of absorbed energy and the acoustic phase shift associated with the skull and determining the transmit energy of ultrasonic wave to create thermal lesions at a desired focal spot...
Source: Physics in Medicine and Biology - March 24, 2019 Category: Physics Authors: Guo S, Zhuo J, Li G, Gandhi D, Dayan M, Fishman PS, Eisenberg HM, Melhem ER, Gullapalli RP Tags: Phys Med Biol Source Type: research

A novel method for fast image simulation of flat panel detectors.
Abstract We have developed a novel method for fast image simulation of flat panel detectors, based on the photon energy deposition efficiency and the optical spread function (OSF). The proposed method, FastEPID, determines the photon detection using photon energy deposition and replaces particle transport within the detector with precalculated OSFs. The FastEPID results are validated against experimental measurement and conventional Monte Carlo simulation in terms of modulation transfer function (MTF), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contrast, and relative difference of pixel value, obt...
Source: Physics in Medicine and Biology - March 21, 2019 Category: Physics Authors: Shi M, Myronakis ME, Hu YH, Jacobson MW, Lehmann M, Fueglistaller R, Huber P, Baturin P, Wang AS, Ferguson D, Harris T, Morf D, Berbeco RI Tags: Phys Med Biol Source Type: research

Exploring light confinement in laser-processed LYSO:Ce for photon counting CT application.
Abstract With the goal of developing a low-cost scintillator-based photon counting detector (PCD) with high dose efficiency suitable for CT, the light transport characteristics in LYSO:Ce detectors containing Laser Induced Optical Barriers (LIOB) are simulated. Light confinement and light collection efficiencies (LCE) are studied for a variety of optical barrier patterns and properties (refractive index (RI) and barrier/crystal interface roughness). Up to 80% confinement is achievable with a simple pixel pattern with one barrier wall separating each pixel coupled one-to-one to a photodetector (PD) pixel. Confineme...
Source: Physics in Medicine and Biology - March 20, 2019 Category: Physics Authors: Blackberg L, Sajedi S, Mandl S, Mohan A, Vittum B, El Fakhri G, Sabet H Tags: Phys Med Biol Source Type: research

Impact of machine log-files uncertainties on the quality assurance of proton pencil beam scanning treatment delivery.
In conclusion our new PSQA protocol allows for a fast verification of the dose delivered after every treatment fraction through the use of machine log-files and an independent Monte Carlo dose engine. Moreover, the inclusion of log-file uncertainties in the dose calculation allows for a correct evaluation of the quality of the treatment plan delivery. . PMID: 30897559 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 20, 2019 Category: Physics Authors: Toscano S, Souris K, Gomà C, Barragan A, Puydupin S, Vander Stappen F, Janssens G, Matic A, Geets X, Sterpin E Tags: Phys Med Biol Source Type: research

Reconfigurable energy-resolving method for a layered edge-on detector scheme.
Abstract Currently, most of the X-ray spectral detectors can extract signals in a fixed number of energy bins, which inevitably reduces the dynamic range and energy resolution of the imaging system. Inspired by the idea of dynamic thresholding, we previously proposed a pixel architecture and the energy-resolving method for layered edge-on detector. However, the complicated energy exchange mechanism of X-rays in the detector had not been considered, which affects the practical application of the layered detectors. In this paper, we modify the energy-depositing model of X-ray photons and propose a reconfigurable ene...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Shi Z, Xie X, Li H, Meng Q, Cong W, Wang G Tags: Phys Med Biol Source Type: research

Intercrystal scatter studies for a 1 mm < sup > 3 < /sup > resolution clinical PET system prototype.
Intercrystal scatter studies for a 1 mm3 resolution clinical PET system prototype. Phys Med Biol. 2019 Mar 20;: Authors: Hsu DF, Freese DL, Innes DR, Levin CS Abstract Positron emission tomography (PET) systems designed with multiplexed readout do not usually have the capability to resolve individual intercrystal scatter (ICS) interactions, leading to interaction mispositioning that degrades spatial resolution and contrast. A 3D position sensitive scintillation detector capable of individual ICS readout has been designed and incorporated into a 1 mm&lt;sup&gt;3&lt;/sup&gt; resolution c...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Hsu DF, Freese DL, Innes DR, Levin CS Tags: Phys Med Biol Source Type: research

Comparing the effectiveness and efficiency of various gating approaches for PBS proton therapy of pancreatic cancer using 4D-MRI datasets.
This study aims to, first, determine suitable gating windows with respect to effectiveness (low interplay effect) and efficiency (high duty cycles). Second, it investigates whether beam gating allows a better mitigation of the interplay effect along the treatment course than free-breathing irradiations. Based on synthetic 4D-CTs, generated by warping 3D-CTs with vector fields extracted from time-resolved magnetic resonance imaging (4D-MRI) for 8 pancreatic cancer patients, 4D dose calculations (4DDC) were performed to analyze the duty cycle and homogeneity index HI=d5/d95 for four different gating scenarios. Th...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Dolde K, Naumann P, Dávid C, Kachelriess M, Lomax AJ, Weber DC, Saito N, Burigo LN, Pfaffenberger A, Zhang Y Tags: Phys Med Biol Source Type: research

The dependence of interplay effects on the field scan direction in PBS proton therapy.
Abstract The literature is controversial about the scan direction dependency of interplay effects in pencil beam scanning (PBS) treatment of moving targets. A directional effect is supported by many simulation studies, whereas the experimental data are mostly limited to simple geometries, not reflecting realistically clinical treatment plans. We have compared increasingly complex treatment fields, from a homogeneous single energy layer to a more modulated lung plan, under identical experimental settings, seeking evidence for differences in motion mitigation due to the selection of primary scanning direction. In to...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Fattori G, Klimpki G, Hrbacek J, Zhang Y, Krieger M, Placidi L, Psoroulas S, Weber DC, Lomax AJ, Safai S Tags: Phys Med Biol Source Type: research

Atherosclerotic carotid bifurcation phantoms with stenotic soft inclusions for ultrasound flow and vessel wall elastography imaging.
Abstract As the complexity of ultrasound signal processing algorithms increases, it becomes more difficult to demonstrate their added value and thus robust validation strategies are required. We propose a method of manufacturing ultrasonic vascular phantoms mimicking an atheromatous plaque in an internal carotid artery bifurcation for applications in flow imaging and elastography. During the fabrication process, a soft inclusion mimicking a stenotic lipid pool was embedded within the vascular wall. Mechanical testing measured Young's moduli of the vascular wall and soft inclusion at 342 ± 25 kPa and 17 &plu...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Chayer B, Van Den Hoven M, Roy Cardinal MH, Li H, Swillens A, Lopata RGP, Cloutier G Tags: Phys Med Biol Source Type: research

Performance of a depth encoding PET detector module using light sharing and single-ended readout with SiPMs.
Abstract Detectors with depth encoding capability, good energy resolution and good timing resolution are required to develop high performance whole body and total body PET scanners. In this work, an 8×8 LYSO array with crystal size of 3×3×20 mm3 was fabricated by using coupling materials that including 5 mm optical glue, 9 mm triangle ESR reflector and 6 mm rectangle ESR reflector from the top to the bottom in between adjacent crystals in one direction. The LYSO array was single-ended read out by an 8×8 SiPM array with one-to-one coupling. Row and column summing circuit was used to read out...
Source: Physics in Medicine and Biology - March 19, 2019 Category: Physics Authors: Kuang Z, Yang Q, Wang X, Fu X, Ren N, Wu S, Zhang C, Zhao B, Sang Z, Hu Z, Du J, Liang D, Liu X, Zheng H, Yang Y Tags: Phys Med Biol Source Type: research

4D simultaneous tissue and blood flow Doppler imaging: Revisiting cardiac Doppler index with single heart beat 4D ultrafast echocardiography.
Conclusions 4D ultrafast echocardiography can quantify the major cardiac Doppler indices in a single heart beat acquisition. PMID: 30889552 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 18, 2019 Category: Physics Authors: Papadacci C, Finel V, Villemain O, Goudot G, Provost J, Messas E, Tanter M, Pernot M Tags: Phys Med Biol Source Type: research

A patient-specific mass-spring model for biomechanical simulation of aortic root tissue during transcatheter aortic valve implantation.
lli F Abstract The success of transcatheter aortic valve implantation (TAVI) is highly dependent on the prediction of the interaction between the prosthesis and the aortic root anatomy. The simulation of the surgical procedure may be useful to guide artificial valve selection and delivery, nevertheless the introduction of simulation models into the clinical workflow is often hindered by model complexity and computational burden. To address this point, we introduced a patient-specific mass-spring model (MSM) with viscous damping, as a good trade-off between simulation accuracy and time-efficiency. The anatomical mo...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Cristoforetti A, Masè M, Bonmassari R, Dallago M, Nollo G, Ravelli F Tags: Phys Med Biol Source Type: research

A track repeating algorithm for intensity modulated carbon ion therapy.
Abstract The Fast Dose Calculator (FDC), a track repeating Monte Carlo algorithm was initially developed for proton therapy. The validation for proton therapy has been demonstrated in a previous work. In this work we present the extension of FDC to the calculation of dose distributions for ions, particularly for carbon. Moreover the code algorithm is validated versus full Monte Carlo, by comparing 3D dose distributions and Dose Volume Histograms (DVH) calculated by FDC with GEANT 4. A total of 19 patients were employed, including 3 patients of prostate, 5 of brain, 3 of head and neck,...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Wang Q, Adair AH, Deng Y, Chen H, Moyers M, Lin J, Yepes PP Tags: Phys Med Biol Source Type: research

An experimental method to directly measure DQE(k) at k = 0 for 2D x-ray imaging systems.
Abstract The zero-frequency DQE, viz., DQE0, is defined as the ratio between output and input squared SNR of an imaging system. In 1963, R. Shaw applied Fourier analysis to generalize DQE0 to the frequency-dependent DQE, i.e., DQE(k). Under conditions specified by Shaw, DQE(k) is the same as DQE0 at k=0. The experimental measurement of DQE(k) involves the measurement of system modulation transfer function (MTF) and noise power spectrum (NPS). Although the measurement of MTF is straightforward, the experimental measurements of NPS(k) encountered several challenges. As a result, some experimental methods may yield n...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Ji X, Feng M, Zhang R, Chen GH, Li K Tags: Phys Med Biol Source Type: research

Dosimetric properties of colloidal quantum dot-based systems for scintillation dosimetry.
en CN, Beaulieu L Abstract Colloidal quantum dots (cQDs) are starting to be used in radiation detection, either combined with an organic fluorophore or used as a sole luminescent material. In the latter case, only few studies report on cQD-based detectors for medical applications, especially for scintillation dosimetry in radiation therapy. Moreover, most of these studies focus on the effects of radiation on cQD photoluminescence but do not look into the properties of the scintillation signal itself. The present article provides a study of those cQD scintillation properties not previously investigated including th...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Delage MÈ, Lecavalier MÈ, Larivière D, Allen CN, Beaulieu L Tags: Phys Med Biol Source Type: research

Rigid-body motion correction in hybrid PET/MRI using spherical navigator echoes.
Abstract Integrated positron emission tomography and magnetic resonance imaging (PET/MRI) is an imaging technology that provides complementary anatomical and functional information for medical diagnostics. Both PET and MRI are highly susceptible to motion artifacts due, in part, to long acquisition times. The simultaneous acquisition of the two modalities presents the opportunity to use MRI navigator techniques for motion correction of both PET and MRI data. For this task, we propose spherical navigator echoes (SNAVs) - 3D k-space navigators that can accurately and rapidly measure rigid body motion in all six degr...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Johnson PM, Taylor R, Whelan T, Thiessen JD, Anazodo U, Drangova M Tags: Phys Med Biol Source Type: research

An atlas-based method to predict three-dimensional dose distributions for cancer patients who receive radiotherapy.
Abstract Due to the complexity of advanced radiotherapy techniques, the treatment planning process is usually time consuming and the plan quality can vary considerably among planners and institutions. It is also impractical to generate all possible treatment plans based on available radiotherapy techniques and select the best option for a specific patient. Automatic dose prediction will be very helpful in these situations, while there were a few studies of three-dimensional (3D) dose prediction for patients who received radiotherapy. The purpose of this work was to develop a novel atlas-based method to predict 3D ...
Source: Physics in Medicine and Biology - March 17, 2019 Category: Physics Authors: Sa Y, Zhang R Tags: Phys Med Biol Source Type: research

Dosimetric evaluation and beam characterization of pair production enhanced radiotherapy (PPER) with the use of organometallics.
Abstract The current study evaluates dosimetric and spectral effects when platinum (Pt)-based chemotherapeutics and less toxic tungstophosphoric-acid (TPA) organometallics are present during x-ray radiotherapy. We hypothesize that the use of high energy photon beams (i.e. 18 MV) will increase absorbed dose due to increased pair production from high Z elements and thus result in additional tumor cell kill. EGSnrc code was used to examine the contribution of pair production to dose in the presence of the high Z material (TPA, Pt mixtures and tungsten, W) as a function of beam energy. Variables included different con...
Source: Physics in Medicine and Biology - March 14, 2019 Category: Physics Authors: Tsiamas P, Brown SL, Chetty IJ, Kim JH, Isrow D Tags: Phys Med Biol Source Type: research

Discriminating nanoparticle core size using multi-contrast MPI.
l M Abstract Magnetic particle imaging (MPI) is an imaging modality that detects the response of a distribution of magnetic nanoparticle tracers to static and alternating magnetic fields. There has recently been exploration into multi-contrast MPI, in which the signal from different tracer materials or environments is separately reconstructed, resulting in multi-channel images that could enable temperature or viscosity quantification. In this work, we apply a multi-contrast reconstruction technique to discriminate between nanoparticle tracers of different core sizes. Three nanoparticle types with core diameters of...
Source: Physics in Medicine and Biology - March 13, 2019 Category: Physics Authors: Shasha C, Teeman E, Krishnan KM, Szwargulski P, Knopp T, Möddel M Tags: Phys Med Biol Source Type: research

Coincidence time resolution of 30 ps FWHM using a pair of Cherenkov-radiator-integrated MCP-PMTs.
Abstract Radiation detectors dedicated to time-of-flight positron emission tomography (PET) have been developed, and coincidence time resolution (CTR) of sub-100 ps full width at half maximum (FWHM) has been achieved by carefully optimizing scintillators and photodetectors. Achieving a CTR of 30 ps FWHM by using a pair of annihilation -rays would allow us to directly localize the annihilation point within an accuracy of 4.5 mm. Such direct localization can potentially eliminate the requirement of image reconstruction processes in clinical PET systems, that would have a huge impact on clinical protocols and mole...
Source: Physics in Medicine and Biology - March 13, 2019 Category: Physics Authors: Ota R, Nakajima K, Ogawa I, Tamagawa Y, Shimoi H, Suyama M, Hasegawa T Tags: Phys Med Biol Source Type: research

Dosimetric accuracy and radiobiological implications of ion computed tomography for proton therapy treatment planning.
Abstract Ion computed tomography (iCT) represents a potential replacement for X-ray CT (xCT) in ion therapy treatment planning to reduce range uncertainties, inherent in the semi-empirical conversion of xCT information into relative stopping power (RSP). In this work, we aim at quantifying the increase in dosimetric accuracy associated with using proton-, helium- and carbon-iCT compared to conventional xCT for clinical scenarios in proton therapy. Three cases imaged with active beam-delivery using an ideal single-particle-tracking detector were investigated using FLUKA Monte-Carlo simulations. The RSP accuracy of ...
Source: Physics in Medicine and Biology - March 13, 2019 Category: Physics Authors: Meyer S, Kamp F, Tessonnier T, Mairani A, Belka C, Carlson DJ, Gianoli C, Parodi K Tags: Phys Med Biol Source Type: research

Deep feature regression (DFR) for 3D vessel segmentation.
In this study, a deep feature regression (DFR) method based on a convolutional regression network (CRN) and a stable point clustering mechanism for 3D vessel segmentation is proposed. First, the vessel model is constructed by a vessel section generator and a series of deviation parameter estimators. The generator provides 2D images for the training and prediction processes, while the estimators calculate pose parameters of an input vessel section. Second, estimators are trained by a series of CRNs, in which deep vessel features are automatically learned from 600,000 sample images. Third, we propose a stable point clusterin...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Zhao J, Ai D, Yang Y, Song H, Huang Y, Wang Y, Yang J Tags: Phys Med Biol Source Type: research

Automatic segmentation of levator hiatus from ultrasound images using U-net with dense connections.
Abstract In this paper, we propose a fully automatic method based on densely connected convolutional network for the segmentation of the levator hiatus from ultrasound images. A densely connected path is incorporated into a U-net to achieve a deep architecture and improve the segmentation performance. The proposed network architecture provides dense connections between layers that encourage feature reuse and reduce the number of parameters while maintaining good performance. The parameters of the network are optimized by training with a binary cross entropy i.e. logarithmic loss funct...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Li X, Hong Y, Kong D, Zhang X Tags: Phys Med Biol Source Type: research

Towards a second-generation PET/MR insert with enhanced timing and count rate performance.
Abstract Previously we have developed a first-generation PET insert prototype for small animal PET/MR imaging, which used resistor-based charge division multiplexing circuits and SensL B-series silicon photomultipliers (SiPMs). In this work we present results from a second-generation readout board with improved timing and count rate performance Three detector boards were tested: the first-generation readout board with SensL SPMArray4B (SiPM-B), the second-generation readout board with SensL ArrayC-30035-16P-PCB (SiPM-C) using the 'fast' outputs for timing, and the second generation board using Hamamatsu S11361-305...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Van Elburg DJ, Shrestha R, Goertzen AL Tags: Phys Med Biol Source Type: research

CT beam dosimetric characterization procedure for personalized dosimetry.
Abstract Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patients body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verication by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent...
Source: Physics in Medicine and Biology - March 10, 2019 Category: Physics Authors: Rosendahl S, Bueermann L, Borowski M, Kortesniemi M, Sundell VM, Kosunen A, Siiskonen T Tags: Phys Med Biol Source Type: research

Time efficient scatter correction for time-of-flight PET: the immediate scatter approximation.
Abstract Utilization of Time-Of-Flight (TOF) information allows to improve image quality and convergence rate in iterative PET image reconstruction. In order to obtain quantitatively correct images accurate scatter correction (SC) is required that accounts for the non-uniform distribution of scatter events over the TOF bins. However, existing simplified TOF-SC algorithms frequently exhibit limited accuracy while the currently accepted gold standard - the TOF extension of the single scatter simulation approach (TOF-SSS) - is computationally demanding and can substantially slow down the reconstruction. In this paper...
Source: Physics in Medicine and Biology - March 10, 2019 Category: Physics Authors: Nikulin P, Maus J, Hofheinz F, Lougovski A, van den Hoff J Tags: Phys Med Biol Source Type: research

Feasibility of multi-atlas cardiac segmentation from thoracic planning CT in a probabilistic framework.
We present a probabilistic approach to segmentation, which provides a simple method to incorporate inter-observer variation, as well as a useful tool for evaluating the accuracy and sources of error in segmentation. A dataset consisting of 20 planning computed tomography images of Australian breast cancer patients with delineations of 17 structures (including whole heart, 4 chambers, coronary arteries and valves) was manually contoured by 3 independent observers, following a protocol based on a published reference atlas, with verification by a cardiologist. To develop and validate the segmentation framework a le...
Source: Physics in Medicine and Biology - March 10, 2019 Category: Physics Authors: Finnegan RN, Dowling JA, Koh ES, Tang S, Otton J, Delaney G, Batumalai V, Luo C, Atluri P, Satchithanandha A, Thwaites DI, Holloway L Tags: Phys Med Biol Source Type: research

Experimental validation of magnetically focused proton beams for radiosurgery.
Abstract We performed experiments using a triplet of quadrupole permanent magnets to focus protons and compared their dose distributions with unfocused collimated beams using energies and field sizes typically employed in proton radiosurgery. Experiments were performed in a clinical treatment room wherein small-diameter proton beams were focused by a magnet triplet placed immediately upstream of a water tank. The magnets consisted of segments of Sm&lt;sub&gt;2&lt;/sub&gt;Co&lt;sub&gt;17&lt;/sub&gt; rare-earth permanent magnetic material adhered into Halbach cylinders with nominal fi...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: McAuley GA, Teran AV, McGee PQ, Nyguen TT, Slater JM, Slater JD, Wroe AJ Tags: Phys Med Biol Source Type: research

Precise delineation and tumor localization based on novel image registration strategy between optical coherence tomography and computed tomography in the radiotherapy of intraocular cancer.
Abstract Radiation-associated toxicities due to sophisticated ocular anatomy and shape variability of organs at risk (OARs) are major concerns during external beam radiation therapy (EBRT) of patients with intraocular cancer. A novel two-step image registration strategy between optical coherence tomography (OCT) and computed tomography (CT) images was proposed and validated to precisely localize the target in the EBRT of patients with intraocular cancer. Specifically, multiple features from OCT and CT images were extracted automatically, then spatial transformation based on thin-plate spline function was performed...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Gong C, Shen M, Zheng X, Han C, Zhou Y, Xie C, Jin X Tags: Phys Med Biol Source Type: research

Dielectric properties of muscle and tissue-mimicking solutions for microwave medical imaging applications.
Abstract The aim of the present study was to synthesize mixture solutions which can accurately mimic the dielectric properties of biological tissues, specifically muscle and adipose tissues between 500 MHz and 50 GHz. Mixtures utilizing concentrations of bovine serum albumin (BSA) dissolved in phosphate buffered saline (PBS) and Ringer's solutions were synthesized to mimic in vivo and ex vivo muscle tissues. Solutions consisting of concentrations of peanut oil and Triton X 100 (TX) in PBS and Ringer's solutions were also synthesized to mimic in vivo and ex vivo adipose tissue. Results were then analysed and compar...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Pollacco DA, Caligari Conti M, Farrugia L, Schembri Wismayer P, Farina L, Sammut CV Tags: Phys Med Biol Source Type: research

Determination of ion recombination and polarity effect correction factors for a plane-parallel ionization Bragg Peak chamber under proton and carbon ion pencil beams.
Abstract Within the dosimetric characterization of particle beams, laterally-integrated depth-dose-distributions (IDDs) are measured and provided to the treatment planning system (TPS) for beam modeling or used as a benchmark for Monte Carlo (MC) simulations. The purpose of this work is the evaluation, in terms of ion recombination and polarity effect, of the dosimetric correction to be applied to proton and carbon ion curves as a function of linear energy transfer (LET). LET was calculated with a MC code for selected IDDs. Several regions of Bragg Peak (BP) curve were investigated. The charge was measured wi...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Mirandola A, Magro G, Maestri D, Mairani A, Mastella E, Molinelli S, Russo S, Vai A, Ciocca M Tags: Phys Med Biol Source Type: research

Single-arc VMAT optimization for dual-layer MLC.
In this study, we develop a novel single-arc VMAT optimization framework to take advantage of the unique DLMLC characteristics fully. Direct Aperture Optimization (DAO) for single-arc DLMLC VMAT was formulated as a least square dose fidelity objective, along with an anisotropic total variation term to regulate the fluence smoothness and a single segment term for forming simple apertures. The DAO was solved through alternating optimization approach. The DLMLC deliverability constraint and the MLC leaf speed constraint were formulated as the optimization constraints and solved using a graph optimization algorithm. Feasibilit...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Lyu Q, Neph R, Yu VY, Ruan D, Sheng K Tags: Phys Med Biol Source Type: research

Synthetic 4D-CT of the thorax for treatment plan adaptation on MR-guided radiotherapy systems.
Abstract MR-guided radiotherapy treatment planning utilises the high soft-tissue contrast of MRI to reduce uncertainty in delineation of the target and organs at risk. Replacing 4D-CT with MRI-derived synthetic 4D-CT would support treatment plan adaptation on hybrid MR-guided radiotherapy systems for inter- and intrafractional differences in anatomy and respiration, whilst mitigating the risk of CT to MRI registration errors. Three methods were devised to calculate synthetic 4D and midposition (time-weighted mean position of the respiratory cycle) CT from 4D-T1w and Dixon MRI. The first approach employe...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Freedman JN, Bainbridge H, Nill S, Collins DJ, Kachelriess M, Leach MO, McDonald F, Oelfke U, Wetscherek A Tags: Phys Med Biol Source Type: research

pGPUMCD: an efficient GPU-based Monte Carlo code for accurate proton dose calculations.
e;s P Abstract In proton therapy, Monte Carlo simulations are desirable to accurately predict the delivered dose. This paper introduces and benchmarks pGPUMCD, a GPU-based Monte Carlo code implementing the physical processes required for protontherapy applications. In pGPUMCD, the proton transport is carried out in a voxelized geometry with a class II condensed history scheme. For this purpose, the equivalent restricted stopping power formalism (L&lt;sub&gt;eq&lt;/sub&gt; formalism), the Fermi-Eyges scattering theory and the discrete electromagnetic/nuclear interactions were considered. pGPUMCD was...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Maneval D, Ozell B, Després P Tags: Phys Med Biol Source Type: research

Fast gamma-ray interaction-position estimation using k-d tree search.
Abstract We have developed a fast gamma-ray interaction-position estimation method using k-d tree search, which can be combined with various kinds of closeness metrics such as Euclidean distance, maximum-likelihood estimation, etc.. Compared with traditional search strategies, this method can achieve both speed and accuracy at the same time using the k-d tree data structure. The k-d tree search method has a time complexity of O(log2(N)), where N is the number of entries in the reference data set, which means large reference datasets can be used to efficiently estimate each event's interaction position. This method...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Li X, Tao L, Levin CS, Furenlid LR Tags: Phys Med Biol Source Type: research

Higher SNR PET image prediction using a deep learning model and MRI image.
Conclusions Our proposed method could improve the PET SNR without having higher SNR PET images. . PMID: 30844784 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Liu CC, Qi J Tags: Phys Med Biol Source Type: research

Intravascular optical coherence tomography to validate finite-element simulation of angioplasty balloon inflation.
Abstract Concrete methods are lacking to examine angioplasty simulation results. For the first time, we explored the application of intravascular optical coherence tomography (IVOCT) to experimentally validate results obtained from finite-element simulation of angioplasty balloon deployment. In order to simulate each experimental scenario, IVOCT images were used to create initial geometrical models for the balloon and the phantoms. The study comprised three scenarios. The first scenario involved experimentally monitoring as well as simulating free expansion of the balloon. The second scenario involved experimental...
Source: Physics in Medicine and Biology - March 5, 2019 Category: Physics Authors: Azarnoush H, Pazos V, Vergnole S, Boulet B, Lamouche G Tags: Phys Med Biol Source Type: research

Four-dimensional digital tomosynthesis image reconstruction using brute force-based adaptive total variation (BF-ATV) in a prototype LINAC system.
In conclusion, the proposed low-dose 4D-DTS reconstruction scheme may provide better performance due in part to its rapid scanning. Therefore, it is potentially applicable to practical 4D imaging for radiotherapy. PMID: 30840940 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 5, 2019 Category: Physics Authors: Choi S, Lee S, Kang YN, Hsieh SS, Kim HJ Tags: Phys Med Biol Source Type: research

A comparative study of information retrieval in grating-based X-ray phase-contrast imaging.
Abstract The cosine-model analysis (CMA) method and the small angle X-ray scattering (SAXS) method are two major types of information retrieval algorithms, commonly utilized in X-ray phase-contrast imaging with a grating interferometer. However, there are significant differences between the two methods in algorithm implementation, and the existing literature has not completely revealed their intrinsic relationship. In this paper, we theoretically derive and experimentally verify the intrinsic connections between CMA and SAXS, and it is seen that SAXS can be interpreted well by the cosine-model assumption of CMA. T...
Source: Physics in Medicine and Biology - March 5, 2019 Category: Physics Authors: Li X, Gao H, Chen Z, Zhang L, Zhu X, Wang S, Peng W Tags: Phys Med Biol Source Type: research

Evaluation of ge-doped silica fibre TLDs for < i > in vivo < /i > dosimetry during intraoperative radiotherapy.
In this study, using the INTRABEAM® system, investigation was made of the potential application of GDSF TLDs for in vivo IORT dosimetry. The GDSFs were calibrated over the respective dose- and depth-range 1 to 20 Gy and 3 to 45 mm from the X-ray probe. The effect of different sizes of spherical applicator on TL response of the fibres was also investigated. The results show the GDSF TLDs to be applicable for IORT dose assessment, with the important incorporated correction for beam quality effects using different spherical applicator sizes. The total uncertainty in use of this type of GDSF for dosimetry has been found to...
Source: Physics in Medicine and Biology - March 5, 2019 Category: Physics Authors: Moradi F, Ung NM, Mahdiraji GA, Khandaker MU, See MH, Mohd Taib NA, Bradley DA Tags: Phys Med Biol Source Type: research

Hydrogels as a water bolus during hyperthermia treatment.
m A Abstract The feasibility of using hydrogels as a water bolus during hyperthermia treatment was assessed. Three types of gels, high methoxyl (HM) pectin/alginate, xanthan/locust bean gum (LBG) and xanthan/LBG/agarose were evaluated based on their dielectric properties, rheological and mechanical properties. The most suitable, xanthan/LBG/agarose, gel was further used as a water bolus in a hyperthermia array applicator. The gels composed of polysaccharides carrying low charge displayed dielectric properties close to those of water, while the dielectric properties of HM pectin/alginate gel was deemed unsuitable&#...
Source: Physics in Medicine and Biology - March 3, 2019 Category: Physics Authors: Dobsicek Trefna H, Ström A Tags: Phys Med Biol Source Type: research

Event-by-event non-rigid data-driven PET respiratory motion correction methods: comparison of principal component analysis and centroid of distribution.
Abstract Respiratory motion is a major cause of degradation of PET image quality. Respiratory gating and motion correction can be performed to reduce the effects of respiratory motion; these methods require motion information, typically obtained from external tracking systems. Various groups have studied data-driven (DD) motion estimation methods. Recently, a data-driven respiratory motion estimation method was established by calculating the centroid of distribution (COD) of listmode events, which was then used with event-by-event respiratory motion correction (EBE-MC), and showed results comparable to those with ...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Ren S, Lu Y, Bertolli O, Thielemans K, Carson RE Tags: Phys Med Biol Source Type: research

Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): A Monte Carlo study.
Abstract The CT dose index (CTDI&lt;sub&gt;vol&lt;/sub&gt;) is the dosimetric quantity used for multi-slice CT (MSCT) with beams ≤4 cm. Conversion factors (f&lt;sub&gt;size&lt;/sub&gt;) based on patient size are applied to CTDI&lt;sub&gt;vol&lt;/sub&gt; to adjust for differences in patient size and derive size-specific dose estimates (SSDE) relating to patient dose. The aim of this study is to: (1) investigate use of a similar technique to provide SSDE values for cone beam CT (CBCT) scans, (2) determine whether factors derived for narrow beam MSCT are suitable for...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Abuhaimed A, Martin CJ, Demirkaya O Tags: Phys Med Biol Source Type: research

VirtualDose-IR: A cloud-based software for reporting organ doses in interventional radiology.
Abstract A cloud-based software, VirtualDose-IR, designed to report organ doses and effective doses for a diverse patient population from interventional radiology (IR) procedures has been developed and tested. This software is based on a comprehensive database of Monte Carlo-generated organ dose built with a set of 21 anatomically realistic patient phantoms. The patient types included in this database are both male and female people with different ages reflecting reference adults, obese people with different BMIs and pregnant women at different gestational stages. Selectable parameters such as patient type, tube v...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Huo W, Pi Y, Feng M, Qi Y, Gao Y, Caracappa PF, Chen Z, Xu XG Tags: Phys Med Biol Source Type: research