Performance of a dual-layer scanner for hybrid SPECT/CBCT.
Conclusion A dual-layer detector is able to simultaneously acquire SPECT and CBCT. Both CNR and T/N ratio are worse than that of a clinical system, but the phantom experiments showed that extrahepatic depositions with volumes and activities close to the median values encountered in hepatic radioembolization could be distinguished. PMID: 30947146 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - April 4, 2019 Category: Physics Authors: Dietze MMA, Kunnen B, van der Velden S, Steenbergen LJH, Koppert WJC, Viergever MA, de Jong HWAM Tags: Phys Med Biol Source Type: research

A hybrid proton and hyperpolarized gas tagging MRI technique for lung respiratory motion imaging: the feasibility study.
Conclusion: These preliminary results showed that the hybrid HP gas tagging MRI technique revealed different lung motion patterns as compared to the DIR methods. It may provide unique perspectives in developing and evaluating DIR of the lungs. PMID: 30947154 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - April 4, 2019 Category: Physics Authors: Hu L, Huang Q, Cui T, Duarte I, Miller W, Mugler JP, Cates GD, Mata JF, de Lange EE, Altes TA, Yin FF, Cai J Tags: Phys Med Biol Source Type: research

NEMA NU-4 performance evaluation of a non-human primate animal PET.
This article presents a performance evaluation of the PET scanner according to the National Electrical Manufacturers Association NU-4 2008 standards. All measurements were made for an energy window of 360~660 keV and a coincidence timing window of 2 ns. In terms of the FWHM, the FBP reconstructed spatial resolution results in all three directions at the radial position of 5 mm were better than or approached to 2 mm, and remained below 3.0 mm within the central 5 cm diameter of the FOV. The peak absolute sensitivity of the scanner was measured 1.80%. For a monkey-sized phantom, the scatter fraction was 34.2% and the peak no...
Source: Physics in Medicine and Biology - April 4, 2019 Category: Physics Authors: Chai P, Feng B, Zhang Z, Tang H, Liu S, Sun X, Wang P, Wang X, Zhao X, Wei L Tags: Phys Med Biol Source Type: research

Evaluation of pinhole collimator materials for micron-resolution < i > ex-vivo < /i > SPECT.
Evaluation of pinhole collimator materials for micron-resolution ex-vivo SPECT. Phys Med Biol. 2019 Apr 04;: Authors: Nguyen MP, Goorden MC, Kamphuis C, Beekman FJ Abstract Pinhole collimation is widely recognized for offering superior resolution-sensitivity trade-off in SPECT imaging of small subjects. The newly developed EXIRAD-3D autoradiography technique (MILabs B.V.) based on a highly focusing multi-pinhole collimator achieves micron-resolution SPECT for cryo-cooled tissue samples. For such high resolutions, the choice of pinhole material may have a significant impact on images. Therefore, this p...
Source: Physics in Medicine and Biology - April 4, 2019 Category: Physics Authors: Nguyen MP, Goorden MC, Kamphuis C, Beekman FJ Tags: Phys Med Biol Source Type: research

MRI artifact simulation for clinically relevant MRI sequences for guidance of prostate HDR brachytherapy.
This study demonstrated that the MRI artifact induced by an HDR source or a titanium needle could be simulated for the four investigated types of MRI sequences (spoiled gradient echo, spin echo, bSSFP and bSSFP-SPAIR), valuable for real-time object localization in clinical practice. This leads to more flexibility in the choice of MRI sequences for guidance of HDR brachytherapy, as they are suitable for both object localization and anatomy visualization. PMID: 30947159 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - April 4, 2019 Category: Physics Authors: Beld E, Moerland MA, van der Voort van Zyp JRN, Viergever MA, Lagendijk JJW, Seevinck PR Tags: Phys Med Biol Source Type: research

Dynamic fluence field modulation in computed tomography using multiple aperture devices.
Abstract A novel beam filter consisting of multiple aperture devices (MADs) has been developed for dynamic fluence field modulation (FFM) in CT. Each MAD achieves spatial modulation of x-ray through fine-scale, highly attenuating tungsten bars of varying widths and spacings. Moir\'e patterns produced by relative motions between two MADs provide versatile classes of modulation profiles. The dual-MAD filter can be designed to achieve specific classes of target profiles. The designed filter was manufactured through a laser-sintering process and integrated to an experimental imaging system that enables linear actuatio...
Source: Physics in Medicine and Biology - April 2, 2019 Category: Physics Authors: Gang GJ, Mao A, Wang W, Siewerdsen JH, Mathews A, Kawamoto S, Levinson R, Stayman JW Tags: Phys Med Biol Source Type: research

A study of inter-crystal scatter in dual-layer offset scintillator arrays for brain-dedicated PET scanners.
Abstract A dual-layer offset (DLO) detector enables depth-of-interaction (DOI) through light sharing between two layers of scintillation arrays with a single-ended readout (SER) scheme. However, the SER scheme in DLO detectors may lead to a layer misassignment when inter-crystal scattering occurs. The aim of this work is to study inter-crystal scattering and evaluate the effects of layer misidentifications in DLO detectors on the performance of scanners suitable for a brain-dedicated PET insert. The influence of layer misidentification on the coincidence response functions (CRFs) of 3 different DLO detectors with ...
Source: Physics in Medicine and Biology - April 1, 2019 Category: Physics Authors: Teimoorisichani M, Goertzen AL Tags: Phys Med Biol Source Type: research

Direct measurement of ion chamber correction factors, < i > k < /i > < sub > Q < /sub > and < i > k < sub > B < /sub > < /i > , in a 7 MV MRI-linac.
In this study, for the first time, both &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;Q&lt;/sub&gt; and &lt;i&gt;k&lt;sub&gt;B&lt;/i&gt;&lt;/sub&gt; were measured directly for 6 waterproof ion chambers (3 × PTW 30013 and 3 × IBA FC65-G) in a pre-clinical 7 MV MRI-linac at 0 T and at 1.5 T. Measurements were done with the only available primary standard build for this purpose, a water calorimeter. Resulting &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;Q&lt;/sub&gt; factors for PTW and IBA chambers were respectively 0.985(5) and 0.990(4). &lt;...
Source: Physics in Medicine and Biology - April 1, 2019 Category: Physics Authors: de Prez LA, Woodings SJ, de Pooter JA, van Asselen B, Wolthaus JWH, Jansen BJ, Raaymakers BW Tags: Phys Med Biol Source Type: research

Correlations between the shifts in prompt gamma emission profiles and the changes in daily target coverage during simulated pencil beam scanning proton therapy.
Abstract The aim of this study was to investigate the feasibility of using prompt gamma (PG) ray emission profiles to monitor changes in dose to the planning target volume (PTV) during pencil beam scanning (PBS) proton therapy as a result of day-to-day variation in patient anatomy. For 11 prostate patients, we simulated treatment plan delivery using the patients' daily anatomy as observed in the planning CT and 7-9 control CT scans, including the detected PG profiles resulting from the 5%, 10%, and 20% most intense proton pencil beams. For each patient, we determined the changes in dosimetric parameters for t...
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Lens E, Jagt TZ, Hoogeman MS, Schaart DR Tags: Phys Med Biol Source Type: research

Impact of setup and range uncertainties on TCP and NTCP following VMAT or IMPT of oropharyngeal cancer patients.
Conclusion: The estimated population impact of setup and range uncertainties on TCP/NTCP following VMAT or IMPT of oropharyngeal cancer patients was small for both treatment modalities. The use of TCP/NTCP models allows for clinical interpretation of the population effect and could be considered for incorporation in robust evaluation methods. . PMID: 30921775 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Hamming-Vrieze O, Depauw N, Craft DL, Chan AW, Rasch CRN, Verheij M, Sonke JJ, Kooy HM Tags: Phys Med Biol Source Type: research

Characterization of GE discovery IGS 740 angiography system by means of channelized hotelling observer (CHO).
Abstract The aim of the study is to use the well-known Channelized Hotelling Observer model (CHO) to characterize a recently installed angiography system (GE Discovery IGS 740) using sets of images of a contrast-detail phantom acquired with clinical protocols. A Leeds TO10 phantom was used. The phantom has 108 details: 12 diameters (size range: 0.25 mm - 11 mm), each with 9 contrasts (declared range: 0.012 - 0.930 at 70 kVp 1.00 with 1 mm Cu filtration). TO10 has been imaged between two 10 cm thick homogeneous solid water slabs. Two FOVs (32 cm and 20 cm) were used. Fluoroscopy images were taken using an abdominal...
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Bertolini M, Trojani V, Nitrosi A, Iori M, Sassatelli R, Ortenzia O, Ghetti C Tags: Phys Med Biol Source Type: research

Assessment of histotripsy-induced liquefaction with diagnostic ultrasound and magnetic resonance imaging < i > in vitro < /i > and < i > ex vivo < /i > .
In this study, magnetic resonance (MR) and diagnostic ultrasound imaging were combined to assess histotripsy treatment in vitro and ex vivo. Mechanically ablative histotripsy pulses were applied to agarose phantoms or porcine livers. Bubble cloud emissions were monitored with passive cavitation imaging (PCI), and hyperechogenicity via plane wave imaging. Changes in the medium structure due to bubble activity were assessed with diagnostic ultrasound using conventional B-mode imaging and T1-, T2-, and diffusion-weighted MR images acquired at 3 Tesla. Liquefaction zones were correlated with diagnostic ultrasound and MR imagin...
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Anthony GJ, Bollen V, Hendley S, Antic T, Sammet S, Bader KB Tags: Phys Med Biol Source Type: research

Quantifying T < sub > 2 < /sub > relaxation time changes within lesions defined by apparent diffusion coefficient in grey and white matter in acute stroke patients.
Quantifying T2 relaxation time changes within lesions defined by apparent diffusion coefficient in grey and white matter in acute stroke patients. Phys Med Biol. 2019 Mar 28;: Authors: Damion R, Knight MJ, McGarry BL, Bosnell R, Jezzard P, Harston GWJ, Carone D, Kennedy J, El-Tawil S, Elliot J, Muir KW, Clatworthy P, Kauppinen RA Abstract Apparent diffusion coefficient (ADC) of cerebral water, as measured by diffusion MRI, rapidly decreases in ischaemia highlighting a lesion in acute stroke patients. The MRI T2 relaxation time changes in ischaemic brain such that T2 in ADC lesions may be informative o...
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Damion R, Knight MJ, McGarry BL, Bosnell R, Jezzard P, Harston GWJ, Carone D, Kennedy J, El-Tawil S, Elliot J, Muir KW, Clatworthy P, Kauppinen RA Tags: Phys Med Biol Source Type: research

Atlas-based automatic planning and 3D-2D fluoroscopic guidance in pelvic trauma surgery.
Conclusion. The approach yields a method for automatic planning of pelvic fracture fixation and augmentation of fluoroscopy for improved surgical precision and safety. The method does not require segmentation of the patient CT, operates without additional tracking hardware, and is consistent with common workflow in fluoroscopically guided procedures. The approach has the potential to reduce operating time and radiation dose by minimizing trial-and-error attempts in percutaneous screw placement. PMID: 30921783 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Han R, Uneri A, De Silva T, Ketcha MD, Goerres J, Vogt S, Kleinszig G, Osgood GM, Siewerdsen JH Tags: Phys Med Biol Source Type: research

Predicting VMAT patient-specific QA results using a support vector classifier trained on treatment plan characteristics and linac QC metrics.
Abstract The use of treatment plan characteristics to predict patient-specific quality assurance (QA) measurement results has recently been reported as a strategy to help facilitate automated pre-treatment verification workflows or to provide a virtual assessment of delivery quality. The goal of this work is to investigate the potential of using treatment plan characteristics and linac performance metrics (i.e., quality control test results) in combination with machine learning techniques to predict the results of VMAT patient-specific QA measurements. Using features that describe treatment plan comple...
Source: Physics in Medicine and Biology - March 28, 2019 Category: Physics Authors: Granville DA, Sutherland JG, Belec JG, La Russa DJ Tags: Phys Med Biol Source Type: research

Towards real-time respiratory motion prediction based on long short-term memory neural networks.
This study demonstrates the potential of deep LSTM models for the respiratory signal prediction and illustrates the impacts of major hyper-parameters in LSTM models. PMID: 30917344 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 27, 2019 Category: Physics Authors: Lin H, Shi C, Wang B, Chan MF, Tang X, Ji W Tags: Phys Med Biol Source Type: research

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 27, 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 27, 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 26, 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 26, 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 26, 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 25, 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 25, 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 22, 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 21, 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 21, 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 20, 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 20, 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 20, 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 20, 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 20, 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 20, 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 19, 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 18, 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 18, 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 18, 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 18, 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 18, 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 18, 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 15, 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 14, 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 14, 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 14, 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 12, 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 12, 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 12, 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 11, 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 11, 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 11, 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 7, 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