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Physics in Medicine and Biology

Seyoun Park, Rana Farah, Steven M Shea, Erik J Tryggestad, Russell Hales, Junghoon Lee
Respiration-induced tumor motion is a major obstacle for achieving high-precision radiotherapy of cancers in the thoracic and abdominal regions. Surrogate-based estimation and tracking methods are commonly used in radiotherapy, but with limited understanding of quantified correlation to tumor motion. In this study, we propose a method to simultaneously track the lung tumor and external surrogates to evaluate their spatial correlation in a quantitative way using dynamic MRI, which allows real-time acquisition without ionizing radiation exposure...
December 15, 2017: Physics in Medicine and Biology
Konstantin Bolwin, Björn Czekalla, Lynn Johann Frohwein, Florian Buther, Klaus P Schäfers
Patient motion during medical imaging using techniques such as computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), or single emission computed tomography (SPECT) is well known to degrade images leading to blurring effects or severe artifacts. Motion correction methods try to overcome this degrading effects. However, they need to be validated under realistic conditions. In the present work, a sophisticated anthropomorphic thorax phantom is presented that combines several aspects of a simulator for cardio-respiratory motion...
December 15, 2017: Physics in Medicine and Biology
Kevin C Jones, Gage Redler, Alistair Templeton, Damian Bernard, Julius V Turian, James C H Chu
By collimating the photons scattered when a megavoltage therapy beam interacts with the patient, a Compton-scatter image may be formed without the delivery of extra dose. To characterize and assess the potential of the technique, an analytical model for simulating scatter images was developed and validated against Monte Carlo (MC). For three phantoms, the scatter images collected during irradiation with a 6 MV flattening-filter-free therapy beam were simulated. Images, profiles, and spectra were compared for different phantoms and different irradiation angles...
December 15, 2017: Physics in Medicine and Biology
Morteza Heidari, Abolfazl Zargari Khuzani, Alan B Hollingsworth, Gopichandh Danala, Seyedehnafiseh Mirniaharikandehei, Yuchen Qiu, Hong Liu, Bin Zheng
In order to automatically identify a set of effective mammographic image features and build an optimal breast cancer risk stratification model, this study aims to investigate advantages of applying a machine learning approach embedded with a locally preserving projection (LPP) based feature combination and regeneration algorithm to predict short-term breast cancer risk. A dataset involving negative mammograms acquired from 500 women was assembled. This dataset was divided into two age-matched classes of 250 high risk cases in which cancer was detected in the next subsequent mammography screening and 250 low risk cases, which remained negative...
December 14, 2017: Physics in Medicine and Biology
Simon J Woodings, Jochem W H Wolthaus, Bram van Asselen, J H Wilfred de Vries, Jan G M Kok, Jan J W Lagendijk, Bas W Raaymakers
Accurate small-field dosimetry is critical for a magnetic resonance linac (MRI-linac). The PTW 60019 microDiamond is close to an ideal detector for small field dosimetry due to its small physical size, high signal-to-noise ratio and approximate water equivalence. It is important to fully characterise the performance of the detector in a 1.5 T magnetic field prior to its use for MRI-linac commissioning and quality assurance. Standard techniques of detector testing have been implemented, or adapted where necessary to suit the capabilities of the MRI-linac...
December 14, 2017: Physics in Medicine and Biology
Christian Möhler, Tom Russ, Patrick Wohlfahrt, Alina Elter, Armin Runz, Christian Richter, Steffen Greilich
An experimental setup for consecutive measurement of ion and x-ray absorption in tissue or other materials is introduced. With this setup using a 3D-printed sample container, the reference stopping-power ratio (SPR) of materials can be measured with an uncertainty of below 0.1%. A total of 65 porcine and bovine tissue samples were prepared for measurement, comprising five samples each of 13 tissue types representing about 80% of the total body mass (three different muscle and fatty tissues, liver, kidney, brain, heart, blood, lung and bone)...
December 14, 2017: Physics in Medicine and Biology
Miran Han, Ae-Kyoung Lee, Hyung-Do Choi, Yong Wook Jung, Jin Seo Park
Increased use of mobile phones raises concerns about the health risks of electromagnetic radiation. Phantom heads are routinely used for radiofrequency dosimetry simulations, and the purpose of this study was to construct averaged phantom heads for children and young adults. Using magnetic resonance images (MRI), sectioned cadaver images, and a hybrid approach, we initially built template phantoms representing 6-, 9-, 12-, 15-year-old children and adult. Our subsequent approach revised the template phantoms using 29 averaged items that were identified by averaging the MRI data from 500 children and young adults...
December 14, 2017: Physics in Medicine and Biology
Christian Harry Allen, Achint Kumar, Sami Qutob, Balazs J Nyiri, Vinita Chauhan, Sangeeta Murugkar
Recent findings in populations exposed to ionizing radiation (IR) indicate dose-related lens opacification occurs at much lower doses (< 2Gy) than indicated in radiation protection guidelines. As a result, research efforts are now being directed towards identifying early predictors of lens degeneration resulting in cataractogenesis. In this study, Raman micro-spectroscopy was used to investigate the effects of varying doses of radiation, ranging from 0.01 Gy to 5 Gy, on human lens epithelial (HLE) cells which were chemically fixed 24 hrs post-irradiation...
December 13, 2017: Physics in Medicine and Biology
Quim Castellví, Borja Mercadal, Xavier Moll, Dolors Fondevila, Anna Andaluz, Antoni Ivorra
Electroporation based treatments typically consist in applying high voltage dc pulses. As an undesired side effect, these dc pulses cause electrical stimulation of excitable tissues such as motor nerves. In the present in vivo study, it was explored the use of bursts of sinusoidal voltage in the frequency range from 50 kHz to 2 MHz to induce irreversible electroporation (IRE) whilst avoiding neuromuscular stimulation. Series of 100 dc pulses or sinusoidal bursts, both with an individual duration of 100 µs, were delivered to rabbit liver through thin needles in a monopolar electrode configuration and thoracic movements were recorded with an accelerometer...
December 13, 2017: Physics in Medicine and Biology
Mitsutaka Yamaguchi, Yuto Nagao, Koki Ando, Seiichi Yamamoto, Makoto Sakai, Raj Kumar Parajuli, Kazuo Arakawa, Naoki Kawachi
A feasibility study on the imaging of monochromatic carbon-ion beams for carbon-ion therapy was performed. The evaluation was based on Monte Carlo simulations and beam-irradiation experiments, using a pinhole X-ray camera, which measured secondary electron bremsstrahlung (SEB). The simulation results indicated that the trajectories of the carbon-ion beams with injection energies of 278, 249 and 218 MeV/u in a water phantom, were clearly imaged by measuring the SEB with energies from 30 to 60 keV, using a pinhole camera...
December 13, 2017: Physics in Medicine and Biology
Juergen Weizenecker
Calculating the dynamic properties of magnetization of single-domain particles is of great importance for the tomographic imaging modality known as magnetic particle imaging (MPI). Although the assumption of instantaneous thermodynamic equilibrium (Langevin function) after application of time-dependent magnetic fields is sufficient for understanding the fundamental behavior, it is essential to consider the finite response times of magnetic particles for optimizing or analyzing various aspects, e.g., interpreting spectra, optimizing MPI sequences, developing new contrasts, and evaluating simplified models...
December 13, 2017: Physics in Medicine and Biology
Sebastian Sauppe, Julian Kuhm, Marcus Brehm, Pascal Paysan, Dieter Seghers, Marc Kachelriess
We propose a phase-to-amplitude resampling (PTAR) method to reduce motion blurring in motion-compensated (MoCo) 4D cone-beam CT (CBCT) image reconstruction, without increasing the computational complexity of the motion vector field (MVF) estimation approach. PTAR is able to improve the image quality in reconstructed 4D volumes including both regular and irregular respiration patterns. The PTAR approach starts with a robust phase gating procedure for the initial MVF estimation and then switches to a phase-adapted amplitude gating method...
December 13, 2017: Physics in Medicine and Biology
Matthew Scarpelli, Jens Eickhoff, Enrique Cuna, Scott Perlman, Robert Jeraj
The statistical analysis of positron emission tomography (PET) standardized uptake value (SUV) measurements is challenging due to the skewed nature of SUV distributions. This limits utilization of powerful parametric statistical models for analyzing SUV measurements. An ad-hoc approach, which is frequently used in practice, is to blindly use a log transformation, which may or may not result in normal SUV distributions. This study sought to identify optimal transformations leading to normally distributed PET SUVs extracted from tumors and assess the effects of therapy on the optimal transformations...
December 13, 2017: Physics in Medicine and Biology
Charlotte Constans, Philippe Mateo, Mickael Tanter, Jean-Francois Aubry
In the past decade, a handful but growing number of groups have reported worldwide successful low intensity focused ultrasound induced neurostimulation trials on rodents with effects ranging from movement elicitations to reduction of anesthesia time or reduction of the duration of drug induced seizures. The mechanisms underlying ultrasonic neuromodulation are still not fully understood. Given the low intensities used in most of the studies, a mechanical effect is more likely to be responsible for the neuromodulation effect, but a clear description of the thermal and mechanical effects is necessary to optimize clinical applications...
December 13, 2017: Physics in Medicine and Biology
Yue-Houng Hu, Joerg Rottmann, Rony Fueglistaller, Marios E Myronakis, Adam Wang, Pascal Huber, Daniel Shedlock, Daniel Morf, Paul Baturin, Josh M Star-Lack, Ross I Berbeco
While megavoltage (MV) cone-beam computed tomography (CBCT) using an electronic portal imaging device (EPID) provides many advantages over kilovoltage (kV) CBCT, clinical adoption is limited by its high doses. Multi-layer imager (MLI) EPIDs increase DQE(0) while maintaining high resolution. However, even well-designed, high-performance MLIs suffer from increased electronic noise from each readout, degrading low-dose image quality. To improve low-dose performance, shift-and-bin addition (ShiBA) imaging is proposed, leveraging the unique architecture of the MLI...
December 13, 2017: Physics in Medicine and Biology
Hideaki Ueda, Michihiro Furusaka, Taeko Matsuura, Shusuke Hirayama, Kikuo Umegaki
In spot-scanning proton therapy, highly precise beam control is required in the treatment nozzle such that the proton beam does not spread out during transportation by restraining the divergence of the beam angle and spot size, simultaneously. In order to evaluate the beam-broadening behaviour induced by passing through the various nozzle components, we have developed a new method to calculate the angular divergence profile of a proton beam in the nozzle. The angular divergence of the proton beam for each nozzle component is calculated by the Monte Carlo simulation code, Geant4, assuming that the initial beam has no divergence...
December 13, 2017: Physics in Medicine and Biology
Yane Li, Ming Fan, Hu Cheng, Peng Zhang, Bin Zheng, Lihua Li
This study aims to develop and test a new imaging marker-based short-term breast cancer risk prediction model. An age-matched dataset of 566 screening mammography cases was used. All "prior" images acquired in the two screening series were negative, while in the "current" screening images, 283 cases were positive for cancer and 283 cases remained negative. For each case, two bilateral cranio-caudal view mammograms acquired from the "prior" negative screenings were selected and processed by a computer-aided image processing scheme, which segmented the entire breast area into 9 strip-based local regions, extracted the element regions using difference of Gaussian filters, and computed both global- and local-based bilateral asymmetrical image features...
December 11, 2017: Physics in Medicine and Biology
Guillaume Maimbourg, Alexandre Houdouin, Thomas Deffieux, Mickael Tanter, Jean-Francois Aubry
The development of multi-element arrays for better control of the shape of ultrasonic beams has opened the way for focusing through highly aberrating media, such as the human skull. As a result, the use of brain therapy with transcranial-focused ultrasound has rapidly grown. Although effective, such technology is expensive. We propose a disruptive, low-cost approach that consists of focusing a 1-MHz ultrasound beam through a human skull with a single-element transducer coupled with a tailored silicone acoustic lens cast in a 3D-printed mold and designed using computed tomography-based numerical acoustic simulation...
December 8, 2017: Physics in Medicine and Biology
Pablo Botas, Clemens Grassberger, Gregory Sharp, Harald Paganetti
The purpose of this study was to investigate Internal Tumor Volume (ITV) density overwrite strategies to minimize Intensity Modulated Proton Therapy (IMPT) plan degradation of mobile lung tumors. Four planning paradigms were compared for nine lung cancer patients. IGTV and ICTV structures were defined encompassing their respective volumes in every 4DCT phase. The paradigms use different planning CT (pCT) created from the Average Intensity Projection (AIP) of the 4DCT, overwriting the density within the IGTV to account for movement...
December 8, 2017: Physics in Medicine and Biology
Jean-Guy Belliveau, Michael D Jensen, James M P Stewart, Igor Solovey, Martyn L Klassen, Glenn S Bauman, Ravi S Menon
Radiation necrosis remains an irreversible long-term side-effect following radiotherapy to the brain. The ability to predict areas that could ultimately develop into necrosis could lead to prevention and management of radiation necrosis. Materials and Methods: Fischer 344 rats were irradiated using two platforms (micro-CT irradiator and x-RAD 225 IGRT) with radiation up to 30 Gy for the micro-CT and 40 Gy for the xRAD-224 to half the brain. Animals were subsequently imaged using a 9.4T MRI scanner every 2-4 weeks for up to 28 weeks using a 7-echo gradient echo sequence...
December 8, 2017: Physics in Medicine and Biology
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