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Zeitschrift Für Medizinische Physik

S Howitz, T Wiezorek, A Wittig, H Vorwerk, K Zink
INTRODUCTION: Helical TomoTherapy allows a highly conformal dose distribution to complex target geometries with a good protection of organs at risk. However, the small field sizes associated with this method are a possible source of dosimetrical uncertainties. The IAEA has published detector-specific field output correction factors for static fields of the TomoTherapy in the TRS483. This work investigates the average subfield size of helical TomoTherapy plans. MATERIAL AND METHODS: A new parameter for helical TomoTherapy was defined - the fluence-weighted average subfield size...
May 2, 2019: Zeitschrift Für Medizinische Physik
Isabel Büsing, Andre Brant, Tobias Lange, Björn Delfs, Daniela Poppinga, Rafael Kranzer, Hui Khee Looe, Björn Poppe
INTRODUCTION: The aim of the present work is to perform dosimetric characterization of a novel vented PinPoint ionization chamber (PTW 31023, PTW-Freiburg, Germany). This chamber replaces the previous model (PTW 31014), where the diameter of the central electrode has been increased from 0.3 to 0.6mm and the guard ring has been redesigned. Correction factors for reference and non-reference measurement conditions were examined. MATERIALS AND METHODS: Measurements and calculations of the correction factors were performed according to the DIN 6800-2...
March 13, 2019: Zeitschrift Für Medizinische Physik
Jan Martin, Sebastian Endt, Andreas Wetscherek, Tristan Anselm Kuder, Arnd Doerfler, Michael Uder, Bernhard Hensel, Frederik Bernd Laun
Diffusion anisotropy in diffusion tensor imaging (DTI) is commonly quantified with normalized diffusion anisotropy indices (DAIs). Most often, the fractional anisotropy (FA) is used, but several alternative DAIs have been introduced in attempts to maximize the contrast-to-noise ratio (CNR) in diffusion anisotropy maps. Examples include the scaled relative anisotropy (sRA), the gamma variate anisotropy index (GV), the surface anisotropy (UAsurf ), and the lattice index (LI). With the advent of multidimensional diffusion encoding it became possible to determine the presence of microscopic diffusion anisotropy in a voxel, which is theoretically independent of orientation coherence...
March 7, 2019: Zeitschrift Für Medizinische Physik
Jürgen R Reichenbach
No abstract text is available yet for this article.
February 19, 2019: Zeitschrift Für Medizinische Physik
Steffen Bollmann, Matilde Holm Kristensen, Morten Skaarup Larsen, Mathias Vassard Olsen, Mads Jozwiak Pedersen, Lasse Riis Østergaard, Kieran O'Brien, Christian Langkammer, Amir Fazlollahi, Markus Barth
Quantitative susceptibility mapping (QSM) reveals pathological changes in widespread diseases such as Parkinson's disease, Multiple Sclerosis, or hepatic iron overload. QSM requires multiple processing steps after the acquisition of magnetic resonance imaging (MRI) phase measurements such as unwrapping, background field removal and the solution of an ill-posed field-to-source-inversion. Current techniques utilize iterative optimization procedures to solve the inversion and background field correction, which are computationally expensive and lead to suboptimal or over-regularized solutions requiring a careful choice of parameters that make a clinical application of QSM challenging...
February 14, 2019: Zeitschrift Für Medizinische Physik
A-K Schnurr, K Chung, T Russ, L R Schad, F G Zöllner
Non-conventional scan trajectories for interventional three-dimensional imaging promise low-dose interventions and a better radiation protection to the personnel. Circular tomosynthesis (cTS) scan trajectories yield an anisotropical image quality distribution. In contrast to conventional Computed Tomographies (CT), the reconstructions have a preferred focus plane. In the other two perpendicular planes, limited angle artifacts are introduced. A reduction of these artifacts leads to enhanced image quality while maintaining the low dose...
February 13, 2019: Zeitschrift Für Medizinische Physik
Matthias Malzacher, Jorge Chacon-Caldera, Nadia Paschke, Lothar R Schad
Sodium magnetic resonance imaging (MRI) of the human abdomen is of increasing clinical interest for e.g. kidney, intervertebral disks, prostate and tumor monitoring examinations in the abdomen. To overcome the low MR sensitivity of sodium, optimal radio frequency (RF) structures should be used. A common approach is to combine a volumetric transmit coil for homogeneous excitation with an array of sensitive receive coils adapted to the human shape. Additionally, proton imaging is required to match the physiological sodium images to the morphological proton images...
February 11, 2019: Zeitschrift Für Medizinische Physik
Andreas Maier, Christopher Syben, Tobias Lasser, Christian Riess
This paper tries to give a gentle introduction to deep learning in medical image processing, proceeding from theoretical foundations to applications. We first discuss general reasons for the popularity of deep learning, including several major breakthroughs in computer science. Next, we start reviewing the fundamental basics of the perceptron and neural networks, along with some fundamental theory that is often omitted. Doing so allows us to understand the reasons for the rise of deep learning in many application domains...
January 24, 2019: Zeitschrift Für Medizinische Physik
Andreas Rinscheid, Jeesoo Lee, Peter Kletting, Ambros J Beer, Gerhard Glatting
AIM: For dosimetry in radioligand therapy, the time-integrated activity coefficients (TIACs) for organs at risk and for tumour lesions have to be determined. The used sampling scheme affects the TIACs and therefore the calculated absorbed doses. The aim of this work was to develop a general and flexible method, which analyses numerous clinically applicable sampling schedules using true time-activity curves (TACs) of virtual patients. METHOD: Nine virtual patients with true TACs of the tumours were created using a physiologically-based pharmacokinetic (PBPK) model and individual biokinetic data of five patients with neuroendocrine tumours and four with meningioma...
January 2, 2019: Zeitschrift Für Medizinische Physik
Nina Jacobsen, Andreas Deistung, Dagmar Timmann, Sophia L Goericke, Jürgen R Reichenbach, Daniel Güllmar
INTRODUCTION: Convolutional neural networks have begun to surpass classical statistical- and atlas based machine learning techniques in medical image segmentation in recent years, proving to be superior in performance and speed. However, a major challenge that the community faces are mismatch between variability within training and evaluation datasets and therefore a dependency on proper data pre-processing. Intensity normalization is a widely applied technique for reducing the variance of the data for which there are several methods available ranging from uniformity transformation to histogram equalization...
December 19, 2018: Zeitschrift Für Medizinische Physik
Gunnar Brix, Jürgen Griebel, Renate Czarwinski
The increasing frequency and complexity of medical radiation exposures to humans inevitably result in higher risks of harmful unintended or accidental radiation exposures. To ensure a high level of protection and its continuous improvement, the Directive 2013/59/Euratom thus requires to systematically record and analyze both events and near-miss events as well as, in the case of their significance, to disseminate information regarding lessons learned from these events promptly and nationwide to improve radiation protection in medicine...
December 15, 2018: Zeitschrift Für Medizinische Physik
Alexander Selvikvåg Lundervold, Arvid Lundervold
What has happened in machine learning lately, and what does it mean for the future of medical image analysis? Machine learning has witnessed a tremendous amount of attention over the last few years. The current boom started around 2009 when so-called deep artificial neural networks began outperforming other established models on a number of important benchmarks. Deep neural networks are now the state-of-the-art machine learning models across a variety of areas, from image analysis to natural language processing, and widely deployed in academia and industry...
December 12, 2018: Zeitschrift Für Medizinische Physik
Gregor Bruggmoser, Rainer Saum, Rafael Kranzer
This addendum provides correction factors for the recombination and the polarity effect for the new ionization chamber PTW PinPoint (type 31023). The measurements were made in filtered (WFF) and unfiltered (FFF) high-energy photon beams. It could be confirmed that both the initial and the general recombination effect of the chamber mainly depends on dose per pulse at the point of measurement and is independent of the filtration of the photon beam.
December 5, 2018: Zeitschrift Für Medizinische Physik
Alina Nickel, David Milford, Manuel Fischer, Martin Bendszus, Sabine Heiland
INTRODUCTION: Glioblastoma multiforme is the most frequent innate brain tumor and still yields an unfavorable prognosis of 15 months of survival after diagnosis. Animal models play an important role in the investigation of therapeutic strategies of brain tumors. Thereby, MRI is substantial to individual follow-up examination for therapeutic response. Contrast agent dosage at 1.5 and 3T MRI has been thoroughly tested, while there is hardly any data for 9.4T. Therefore, the aim of this study was to find the optimal contrast agent dosage at 9...
November 20, 2018: Zeitschrift Für Medizinische Physik
Daniela Thorwarth
No abstract text is available yet for this article.
November 15, 2018: Zeitschrift Für Medizinische Physik
K Niepel, F Kamp, C Kurz, D Hansen, S Rit, S Neppl, J Hofmaier, D Bondesson, C Thieke, J Dinkel, C Belka, K Parodi, G Landry
Inter-fractional variations of breathing pattern and patient anatomy introduce dose uncertainties in proton therapy. One approach to monitor these variations is to utilize the cone-beam computed tomography (CT, CBCT) scans routinely taken for patient positioning, reconstruct them as 4DCBCTs, and generate 'virtual CTs' (vCTs), combining the accurate CT numbers of the diagnostic 4DCT and the geometry of the daily 4DCBCT by using deformable image registration (DIR). In this study different algorithms for 4DCBCT reconstruction and DIR were evaluated...
November 14, 2018: Zeitschrift Für Medizinische Physik
Heiko Neeb, Jochen Schenk
OBJECTIVES: The current work investigates the performance of different multivariate supervised machine learning models to predict the presence or absence of multiple sclerosis (MS) based on features derived from quantitative MRI acquisitions. The performance of these models was evaluated for images which are significantly degraded due to subject motion, a problem which is often observed in clinical routine diagnostics. Finally, the difference between a true multivariate analysis and the corresponding univariate analysis based on single parameters alone was addressed...
November 12, 2018: Zeitschrift Für Medizinische Physik
Christopher Kurz, Philipp Süss, Carolin Arnsmeyer, Jonas Haehnle, Katrin Teichert, Guillaume Landry, Jan Hofmaier, Florian Exner, Lucas Hille, Florian Kamp, Christian Thieke, Ute Ganswindt, Chiara Valentini, Tobias Hölscher, Esther Troost, Mechthild Krause, Claus Belka, Karl-Heinz Küfer, Katia Parodi, Christian Richter
Proton radiotherapy (PT) requires accurate target alignment before each treatment fraction, ideally utilizing 3D in-room X-ray computed tomography (CT) imaging. Typically, the optimal patient position is determined based on anatomical landmarks or implanted markers. In the presence of non-rigid anatomical changes, however, the planning scenario cannot be exactly reproduced and positioning should rather aim at finding the optimal position in terms of the actually applied dose. In this work, dose-guided patient alignment, implemented as multicriterial optimization (MCO) problem, was investigated in the scope of intensity-modulated and double-scattered PT (IMPT and DSPT) for the first time...
November 5, 2018: Zeitschrift Für Medizinische Physik
Martin Fiebich, Ulrich Wolf
No abstract text is available yet for this article.
October 29, 2018: Zeitschrift Für Medizinische Physik
Giulio Rossi, Mark Gainey, Benedikt Thomann, Michael Kollefrath, Jan Würfel, Bernd Allgaier, Dimos Baltas
The purpose of this study was to investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW-Freiburg, Germany) for radial dose function measurements with High Dose Rate (HDR) 192 Ir brachytherapy sources. An HDR 192 Ir source model mHDR v2r (Nucletron BV, an Elekta company, The Netherlands) was placed at the centre of a MP3 water phantom (PTW-Freiburg, Germany) within a 4F needle. Three mDDs were employed to measure the radial dose function of the source by acquiring profiles along the source transverse axis...
October 16, 2018: Zeitschrift Für Medizinische Physik
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