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  • 1
    Keywords: HEALTH ; MOBILE
    Type of Publication: Journal article published
    PubMed ID: 16008077
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  • 2
    Keywords: brain ; IMAGES ; imaging ; SYSTEM ; TISSUE ; CONTRAST ; MR ; MRI ; SEQUENCE ; SEQUENCES ; SIGNAL ; FIELD ; WATER ; magnetic resonance imaging ; NMR ; PARAMETERS ; MR imaging ; HEALTHY-VOLUNTEERS ; methods ; technique ; correlation ; Sensitivity and Specificity ; LIQUID ; PHANTOMS ; DISTANCES ; Image Processing,Computer-Assisted ; Protons ; Quantum Theory
    Abstract: Dipole-dipole interactions in 1H NMR of liquids permit a new tissue contrast in MR imaging (MRI). For this purpose, the CRAZED (COSY Revamped by Asymmetric Z-gradient Echo Detection) sequence which simply consists of two radiofrequency pulses of delay tau and a magnetic field gradient pulse of strength G, is applied to create intermolecular multiple-quantum coherences of dipolar-coupled ensembles of water protons with spatial distance d = pi/(gammaGtau). As a consequence, the measured signal originates from "sources" that have a tunable dimension. CRAZED was first applied to MR imaging at 1.5 T by Zhong et al. To study the contrast properties and influence of sequence parameters of this technique, we implemented different sequences of this type on a clinical 1.5-T whole-body tomograph. The sequences were optimized in experiments with agar gel phantoms. We obtained images with dipolar contrast from the brain of healthy volunteers. The gradient system enabled correlation distances d in the range of 0.05 mm to 1 mm
    Type of Publication: Journal article published
    PubMed ID: 16986458
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  • 3
    Keywords: imaging ; TIME ; magnetic resonance imaging ; RELAXATION ; MR imaging ; methods ; PROFILES ; Sensitivity and Specificity ; EXCITATION ; Time Factors ; Image Processing,Computer-Assisted
    Abstract: Half pulse excitation plays an important role in imaging with ultra-short echo times (UTE imaging) of the order of TE 〈 100 micros. Based on half RF-pulses this method was theoretically modeled and experimentally applied in 1991 for the first time. Following this work, measurements of slice profiles produced by half pulses were performed and results were compared to the slice profiles produced by the original full pulse. Furthermore, the hypothesis was tested that short RF pulses may be of advantage in minimizing the relaxation effects during the pulse. Within the scope of these measurements no dependency of slice profile on the pulse duration could be found
    Type of Publication: Journal article published
    PubMed ID: 16986459
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  • 4
    Keywords: SPECTRA ; Germany ; human ; IN-VIVO ; VIVO ; INFORMATION ; QUANTIFICATION ; SYSTEM ; SYSTEMS ; TISSUE ; DYNAMICS ; FIELD ; magnetic resonance ; MAGNETIC-RESONANCE ; MAGNETIC-RESONANCE-SPECTROSCOPY ; METABOLITES ; SPECTROSCOPY ; NMR ; NMR-SPECTROSCOPY ; LINE ; PARAMETERS ; PREDICTION ; IMMOBILIZATION ; METABOLITE ; MOLECULAR-DYNAMICS ; biosensor ; molecular ; review ; TRANSITION ; interaction ; SPINS ; muscle tissue ; carnosine ; human calf muscle ; analysis ; NUCLEAR ; MECHANICS ; USA ; in vivo ; SPECTRUM ; magnetic resonance spectroscopy ; comparison ; RESONANCE ; German ; SHAPE ; TRANSITIONS ; CONSTRAINTS ; molecular dynamics ; Breit-Rabi equation ; H-1-NMR ; H-1-NMR SPECTROSCOPY ; hyperfine structure ; in vivo spectroscopy ; interactions ; P-31-NMR ; PHOSPHOCREATINE ; SPIN
    Abstract: The hyperfine interaction of two spins is a well studied effect in atomic systems. Magnetic resonance experiments demonstrate that the detectable dipole transitions are determined by the magnetic moments of the constituents and the external magnetic field. Transferring the corresponding quantum mechanics to molecular bound nuclear spins allows for precise prediction of NMR spectra obtained from metabolites in human tissue. This molecular hyperfine structure has been neglected so far in in vivo NMR spectroscopy but contains useful information, especially when studying molecular dynamics. This contribution represents a review of the concept of applying the Breit-Rabi formalism to coupled nuclear spins and discusses the immobilization of different metabolites in anisotropic tissue revealed by H-1 NMR spectra of carnosine, phosphocreatine and taurine. Comparison of atomic and molecular spin systems allows for statements on the biological constraints for direct spin-spin interactions. Moreover, the relevance of hyperfine effects on the line shapes of multiplets of indirectly-coupled spin systems with more than two constituents can be predicted by analyzing quantum mechanical parameters. As an example, the superposition of eigenstates of the AMX system of adenosine 5'-triphosphate and its application for better quantification of P-31-NMR spectra will be discussed
    Type of Publication: Journal article published
    PubMed ID: 17665732
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  • 5
    Keywords: OPTIMIZATION ; radiotherapy ; Germany ; THERAPY ; ALGORITHM ; ALGORITHMS ; imaging ; TOOL ; NUCLEAR-MEDICINE ; radiation ; TIME ; FIELD ; RADIATION-THERAPY ; MODULATION ; nuclear medicine ; IMRT ; proton therapy ; radiology ; RE ; THERAPIES ; intensity ; radiation therapy ; methods ; NUCLEAR ; technique ; IMPROVEMENT ; PHOTON ; IMPT ; MEDICINE ; comparison ; conjugate gradient ; TREATMENT PLANS ; L-BFGS ; quasi-newton methods
    Abstract: In intensity modulated treatment techniques, the modulation of each treatment field is obtained using an optimization algorithm. Multiple optimization algorithms have been proposed in the literature, e.g. steepest descent, conjugate gradient, quasi-Newton methods to name a few. The standard optimization algorithm in our in-house inverse planning tool KonRad is a quasi-Newton algorithm. Although this algorithm yields good results, it also has some drawbacks. Thus we implemented an improved optimization algorithm based on the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) routine. In this paper the improved optimization algorithm is described. To compare the two algorithms, several treatment plans are optimized using both algorithms. This included photon (IMRT) as well as proton (IMPT) intensity modulated therapy treatment plans. To present the results in a larger context the widely used conjugate gradient algorithm was also included into this comparison. On average, the improved optimization algorithm was six times faster to reach the same objective function value. However, it resulted not only in an acceleration of the optimization. Due to If the faster convergence, the improved optimization algorithm usually terminates the optimization process at a lower objective function value. The average of the observed improvement in the objective function value was 37%. This improvement is clearly visible in the corresponding dose-volume-histograms. The benefit of the improved optimization algorithm is particularly pronounced in proton therapy plans. The conjugate gradient algorithm ranked in between the other two algorithms with an average speedup factor of two and an average improvement of the objective function value of 30%
    Type of Publication: Journal article published
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  • 6
    Keywords: SPECTRA ; Germany ; ALGORITHM ; CT ; IMAGES ; imaging ; SYSTEM ; TISSUE ; RESOLUTION ; radiation ; CONTRAST ; ENERGY ; tomography ; COMPUTED-TOMOGRAPHY ; CALIBRATION ; radiology ; ENHANCEMENT ; ACCURATE ; BONE ; PHANTOMS ; phantom ; COEFFICIENTS ; IGRT ; 3 ; WELL ; NOISE ; AIR GAPS ; CORRECTION ALGORITHM ; CT SCANNERS ; DIAGNOSTIC-RADIOLOGY ; DIGITAL RADIOGRAPHY ; fast beam hardening correction ; fast iterative scatter correction ; FLAT-PANEL IMAGER ; kV CBCT ; MONTE-CARLO SIMULATION ; RADIATION DISTRIBUTION ; X-RAY SCATTER
    Abstract: The problem of the enormous amount of scattered radiation in kV CBCT (kilo voltage cone beam computer tomography) is addressed Scatter causes undesirable streaks and cup-artifacts and results in a quantitative inaccuracy of reconstructed CT numbers, so that an accurate close calculation might be impossible Image contrast is also significantly reduced. Therefore we checked whether at? appropriate implementation of the fast iterative scatter correction algorithm we have developed for M V (mega voltage) CBCT reduces the scatter contribution in a kV CBCT as well. This scatter correction method is based on a superposition of pre-calculated Monte Carlo generated pencil beam scatter kernels. The algorithm requires only a system calibration by measuring homogeneous slab phantoms with known water-equivalent thicknesses.It this study we compare scatter corrected CBCT images of several phantoms to the fan beam CT images acquired with a reduced cone angle (a slice-thickness of 14 mm in the isocenter) at the same system. Additional measurements at a different CBCT system were made (different, energy spectrum and phantom-to-detector distance) and a first order approach of a fast beam hardening correction will be introduced. The observed image quality of the scatter corrected CBCT images is comparable concerning resolution, noise and contrast-to-noise ratio to the images acquired in fan beam geometry. Compared to the CBCT without any corrections the contrast of the contrast-and-resolution phantom with scatter correction and additional beam hardening correction is improved by a factor of about 1.5. The reconstructed attenuation coefficients and the CT numbers of the scatter corrected CBCT images are close to the values of the images acquired in fan beam geometry for the most pronounced tissue types. Only for extreme dense tissue types like cortical bone we see a difference in CT numbers of 5.2%, which can be improved to 4.4% with the additional beam hardening correction. Capping is reduced from 20% to 4% with scatter correction and 3% with an additional beam hardening correction. After 3 iterations (small phantoms,) and 6 to 7 iterations (large phantoms) the algorithm converges. Therefore the algorithm is very fast, that means 1.3 seconds per projection for 3 iterations, on a standard PC
    Type of Publication: Journal article published
    PubMed ID: 19761093
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  • 7
    Keywords: DIAGNOSIS ; imaging ; magnetic resonance imaging ; HUMANS ; physiology ; STROKE ; DIFFUSION ; NEURONS ; methods ; multiple sclerosis ; ANISOTROPY ; Alzheimer Disease ; Brain Diseases ; Diagnostic Imaging
    Type of Publication: Journal article published
    PubMed ID: 19459579
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  • 8
    Keywords: THERAPY ; ALGORITHM ; validation ; IMAGE REGISTRATION ; algorithm validation ; evaluation registration ; landmark acquisition ; registration algorithm ; REGISTRATION TECHNIQUES ; software assistant
    Abstract: It is crucial to evaluate registration algorithms in order to make them available in clinical practice. Several evaluation strategies have been proposed in the past, and one approach is to evaluate these algorithms with intrinsic anatomical landmarks identified by a health professional. The acquisition and handling of large amounts of these landmark data is a time-consuming task for the health professional, and it is vulnerable to errors and inconsistencies. Additionally, limited access to appropriate tools makes dealing with landmark data considerably more difficult. We introduce a strategy for the acquisition of landmarks for the landmark-based evaluation of registration algorithms and we present an ontology-driven software tool that assists the different partners involved to act according to that strategy. This tool provides the user with intrinsic knowledge of the registration problems, the possibility to conveniently make the acquired data available to further processing, and an easy-to-use graphical interface.
    Type of Publication: Journal article published
    PubMed ID: 20888204
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  • 9
    Keywords: radiotherapy ; MODEL ; TISSUE ; MONTE-CARLO SIMULATIONS ; CALIBRATION ; SINGLE ; dosimetry ; SCANNER ; PROTON STOPPING POWER ; CT NUMBERS
    Abstract: Inaccurate conversion of CT data to water-equivalent path length (WEPL) is one of the most important uncertainty sources in ion treatment planning. Dual energy CT (DECT) imaging might help to reduce CT number ambiguities with the additional information. In our study we scanned a series of materials (tissue substitutes, aluminum, PMMA, and other polymers) in the dual source scanner (Siemens Somatom Definition Flash). Based on the 80 kVp/140Sn kVp dual energy images, the electron densities rho(e) and effective atomic numbers Z(eff) were calculated. We introduced a new lookup table that translates the rho(e) to the WEPL. The WEPL residuals from the calibration were significantly reduced for the investigated tissue surrogates compared to the empirical Hounsfield-look-up table (single energy CT imaging) from (-1.0 +/- 1.8)% to (0.1 +/- 0.7)% and for non-tissue equivalent PMMA from -7.8% to -1.0%. To assess the benefit of the new DECT calibration, we conducted a treatment planning study for three different idealized cases based on tissue surrogates and PMMA. The DECT calibration yielded a significantly higher target coverage in tissue surrogates and phantom material (i.e. PMMA cylindo; mean target coverage improved from 62% to 98%). To verify the DECT calibration for real tissue, ion ranges through a frozen pig head were measured and compared to predictions calculated by the standard single energy CT calibration and the novel DECT calibration. By using this method, an improvement of ion range estimation from -2.1% water-equivalent thickness deviation (single energy CT) to 0.3% (DECT) was achieved. If one excludes raypaths located on the edge of the sample accompanied with high uncertainties, no significant difference could be observed.
    Type of Publication: Journal article published
    PubMed ID: 23597413
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  • 10
    Abstract: For translational cancer research, preclinical in-vivo studies using small animals have become indispensable in bridging the gap between in-vitro cell experiments and clinical implementation. When setting up such small animal experiments, various biological, technical and methodical aspects have to be considered. In this work we present a comprehensive topical review based on relevant publications on irradiation techniques used for preclinical cancer research in mice and rats. Clinical radiotherapy treatment devices for the application of external beam radiotherapy and brachytherapy as well as dedicated research irradiation devices are feasible for small animal irradiation depending on the animal model and the experimental goals. In this work, appropriate solutions for the technological transfer of human radiation oncology to small animal radiation research are summarised. Additionally, important information concerning the experimental design is provided such that reliable and clinically relevant results can be attained.
    Type of Publication: Journal article published
    PubMed ID: 25125191
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