104 research outputs found
Analysis of the acoustlc transients in the pulse response of the linear electro-optic effect
The pulse response of the linear electro-optic effect is investigated with high temporal and spatial resolution in KDP, KD*P, and biaxial LiCOOH · H2O. Experimental results, which are explained theoretically, show that the piezo-optic transients induced by the piezoelectric effect, are generated by stress release waves. Starting from the surfaces, these excite by reflection, diffraction, and superposition, due to the finite crystal dimensions, normal vibration modes too. It is shown that the direct electro-optic effect can be measured for all crystal classes at the beginning of the pulse response. The pulse method also yields static electro-optic, piezo-optic, and elastic constants. The values of r63, r63, p66 and c66 measured in KDP, agree well with those of other authors. Measurement of the direct electro-optic effect of LiCOOH · H2O in some directions yields values within 1 to 4 × 10-12 m/V
Sarrazin
Debatte um die Thesen von Sarrazin.Debate about Sarrazin\u27s book
Normalized STEAM-based diffusion tensor imaging provides a robust assessment of muscle tears in football players: preliminary results of a new approach to evaluate muscle injuries
Objectives: To assess acute muscle tears in professional football players by diffusion tensor imaging (DTI) and evaluate the impact of normalization of data.
Methods: Eight football players with acute lower limb muscle tears were examined. DTI metrics of the injured muscle and corresponding healthy contralateral muscle and of ROIs drawn in muscle tears (ROItear) in the corresponding healthy contralateral muscle (ROIhc_t) in a healthy area ipsilateral to the injury (ROIhi) and in a corresponding contralateral area (ROIhc_i) were compared. The same comparison was performed for ratios of the injured (ROItear/ROIhi) and contralateral sides (ROIhc_t/ROIhc_i). ANOVA, Bonferroni corrected post-hoc and Students t-tests were used.
Results: Analyses of the entire muscle did not show any differences (p>0.05 each) except for axial diffusivity (AD; p=0.048). ROItear showed higher mean diffusivity (MD) and AD than ROIhc_t (p<0.05). Fractional anisotropy (FA) was lower in ROItear than in ROIhi and ROIhc_t (p<0.05). Radial diffusivity (RD) was higher in ROItear than in any other ROI (p<0.05). Ratios revealed higher MD and RD and lower FA and reduced number and length of fibre tracts on the injured side (p<0.05 each).
Conclusions: DTI allowed a robust assessment of muscle tears in athletes especially after normalization to healthy muscle tissue.
Key Points
STEAM-based DTI allows the investigation of muscle tears affecting professional football players.
Fractional anisotropy and mean diffusivity differ between injured and healthy muscle areas.
Only normalized data show differences of fibre tracking metrics in muscle tears.
The normalization of DTI-metrics enables a more robust characterization of muscle tears.(VLID)475075
Real-time motion and retrospective coil sensitivity correction for CEST using volumetric navigators (vNavs) at 7T
Purpose To explore the impact of temporal motion-induced coil sensitivity changes on CEST-MRI at 7T and its correction using interleaved volumetric EPI navigators, which are applied for real-time motion correction. Methods Five healthy volunteers were scanned via CEST. A 4-fold correction pipeline allowed the mitigation of (1) motion, (2) motion-induced coil sensitivity variations, Delta B1-, (3) motion-induced static magnetic field inhomogeneities, Delta B-0, and (4) spatially varying transmit RF field fluctuations, Delta B1+. Four CEST measurements were performed per session. For the first 2, motion correction was turned OFF and then ON in absence of voluntary motion, whereas in the other 2 controlled head rotations were performed. During post-processing Delta B1- was removed additionally for the motion-corrected cases, resulting in a total of 6 scenarios to be compared. In all cases, retrospective increment B-0 and -Delta B1+ corrections were performed to compute artifact-free magnetization transfer ratio maps with asymmetric analysis (MTRasym). Results Dynamic Delta B1- correction successfully mitigated signal deviations caused by head motion. In 2 frontal lobe regions of volunteer 4, induced relative signal errors of 10.9% and 3.9% were reduced to 1.1% and 1.0% after correction. In the right frontal lobe, the motion-corrected MTRasym contrast deviated 0.92%, 1.21%, and 2.97% relative to the static case for Delta omega = 1, 2, 3 +/- 0.25 ppm. The additional application of Delta B1- correction reduced these deviations to 0.10%, 0.14%, and 0.42%. The fully corrected MTRasym values were highly consistent between measurements with and without intended head rotations. Conclusion Temporal Delta B1- cause significant CEST quantification bias. The presented correction pipeline including the proposed retrospective Delta B1- correction significantly reduced motion-related artifacts on CEST-MRI.Peer reviewe
Noise-reduction techniques for 1H-FID-MRSI at 14.1T: Monte-Carlo validation & in vivo application
Proton magnetic resonance spectroscopic imaging (1H-MRSI) is a powerful tool
that enables the multidimensional non-invasive mapping of the neurochemical
profile at high-resolution over the entire brain. The constant demand for
higher spatial resolution in 1H-MRSI led to increased interest in
post-processing-based denoising methods aimed at reducing noise variance. The
aim of the present study was to implement two noise-reduction techniques, the
Marchenko-Pastur principal component analysis (MP-PCA) based denoising and the
low-rank total generalized variation (LR-TGV) reconstruction, and to test their
potential and impact on preclinical 14.1T fast in vivo 1H-FID-MRSI datasets.
Since there is no known ground truth for in vivo metabolite maps, additional
evaluations of the performance of both noise-reduction strategies were
conducted using Monte-Carlo simulations. Results showed that both denoising
techniques increased the apparent signal-to-noise ratio SNR while preserving
noise properties in each spectrum for both in vivo and Monte-Carlo datasets.
Relative metabolite concentrations were not significantly altered by either
methods and brain regional differences were preserved in both synthetic and in
vivo datasets. Increased precision of metabolite estimates was observed for the
two methods, with inconsistencies noted on lower concentrated metabolites. Our
study provided a framework on how to evaluate the performance of MP-PCA and
LR-TGV methods for preclinical 1H-FID MRSI data at 14.1T. While gains in
apparent SNR and precision were observed, concentration estimations ought to be
treated with care especially for low-concentrated metabolites.Comment: Brayan Alves and Dunja Simicic are joint first authors. Currently in
revision for NMR in Biomedicin
Controlled Stark shifts in Er-doped crystalline and amorphous waveguides for quantum state storage
We present measurements of the linear Stark effect on the I I transition in an Er-doped proton-exchanged
LiNbO crystalline waveguide and an Er-doped silicate fiber. The
measurements were made using spectral hole burning techniques at temperatures
below 4 K. We measured an effective Stark coefficient
kHz/Vcm in the crystalline waveguide and
kHz/Vcm in the silicate fiber.
These results confirm the potential of Erbium doped waveguides for quantum
state storage based on controlled reversible inhomogeneous broadening.Comment: 4 pages, 2 figures v2. typo in formula correcte
A comparison of 7 Tesla MR spectroscopic imaging and 3 Tesla MR fingerprinting for tumor localization in glioma patients
This paper investigates the correlation between magnetic resonance
spectroscopic imaging (MRSI) and magnetic resonance fingerprinting (MRF) in
glioma patients by comparing neuro-oncological markers obtained from MRSI to
T1/T2 maps from MRF.
Data from 12 consenting patients with gliomas were analyzed by defining
hotspots for T1, T2 and various metabolic ratios, and comparing them using
S{\o}rensen-Dice Similarity Coefficients (DSCs) and the distances between their
centers of intensity (COIDs).
Median DSCs between MRF and the tumor segmentation were 0.73 (T1) and 0.79
(T2). The DSCs between MRSI and MRF were highest for Gln/tNAA (T1: 0.75, T2:
0.80, tumor: 0.78), followed by Gly/tNAA (T1: 0.57, T2: 0.62, tumor: 0.54) and
tCho/tNAA (T1: 0.61, T2: 0.58, tumor: 0.45). The median values in the tumor
hotspot were T1=1724 ms, T2=86 ms, Gln/tNAA=0.61, Gly/tNAA=0.28, Ins/tNAA=1.15,
and tCho/tNAA=0.48, and, in the peritumoral region, were T1=1756 ms, T2=102ms,
Gln/tNAA=0.38, Gly/tNAA=0.20, Ins/tNAA=1.06, and tCho/tNAA=0.38, and, in the
NAWM, were T1=950 ms, T2=43 ms, Gln/tNAA=0.16, Gly/tNAA=0.07, Ins/tNAA=0.54,
and tCho/tNAA=0.20.
The results of this study constitute the first comparison of 7T MRSI and 3T
MRF, showing a good correspondence between these methods.Comment: Includes 3 tables, 6 figures, 3 supplementary tables, and 4
supplementary figure
Fast high-resolution metabolite mapping in the rat brain using 1H-FID-MRSI at 14.1T
Magnetic resonance spectroscopic imaging (MRSI) enables the simultaneous
non-invasive acquisition of MR spectra from multiple spatial locations inside
the brain. While 1H-MRSI is increasingly used in the human brain, it is not yet
widely applied in the preclinical settings, mostly because of difficulties
specifically related to very small nominal voxel size in the rodent brain and
low concentration of brain metabolites, resulting in low signal-to-noise ratio
SNR.
In this context, we implemented a free induction decay 1H-MRSI sequence
(1H-FID-MRSI) in the rat brain at 14.1T. We combined the advantages of
1H-FID-MRSI with the ultra-high magnetic field to achieve higher SNR, coverage
and spatial resolution in the rodent brain, and developed a custom dedicated
processing pipeline with a graphical user interface: MRS4Brain toolbox.
LCModel fit, using the simulated metabolite basis-set and in-vivo measured
MM, provided reliable fits for the data at acquisition delays of 1.3 and 0.94
ms. The resulting Cram\'er-Rao lower bounds were sufficiently low (<40%) for
eight metabolites of interest, leading to highly reproducible metabolic maps.
Similar spectral quality and metabolic maps were obtained between 1 and 2
averages, with slightly better contrast and brain coverage due to increased SNR
in the latter case. Furthermore, the obtained metabolic maps were accurate
enough to confirm the previously known brain regional distribution of some
metabolites. The acquisitions proved high repeatability over time.
We demonstrated that the increased SNR and spectral resolution at 14.1T can
be translated into high spatial resolution in 1H-FID-MRSI of the rat brain in
13 minutes, using the sequence and processing pipeline described herein.
High-resolution 1H-FID-MRSI at 14.1T provided reproducible and high-quality
metabolic mapping of brain metabolites with significantly reduced technical
limitations.Comment: Dunja Simicic and Brayan Alves are joint first author
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