TY  - JOUR
A1  - Orzada, Stephan
A1  - Fiedler, Thomas M.
A1  - Bitz, Andreas
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - Local SAR compression with overestimation control to reduce maximum relative SAR overestimation and improve multi-channel RF array performance
JF  - Magnetic Resonance Materials in Physics, Biology and Medicine
N2  - Objective
In local SAR compression algorithms, the overestimation is generally not linearly dependent on actual local SAR. This can lead to large relative overestimation at low actual SAR values, unnecessarily constraining transmit array performance.

Method
Two strategies are proposed to reduce maximum relative overestimation for a given number of VOPs. The first strategy uses an overestimation matrix that roughly approximates actual local SAR; the second strategy uses a small set of pre-calculated VOPs as the overestimation term for the compression.

Result
Comparison with a previous method shows that for a given maximum relative overestimation the number of VOPs can be reduced by around 20% at the cost of a higher absolute overestimation at high actual local SAR values.

Conclusion
The proposed strategies outperform a previously published strategy and can improve the SAR compression where maximum relative overestimation constrains the performance of parallel transmission.
Y1  - 2020
SN  - 1352-8661
U6  - http://dx.doi.org/10.1007/s10334-020-00890-0
IS  - 34 (2021)
SP  - 153
EP  - 164
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Johst, Sören
A1  - Maderwald, Stefan
A1  - Bitz, Andreas
A1  - Solbach, Klaus
A1  - Ladd, Mark E.
T1  - Mitigation of B1(+) inhomogeneity on single-channel transmit systems with TIAMO
JF  - Magnetic Resonance in Medicine
Y1  - 2013
U6  - http://dx.doi.org/10.1002/mrm.24453
SN  - 1522-2594
VL  - 70
IS  - 1
SP  - 290
EP  - 294
PB  - Wiley
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Ladd, Mark E.
A1  - Bitz, Andreas
T1  - A method to approximate maximum local SAR in multichannel transmit MR systems without transmit phase information
JF  - Magnetic Resonance in Medicine
N2  - Purpose
To calculate local specific absorption rate (SAR) correctly, both the amplitude and phase of the signal in each transmit channel have to be known. In this work, we propose a method to derive a conservative upper bound for the local SAR, with a reasonable safety margin without knowledge of the transmit phases of the channels.

Methods
The proposed method uses virtual observation points (VOPs). Correction factors are calculated for each set of VOPs that prevent underestimation of local SAR when the VOPs are applied with the correct amplitudes but fixed phases.

Results
The proposed method proved to be superior to the worst-case calculation based on the maximum eigenvalue of the VOPs. The mean overestimation for six coil setups could be reduced, whereas no underestimation of the maximum local SAR occurred. In the best investigated case, the overestimation could be reduced from a factor of 3.3 to a factor of 1.7.

Conclusion
The upper bound for the local SAR calculated with the proposed method allows a fast estimation of the local SAR based on power measurements in the transmit channels and facilitates SAR monitoring in systems that do not have the capability to monitor transmit phases
Y1  - 2016
U6  - http://dx.doi.org/10.1002/mrm.26398
SN  - 1522-2594
VL  - 78
IS  - 2
SP  - 805
EP  - 811
PB  - International Society for Magnetic Resonance in Medicine
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Maderwald, Stefan
A1  - Poser, Benedikt Andreas
A1  - Bitz, Andreas
A1  - Quick, Harald H.
A1  - Ladd, Mark E.
T1  - RF excitation using time interleaved acquisition of modes (TIAMO) to address B1 inhomogeneity in high-field MRI
JF  - Magnetic Resonance in Medicine
N2  - As the field strength and, therefore, the operational frequency in MRI is increased, the wavelength approaches the size of the human head/body, resulting in wave effects, which cause signal decreases and dropouts. Several multichannel approaches have been proposed to try to tackle these problems, including RF shimming, where each element in an array is driven by its own amplifier and modulated with a certain (constant) amplitude and phase relative to the other elements, and Transmit SENSE, where spatially tailored RF pulses are used. In this article, a relatively inexpensive and easy to use imaging scheme for 7 Tesla imaging is proposed to mitigate signal voids due to B1 field inhomogeneity. Two time-interleaved images are acquired using a different excitation mode for each. By forming virtual receive elements, both images are reconstructed together using GRAPPA to achieve a more homogeneous image, with only small SNR and SAR penalty in head and body imaging at 7 Tesla.
Y1  - 2010
U6  - http://dx.doi.org/10.1002/mrm.22527
SN  - 1522-2594
VL  - 64
IS  - 2
SP  - 327
EP  - 333
PB  - Wiley-Liss
CY  - New York
ER  - 
TY  - JOUR
A1  - Orzada, Stephan
A1  - Solbach, Klaus
A1  - Gratz, Marcel
A1  - Brunheim, Sascha
A1  - Fiedler, Thomas M.
A1  - Johst, Sören
A1  - Bitz, Andreas
A1  - Shooshtary, Samaneh
A1  - Abuelhaija, Asjraf
A1  - Voelker, Maximilian N.
A1  - Rietsch, Stefan H. G.
A1  - Kraff, Oliver
A1  - Maderwald, Stefan
A1  - Flöser, Martina
A1  - Oehmingen, Mark
A1  - Quick, Harald H.
A1  - Ladd, Mark E.
T1  - A 32-channel parallel transmit system add-on for 7T MRI
JF  - Plos one
Y1  - 2019
U6  - http://dx.doi.org/10.1371/journal.pone.0222452
ER  - 
TY  - CHAP
A1  - Ostkotte, Sebastian
A1  - Peters, Constantin
A1  - Hüning, Felix
A1  - Bragard, Michael
T1  - Design, implementation and verification of an rotational incremental position encoder based on the magnetic Wiegand effect
T2  - 2022 ELEKTRO (ELEKTRO)
N2  - This paper covers the use of the magnetic Wiegand effect to design an innovative incremental encoder. First, a theoretical design is given, followed by an estimation of the achievable accuracy and an optimization in open-loop operation.
Finally, a successful experimental verification is presented. For this purpose, a permanent magnet synchronous machine is controlled in a field-oriented manner, using the angle information of the prototype.
KW  - Position Encoder
KW  - Rotational Encoder
KW  - Wiegand Effect
KW  - Angle Sensor
KW  - Incremental Encoder
Y1  - 2022
SN  - 978-1-6654-6726-1
SN  - 978-1-6654-6727-8
U6  - http://dx.doi.org/10.1109/ELEKTRO53996.2022.9803477
SN  - 2691-0616
N1  - 2022 ELEKTRO (ELEKTRO), 23-26 Mai 2022, Krakow, Poland.
PB  - IEEE
ER  - 
TY  - JOUR
A1  - Oßmann, Martin
A1  - Hattrup, C.
A1  - Broeck, H. W. van der
T1  - Fast estimation techniques for digital control of resonant converters / Hattrup, C.; van der Broeck, H.W.; Ossmann, M.;
JF  - IEEE Transaction on Power Electronics. 18 (2003), H. 1
Y1  - 2003
SN  - 0885-8993
N1  - Part 2
SP  - 365
EP  - 372
ER  - 
TY  - JOUR
A1  - Oßmann, Martin
A1  - Kazay, B.
T1  - Simple circuit provides high-side current sensing / Ossmann, M ; Kazay, B.
JF  - EDN. 45 (2000), H. 21
Y1  - 2000
SN  - 0012-7515
SP  - 200
EP  - 200
ER  - 
TY  - JOUR
A1  - Oßmann, Martin
A1  - Kazay, B.
T1  - Single mu C pin makes half-duplex RS-232C / Ossmann, M
JF  - EDN. 44 (1999), H. 16
Y1  - 1999
SN  - 0012-7515
SP  - 118
ER  - 
TY  - CHAP
A1  - Penne, Jochen
A1  - Profittlich, Martin
A1  - Ringbeck, Thorsten
A1  - Buxbaum, Bernd
ED  - D, Nicola D'Apuzzo
T1  - Touchless detailed 3D scan of human hand anatomy using time-of-flight cameras
T2  - Proceedings of the International Conference on 3D Body Scanning Technologies : Lugano, Switzerland, 19-20 October 2010
Y1  - 2010
SN  - 978-3-033-02714-5
SP  - 361
EP  - 369
PB  - Hometrica Consulting
CY  - Zürich
ER  -