Refine
Year of publication
- 2024 (8)
- 2023 (21)
- 2022 (12)
- 2021 (25)
- 2020 (20)
- 2019 (30)
- 2018 (35)
- 2017 (25)
- 2016 (26)
- 2015 (28)
- 2014 (24)
- 2013 (29)
- 2012 (24)
- 2011 (31)
- 2010 (26)
- 2009 (27)
- 2008 (27)
- 2007 (28)
- 2006 (17)
- 2005 (15)
- 2004 (19)
- 2003 (12)
- 2002 (20)
- 2001 (20)
- 2000 (19)
- 1999 (23)
- 1998 (16)
- 1997 (13)
- 1996 (10)
- 1995 (11)
- 1994 (15)
- 1993 (9)
- 1992 (8)
- 1991 (4)
- 1990 (6)
- 1989 (5)
- 1988 (5)
- 1987 (2)
- 1986 (1)
- 1985 (6)
- 1984 (1)
- 1982 (2)
- 1981 (1)
- 1980 (4)
- 1979 (2)
- 1978 (3)
- 1976 (1)
- 1975 (1)
- 1974 (1)
Institute
- Fachbereich Elektrotechnik und Informationstechnik (718) (remove)
Language
- English (718) (remove)
Document Type
- Article (414)
- Conference Proceeding (234)
- Part of a Book (38)
- Book (23)
- Conference: Meeting Abstract (5)
- Patent (2)
- Conference Poster (1)
- Doctoral Thesis (1)
Keywords
- Enterprise Architecture (5)
- MINLP (5)
- Engineering optimization (4)
- Optimization (3)
- Powertrain (3)
- Technical Operations Research (3)
- Telecommunication (3)
- Competence Developing Games (2)
- Energy efficiency (2)
- Engineering education (2)
Phase Repeatable Synthesizers as a New Harmonic Phase Standard for Nonlinear Network Analysis
(2018)
Performance Investigations of the IP Multicast Architecture / Hermanns, Oliver ; Schuba, Marko
(1995)
In this study, the performance of an integrated body-imaging array for 7 T with 32 radiofrequency (RF) channels under consideration of local specific absorption rate (SAR), tissue temperature, and thermal dose limits was evaluated and the imaging performance was compared with a clinical 3 T body coil.
Thirty-two transmit elements were placed in three rings between the bore liner and RF shield of the gradient coil. Slice-selective RF pulse optimizations for B1 shimming and spokes were performed for differently oriented slices in the body under consideration of realistic constraints for power and local SAR. To improve the B1+ homogeneity, safety assessments based on temperature and thermal dose were performed to possibly allow for higher input power for the pulse optimization than permissible with SAR limits.
The results showed that using two spokes, the 7 T array outperformed the 3 T birdcage in all the considered regions of interest. However, a significantly higher SAR or lower duty cycle at 7 T is necessary in some cases to achieve similar B1+ homogeneity as at 3 T. The homogeneity in up to 50 cm-long coronal slices can particularly benefit from the high RF shim performance provided by the 32 RF channels. The thermal dose approach increases the allowable input power and the corresponding local SAR, in one example up to 100 W/kg, without limiting the exposure time necessary for an MR examination.
In conclusion, the integrated antenna array at 7 T enables a clinical workflow for body imaging and comparable imaging performance to a conventional 3 T clinical body coil.
The aim of the current study was to investigate the performance of integrated RF
transmit arrays with high channel count consisting of meander microstrip antennas
for body imaging at 7 T and to optimize the position and number of transmit ele-
ments. RF simulations using multiring antenna arrays placed behind the bore liner
were performed for realistic exposure conditions for body imaging. Simulations were
performed for arrays with as few as eight elements and for arrays with high channel
counts of up to 48 elements. The B1+ field was evaluated regarding the degrees of
freedom for RF shimming in the abdomen. Worst-case specific absorption rate
(SARwc ), SAR overestimation in the matrix compression, the number of virtual obser-
vation points (VOPs) and SAR efficiency were evaluated. Constrained RF shimming
was performed in differently oriented regions of interest in the body, and the devia-
tion from a target B1+ field was evaluated. Results show that integrated multiring
arrays are able to generate homogeneous B1+ field distributions for large FOVs, espe-
cially for coronal/sagittal slices, and thus enable body imaging at 7 T with a clinical
workflow; however, a low duty cycle or a high SAR is required to achieve homoge-
neous B1+ distributions and to exploit the full potential. In conclusion, integrated
arrays allow for high element counts that have high degrees of freedom for the pulse
optimization but also produce high SARwc , which reduces the SAR accuracy in the
VOP compression for low-SAR protocols, leading to a potential reduction in array
performance. Smaller SAR overestimations can increase SAR accuracy, but lead to a
high number of VOPs, which increases the computational cost for VOP evaluation
and makes online SAR monitoring or pulse optimization challenging. Arrays with
interleaved rings showed the best results in the study.