Improving peak local SAR prediction in parallel transmit using in situ S-matrix measurements
| Autor: | Hans Hoogduin, Alexander J.E. Raaijmakers, Peter R. Luijten, Cornelis A. T. van den Berg, Matthew C. Restivo |
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| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
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Hot Temperature Radio Waves Imaging phantom 030218 nuclear medicine & medical imaging 03 medical and health sciences Matrix (mathematics) 0302 clinical medicine Image Processing Computer-Assisted Journal Article Humans Scattering Radiation Radiology Nuclear Medicine and imaging Computer Simulation parallel transmit Simulation Coupling Physics Scattering Phantoms Imaging Specific absorption rate Reproducibility of Results Equipment Design Models Theoretical Magnetic Resonance Imaging Computational physics Transmission (telecommunications) numerical simulation Power dividers and directional couplers Patient Safety network cosimulation 030217 neurology & neurosurgery Algorithms SAR |
| Zdroj: | Magnetic Resonance in Medicine, 77(5), 2040–2047. John Wiley and Sons Inc. |
| ISSN: | 0740-3194 |
| Popis: | PURPOSE Peak local specific absorption rate (pSAR10g) is an important parameter used to determine patient safety during radiofrequency transmission. pSAR10g predictions for parallel transmit MRI are affected by the level of coupling exhibited by a modeled array in the simulation environment. However, simulated array coupling is rarely equal to the physical array coupling. Accurately simulating the physical array coupling may improve the accuracy of predicted SAR levels. METHODS The scattering parameter matrix (S-matrix) of a prototype 4-channel array was measured in situ using directional couplers installed on a 7T scanner. Agreement between the simulated and measured S-matrix was achieved by using network co-simulation with a modified cost function. B1+ maps acquired in a phantom were compared to B1+ distributions determined from simulations. RESULTS The modified co-simulation technique forces the simulations to have S-matrices similar to the measured values. A comparison of realistically versus ideally simulated coupling conditions shows that ideally simulated coupling can result in large ( > 40%) error in pSAR10g predictions, even when the array is reasonably tuned. The simulated B1+ distributions match the measured B1+ distributions better when the coupling is accurately simulated. CONCLUSION Considering the measured array coupling matrix in numerical simulations eliminates a potential confound in pSAR10g prediction. Magn Reson Med 77:2040-2047, 2017. © 2016 International Society for Magnetic Resonance in Medicine. |
| Databáze: | OpenAIRE |
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