Global optimization of default phases for parallel transmit coils for ultra-high-field cardiac MRI

• Published in: PloS one Vol. 16; no. 8; p. e0255341
• Main Authors: Terekhov, Maxim, Elabyad, Ibrahim A., Schreiber, Laura M.
• Format: Journal Article
• Language: English
• Published: San Francisco, CA USA Public Library of Science 06.08.2021; Public Library of Science (PLoS)
• Subjects: Analysis; Biology and Life Sciences; Engineering and Technology; Evaluation; Magnetic resonance imaging; Mathematical optimization; Medicine and Health Sciences; Physical Sciences; Research and Analysis Methods; Germany
• DOI: 10.1371/journal.pone.0255341
• ISSN: 1932-6203

The development of novel multiple-element transmit-receive arrays is an essential factor for improving B 1 + field homogeneity in cardiac MRI at ultra-high magnetic field strength (B 0 > = 7.0T). One of the key steps in the design and fine-tuning of such arrays during the development process is finding the default driving phases for individual coil elements providing the best possible homogeneity of the combined B 1 + -field that is achievable without (or before) subject-specific B 1 + -adjustment in the scanner. This task is often solved by time-consuming (brute-force) or by limited efficiency optimization methods. In this work, we propose a robust technique to find phase vectors providing optimization of the B 1 -homogeneity in the default setup of multiple-element transceiver arrays. The key point of the described method is the pre-selection of starting vectors for the iterative solver-based search to maximize the probability of finding a global extremum for a cost function optimizing the homogeneity of a shaped B 1 + -field. This strategy allows for (i) drastic reduction of the computation time in comparison to a brute-force method and (ii) finding phase vectors providing a combined B 1 + -field with homogeneity characteristics superior to the one provided by the random-multi-start optimization approach. The method was efficiently used for optimizing the default phase settings in the in-house-built 8Tx/16Rx arrays designed for cMRI in pigs at 7T.