Key result
The proposed optimized multi-start strategy for finding default phase vectors improved B1+ field homogeneity and reduced computation time compared to standard random multi-start optimization.
Why the study?
Finding default driving phases for individual coil elements to improve B1+ field homogeneity in ultra-high-field cardiac MRI is often limited to time-consuming brute-force or inefficient optimization methods.
A novel dual-stage optimization strategy significantly reduces computation time and improves B1+ field homogeneity for ultra-high-field cardiac MRI transmit coils.
Accelerates ultra-high-field cardiac MRI coil optimization; leaves open human validation and clinical translation.
The development of novel multiple-element transmit-receive arrays is an essential factor for improving B1+ field homogeneity in cardiac MRI at ultra-high magnetic field strength (B0 > = 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 B1+-field that is achievable without (or before) subject-specific B1+-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 B1-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 B1+-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 B1+-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.
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Terekhov et al. (2021) studied Cardiac MRI at ultra-high magnetic field strength. Optimized multi-start phase optimization strategy vs. Random multi-start optimization was evaluated on B1+ field homogeneity. The proposed optimized multi-start strategy for finding default phase vectors improved B1+ field homogeneity and reduced computation time compared to standard random multi-start optimization.
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