Jonathan B Martin1, Benjamin M Hardy2, and William A Grissom1
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, 2Physics and Astronomy, Vanderbilt University, Nashville, TN, United States
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, 2Physics and Astronomy, Vanderbilt University, Nashville, TN, United States
A singular vector minibatching Gerchberg-Saxton algorithm for parallel transmission RF shimming is presented, which achieves increased robustness against local minima and RF shimming holes and can be adapted to a wide range of problems.
a) An example B1+ shim field designed using the conventional GS algorithm, with a large signal void in it. B1+ maps are from a healthy volunteer on an 8 channel transmit system at 7T b) To help avoid signal voids, we propose the modified singular vector minibatched GS algorithm above, with the A singular vector sampling step shaded gray
Parameter space of regularization factor s versus k with random initialization for an 8 channel (a) and 30 channel (b) system. Average number of shimming failures per head is shown in the left column, and average slice B1+ CoV is shown in the right column. Note that the far right column in each plot corresponds to a full-rank A, equivalent to conventional GS. Using random low-rank approximations in the initial minibatched stage produced fewer voids than full-rank conventional GS when less than approximately 2/3 of the SVD components were kept.
