Daniel A. Herzka1,
Haiyan Ding2, 3, Michael Schar4, 5
1Biomedical
Engineering, Johns Hopkins University, Baltimore, MD, United States; 2Biomedical
Engineering, Tsinghua University, Beijing, China; 3Biomedical
Engineering, Johns Hopkins School of Medicine, Baltimore, MD, United States; 4Russell
H. Morgan Department of Radiology and Radiological Science, Johns Hopkins
School of Medicine, Baltimore, MD, United States; 5Clinical
Science, Philips Healthcare, Cleveland, OH, United States
MRI scanners use an integrated birdcage coil to generate radio frequency (RF) excitation fields (B1+). It has been reported that at 3T variations in flip angle can range from 31 to 66% (B1+ inhomogeneities) over the left ventricle and average flip angles can be reduced by ~20% (RF power). Multi-channel transmit systems allow RF-shimming to locally improve the B1+ field. We quantify improvements in B1+ field homogeneity and average RF power resulting from dual-source parallel RF excitation in cardiac swine imaging. Correlation with animal size demonstrates that larger subjects suffer more B1+ field inhomogeneity and benefit more from RF shimming.