Riccardo Lattanzi1, 2, Manushka Vaidya1, 2, Graham C. Wiggins1, Daniel K. Sodickson1, 2
1The Bernard and Irene Schwartz Center for Biomedical Imaging, Radiology, New York University Langone Medical Center, New York, NY, United States; 2The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States
Using an electrodynamic formulation based on a current mode expansion and dyadic Greens functions, we showed that only 2 divergence-free (i.e. magnetic-type) modes contribute to the ultimate intrinsic SNR (UISNR) in the center of a homogeneous sphere. However, discrete loop coils carry larger noise contributions than the ideal current modes in question, and UISNR cannot therefore be completely achieved with a modest number of loops. At higher field strengths, loops become less and less efficient because noise scales up by a larger factor than the signal. Away from the center, electric-dipole contributions are more significant and loops are increasingly inefficient.