On the superlinear increase of the ultimate intrinsic signal-to-noise ratio with regard to main magnetic field strength in a spherical sample

In this study, the increase of the ultimate intrinsic signal-to-noise ratio (UISNR) with regard to main magnetic field strength B
₀
is investigated. A simplified spherical phantom of human head size is used. In the center of the sphere, the UISNR grows more than quadratically. Within the volume, in which the distance to the center is smaller than 85% of the sphere's radius, the UISNR increases superlinearly. At the surface, the UISNR grows only sublinearly. The SNR of curl-free current patterns grows more than cubically in the center, whereas the SNR of divergence-free current patterns increases quadratically. However, this does not imply, that curl-free modes result in higher SNR than divergence-free modes.