Visualizing the role of ideal current patterns in minimizing sample noise using dark mode current patterns for a spherical sample

We show that the ideal surface current patterns maximizing internal signal-to-noise ratio (SNR) are composed of a) signal-optimizing current patterns which maximize the signal sensitivity without considering sample noise, and b) “dark mode” current patterns which minimize sample noise without affecting signal. For a central voxel in a spherical sample, the absence of dark mode current patterns on an encircling sphere suggests that optimally tracking the precessing spin while ignoring sample noise is sufficient to achieve the best possible SNR. For an off-center voxel, however, the dark mode current patterns form high magnitude localized currents that efficiently minimize sample noise.