On-site characterization of the spatio-temporal structure of the noise for MRS measurements using a pair of eight-shape loops

Abstract Many methodologies have been proposed to improve the signal to noise ratio of the magnetic resonance measurements. Nevertheless, in many places MRS remains unrealizable even though it would provide valuable contribution. We propose to combine figure-of-eight shape loops with multichannel equipment to challenge this issue. We propose to use the gradient of the vertical component of the magnetic field measured via a pair of small figure-of-eight loops to estimate the noise in a large eight-shape loop of any orientation. We demonstrate on synthetic data the efficiency and limitation of this approach. The methodology applied on a field dataset allows finding a stable best direction in this case, and underlines a surprising roughly common behavior for the harmonics of the industrial current and frequencies in-between where a less organized structure was expected. This approach proves to be a convenient and efficient way to characterize quickly a site before measuring a MRS sounding, to choose the optimal orientation of the MRS loop, and provide an estimate of the final noise level that can be expected.