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With the increasing number of elements in receive arrays, the need to accurately predict coil performance is crucial. Decoupling is usually performed with low-input impedance preamplifier decoupling. Recently, new schematics have been proposed that rely on high-input impedance preamplifiers. A simulation method is proposed here to evaluate preamplifier decoupling performance in this context on a 2-layer array at 7T. Results show a strong influence on the thermal SNR according to the impedance presented by the preamplifier to the coil output. The higher this impedance the higher the SNR, but practical implementation need a trade-off between high impedance and noise-matching.

The noise covariance matrix is useful for SNR and g-map computation and, with the noise correlation matrix, commonly taken as metrics to characterize decoupling of denser and denser receive arrays. Roemer provided a resistance matrix accounting for noise correlation. In the literature, Bosma defined the noise covariance matrix from the scattering matrix, easing predictions based on electromagnetic simulations or VNA measurements. Here noise correlation is analyzed for 50 Ω power-matched and low-input impedance preamplifiers. As predicted by Bosma, strong coupling does not necessarily imply a high noise correlation, which also depends on the ports impedance matching.