Improved Decoupling for Low Frequency MRI Arrays using Non-conventional Preamplifier Impedance.

ABSTRACT

OBJECTIVE: In this study, we describe a method to improve preamplifier decoupling in low frequency MRI receive coil arrays, where sample loading is low and coils exhibit a high Q-factor. METHODS: The method relies on the higher decoupling obtained when coils are matched to an impedance higher than 50 Ω. Preamplifiers with inductive (and low resistive) input impedance, increase even further the effectiveness of the method. RESULTS: We show that for poorly sample loaded coils, coupling to other elements in an array is a major source of SNR degradation due to a reduction of the coil Q-factor. An 8-channel 13C array at 32 MHz for imaging of the human head has been designed following this strategy. The improved decoupling even allowed constructing the array without overlapping of neighboring coils. Parallel imaging performance is also evaluated demonstrating a better spatial encoding of the array due to its non-overlapped geometry. CONCLUSION: The proposed design strategy for coil arrays is beneficial for low frequency coils where the coil thermal noise is dominant. The method has been demonstrated on an 8-channel array for the human head for 13C MRI at 3 T (32 MHz), with almost 2-fold SNR enhancement when compared to a traditional array of similar size and number of elements. SIGNIFICANCE: The proposed method is of relevance for low frequency arrays, where sample loading is low, and noise correlation is high due to insufficient coil decoupling.