Development and optimization of a receive-only surface array with purely geometrical decoupling for rat brain MRI at 2 T

Introduction Magnetic resonance imaging (MRI) experiments on small animals, as well as in humans, require specific radiofrequency (RF) coil designs in order to maximize field homogeneity during excitation and signal-to-noise ratio (SNR) during reception. Therefore, the use of dedicated transmit-only and receive-only coil geometries has been preferred as standard technology configuration. Among the receive coil geometries, the surface coil has been widely used to increase the SNR in localized regions of interest. With the advent of MRI-phased arrays, the high sensitivity of surface coils can be achieved in extended regions, further allowing parallel imaging acquisition methodologies to accelerate acquisition time. Objectives This work describes the development and characterization of a two-channel receive-only RF coil set specifically designed for MRI acquisition of rat brain in a 2 T system for neuroscience studies. Methods We have developed and compared the performance of one common surface coil with a two-channel phased array with purely geometric decoupling between coil elements (i.e., without using low input impedance preamplifiers), both actively detuned during reception and having exactly the same dimensions. Results The results have shown that the single-channel surface coil achieved up to 5 times higher SNR at 5 mm depth compared to a volume coil commonly used for rat brain MRI in our laboratory, while the two-channel array achieved 4 times higher SNR at the same depth, with the additional advantage of producing an extended area with higher sensitivity. Conclusion In vivo brain images of anesthetized rats confirmed the SNR gain for both receive-only single-channel surface coil and two-channel array in comparison with a volume coil. We have verified that only using the partial overlapping technique does not provide sufficient isolation to eliminate mutual coupling interaction between elements, since residual coupling can still affect the coil performance.