ASK-Asymmetric Saddle K-topology for Spinal Cord Imaging

Introduction: Surface coil arrays are particularly suitable for spinal cord MR imaging. Demand for higher channel count systems has lead to an increased need for optimized performance of constituent coil elements in order to obtain high SNR, adequate penetration depth, ease of isolation, and uniformity of response. In this study we have analyzed the performance characteristics of 6 different array building block designs for use in a posterior/spinal application. As a result of this analysis we propose a design based upon the Asymmetric Saddle motif that yields the best balance of performance characteristics for a full posterior coverage (44cm) application. Methods and Materials: The methods consisted of hardware development, modeling and data measurement. Hardware Development: Fig. 1.2 contains a photographic montage of the various coil array systems that were compared in this work. Again, the QD was used as a standard to judge all other motifs on the basis of SNR at clinically relevant depths (especially those pertinent to spinal imaging). The 3-loop, 4-loop, and single layer surface arrays were used as comparative standards for assessing the performance metric of directivity. Modeling: Initial prediction of SNR profile for 3 cases, namely i) Single loop; ii) A loop pair and iii) Asymmetric Saddle (AS) having covering the same field of view (FOV) were numerically calculated using the Remcom XFDT package, College Station, PA. Fig.1.1 shows the contour plots. The single loop has best uniformity but worst SNR, whereas the double loop has best SNR but worst uniformity and penetration depth, and AS has optimum SNR and homogeneity. Data Measurement: Phantom testing for each topology was done using 1.5T GE Exite scanner and a sequence (TR/TE = ms/ms; 256*128; FOV = 44cm) and a SOS reconstruction.