Evaluation of the RF field uniformity of a double-tuned 31P/1H birdcage RF coil for spin-echo MRI/MRS of the diabetic foot

Abstract

Purpose: To evaluate the B1 field uniformity of a double-tuned birdcage coil designed for 31P/1H MRI/MRS spin-echo (SE) imaging of the metatarsal head region of the foot in neuropathic diabetic patients. Materials and Methods: A low-pass double-tuned 31P/1H RF birdcage coil was constructed to fit over the adult fore-foot. Flip angle (FA) maps were created from B1 data acquired at the 3T 31P (four normal subjects) and 1H (five normal subjects) frequencies. T2-weighted (T2-W) 1H images, 31P rapid acquisition with relaxation enhancement (RARE) images, and composite SE pulse CSI data were acquired to demonstrate the uniformity of the resulting images and data. Results: The means and standard deviations (SDs) of the range of FAs across the feet of the volunteer subjects indicated good uniformity (the maximum coefficients of variation (CVs) for all of the 31P and 1H FA maps were 7.6% and 7.3%, respectively). The FA values across the metatarsal head region indicated a maximum signal intensity variation of ±3% in a RARE image acquired using an echo train length of 32. Conclusion: A 31P/ 1H birdcage coil constructed for MRI/ MRS studies of the human forefoot provided sufficient signal uniformity of SE data to facilitate accurate 31P concentration measurements in muscle. © 2005 Wiley-Liss, Inc.