A novel multifrequency-tuned transceiver array for human-brain ³¹P-MRSI at 7 T

Purpose: Phosphorus-31 (³¹P) MR spectroscopy imaging (MRSI) at 7 T is a powerful tool for investigating high-energy phosphate metabolism in human brains with significantly improved signal-to-noise ratio (SNR) and spectral resolution. However, this imaging technique requires dual-frequency radiofrequency coil for performing brain anatomical imaging and B₀ shimming at proton (¹H) operation frequency, and ³¹P MRSI at lower operation frequency. Herein, we introduce a novel ³¹P-¹H dual-frequency radiofrequency coil design using a double-tuned and double-matched (DODO) coil that does not require complex circuitry or two coil layers and exhibits similar imaging performance as to single-frequency control coils for both ³¹P and ¹H imaging operations. Methods: We constructed an eight-element ³¹P-¹H dual-frequency DODO transceiver array and compared its performance with a quadrature-driven dual-tuned eight-element ³¹P and eight-element ¹H transverse electromagnetic volume coil for both phantom and in vivo human-brain ³¹P-MRSI studies at 7 T. Results: The DODO transceiver array achieved high spatiotemporal resolution ³¹P MRSI with 2.5-cc nominal voxel size and 22-min scan time covering the entire human brain, showing excellent SNR for mapping cerebral phosphorous metabolites such as phosphocreatine, adenosine triphosphate, and other low-concentration metabolites. Compared with the transverse electromagnetic volume coil, the DODO array demonstrated large improvements in ³¹P-MRSI SNR in both phantom and human brain studies, with over 5-fold SNR gain in peripheral regions and over 2-fold SNR gain in central brain regions. Conclusion: This simple and cost-effective array design and excellent performance can greatly benefit human-brain ³¹P-MRSI applications at 7 T.