RF coil design for accurate parallel imaging on 13C MRSI using 23Na sensitivity profiles

Purpose: To develop a coil-based method to obtain accurate sensitivity profiles in 13C MRI at 3T from the endogenous 23Na. An eight-channel array is designed for 13C MR acquisitions. As application examples, the array is used for two-fold accelerated acquisitions of both hyperpolarized 13C metabolic imaging of pig kidneys and the human brain. Methods: A flexible coil array was tuned optimally for 13C at 3T (32.1 MHz), with the coil coupling coefficients matched to be nearly identical at the resonance frequency of 23Na (33.8 MHz). This is done by enforcing a high decoupling (obtained through highly mismatched preamplifiers) and adjusting the coupling frequency response. The SNR performance is compared to reference coils. Results: The measured sensitivity profiles on a phantom showed high spatial similarity for 13C and 23Na resonances, with average noise correlation of 9 and 11%, respectively. For acceleration factors 2, 3, and 4, the obtained maximum g-factors were 1.0, 1.1, and 2.6, respectively. The 23Na profiles obtained in vivo could be used successfully to perform two-fold acceleration of hyperpolarized 13C 3D acquisitions of both pig kidneys and a healthy human brain. Conclusion: A receive array has been developed in such a way that the 13C sensitivity profiles could be accurately obtained from measurements at the 23Na frequency. This technique facilitates accelerated acquisitions for hyperpolarized 13C imaging. The SNR performance obtained at the 13C frequency, compares well to other state-of-the-art coils for the same purpose, showing slightly better superficial and central SNR.