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

Purpose To develop a coil-based method to obtain accurate sensitivity profiles in C-13 MRI at 3T from the endogenous Na-23. An eight-channel array is designed for C-13 MR acquisitions. As application examples, the array is used for two-fold accelerated acquisitions of both hyperpolarized C-13 metabolic imaging of pig kidneys and the human brain. Methods A flexible coil array was tuned optimally for C-13 at 3T (32.1 MHz), with the coil coupling coefficients matched to be nearly identical at the resonance frequency of Na-23 (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 C-13 and Na-23 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 Na-23 profiles obtained in vivo could be used successfully to perform two-fold acceleration of hyperpolarized C-13 3D acquisitions of both pig kidneys and a healthy human brain. Conclusion A receive array has been developed in such a way that the C-13 sensitivity profiles could be accurately obtained from measurements at the Na-23 frequency. This technique facilitates accelerated acquisitions for hyperpolarized C-13 imaging. The SNR performance obtained at the C-13 frequency, compares well to other state-of-the-art coils for the same purpose, showing slightly better superficial and central SNR.

Automated summary

A coil-based method was developed to obtain accurate sensitivity profiles in C-13 MRI at 3T from endogenous Na-23. A flexible coil array was designed and optimized for C-13 imaging, and the SNR performance was evaluated and compared to reference coils. The results show that the developed method can successfully accelerate the acquisition of hyperpolarized C-13 imaging, with slightly better SNR compared to other state-of-the-art coils.