Interleaved Na/H MRI of the human heart at 7 T using a combined Na/H coil setup and H parallel transmission.

Purpose: To evaluate the feasibility of interleaved Na/H cardiac MRI at 7 T using H parallel transmission (pTx) pulses.

Methods: A combined setup consisting of a Na volume coil and two H transceiver arrays was employed and the transmit and receive characteristics were compared in vitro with those of the uncombined radiofrequency coils. Furthermore, the implemented interleaved Na/H pTx sequence was validated in phantom measurements and applied to four healthy subjects. For the latter, three customized H excitation pulses (universal and individual phase shims (UPS/IPS) and individual 4kT pulses (4kT)) were employed in the interleaved Na/H pTx sequence and compared with the vendor-provided default cardiac phase shim (DPS).

Results: Combining both coils resulted in a reduction of the mean Na transmit field (B ) efficiency and Na signal-to-noise ratio by 18.9% and 15.4% for the combined setup, whereas the H B efficiency was less influenced (-4.7%). Compared with single-nuclear acquisitions, interleaved dual-nuclear Na/H MRI showed negligible influence on Na and H image quality. For all three customized H pTx pulses the B homogeneity was improved (coefficients of variation: CV = 0.30, CV = 0.23, CV = 0.15) and no H signal dropouts occurred compared with the vendor-provided default phase shim (CV = 0.37).

Conclusion: The incorporation of customized H pTx pulses in an interleaved Na/H sequence scheme was successfully demonstrated at 7 T and improvements of the H B homogeneity within the heart were shown. Combining interleaved Na/H MRI with H pTx is an important tool to enable robust quantification of myocardial tissue sodium concentrations at 7 T within clinically acceptable acquisition times.