Abstract
PURPOSE: To evaluate the feasibility of interleaved (23)Na/(1)H cardiac MRI at 7 T using (1)H parallel transmission (pTx) pulses. METHODS: A combined setup consisting of a (23)Na volume coil and two (1)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 (23)Na/(1)H pTx sequence was validated in phantom measurements and applied to four healthy subjects. For the latter, three customized (1)H excitation pulses (universal and individual phase shims (UPS/IPS) and individual 4kT pulses (4kT)) were employed in the interleaved (23)Na/(1)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 (23)Na transmit field (B(1) (+)) efficiency and (23)Na signal-to-noise ratio by 18.9% and 15.4% for the combined setup, whereas the (1)H B(1) (+) efficiency was less influenced (-4.7%). Compared with single-nuclear acquisitions, interleaved dual-nuclear (23)Na/(1)H MRI showed negligible influence on (23)Na and (1)H image quality. For all three customized (1)H pTx pulses the B(1) (+) homogeneity was improved (coefficients of variation: CV(UPS) = 0.30, CV(IPS) = 0.23, CV(4kT) = 0.15) and no (1)H signal dropouts occurred compared with the vendor-provided default phase shim (CV(DPS) = 0.37). CONCLUSION: The incorporation of customized (1)H pTx pulses in an interleaved (23)Na/(1)H sequence scheme was successfully demonstrated at 7 T and improvements of the (1)H B(1) (+) homogeneity within the heart were shown. Combining interleaved (23)Na/(1)H MRI with (1)H pTx is an important tool to enable robust quantification of myocardial tissue sodium concentrations at 7 T within clinically acceptable acquisition times.