Original Research Measuring Human Cardiac Tissue Sodium Concentrations Using Surface Coils, Adiabatic Excitation, and Twisted Projection Imaging With Minimal T2 Losses

Purpose: To measure tissue sodium concentrations in the human heart with 23Na MRI using a surface coil, thereby eliminating the effects of inhomogeneous excitation by sur-face coils and minimizing T1 and T2 relaxation. Materials and Methods: We combined fully relaxed, very short-echo, 23Na twisted projection imaging (TPI) with adia-batic half passage (AHP) excitation and external referencing on subjects and comparing with a concentration reference phantom scan to quantify TSC with surface coils. 23Na signal losses during hard (square), composite, and tanh/tan ampli-tude/frequency-modulated AHP excitation pulses were ana-lyzed over a wide range of RF field strengths and T2short values. Results: AHP excitation yielded a homogeneous excitation flip angle and negligible losses compared to a 90 ° hard pulse wherever the B1 field exceeded the adiabatic thresh-old, rendering this sequence suitable for applications that use surface coil excitation. An AHP 23Na TPI sequence was used with a surface coil at 1.5 T to noninvasively quantify myocardial TSC in 10 normal volunteers. The mean TSC was 43 4, 53 12, and 17 4 mol/g in the left ventricular (LV) free wall, septum, and adipose tissue, re-spectively, consistent with prior invasive measurements on biopsy and autopsy specimens. Conclusion: It is now possible to noninvasively quantify TSC in the human heart with surface coil 23Na MRI