High Spatial Resolution and Temporally Resolved T2* Mapping of Normal Human Myocardium at 7.0 Tesla: An Ultrahigh Field Magnetic Resonance Feasibility Study

Myocardial tissue characterization using T-2* relaxation mapping techniques is an emerging application of (pre)clinical cardiovascular magnetic resonance imaging. The increase in microscopic susceptibility at higher magnetic field strengths renders myocardial T-2* mapping at ultrahigh magnetic fields conceptually appealing. This work demonstrates the feasibility of myocardial T-2* imaging at 7.0 T and examines the applicability of temporally-resolved and high spatial resolution myocardial T-2* mapping. In phantom experiments single cardiac phase and dynamic (CINE) gradient echo imaging techniques provided similar T-2* maps. In vivo studies showed that the peak-to-peak B-0 difference following volume selective shimming was reduced to approximately 80 Hz for the four chamber view and mid-ventricular short axis view of the heart and to 65 Hz for the left ventricle. No severe susceptibility artifacts were detected in the septum and in the lateral wall for T-2* weighting ranging from TE = 2.04 ms to TE = 10.2 ms. For TE > 7 ms, a susceptibility weighting induced signal void was observed within the anterior and inferior myocardial segments. The longest T-2* values were found for anterior (T-2* = 14.0 ms), anteroseptal (T-2* = 17.2 ms) and inferoseptal (T-2* = 16.5 ms) myocardial segments. Shorter T-2* values were observed for inferior (T-2* = 10.6 ms) and inferolateral (T-2* = 11.4 ms) segments. A significant difference (p = 0.002) in T-2* values was observed between end-diastole and end-systole with T-2* changes of up to approximately 27% over the cardiac cycle which were pronounced in the septum. To conclude, these results underscore the challenges of myocardial T-2* mapping at 7.0 T but demonstrate that these issues can be offset by using tailored shimming techniques and dedicated acquisition schemes.