Measuring renal tissue relaxation times at 7 T

As developments in RF coils and RF management strategies make performing ultra-high-field renal imaging feasible, understanding the relaxation times of the tissue becomes increasingly important for tissue characterization, sequence optimization and quantitative functional renal imaging, such as renal perfusion imaging using arterial spin labeling. By using a magnetization-prepared single-breath-hold fast spin echo imaging method, human renal T₁ and T₂ imaging studies were successfully performed at 7 T with 11 healthy volunteers (eight males, 45±17 years, and three females, 29±7 years, mean±standard deviation, S.D.) while addressing challenges of B₁⁺ inhomogeneity and short-term specific absorption rate limits. At 7 T, measured renal T₁ values for the renal cortex and medulla (mean±S.D.) from five healthy volunteers who participated in both 3 T and two-session 7 T studies were 1661±68 ms and 2094±67 ms, and T₂ values were 108±7 ms and 126±6 ms. For comparison, similar measurements were made at 3 T, where renal cortex and medulla T₁ values of 1261±86 ms and 1676±94 ms and T₂ values of 121±5 ms and 138±7 ms were obtained. Measurements at 3 T and 7 T were significantly different for both T₁ and T₂ values in both renal tissues. Reproducibility studies at 7 T demonstrated that T₁ and T₂ estimations were robust, with group mean percentage differences of less than 4%.