It is important to determine the longitudinal relaxation time of blood for black blood imaging, as well as for quantifying blood flow by arterial spin labeling (ASL). In this study a circulation system was used to measure blood T1 under physiological conditions at the new clinical field strength of 3.0T. It was found that 1/T1 in s(-1) was linearly dependent (P < 0.05) on hematocrit (Hct) within a normal range of 0.38-0.46. The relationships were 1/T1 = (0.52 +/- 0.15). Hct + (0.38 +/- 0.06) and 1/T1 = (0.83 +/- 0.07). Hct + (0.28 +/- 0.03) for arterial (oxygenation = 92% +/- 7%) and venous blood (69% +/- 8%), respectively, which led to estimated T1 values of 1664 +/- 14 ms (arterial) and 1584 +/- 5 ms (venous) at a typical human Hct of 0.42. The temperature dependencies of blood T1 were 22.3 +/- 0.6 ms/ degrees C and 19.8 +/- 0.8 ms/ degrees C for Hct values of 0.42 and 0.38, respectively. When a head coil transmit/receive setup was used, radiation damping caused a slight reduction (19 ms) of the measured T1 values.
Copyright 2004 Wiley-Liss, Inc.