Determining the longitudinal relaxation time (T₁) of blood at 3.0 tesla

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 thet 1/T₁ in s^-1 was linearly dependent (P < 0.05) on hemetocrit (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/°C and 19.8 ± 0.8 ms/°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 T ₁ values.