Hematocrit and oxygenation dependence of blood 1H2O T1 at 7 tesla

Knowledge of blood ¹H₂O T₁ is critical for perfusion‐based quantification experiments such as arterial spin labeling and cerebral blood volume‐weighted MRI using vascular space occupancy. The dependence of blood ¹H₂O T₁ on hematocrit fraction (Hct) and oxygen saturation fraction (Y) was determined at 7 T using in vitro bovine blood in a circulating system under physiological conditions. Blood ¹H₂O R₁ values for different conditions could be readily fitted using a two‐compartment (erythrocyte and plasma) model, which are described by a monoexponential longitudinal relaxation rate constant dependence. It was found that T₁ = 2171 ± 39 ms for Y = 1 (arterial blood) and 2010 ± 41 ms for Y = 0.6 (venous blood), for a typical Hct of 0.42. The blood ¹H₂O T₁ values in the normal physiological range (Hct from 0.35 to 0.45, and Y from 0.6 to 1.0) were determined to range from 1900 to 2300 ms. The influence of oxygen partial pressure (pO₂) and the effect of plasma osmolality for different anticoagulants were also investigated. It is discussed why blood ¹H₂O T₁ values measured in vivo for human blood may be about 10–20% larger than found in vitro for bovine blood at the same field strength. Magn Reson Med, 70:1153–1159, 2013. © 2012 Wiley Periodicals, Inc.