Hematocrit and oxygenation dependence of blood (1) H(2) O T(1) at 7 tesla.

Knowledge of blood (1) H(2) O T(1) 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 (1) H(2) O T(1) 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 (1) H(2) O R(1) 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 T(1) = 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 (1) H(2) O T(1) 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 (pO(2) ) and the effect of plasma osmolality for different anticoagulants were also investigated. It is discussed why blood (1) H(2) O T(1) 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, 2012. © 2012 Wiley Periodicals, Inc.