High temporal resolution in vivo blood oximetry via projection-based T2 measurement.

Measuring venous oxygen saturation (HbO2) in large blood vessels can provide important information about oxygen delivery and its consumption in vital organs. Quantification of blood's T2 value via MR can be utilized to determine HbO2 noninvasively. We propose a fast method for in vivo blood T2 quantification via computing the complex difference of velocity-encoded projections. As blood flows continuously, its signal can be robustly isolated from the surrounding tissue by computing the complex difference of two central k-space lines with different velocity encodings. This resultant signal can then be measured as a function of echo time for rapidly quantifying T2 of blood. We applied the method to quantify HbO2 in three cerebral veins at rest and in one of the veins in response to hypercapnia. Average HbO2 measurements in superior sagittal sinus (SSS), straight sinus and internal jugular vein in the group were 63 ± 3%, 68 ± 4% and 65 ± 4%, respectively. Average HbO2 values in SSS during baseline, hypercapnia, and recovery were 63 ± 2%, 79 ± 5%, and 61 ± 3%, respectively. When compared with standard T2 quantification techniques, the proposed method is fast, reliable, and robust against partial volume effects.