Determination of whole-brain oxygen extraction fractions by fast measurement of blood T(2) in the jugular vein.

The oxygen extraction fraction of the brain reports on the balance between oxygen delivery and consumption and can be used to assess deviations in physiological homeostasis. This is relevant clinically as well as for calibrating blood oxygen level-dependent functional MRI responses. Oxygen extraction fraction is reflected in the arteriovenous difference in oxygen saturation fraction (Y(v) - Y(a) ), which can be determined from venous T(2) values when arterial oxygenation is known. A pulse sequence is presented that allows rapid measurement (<1 min) of blood T(2) s in the internal jugular vein. The technique combines slice-saturation and blood inflow to attain high signal-to-noise ratio in blood and minimal contamination from tissue. The sequence is sensitized to T(2) using a nonselective Carr-Purcell-Meiboom-Gill T(2) preparation directly after slice saturation. Fast scanning (pulse repetition time of about 2 sec) is possible by using a nonselective saturation directly after acquisition to rapidly achieve steady-state longitudinal magnetization. The venous T(2) (for 10 msec Carr-Purcell-Meiboom-Gill interecho time) for normal volunteers was 62.4 ± 6.1 msec (n = 20). A calibration curve relating T(2) to blood oxygenation was established using a blood perfusion phantom. Using this calibration, a whole-brain oxygen extraction fraction of 0.37 ± 0.04 was determined (n = 20), in excellent agreement with literature values.