Metabolism of oxygen via T₂ and interleaved velocity encoding: A rapid method to quantify whole-brain cerebral...

Cerebral metabolic rate of oxygen (CMRO₂ ) is an important biomarker of brain function. Key physiological parameters required to quantify CMRO₂ include blood flow rate in the feeding arteries and venous oxygen saturation (SvO₂ ) in the draining vein. Here, a pulse sequence, metabolism of oxygen via T₂ and interleaved velocity encoding (MOTIVE), was developed to measure both parameters simultaneously and enable CMRO₂ quantification in a single pass.

The MOTIVE sequence interleaves a phase-contrast module between a nonselective saturation and a background-suppressed T₂ -prepared EPI readout (BGS-EPI) to measure T₂ of blood water protons and cerebral blood flow in 20 s or less. The MOTIVE and standalone BGS-EPI sequences were compared against TRUST ("T₂ relaxation under spin tagging") in the brain in healthy subjects (N = 24). Variants of MOTIVE to enhance resolution or shorten scan time were explored. Intrasession and intersession reproducibility studies were performed.

MOTIVE experiments yielded an average SvO₂ of 61 ± 6% in the superior sagittal sinus of the brain and an average cerebral blood flow of 56 ± 10 ml/min/100 g. The bias in SvO₂ of MOTIVE and BGS-EPI to TRUST was +2 ± 4% and +1 ± 3%, respectively. The bias in cerebral blood flow of MOTIVE to Cartesian phase-contrast reference was +1 ± 6 ml/min/100 g.

The MOTIVE sequence is an advance over existing T₂ -based oximetric methods. It does not require a control image and simultaneously measures SvO₂ and flow velocity. The measurements agree well with TRUST and reference phase-contrast sequences. This noninvasive technique enables CMRO₂ quantification in under 20 s and is reproducible for in vivo applications.