Metabolism of oxygen via T-2 and interleaved velocity encoding: A rapid method to quantify whole-brain cerebral metabolic rate of oxygen

Purpose 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 (SvO(2)) in the draining vein. Here, a pulse sequence, metabolism of oxygen via T-2 and interleaved velocity encoding (MOTIVE), was developed to measure both parameters simultaneously and enable CMRO2 quantification in a single pass. Methods The MOTIVE sequence interleaves a phase-contrast module between a nonselective saturation and a background-suppressed T-2-prepared EPI readout (BGS-EPI) to measure T-2 of blood water protons and cerebral blood flow in 20 s or less. The MOTIVE and standalone BGS-EPI sequences were compared against TRUST (T-2 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. Results MOTIVE experiments yielded an average SvO(2) 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 SvO(2) 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. Conclusions The MOTIVE sequence is an advance over existing T-2-based oximetric methods. It does not require a control image and simultaneously measures SvO(2) 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.

Automated summary

In this study, a pulse sequence called MOTIVE was developed to simultaneously measure blood flow rate and venous oxygen saturation for quantifying cerebral metabolic rate of oxygen (CMRO2). The MOTIVE sequence showed good reproducibility and agreement with traditional methods. It has the advantage of shorter scan time and does not require a control image.