Vascular space occupancy asymmetric spin echo (VASO-ASE) for non-invasive quantification of cerebral oxygen extraction fraction
Spencer L. Waddle, Maria Garza, Chunwei Ying, L. Taylor Davis, Lori C. Jordan, Hongyu An, Manus J. Donahue
Abstract
Purpose
Asymmetric spin echo (ASE) MRI is a method for measuring regional oxygen extraction fraction (OEF); however, extravascular tissue models have been shown to under-estimate OEF. The hypothesis investigated here is that the addition of a vascular-space-occupancy (VASO) pre-pulse will more fully suppress blood water signal and provide global OEF values more consistent with physiological expectation and 15O positron emission tomography (PET)-validated T 2-relaxation-under-spin-tagging (TRUST) OEF measures.
Methods
Healthy adults (n = 14; age = 27.7 ± 5.2 y; sex = 7/7 male/female) were scanned at 3.0T. Multi-echo ASE without inter-readout refocusing (ASERF−), multi-echo ASE with inter-readout refocusing (ASERF+), and single-echo VASO-ASE were acquired twice each with common spatial resolution = 3.44 × 3.44 × 3.0 mm and τ = 0–20 ms (interval = 0.5 ms). TRUST was acquired twice sequentially for independent global OEF assessment (τ CPMG = 10 ms; effective TEs = 0, 40, 80, and 160 ms; spatial resolution = 3.4 × 3.4 × 5 mm). OEF intraclass-correlation-coefficients (ICC), summary statistics, and group-wise differences were assessed (Wilcoxon rank-sum; significance: two-sided p < 0.05).
Results
ASERF+ (OEF = 36.8 ± 1.9%) and VASO-ASE (OEF = 34.4 ± 2.3%) produced OEF values similar to TRUST (OEF = 36.5 ± 4.6%, human calibration model; OEF = 32.7 ± 4.9%, bovine calibration model); however, ASERF− yielded lower OEF (OEF = 26.1 ± 1.0%; p < 0.01) relative to TRUST. VASO-ASE (ICC = 0.61) yielded lower ICC compared to other ASE variants (ICC >0.89).
Conclusion
VASO-ASE and TRUST provide similar OEF values; however, VASO-ASE spatial coverage and repeatability improvements are required.