Table 3.
Quantitative MRI metrics
| Vascular Territory Targeted/Acronymn units | Physiological Meaning | Technique |
|---|---|---|
| Femoral artery | ||
| RI (adim.) | Resistivity index, a measure of vascular resistance | Velocity projections:PI and RI are obtained from the arterial BFV waveform before cuff occlusion (at rest);VP, TTP, HI, and AUC are obtained from the reactive hyperemia response to cuff occlusion |
| PI (adim.) | Pulsatility index, a measure of vascular resistance | |
| HI, cm/s2 | Hyperemic index, or blood flow acceleration during early hyperemia | |
| VP, cm/s | Peak blood flow velocity (BFV), or maximum BFV after cuff release | |
| TTP, s | Time to peak, or time of maximum velocity | |
| AUC (adim.) | Area under the hyperemic curve | |
| FMD, % | Luminal flow-mediated dilation, or maximum dilation of the artery during hyperemia | Vessel wall imaging |
| Femoral vein | ||
| SvO2b, %HbO2 | Baseline SvO2, or venous blood oxygen saturation before cuff occlusion | Susceptometry-based oximetry |
| Tw, s | Washout time, or time for oxygen depleted blood to reach the imaged slice | |
| Upslope, %HbO2/s | Slope of the resaturation curve | |
| Overshoot, %HbO2 | Maximum venous resaturation after cuff release referred to the baseline SvO2 | |
| Superior sagittal sinus | ||
| BHI, cm/s | Breath-hold index, or blood flow acceleration due to hypercapnia | Phase-contrast MRI |
| Aorta | ||
| PWV, m/s | Pulse wave velocity, pulse wave transmitted upon contraction of the left ventricle | Velocity projections |