There are multiple definitions:

1. volume flow rate(English)

   • clinically useful imaging method for the study of cerebrovascular disease
   • CCA, CVA, CVI, DM, ICA
   • Cerebrovascular event, Medical imaging
   • https://doi.org…051228405001523

2. velocity fluctuation ratio(English)

   • the ratio of flow velocity to pulse wave velocity (PWV) in terms of blood pulse wave propagation
   • PWV, Re
   • Hemodynamics, Ratio-based metric
   • https://doi.org…-319-77932-4_14

3. venous flow resistance(English)

   • ABS, VC, VER, VVV
   • Vessel properties, Hemodynamics
   • https://doi.org…038/sc.1994.128

4. virtual flow reserve(English)

   • uses the 3-dimensional arterial tree with each branch considered a resistor as in an electrical circuit. Each branch point and vessel length add resistance to flow and become part of the lumped resistance model to deliver a ratio of pressure at rest to (assumed / virtual) hyperemia, thus producing FFR. Can be derived from optical coherence tomography, thus providing information on FFR
   • FFR, IVI, OCT, PCI, RFR, MSA, TVF
   • Coronary circulation, Ratio-based metric
   • https://doi.org…IONS.123.013702
   • https://doi.org…acc.2025.05.019