Table 1 Flow-related parameters
From: A clinician’s guide to understanding aortic 4D flow MRI
Flow parameters | Short definition | Unit |
|---|---|---|
Flow rate | The amount of blood passing through a plane per time unit (also known as through-plane volume per second) | mL/s |
Flow volume | Volume of blood passing through a plane within a certain amount of time. Derived from the area under the curve of the flow rate graph (flow [ml/s] versus time [s]) | mL |
Flow velocity vector | Magnitude and direction of blood flow through a plane (also known as through-plane propagation speed of blood) | m/s or cm/s |
Flow jet angle | The angle between the direction of blood flow and the centerline of the vessel | ° (degrees) |
Flow displacement | The degree of eccentric flow, defined as the distance between the center of the vessel and the center of velocity (often normalized to lumen diameter) | mm (or relative to lumen diameter) |
Vorticity | Local in-plane rotation of a fluid particle around a common axis (comparable to the angular velocity of solid objects) | 1/s |
Helicity | Alignment of vorticity with the main velocity vector | m/s2 |
Wall shear stress | The tangential force caused by friction of blood as it flows along the vessel wall | Pascal or dyne/cm2 |
Kinetic energy | The energy that is stored in movement of blood | Joules |
Viscous energy loss | The energy that is lost due to frictional forces | Joules |
Turbulent kinetic energy | The energy that is stored in turbulent flow of blood | Joules |
Pulse wave velocity | The propagation speed of a pulse wave created by the systolic contraction of the left ventricle (a measure of arterial stiffness) | m/s |
Pressure fields | Differences in distribution of local pressure within a vessel (gradients between local pressure fields are used to assess hemodynamic significance of obstructions) | mmHg or Pascal |