Flow velocity measurements for pulsatile flow

The inherent sensitivity of magnetic resonance imaging to motion makes it particularly well-suited as a noninvasive flow measurement modality. A pulse sequence which labels moving material by subjecting it to a pulse that inverts the longitudinal magnetization is discussed. Repeated application of this pulse produces a steady-state distribution of magnetization reflecting the history of material motion through the region of excitation. The sequence produces a strong suppression of signal from stationary material enhancing the dynamic range available to signal from moving material. In particular, angiographic-type projection images of flow in human subjects have been obtained with gated acquisition. These images display boli of tagged blood moving in arteries and veins. The boli are displaced in a direction and through a distance reflecting the temporal and spatial variation of velocity in the vessel.<>