Flow void

Refer to a signal loss occurring with blood and other fluids, like CSF or urine, moving at sufficient velocity relative to the MRI apparatus. It is a combination of time-of-flight and spin-phase effects usually seen in spin-echo techniques (such as T2-weighted images)

1. in MRI, absence of signal from blood whose activated protons leave a bodily area before the magnetization is measured.

2. In MRI, any loss of signal caused by combined turbulence and intravoxel dephasing.