Time-of-Flight and Phase-Contrast imaging will be discussed for their role in aniography. Phase contrast imaging is sensitized to flow velocity, affecting the phase signal of flowing spins. This encoding of velocity enables flow velocity quantitation. Quantitative measures derived from velocity encoding will be discussed: valvular flow mapping with regurgitation assessment, transstenotic pressure drop, kinetic energy distribution and wall shear stress. Furthermore, some potential sources of error of phase contrast imaging will be discussed.
Spins that move during an MRI acquisition exhibit different imaging characteristics than neighboring stationary spins. Flowing spins, either from blood flow or CSF, cause mismapping and will appear as an artefact in the image. However, by understanding these characteristics of flowing spins, their appearance can be utilized for angiographic purposes. In this presentation, Time-of-Flight and Phase-Contrast imaging will be discussed for their role in MR angiography.
Phase contrast imaging is sensitized to flow as it uses a series of bipolar gradients to affect the phase signal of spins that flow with a uniform velocity in the direction parallel to the gradients. This encoding of velocity enables flow velocity quantitation. Other quantitative measures that can be derived from velocity encoding will be discussed: valvular flow mapping with assessment of regurgitant flow, transstenotic pressure drop from Bernoulli's equation, kinetic energy distribution and wall shear stress. Furthermore, some potential sources of error of this technique will be discussed: misalignment of flow, phase aliasing and phase offset errors.
Lotz J, Meier C, Leppert A, Galanski M. Cardiovascular flow measurement with phase-contrast MR imaging: basic facts and implementation. Radiographics. 2002 May-Jun;22(3):651-71.
Kamphuis VP, Westenberg JJM, van der Palen RLF, Blom NA, de Roos A, van der Geest R, Elbaz MSM, Roest AAW. Unravelling cardiovascular disease using four dimensional flow cardiovascular magnetic resonance. Int J Cardiovasc Imaging. 2017 Jul;33(7):1069-1081.