MR phase-contrast flow measurement with limited spatial resolution in small vessels: Value of model-based image analysis

Magnetic resonance phase-contrast volume flow rate (VFR) measurement with l imited resolution in small vessels is subject to two major sources of error : a) partial volume artifacts, causing systematic overestimation of the VFR , and b) errors related to the selection of vessel pixels [region of intere st (ROI)], causing large inter-observer and intra-observer variability. Add itionally, limited resolution results in Gibbs-ringing around vessels, whic h adversely affects VFR determination. In this paper, a semi-automatic mode l-based method is presented that effectively eliminates errors due to both partial volume effect and Gibbs-ringing and also minimizes errors from vari ability in the ROI selection. The model assumes a parabolic flow profile an d cylindrical vessel geometry, incorporates inflow effects, and takes into account the point-spread function of the acquisition. The method automatica lly estimates maximum velocity, vessel radius, and VFR. The method is valid ated in phantoms under various conditions and evaluated in vivo. Far small vessels with moderately pulsatile flow, it is demonstrated that accurate VF Rs and diameter estimates are obtained, virtually independent of the ROI se lection, even in vessels covered by just a few pixels. Compared with conven tional VFR analysis, both accuracy and reproducibility Improve significantl y. Magn Reson Med 41:520-528, 1999. (C) 1999 Wiley-Liss, Inc.