PHASE-DERIVATIVE ANALYSIS IN MR-ANGIOGRAPHY - REDUCED V-ENC DEPENDENCY AND IMPROVED VESSEL WALL DETECTION IN LAMINAR AND DISTURBED FLOW

A problem of current MRA techniques is the inability to accurately dep ict the vascular anatomy, particularly in areas of disturbed now. Vari ous reasons, such as intravoxel phase dispersion, saturation, temporal variations, and maximum intensity projection (MIP) nonlinearity, caus e a wrong delineation of vessel boundaries. A phase contrast (PC)-base d postprocessing operation, the phase derivative (PhD), is introduced to detect phase fluctuations indicating flow. Two-dimensional and thre e-dimensional angiographic reconstruction algorithms are presented. Ma thematical formulas are derived to predict the effect of sampling to n ow profiles and the effect on the PhD of these profiles. Numerical, ph antom, and preliminary in vivo experiments demonstrate that PhD images do not suffer from phase wraps and allow a velocity dynamic range ext ension only limited by a differential phase change. It is also shown t hat PhD MIPs produce higher signal-to-noise ratios than conventional P C angiograms and give a better impression of the anatomy of (stenotic) vessels and of their diameters for both laminar and disturbed flow.