Three-dimensional visualization of velocity profiles in the human main pulmonary artery with magnetic resonance phase-velocity mapping.

Detailed data on blood velocity fields in the normal human main pulmonary artery are an essential platform for discriminating physiologic from pathologic pulmonary flow patterns. Over the years, many studies have revealed quite inconsistent data mainly because of lack of suitable measuring techniques. By using combined cardiac- and respiratory-triggered magnetic resonance phase velocity mapping, very consistent data were obtained in 12 volunteers. In all subjects the location of the highest axial velocities was shifted from the inferior-right toward the superior-left part of the vessel area during the right ventricular contraction, with rapidly decreasing velocities to the inferior right evolving into retrograde flow in the deceleration phase. The mean temporal velocity profile was consistently skewed with a low flow region also toward the inferior-right vessel wall. The magnetic resonance phase shift method used in this study provided remarkably consistent high-quality data about human pulmonary artery velocity fields. This is most likely because of the use of combined cardiac and respiratory triggering.