Quantification of blood flow using phase contrast magnetic resonance imaging

Abstract

Phase contrast magnetic resonance (PC MR) imaging provides an accurate, non- invasive method for blood flow quantification. Unlike conventional MR images that are derived from the amplitude of the proton signal, velocity maps are reconstructed from the phase information of the MR signal. When a magnetic field gradient is applied along the axis of a vessel, intravascular magnetic spins accumulate a phase- shift that is proportional to flow velocity. The phase-shifts are mapped into a 2D array composed of flow velocities. The velocities over an entire cross-sectional area of a blood vessel can then be summed to quantitate actual blood flow. We have used PC MR imaging to quantitate flow in a flow phantom and human subjects. In flow phantom studies, a significant correlation was found between PC MR flow measurements made proximal and distal to a bifurcation (r<SUP>2</SUP> equals 0.999, N equals 5). In 6 human subjects, we found right pulmonary artery (PA) blood flow comprised 53% +/- 1% (mean +/- SEM) of total PA blood flow with the remaining 47% +/- 1% provided by the left PA (difference not statistically significant). Blood flow in the descending aorta, distal to the takeoffs of arteries to the head and upper extremeties, equaled 75% +/- 5% of the blood flow in the ascending aorta. PC MR imaging promises to be a useful tool in the evaluation of blood flow. Advantages of this method include the ability to profile flow velocities over the entire cross-sectional area of the vessel and non-invasive analysis of structures not accessible by other imaging modalities.