Real-time volumetric flow measurements with complex-difference MRI.
Blood flow in large vessels can be noninvasively evaluated with phase-contrast (PC) MRI by encoding the spin velocity to the image phase. Conventional phase-difference processing of the flow-encoded image data yields velocity images. Complex-difference processing is an alternative to phase-difference methods, and has the advantage of eliminating signal from stationary spins. In this study, two acquisitions with differential flow encoding are subtracted to yield a single projection that contains signal from only those spins moving in the direction of the flow-encoding gradients. The increase in acquisition efficiency allows real-time flow imaging with a temporal window as short as two acquisition lengths (60 ms). Validation of the complex-difference method by comparison with conventional gated-segmented PC-MRI in a flow phantom yielded a correlation of r > 0.99. Peak arterial flow rates in the popliteal artery and desending aorta measured in vivo with the complex-difference method were 0.92 +/- 0.06 of the values measured with conventional PC imaging. Real-time in vivo volumetric flow imaging of transient flow events is also presented.
Thompson
Richard B
RB
Laboratory of Cardiac Energetics, National Institutes of Health, Bethesda, Maryland 20892, USA. thompson@nhlbi.nih.gov
McVeigh
Elliot R
ER
D001012:Aorta, Abdominal; D001783:Blood Flow Velocity; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011150:Popliteal Artery; D014682:Vena Cava, Inferior