Magnetic resonance imaging of blood flow with a phase subtraction technique: In vitro and in vivo validation

RATIONALE AND OBJECTIVES. One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity- encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers. METHODS. In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of ±12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r² = .99; P = .0001). RESULTS. Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was ±70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r² = .99; P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms. CONCLUSIONS. Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.