Magnetic resonance imaging maps of velocity were acquired with a 1.5-T system in 10 subjects in a plane perpendicular to the main pulmonary artery. Velocity images were successively acquired with a method developed from Fourier-encoding velocity imaging (FEVI) principles with eight gradient steps and one excitation, and with two-point phase-subtraction mapping. Reconstruction in FEVI was implemented by zero-filling interpolation around the eight gradient steps and then around the four central steps. The methods were compared by using estimates of noise in velocity measurements based on the difference between the experimental map and a smooth fitted map. For the same acquisition time, FEVI with four encoding steps was more precise in velocity measurements than phase mapping. Precision was further increased by the use of eight encoding steps, but acquisition time was doubled.

The aims of this study were first to analyze pulmonary flow differences between patients with primary pulmonary hypertension (PPH) and volunteers, and second to determine whether magnetic resonance (MR) 3D Fourier encoding velocity imaging is capable of assessing hemodynamics in PPH. Pulmonary and aortic flows were quantified with MR imaging in 13 patients with PPH confirmed by right heart catheterization (RHC) within the same week and in 10 volunteers. MR pulmonary antegrade velocities, acceleration time (defined as the time from the onset of flow to the peak velocity), and arterial distensibility (maximal surface-minimal surface/minimal surface) were significantly different in patients (p < 0.05). MR pulmonary and aortic flow volumes correlated well with each other in the two populations (r = 0.98). Agreement between MR and RHC data was low: for the right cardiac output (mean difference) the 95% confidence interval was -0.88 to -0.22 L/min and for the right stroke volume 2.83 to 9.71 ml. However, the high coefficient correlations found between the two techniques showed that MR data could be used as indicators of right hemodynamics. 3D Fourier encoding-velocity sequence is a reliable noninvasive flow measurement method for the quantification of right hemodynamics in patients with PPH.

The final result of Fourier velocity mapping is a set of images, each representing the spatial distribution of spins at a given velocity. To acquire data in a short time, the number of encoding gradient steps must be as small as possible, but this can mean sacrificing velocity resolution. We used interpolation methods to obtain high velocity resolution with a small number of encoding steps involving linear interpolation from 16 encoding steps or more and zero-filling interpolation from two to eight encoding steps. Velocity measured by interpolated Fourier-flow encoding agreed well with values obtained using a calibrated phantom. A simulation of noise on the images of the phantom showed that, for a given acquisition time, increasing number of encoding steps in the Fourier flow encoding gave better precision for velocity measurement than did averaging identical signals in phase-mapping methods.