Spatial factors for quantifying constant flow velocity in a small tube phantom: comparison of phase-contrast cine-magnetic resonance imaging and the intraluminal Doppler guidewire method

We examined the spatial factors influencing magnetic resonance (MR) flow velocity measurements in a small tube phantom and used the same measurements obtained with an intraluminal Doppler guidewire as reference. We generated constant flow velocities from approximately 40 to 370 cm/s in a tube 4 mm in diameter. We then performed segmented k-space, phase-contrast cine-MR imaging to quantify spatial peak flow velocities of one pixel and of five adjacent pixels as well as spatial mean velocities within regions of interest in a cross section of the phantom. Pixel dimensions ranged from 1.00 x 1.00 mm to 2.50 x 2.50 mm. We compared the MR measurements with the temporally averaged Doppler spectral peak velocities. For one pixel (r > 0.99: MR flow velocity for pixel dimension 1.00 x 1.00 mm = 1.03x + 9.8 cm/s), the linear correlation was excellent between flow velocities by MR and Doppler guidewire methods. However, for the five adjacent pixels, MR measurements were significantly underestimated using pixels 1.25 x 1.25 mm to 2.50 x 2.50 mm and for mean velocities for all pixel dimensions. Relatively high spatial resolution allows accurate MR measurement of constant flow velocity in a small tube at spatial peak velocities for one pixel.