Accuracy and precision of MR velocity mapping in measurement of stenotic cross‐sectional area, flow rate, and pressure gradient

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Abstract
Reliability of magnetic resonance (MR) velocity mapping to assess severity of stenosis was assessed in vitro. Steady flow at different flow rates through five stenoses with a central orifice area ranging from 17 to 176 mm2 was measured with velocity mapping performed perpendicular to the stenotic jet. Besides determination of the stenotic cross-sectional area and flow rate, the pressure gradient was calculated with the modified Bernoulli equation and compared with manometer measurements. Cross-sectional areas were measured with an accuracy of ⩾76%, a precision of ⩾91%, and an error of ⩽19 mm2. Flow rates had an accuracy of ⩾72%, a precision of ⩽94%, and an error of ⩽1.4 L/min. The modification of the Bernoulli equation limited its reliability to stenoses with areas of 35-113 mm2. Pressure gradients were calculated with an accuracy of ⩾80%, a precision of ⩾88%, and an error of ⩽15 mm Hg. The method was applied in a single patient with aortic stenosis and gave estimates that agreed with those obtained by heart catheterization.