Comparison of hemodialysis arteriovenous fistula blood flow rates measured by Doppler ultrasound and phase-contrast magnetic resonance imaging

Objective: The objective of this study was to compare blood flow rates measured by Doppler ultrasound (DUS) and phase-contrast magnetic resonance imaging (MRI) in patients having a hemodialysis arteriovenous fistula (AVF) and to identify scenarios in which there was significant discordance between these two approaches. Methods: Blood flow rates in the proximal artery (PA) and draining vein (DV) of newly created upper extremity AVFs were measured and compared using DUS and phase-contrast MRI at 1 day, 6 weeks, and 6 months postoperatively. Results: Blood flow rates in the PA measured by DUS (1155+/-907 mL/min, mean+/-standard deviation) and by MRI (1170+/-657 mL/min) were not statistically different (P=.812) based on 78 data pairs from 49 patients. DV DUS flow (1277+/-995 mL/min) and MRI flow (1130+/-655 mL/min) were also not statistically different (P=.071) based on 64 data pairs. In both PA and DV, the two methods substantially agreed with each other (Cohen k: PA, 0.66; DV, 0.67) when flow rates were put into four clinically relevant categories (< 300, 300-599, 600-1499, and $1500 mL/min). The Bland-Altman analyses of DUS and MRI flow identified six and four outliers for PA and DV, respectively. Seven outliers had higher DUS than MRI flow, with all DUS scan sites having a large lumen or significant local curvature; the other three had lower DUS flow, partly due to an underestimation of lumen diameter by DUS. Conclusions: DUS and MRI flow rates are generally comparable in both PA and DV. When DUS is used for flow measurements, careful attention to accurate lumen diameter measurements is needed and scan sites with marked curvature should be avoided. Our result may improve the accuracy of DUS-measured AVF blood flow rate.