Shear stress (SS) is associated with the formation of localised atherosclerosis. Due to the complexities of flow accurate determination of shear stress is difficult. Whilst 2D methods of deriving SS are widely used, computational fluid dynamic (CFD) modelling allows modelling of flow within complex geometry of the carotid bifurcation (CB).

This study compared mean SS using ultrasound based Womersley’s solution and MRI based CFD.

9 untreated hypertensive subjects [median age 42 (range 35–52) yrs] in a double-blind, placebo controlled, randomised, 3 way crossover trial using amlodipine or lisinopril underwent ultrasound examination of the right common carotid (CC) using a 7.5 MHz ultrasound transducer (L12-5 scanhead, HDI 5000, ATL, Bothell, Washington). Pulse wave Doppler was performed using a 1.5mm sample volume placed in the centre of CC 2cm proximal from the carotid bulb. Mean Womersley shear stress was calculated from these data using custom written software.

MRI of the CB was performed (Siemens Magnetom Sonata 1.5 T scanner) using a 2D TOF protocol and 3D PC sequence for flow measurements. These data were combined with custom refined CFD codes (CFX4.4 (AEA Technology, Didcot, Oxfordshire UK).

Mean difference was −0.242 Pa (SD 0.314; 95% limits of agreement

−0.856, 0.373]; Lin’s concordance correlation coefficient (rho_c 0.16; SE 0.13; p = 0.21); Pearson’s r = 0.244; p = 0.219.

Overall the data indicate poor agreement between WSS measured by ultrasound/Womersley and MRI/CFD and underscore the limits of using 2D methods in the investigation of the relationship between SS and atherosclerosis in the CC.