The reliability of high resolution MRI in the measurement of early stage carotid wall thickening.

PURPOSE To study the repeatability of common carotid mean wall thickness (MWT) measured with high resolution MRI, in comparison with intima media thickness (IMT) assessed by ultrasound and to investigate the relative capabilities of these two modalities. MATERIALS AND METHODS Ten healthy volunteers and 10 subjects with carotid artery atherosclerosis were imaged with both high resolution MRI and US. Measurement of both MWT and IMT was performed by three blinded observers. Intra- and inter-observer repeatability was calculated and a Bland-Altman plot used to compare IMT and MWT. Circumferential variation in arterial wall thickness was also evaluated. RESULTS Intra- and inter-observer repeatability were comparable between IMT and MWT. The Bland-Altman plot showed a difference between IMT and MWT in controls with a trend towards equivalence in atherosclerotic patients. Analysis of circumferential variation in wall thickness by MRI identified greater focal thickening in patients compared with controls (p<0.001), which was not evident with ultrasound (p=0.98). CONCLUSION MRI and ultrasound have similar repeatability for the assessment of carotid wall thickness. There are differences between MWT and IMT, potentially due to the inclusion of the adventitia by MRI which, in addition to better detection of focal thickening, may provide a more complete estimation of early stage atherosclerosis.