How should we estimate carotid stenosis using magnetic resonance angiography?

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Abstract
Our purpose was to assess the reproducibility of and differences between the most commonly used methods for assessing carotid artery stenosis using magnetic resonance angiography (MRA). We studied 55 patients who underwent axial three-dimensional time-of-flight MRA (1.5 T). Quantitative caliper measurements were performed from maximum intensity projection (MIP) and multiple planar reconstruction (MPR) images, according to the criteria of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and European Carotid Surgery Trial (ECST). The measurements were compared to each other and to visual interpretation, using conventional angiography as the reference. The measured percentage stenoses were higher on MRA than on digital subtraction angiography (DSA) using both NASCET (mean difference 1.9–3.0%) and ECST (6.3–6.7%) criteria. The kappa coefficients for the agreement between DSA and MRA were higher using the NAS-CET (0.61–0.76) than the ECST criteria (0.52–0.65). No statistically significant differences were found between measurements from MIP and MPR images. The ECST measurement criteria gave significantly higher percentage stenoses than the NASCET criteria (PP=0.01–0.001). There were no statistically significant interobserver differences in the MRA film readings, either in visually estimated degrees of stenosis or stenosis measurements. Thus, the different criteria of the two multicentre trials led to significantly different results, especially in the assessment of mild stenosis, and these differences are more important with MRA than with aging modalities or the reconstruction programs seem less important.