Abstract WP120: Measuring Carotid Stenosis With a Novel Non-contrast Enhanced MR Angiography Technique (SNAP)

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Introduction: Contrast-enhanced MR angiography (CE-MRA) provides highly accurate measurement of carotid stenosis. But non-contrast techniques are desired as contrast agents may lead to anaphylaxis or nephrogenic system fibrosis. Recently, an inversion-recovery gradient echo sequence with phase-sensitive reconstruction was developed for assessment of lumen and intraplaque hemorrhage in one sequence - Simultaneous Noncontrast Angiography and intraPlaque hemorrhage (SNAP).

Hypothesis: We tested the hypothesis that SNAP provides an accurate and reproducible assessment of carotid stenosis compared to CE-MRA.

Methods: Fifty-eight subjects with 16-79% stenosis on ultrasound were scanned using a large-coverage (16 cm), isotropic-resolution (0.8 mm) SNAP sequence. Minimum intensity projections were generated at ten degrees increments to get 3D views of carotid arteries. Carotid stenosis was measured bilaterally according to the NASCET criteria by independent readers to estimate inter-reader reproducibility. To assess agreement between SNAP and CE-MRA, 24 subjects also underwent CE-MRA with same resolution (0.8 mm isotropic) after injection of gadolinium contrast (Magnevist). Maximum intensity projections were generated for CE-MRA and analyzed while blinded to SNAP data.

Results: Of 116 carotid arteries imaged by SNAP, 10 (8.6%) were excluded by at least one reader due to poor image quality or insufficient coverage. Inter-reader reproducibility was high, yielding an intra-class correlation coefficient (ICC) of 0.95 (95% CI: 0.93, 0.96). When stenosis measurements were categorized as no/mild (0-29%), moderate (30-69%) and severe (70-99%), weighted kappa was 0.77 (95% CI: 0.66, 0.88). In the 48 arteries with CE-MRA images, agreement between SNAP and CE-MRA was excellent (ICC: 0.96, 95% CI: 0.92, 0.98; weighted kappa: 0.90, 95% CI: 0.79, 1.00).

Conclusions: SNAP can be used to obtain accurate and reproducible measurement of extracranial carotid artery stenosis without gadolinium contrast. The ability of SNAP to assess both traditional (stenosis) and emerging (intraplaque hemorrhage) risk factors may promote its use in clinical workup of carotid stenosis.

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