Simultaneous non-contrast angiography and intraplaque hemorrhage (SNAP) imaging : Comparison with contrast-enhanced MR angiography for measuring carotid stenosis

Abstract

Purpose

There is a growing interest in detecting intraplaque hemorrhage (IPH) during the clinical management of carotid disease, yet luminal stenosis has remained indispensable during clinical decision-making. Simultaneous Non-contrast Angiography and intraPlaque hemorrhage (SNAP) imaging has been proposed as a novel IPH imaging technique that provides carotid MR angiography (MRA) with no added scan time. Flowing blood shows negative signal on SNAP because of phase-sensitive inversion recovery. In a proof-of-concept study, we evaluated the feasibility of SNAP as a clinical MRA technique for measuring carotid stenosis.

Materials and Methods

58 asymptomatic subjects with 16–79% stenosis on ultrasound were scanned at 3T by SNAP with 0.8 mm isotropic resolution and 16 cm longitudinal coverage. Two readers measured luminal stenosis of bilateral carotid arteries (n=116) on minimum intensity projections of SNAP using the NASCET criteria. In the subset (48 arteries) with contrast-enhanced (CE) MRA available for comparison, luminal stenosis was also measured on maximum intensity projections of CE-MRA.

Results

Intra-class correlation coefficients (ICCs) with 95% confidence intervals were 0.94 (0.90–0.96) and 0.93 (0.88–0.96) for intra- and inter-reader agreement on stenosis measurements, respectively. Corresponding kappas for grading stenosis (0–29%, 30–69%, 70–99%, and 100%) were 0.79 (0.67–0.89) and 0.80 (0.68–0.90). Agreement between SNAP and CE-MRA was high (ICC: 0.95 [0.90–0.98]; kappa: 0.82 [0.71–0.93]).

Conclusion

As a dedicated IPH-imaging sequence, SNAP also provided carotid stenosis measurement that showed high intra- and inter-reader consistency and excellent agreement with CE-MRA. Further comparisons with digital subtraction angiography and other noninvasive techniques are warranted.