Three-Dimensional joint bright, gray and black blood MR imaging technique for multi-parametric imaging of carotid artery: A feasibility and repeatability study.

Background: Multi-parametric imaging of the carotid artery enables quantitative characterization of vulnerable atherosclerotic plaques, which is crucial for preventing ischemic stroke. However, the existing sequential acquisition based multi-parametric imaging techniques of carotid artery lack bright blood imaging, which is essential for plaque components identification and boundary delineation. This study aims to develop a joint bright, gray and black blood imaging technique for carotid artery multi-parametric imaging and validate its accuracy and feasibility.

Methods: The proposed technique incorporated variable flip angles, variable duration of improved motion-sensitized driven equilibrium prepulse and variable time of echo mapping strategies with 3D multi-shot SPGR acquisition, generating T1, T2 and T2* maps. Bright, gray and black blood images were sequentially acquired in six scans covering the entire extracranial artery with isotropic resolution (0.7mm) when natural inflow blood enhancement and imposed blood suppression module were alternatively performed. A B1 specific dictionary was simulated and matched to the measured signal for T1 and T2 estimation while least square fitting was applied for T2* estimation. The proposed technique was compared against reference sequences and validated on healthy volunteers (n=8), and patients (n=4) with carotid atherosclerotic plaques.

Results: The proposed technique achieved an agreement of R = 0.99 in T1, T2, and T2 measurements with standard sequences in phantom study. In healthy volunteer study, the proposed technique reached high intra-class correlation coefficients (ICC: 0.906-0.956) with reference sequences in measuring T1, T2 and T2* of cervical muscle, but overestimation and underestimation were observed in T1 (against MOLLI, bias = 4.8%) and T2 (against multi-echo turbo field echo sequence, bias = -3.3%), respectively. No significant difference was found in the measurement of morphology and quantitative parameters between scan and rescan, while excellent intra- (ICC: 0.804-0.999) and inter-observer (ICC: 0.816-0.982) repeatability was reached. In patient study, the proposed technique demonstrated reliable performance in analyzing vascular morphology and characterizing plaque components with distinctive signal characteristics and quantitative values.

Conclusion: The proposed technique enables joint bright, gray and black blood imaging technique for carotid artery multi-parametric imaging with large coverage and isotropic resolution, indicating clinical potential for comprehensive characterization of carotid vulnerable plaque.