Abstract WMP37: Assessment of Intracranial Atherosclerotic Stenosis Using 4D Flow MRI Derived Hemodynamic Biomarkers

Abstract

Introduction: Despite medical management, 12% of patients with intracranial atherosclerotic disease (ICAD) experience recurrent stroke. Degree of stenosis, the current standard for risk stratification, does not reflect the hemodynamic significance of the lesion. We hypothesized that 4D flow MRI derived parameters including flow rate (FR) and peak velocity (PV) in major cerebral arteries, as well as the pressure drop (PD) in the atherosclerotic stenosis (AS) could be new imaging biomarkers for the hemodynamic impact of AS on local and global cerebrovascular flow redistribution. Methods: Intracranial dual- venc 4D flow MRI and time-of-flight (TOF) MRA were acquired in 23 controls and 13 ICAD patients at 3T (Fig. 1a). AS was graded as moderate (50-69%) and severe (70-99%) based on TOF MRA. 4D flow MRI data was corrected for phase offsets and noise and subsequently processed using an automated analysis tool (Fig. 1b-f). At each analysis plane (Fig.1e), the lumen region was determined from the TOF MRA (registered with 4D flow MRI), and area, PV and FR were calculated. The PD in AS was estimated from the Bernoulli equation using PV and area at AS and the area proximal to the AS. PV and FR ratios between left and right hemispheres for controls and affected to nonaffected hemispheres for patients were also calculated. Results: The PV ratio was significantly different (ranked sum test, p=0.003, Fig. 1g) between control and patient cohorts while FR ratio was similar (p=0.5). In addition, there was a significant correlation between PD in AS and PV ratio for the patient cohort (Spearman correlation, r=0.64, p=0.03, Fig. 1h). Conclusions: In this pilot study, we demonstrated the feasibility of two 4D flow MRI derived hemodynamic parameters, peak velocity and pressure drop, for the characterization of the impacts of ICAD on local and global cerebral flow distribution. Future studies are warranted to assess the prognostic value of these parameters for improved ICAD risk stratification.