Quantifying Intracranial Plaque Permeability with Dynamic Contrast-Enhanced MRI: A Pilot Study

Abstract

Background and purpose: Intracranial atherosclerotic disease plaque hyperintensity and/or gadolinium contrast enhancement have been studied as imaging biomarkers of acutely symptomatic ischemic presentations using single static MR imaging measurements. However, the value in modeling the dynamics of intracranial plaque permeability has yet to be evaluated. The purpose of this study was to use dynamic contrast-enhanced MR imaging to quantify the contrast permeability of intracranial atherosclerotic disease plaques in symptomatic patients and to compare these parameters against existing markers of plaque volatility using black-blood MR imaging pulse sequences.

Materials and methods: We performed a prospective study of contrast uptake dynamics in the major intracranial vessels proximal and immediately distal to the circle of Willis using dynamic contrast-enhanced MR imaging, specifically in patients with symptomatic intracranial atherosclerotic disease. Using the Modified Tofts model, we extracted the volume transfer constant (Ktrans) and fractional plasma volume (Vp) parameters from plaque-enhancement curves. Using regression analyses, we compared these parameters against time from symptom onset as well as intraplaque hyperintensity and postcontrast enhancement derived from T1 SPACE, a black-blood MR vessel wall imaging sequence.

Results: We completed analysis in 10 patients presenting with symptomatic intracranial atherosclerotic disease. Ktrans and Vp measurements were higher in plaques versus healthy white matter and similar or less than values in the choroid plexus. Only Ktrans correlated significantly with time from symptom onset (P = .02). Dynamic contrast-enhanced MR imaging parameters were not found to correlate significantly with intraplaque enhancement or intraplaque hyperintensity (P = .4 and P = .17, respectively).

Conclusions: Elevated Ktrans and Vp values found in intracranial atherosclerotic disease plaques versus healthy white matter suggest that dynamic contrast-enhanced MR imaging is a feasible technique for studying vessel wall and plaque characteristics in the proximal intracranial vasculature. Significant correlations between Ktrans and symptom onset, which were not observed on T1 SPACE-derived metrics, suggest that Ktrans may be an independent imaging biomarker of acute and symptom-associated pathologic changes in intracranial atherosclerotic disease plaques.

© 2017 by American Journal of Neuroradiology.

Figures

Fig 1.

Vessel wall imaging data in a 63-year-old man with symptomatic severe left MCA stenosis resulting in perforator thromboembolic infarcts as seen on 3D TOF MRA MIP and DWI (A). 3D BBMRI with postcontrast T1 SPACE imaging demonstrates plaque enhancement in an axial and coronal cross-sections of the MCA (B). A manual ROI isolates the enhancing plaque on the postcontrast T1 SPACE image (C, right, yellow ROI on the plaque inset). Kinetic modeling of contrast uptake into the plaque was performed by using DCE-MR imaging in the coregistered plaque ROI, and Ktrans values were calculated in each voxel (C, left). Normal control values were calculated in a region of normal white matter (red dotted ROI in C). The mean enhancement signal (white diamonds) and fitted Tofts curve (yellow) are shown from the plaque ROI (D). Note the difference in enhancement relative to healthy brain tissue (D, red ROI and red curve/squares).

Fig 2.

Ktrans and Vp values are shown for ICAD plaques and compared against the paired choroid plexus and NAWM measured in the same subjects. Both mean plaque Ktrans and Vp values were diverse and significantly different from choroid plexus and healthy white matter values (see text for relevant P values).

Fig 3.

Linear regression analysis demonstrates that Ktrans and Vp measured on DCE-MR imaging are more correlated (r2 and P values) to time from symptom onset than intraplaque contrast enhancement and precontrast hyperintensity measured on T1 SPACE imaging. Ktrans is the most associated and significant in its correlation (r2 = 0.46 and P = .03).

Fig 4.

Ktrans plaque permeability differs from relative signal enhancement in T1 SPACE imaging in 2 patients. Each panel shows axial TOF MRA (upper left), axial T1 SPACE (upper right), and sagittal T1 SPACE (middle) MR images confirming vessel patency with eccentric plaque, and Ktrans (lower). A, A 69-year-old man with right posterior cerebral artery stenosis on TOF MRA and corresponding T1 SPACE plaque enhancement measured at 123%. Ktrans measured at 0.39 minutes−1, and Vp at 11%. B, A 54-year-old woman with right MCA stenosis and corresponding T1 SPACE plaque enhancement measured at 226%, Ktrans measured at 0.45 minutes−1, and Vp at 12%.