Relationship between carotid plaque surface morphology and perfusion: a 3D DCE-MRI study

Abstract

Objective: This study aims to explore the relationship between plaque surface morphology and neovascularization using a high temporal and spatial resolution 4D contrast-enhanced MRI/MRA sequence.

Materials and methods: Twenty one patients with either recent symptoms or a carotid artery stenosis ≥40% were recruited in this study. Plaque surface morphology and luminal stenosis were determined from the arterial phase MRA images. Carotid neovascularization was evaluated by a previously validated pharmacokinetic (PK) modeling approach. K ^trans (transfer constant) and v _p (partial plasma volume) were calculated in both the adventitia and plaque.

Results: Image acquisition and analysis was successfully performed in 28 arteries. Mean luminal stenosis was 44% (range 11-82%). Both adventitial and plaque K ^trans in ulcerated/irregular plaques were significantly higher than smooth plaques (0.079 ± 0.018 vs. 0.064 ± 0.011 min^-1, p = 0.02; 0.065 ± 0.013 vs. 0.055 ± 0.010 min^-1, p = 0.03, respectively). Positive correlations between adventitial K ^trans and v _p against stenosis were observed (r = 0.44, p = 0.02; r = 0.55, p = 0.01, respectively).

Conclusion: This study demonstrates the feasibility of using a single sequence to acquire both high resolution 4D CE-MRA and DCE-MRI to evaluate both plaque surface morphology and function. The results demonstrate significant relationships between lumen surface morphology and neovascularization.

Keywords: Carotid atherosclerotic plaque; Contrast enhanced MR angiography (CE-MRA); Dynamic contrast enhanced MRI (DCE-MRI); Neovascularization; Plaque ulceration.

Fig. 1

a Shows DCE images at different time frames at a single slice location within an ICA branch of the plaque. The dashed red and green lines in frame 5 show the boundary of carotid lumen and adventitia. b Shows the corresponding black blood T₁w image with red and green lines delineating the lumen and wall boundary. c Represents the mean signal intensity time course within the lumen (red) and adventitia (green)

Fig. 2

An ulcerated plaque in the multi-contrast MR protocol, including MIP from CE-MRA, oblique and axial reformat of CE-MRA, TOF-MRA, T₁w, DTI, CE-T₁w and VVI. The white arrow in CE-MRA suggests the ulcer arises perpendicularly from the lumen. The ulcer can be clearly seen on the CE-MRA images, while it is not clearly visible on the TOF-MRA images. The pre-contrast T₁w image shows the lumen surface irregularity, and a thin or ruptured FC can be seen on the post-contrast T₁w images (black arrow). The hyperintense area on MR-DTI represents a large intraplaque haemorrhage/thrombus (white arrow). The VVI has the range of v _p from 0 to 65% and K ^trans from 0 to 0.5 min⁻¹ which shows a high K ^trans region at the adventitia

Fig. 3

Comparison of pharmacokinetic parameters in smooth and ulcerated/irregular plaque

Fig. 4

a Shows the significant correlation between stenosis and adventitial K ^trans. b Shows the significant correlation between stenosis and adventitial v _p. There is no significant correlation between plaque K ^trans or v _p and stenosis (c, d)

Fig. 5

Bland-Altman plots of the PK parameters derived after modelling the linear and non-linear relationships of signal intensity and Gd concentration. There is a significantly bias in PK values when using linear and non-linear assumption of image signal to Gd concentration. Note that $K_1^{\text{trans}}$ and v _p1 represent the linear model, and $K_2^{\text{trans}}$ and v _p2 represent the non-linear model