Dual stack black blood carotid artery CMR at 3T: application to wall thickness visualization

Abstract

Background: The increasing understanding of atherosclerosis as an important risk factor for the development of acute ischemic events like ischemic stroke has stimulated increasing interest in non-invasive assessment of the structure, composition and burden of plaque depositions in the carotid artery wall. Vessel wall imaging by means of cardiovascular magnetic resonance (CMR) is conventionally done by 2D dual inversion recovery (DIR) techniques, which often fail in covering large volumes of interest as required in plaque burden assessment. Although the technique has been extended to 2D multislice imaging, its straight extension to 3D protocols is still limited by the prolonged acquisition times and incomplete blood suppression. A novel approach for rapid overview imaging of large sections of the carotid artery wall at isotropic spatial resolutions is presented, which omits excitation of the epiglottis. By the interleaved acquisition of two 3D stacks with the proposed motion sensitized segmented steady-state black-blood gradient echo technique (MSDS) the coverage of the carotid artery trees on both sides in reasonable scan times is enabled.

Results: 10 patients were investigated with the proposed technique and compared to conventional transversal DIR turbo spin and gradient echo approaches centered at the height of the carotid bifurcation. In all MSDS experiments sufficient black-blood contrast could be obtained over the entire covered volumes. The contrast to noise ratio between vessel and suppressed blood was improved by 73% applying the motion sensitizing technique. In all patients the suspicious areas of vessel wall thickening could be clearly identified and validated by the conventional local imaging approach. The average assessable vessel wall segment length was evaluated to be 18 cm. While in 50% of the cases motion artifacts could be appreciated in the conventional images, none were detected for the MSDS technique.

Conclusion: The proposed technique enables the time efficient coverage of large areas of the carotid arteries without compromising wall-lumen CNR to get an overview about detrimental alterations of the vessel wall. Thickening of the vessel wall can be identified and the suspicious segments can be targeted for subsequent high-resolution CMR. The exclusion of the epiglottis may further facilitate reduction of swallowing induced motion artifacts.

Figure 1

Example of the location of the two stacks, planned on the thick-slab PCA images and acquisition order in MSDS.

Figure 2

Examples of dual stack (L: left side, R: right side) carotid imaging (reformats) acquired in two patients (left patient 0.8³ mm³, right patient 1.0 mm³ resolution). The images clearly reveal vessel wall thickening (arrow heads) as well as severe lesions (arrows). The inset demonstrates possible coverage and vessel length measurement on a curved MPR. The length of the indicated path (crosses) is 110 mm.

Figure 3

Original CMR slice data cropped (a) and zoomed to lesion, indicated by arrows (b). The ultrasound image (9 MHz) at the according position, showing the severely calcified lesion in the left carotid artery bifurcation, is depicted in (c). Images correspond to the patient depicted on the right in Fig. 2.

Figure 4

Comparison of PD TSE DIR BB (top center) with motion sensitized dual stack (MSDS) GRE. 0.45 mm vs. 0.8 mm in plane resolution.