Synopsis

· Intracranial artery atherosclerosis (ICAS) is one of the major causes of ischemic stroke.

· MR vessel wall imaging techniques have been proposed and optimized dedicated for characterizing ICAS.

· High risk ICAS features, such as T1-hyperintense, positive remodeling, and contrast-enhancement, can be accurately identified by ICAS MR imaging.

Target audience:

Radiologists or medical imaging scientists who are working on or interested in intracranial artery atherosclerosis

Purpose:

Disruption of vulnerable plaques of intracranial artery atherosclerosis (ICAS) is one of the major causes of ischemic stroke, particularly in Asian populations. Therefore, characterizing intracranial artery plaque vulnerability prior to occurrence of cerebrovascular events is important for stroke prevention. In the recent 10 years, investigators proposed and optimized MR vessel wall imaging sequences for unveiling the histology of intracranial artery stenosis and the nature of ICAS. This lecture will provide updates on MR technical development and clinical application of ICAS imaging.

Methods:

In development of ICAS MR imaging techniques, the technical concerns include spatial resolution and suppression of blood and cerebrospinal fluid (CSF). Since the thickness of normal wall of intracranial artery is less than 0.5 mm, the ideal spatial resolution is around 0.5 mm. To null the blood signal, pre-pulses will be applied to MR sequence design. The signal of CSF surrounding intracranial vessel wall needs to be suppressed to enhance the contrast of arterial wall. Considering the ability of characterizing ICAS compositional features, such as intraplaque hemorrhage and lipid-rich necrotic core, T1- or PD- contrast needs to be provided. In addition, 3D acquisition is preferred to achieve isotropic spatial resolution and large coverage within acceptable scan time. For detecting the inflammation and neovessels of ICAS, which are linked to vulnerability, gadolinium-based contrast agent is administrated. The proposed MR vessel wall imaging is usually performed for identification of ICAS in patients with intracranial artery stenosis. For differentiating from other arterial diseases, such as arteritis, dissection, and Moyamoya disease, pre- and post-contrast MR imaging is suggested. To investigate the nature of ICAS, the proposed MR vessel wall imaging sequences were used in community and hospital-based cohort to characterize lesion distribution, T1-hyperintense, remodeling effect, and wall enhancement.

Results:

In optimization of ICAS MR vessel wall imaging sequences, the inversion recovery, Motion-Sensitized Driven-Equilibrium (MSDE) and Delay Alternating with Nutation for Tailored Excitation (DANTE), were the most popular pre-pulses to null blood signal. DANTE and anti-driven-equilibrium (ADE) were believed to be effective techniques in suppressing the signal of CSF. To preserve the signal to noise ratio and signal contrast, fast spin echo sequences such as VISTA/SPACE/CUBE were used. The current highest isotropic spatial resolution at 3.0T MR reaches 0.52 mm3. In characterization of ICAS, the proposed MR imaging sequences were found to be capable of identifying high risk plaque features, such as T1-hyperintense, positive remodeling, and contrast enhancement. These plaque features have been found to be significantly associated with cerebrovascular symptoms.

Discussion and Conclusions:

Significant advances in technical development and clinical application of ICAS MR imaging in the recent decade have been achieved. Most of high risk features of ICAS can be captured using the current proposed imaging techniques. However, the spatial resolution and ability of tissue characterization of ICAS MR imaging, particularly lipid-rich necrotic core and fibrous cap status, need to be further improved.

Acknowledgements

No acknowledgement found.