Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology

Key points:

  • To review the principles of intracranial VW-MR imaging and provides consensus recommendations for clinical practice.

Conventional techniques for imaging the intracranial arteries can fail to fully characterize disease that resides within the vessel wall. For this reason, there is growing interest in direct visualization of the vessel wall with high-resolution intracranial vessel wall MR imaging (VW-MR imaging).

The principal technical requirements for intracranial VW-MR imaging are the following:

High spatial resolution

The normal middle cerebral artery and basilar artery wall thickness is 0.2– 0.3 mm (smaller than the VW-MR imaging voxel dimensions currently achievable); for this reason it is visible suppressing MR signal of cerebrospinal fluid (CSF) and blood.

3T – 2D sequence 3T – 3D sequence
voxel size (mm) 2.0×0.4×0.4 0.5 isotropic
scan duration (min) 5-7/2-4 cm-thick section 7-10

Multiplanar 2D or 3D acquisitions

Accurate interpretation of VW-MR imaging requires visualization of the vessel wall in both short- and long-axis planes.

3T – 2D sequence 3T – 3D sequence
Advantages better image quality reduced scan time and more flexibility
Disadvantages partial volume averaging effects lower quality

Multiplanar 2D or 3D acquisitions
Time-of-flight (TOF) used to characterize luminal abnormality
Time-of-flight (TOF) with gadolinium helpful to define optimal contour of the lumen
T1 and T1C+ PD-WI has higher SNR, but constrast enhancement is less cospicuous
T2 could be useful
fat-sat sequencies useful for the ECA branches (not needed for intracranial imaging)

Suppression of signal in luminal blood and CSF

The most common methods of blood-signal suppression are the following:

Spin-Echo
Spatial presaturation
Double inversion recovery preparation

Clinical uses of VW-MR

SITUATIONS IN WHICH INTRACRANIAL VW-MR IMAGING IS LIKELY A USEFUL ADJUNCT TO CONVENTIONAL IMAGING
  • Atherosclerotic Plaque. The VW-MR imaging has a layered appearance explicated by carotid endarterectomy specimens, with an enhancing layer adjacent to the lumen (fibrous cap), a non-enhancing layer (lipid core), and a peripheral thin rim of enhancement (increased vasa vasorum in the adventitia of the artery). The lipid core has an hypointensity-isointensity on T1- and T2-weighted images; this is different from the MR imaging appearance of lipids in other tissues, because in carotid plaque the main contributor to MR signal is water protons and the main component of the plaque is cholesterol and cholesteryl esters.
  • Vasculitis. VW-MR imaging often demonstrates smooth, homogeneous, concentric arterial wall thickening and enhancement in patients with CNS vasculitis. Vasa vasorum–related contrast leakage is a potential cause of wall enhancement and dilated neovessels have been demonstrated within the extracranial arterial wall of patients with Takayasu arteritis.
  • Reversible Cerebral Vasoconstriction Syndrome. VW-MR imaging may enable prospective differentiation between vasculitis and vasoconstriction; both disorders result in arterial wall thickening, but the vessel wall in RCVS is typically nonenhancing.
  • Moya-Moya disease. VW-MR imaging have a lack of arterial wall thickening and enhancement, a smaller outer diameter of the vessel wall compared with patients with atherosclerotic plaques.
  • Radiation_Induced Arteriopathy. A study37 of 5 patients with radiation-in- duced narrowing of the intracranial internal carotid arteries found circumferential arterial wall thickening and enhancement in all cases.
  • Arterial Dissection. The VW-MR shows a curvilinear hyperintensity on T2-weighted images (in- timal flap) separating the true lumen from the false lumen and eccentric arterial wall thickening with the signal characteristics of blood (intramural hematoma).

Reference

  • Mandell DM, Mossa-Basha M, Qiao Y, Hess CP, Hui F, Matouk C, Johnson MH, Daemen MJ, Vossough A, Edjlali M, Saloner D, Ansari SA, Wasserman BA, Mikulis DJ; Vessel Wall Imaging Study Group of the American Society of Neuroradiology. Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of NeuroradiologyAJNR Am J Neuroradiol. 2017 Feb;38(2):218-229. doi: 10.3174/ajnr.A4893. Epub 2016 Jul 28.

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