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MRI vessel-wall imaging (MR-VWI) is an exciting new technique that goes beyond traditional luminal imaging tech-niques of computed tomography angiography (CTA), magnetic

resonance angiography (MRA), and digital subtraction angi-ography (DSA). These standard imaging techniques provide details about stenosis but are often limited by the lack of specificity, because different vasculopathies can masquerade each other. In contrast, MR-VWI has the distinct advantage of allowing detailed characterization of vessel wall pathology for

more precise interpretation of vessel abnormalities (Table). The increased visual detail may help narrow differential diagnosis, potentially improving clinical outcomes. Research is ongoing, and although there are considerable gaps in knowledge, this imaging technique is now used clinically at some centers.1-3

TechniqueA variety of techniques are available for MR-VWI with dif-

ferent brand names based on the vendor. At our institution, we use the T1 CUBE (GE Healthcare, Milwaukee, WI), a 3D black-blood imaging technique that employs parallel recon-struction and variable flip-angle excitation to achieve isotropic

Intracranial MRI Vessel- Wall ImagingMagnetic resonance imaging of intracranial vessel walls is a useful adjunctive technique that can aid differential diagnosis and potentially improve outcomes.By Mitchell Barnes, DO and Parham Moftakhar, MD

Table. MR Vessel-Wall Imaging Findings of Different Vascular PathologiesPathology Features on MR-VWI Helpful hints on MR-VMI

Atherosclerotic plaque

Eccentric wall thickening/enhancement. May have T2-bright fibrous cap that commonly enhances. T2-dark lipid core lies between the vessel wall and fibrous cap

Often looks more complex than vasculitis depending on the plaque morphology including if there is intraplaque hemorrhage

Vasculitis Smooth, circumferential/concentric thickening and enhancement

Enhancement may extend beyond the vessel wall into the surrounding perivascular soft tissues

Intracranial dissection

Eccentric wall thickening with enhancement Can be differentiated from atherosclerosis by demonstrating T1 hyperintensity within the wall (methemoglobin) or by visualizing false lumen

RCVS Multifocal circumferential/concentric wall thickening usu-ally with no enhancement

Full resolution of vascular findings usually occurs in 8-12 weeks

Pediatrics: (TCA) Circumferential wall thickening and enhancement Leading cause of pediatric stroke may be post-viral; ICA involvement extending into proximal vessels such as the M1 MCA

Moyamoya disease (distinguish primary vs secondary causes)

Secondary causes show vessel wall enhancement whereas primary does not

Distinction between primary and secondary causes of moyamoya is important because treatment is drastically different

Radiation-induced vasculitis

Circumferential and/or eccentric wall thickening and enhancement

The history will be key in adding this to the differential

Abbreviations: ICA, internal cerebral artery, MCA, middle cerebral artery; MR-VWI, magnetic resonance vessel wall imaging; RCVS, reversible cerebral vasoconstriction syndrome; TCA, transient cerebral arteriopathy

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submillimeter spatial resolution with scan times under 5 min-utes. Although 2D techniques are available, we have found 3D imaging advantageous because it allows us to view vessels with thinner slices and multiple planes, which is essential in distinguishing pathologies in tiny intracranial vessels (mean wall thickness 0.3-0.6 mm).3 Furthermore, 3D imaging is supe-rior when vessels are tortuous.

The 3D technique reduces scan times, which is important for patient comfort because the stroke imaging work-up also includes a full brain MRI study and time-of-flight (ToF) MRA of the brain and neck. MR-VWI is a complementary study not meant to substitute for ToF MRA. Acquiring both sequences has been shown to increase both the sensitivity and specificity of detecting vessel abnormalities.4,5

Although VWI is possible on a 1.5-T magnet, we only use our 3-T magnet for this advanced imaging technique because it provides the higher signal-to-noise ratio needed for subtle vessel wall findings in tiny intracranial vessels. Using a 7-T magnet can provide even more superior resolution, but this is not clinically feasible as most centers in the US do not have access to 7-T MRI equipment.6

The 3D T1 sequence without intravenous (IV) contrast is first acquired to assess for wall thickening. Gadolinium-based IV contrast is then administered to assess wall enhancement. Recently, we have also added a high-resolution T2-weighted sequence with multiplanar reformats to our vessel wall pro-tocol to provide additional information on plaque morphol-ogy as described below.

Technical pitfalls are often related to blood flow and poor spatial resolution. Blood flow near the vessel wall may not be fully suppressed because the flow is often slower at the vessel wall vs the center of the lumen, which can cause arti-ficial wall thickening.3 Additionally, slow flow in small veins can be misinterpreted as arterial wall enhancement after contrast injection. The recirculating or disturbed flow may yield plaque-mimicking flow artifacts caused by incomplete flow suppression, which is commonly seen in the curved and large vessel segments.3 Inadequate spatial resolution can induce partial volume averaging, leading to overestimation of vessel wall thickness that could be misinterpreted as ath-erosclerotic plaque or vasculitis.3,7

Indications and InterpretationSituations where MR-VWI is advantageous compared

with conventional imaging (eg, CTA, MRI and DSA) include differentiating atherosclerotic plaque, vasculitis, intracrani-al dissection, reversible cerebral vasoconstriction syndrome (RCVS), and other causes of intraluminal narrowing (Table, Figures 1-4).

The work-up for intracranial stenosis/vasculopathies may also include invasive procedures such as lumbar puncture for vasculitis, DSA, and intracranial biopsy. These invasive

procedures often have low yield. MR-VWI is a fairly quick noninvasive technique that can yield key information for the stroke neurologist and limit the number of inva-sive procedures.1An expert consensus guideline from the American Society of Neuroradiology provides recommenda-tions for clinical implementation of MR-VWI.1

Figure 1. Time-of-flight magnetic resonance angiography (MRA) shows left M1 middle cerebral artery (MCA) stenosis (A). Axial (B) and coronal (C) postcontrast 3D T1-weighted magnetic resonance vessel wall imaging (MR-VWI) show eccentric wall enhancement of the corresponding left M1 MCA stenosis (white arrow) that iscompatible with a vulnerable hot plaque.

A

B

C

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Atherosclerotic PlaqueOn MR-VWI, atherosclerotic plaque (Figure 1) can pres-

ent as nonuniform arterial wall thickening; this eccentric enhancement is colloquially termed a hot plaque, and potentially increases the risk of stroke.8-10 Preliminary studies also indicate that the degree of enhancement may predict the risk for vulnerable plaque and stroke, and thus studies are underway trying to quantify this enhancement.11,12

If a fibrous cap is present, it is often bright on T2 sequenc-es and may enhance with contrast imaging. The T2-dark, nonenhancing lipid core lies under the fibrous cap.1

Clinicians can use MR-VMI to monitor response to medi-cal treatment (eg, statins and aspirin) as vessel wall enhance-ment can improve and even resolve, rendering a plaque stable rather than vulnerable.

VasculitisA large group of pathologies that causes vessel wall

inflammation comprise vasculitis. On MR-VWI, vasculitis appears as smooth circumferential homogeneous thick-ening, and enhancement can be multifocal (Figure 2).

Enhancement can also extend beyond the vessel wall and into the perivascular soft tissues. Depending on the cause, vasculitis can affect small, medium, and large vessels. Post contrast images demonstrate a tram-track appearance when viewing the vessel in a parallel plane and as a donut when viewing en face.

MR-VWI increases biopsy sensitivity for vasculitis and even for giant cell arteritis, because it can assist in targeting the vessel that shows enhancement specifically.13 Furthermore, MR-VWI allows neurologists to track response to treatments such as steroids that can be monitored on serial MR-VWIs as the degree of improvement in vessel wall enhancement.

Intracranial DissectionMR-VWI demonstrates eccentric wall thickening and

possibly enhancement in the setting of dissection, some-times mimicking atherosclerosis. Dissection may be dif-ferentiated from atherosclerosis by detecting T1-weighted hyperintensity in the vessel wall, which reflects methemo-globin, and by visualization of a false lumen—both signs of dissection (Figure 3).14

Figure 2. Sagittal precontrast 3D T1-weighted magnetic resonance vessel wall imaging (MR-VWI) demonstrates circumferential thick-ening of the internal cerebral artery (A) followed by corresponding circumferential enhancement (arrows) on the sagittal (B), axial (C), and coronal (D) postcontrast 3D T1-weighted MR-VWI in a child with transient cerebral arteriopathym a type of vasculitis.

A

C

B

D

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RCVSRCVS is a syndrome that demonstrates multifocal arterial

lumen narrowing on MRA, CTA, and DSA and presents clini-cally with severe recurrent thunderclap headaches. MR-VWI demonstrates smooth, multifocal circumferential wall thick-ening in RCVS. Because this is a disorder of vascular tone, however, and not an inflammatory process, there is usually no vessel wall enhancement (Figure 4).1

Transient Cerebral Arteriopathy The most common type of arteriopathy and a leading

cause of acute ischemic strokes in children,15 transient cere-bral arteriopathy (TCA) is an inflammatory arteriopathy involving the distal internal carotid artery and its proximal branches, commonly the middle cerebral artery (MCA).16 The main differential to consider is dissection, a distinction that has been difficult to make on imaging before the advent of MR-VMI. TCA demonstrates areas of circumferential and concentric wall thickening and enhancement similar to vasculitis but has a more classic vascular distribution of the internal cerebral artery (ICA) and proximal vessels at the cir-cle of Willis (Figure 2). Earlier studies suggest that the degree of enhancement may also predict disease outcome. Stronger initial enhancement on MR-VWI is typically associated with progression of disease whereas little or no enhancement usually occurs with milder clinical symptoms.17

Moyamoya DiseaseThe role of MR-VWI in moyamoya is not diagnostic, but

rather differentiation between primary and secondary causes. Moyamoya is a steno-occlusive disease of the terminal ICA, causing innumerable collaterals to form, giving the pathog-nomonic puff-of-smoke appearance on angiography. Primary moyamoya is an idiopathic disease, that is considered nonin-

Figure 3. Axial precontrast 3D T1-weighted MRI-VWI demon-strates intrinsic T1 hyperintensity of the right petrous internal cerebral artery (ICA) wall reflecting methemoglobin in an acute dissection.

A

DD

B

E

C

Figure 4. Time-of-flight imaging demon-strates multifocal stenosis in the anterior (A) and posterior circulation (B). Diffusion imaging shows multiple acute infarcts (C) and axial post-contrast 3D T1-weighted magnetic resonance vessel wall imaging (MR-VWI) demonstrated no vessel wall enhancement in both the anterior (D) and posterior (E) circulation. The stenosis resolved on short-term follow-up magnetic resonance angiography (MRA) and diagno-sis was consistent with reversible cerebral vasoconstriction syndrome.

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flammatory and does not exhibit vessel wall enhancement. In contrast, secondary moyamoya can exhibit vessel wall enhancement and is caused by steno-occlusive diseases that happen to occur at the carotid terminus (eg, sickle cell dis-ease, neurofibromatosis-1 [NF-1], atherosclerosis, and vascu-litis).1 Distinguishing between primary and secondary disease is important because the treatment differs greatly. Primary moyamoya is treated with arterial bypass, whereas secondary moyamoya treatment depends on the underlying cause (eg, inflammatory lesions are treated with steroids and immuno-suppressants and atherosclerosis is treated with statins, aspi-rin, and hypertension and diabetes control).

Radiation-Induced VasculitisOn MR-VWI, radiation-induced vasculitis can mimic vascu-

litis and includes circumferential wall thickening and enhance-ment but may exhibit eccentric wall enhancement as well. Vessel involvement is typically confined to the radiation field and long-segment involvement can occur (Figure 5). Diagnosis is dependent on the history of prior radiation treatment.

Conclusion and Future DirectionsMR-VWI is a useful adjunctive technique that can be used

to evaluate intracranial vessels, potentially narrowing the differential for cryptogenic stroke and increasing diagnostic confidence. This may, in turn, improve treatment strategies

and outcomes while reducing use of invasive imaging (eg, DSA) and procedures (eg, lumbar punctures and biopsies). Current and future work focuses on continuously improv-ing resolution of this innovative imaging technique to allow more detailed analysis of plaque morphology, including the ability to observe intraplaque hemorrhage and positive and negative vessel wall remodeling. In the future, applying MR-VWI to cerebral aneurysms may also help predict which aneurysms may go on to rupture. n

1. Mandell DM, Mossa-Basha M, Qiao Y, et al. Intracranial vessel wall MRI: principles and expert consensus recommenda-tions of the American Society of Neuroradiology. Am J Neuroradiol. 2016;38(2):218-229.

2. Mossa-Basha M, Hwang WD, De Havenon A, et al. Multicontrast high-resolution vessel wall magnetic resonance imag-ing and its value in differentiating intracranial vasculopathic processes. Stroke. 2015;46(6):1567-1573.

3. Edjlali M, Qiao Y, Boulouis G, et al. Vessel wall MR imaging for the detection of intracranial inflammatory vasculopa-thies. Cardiovasc Diagn Ther. 2020;10(4):1108-1119.

4. Mossa-Basha M, Shibata DK, Hallam DK, et al. Added value of vessel wall magnetic resonance imaging for differentia-tion of nonocclusive intracranial vasculopathies. Stroke. 2017;48(11):3026-3033.

5. Song JW, Obusez EC, Raymond SB, Rafla SD, Schaefer PW, Romero JM. Vessel wall MRI added to MR angiography in the evaluation of suspected vasculopathies. J Neuroimaging. 2019;29(4):454-457.

6. van der Kolk AG, Zwanenburg JJ, Brundel M, et al. Intracranial vessel wall imaging at 7.0-T MRI. Stroke. 2011;42(9):2478-2484.

7. Antiga L, Wasserman BA, Steinman DA. On the overestimation of early wall thickening at the carotid bulb by black blood MRI, with implications for coronary and vulnerable plaque imaging. Magn Res Med. 2008;60(5):1020-1028.

8. Havenon AD, Mossa-Basha M, Shah L, et al. High-resolution vessel wall MRI for the evaluation of intracranial athero-sclerotic disease. Neuroradiology. 2017;59(12):1193-1202.

9. Lee HN, Ryu C-W, Yun SJ. Vessel-wall magnetic resonance imaging of intracranial atherosclerotic plaque and ischemic stroke: a systematic review and meta-analysis. Front Neurol. 2018;9:1032.

10. Qiao Y, Zeiler SR, Mirbagheri S, et al. Intracranial plaque enhancement in patients with cerebrovascular events on high-spatial-resolution MR images. Radiology. 2014;271(2):534-542.

11. Vakil P, Elmokadem A, Syed F, et al. Quantifying intracranial plaque permeability with dynamic contrast-enhanced MRI: a pilot study. Am J Neuroradiol. 2016;38(2):243-249.

12. Wu F, Ma Q, Song H, et al. Differential features of culprit intracranial atherosclerotic lesions: a whole‐brain vessel wall imaging study in patients with acute ischemic stroke. J Am Heart Assoc. 2018;7(15):e009705. doi:10.1161/JAHA.118.009705

13. Zeiler S, Qiao Y, Pardo C, Lim M, Wasserman B. Vessel wall MRI for targeting biopsies of intracranial vasculitis. Am J Neuroradiol. 2018;39(11):2034-2036.

14. Swartz RH, Bhuta SS, Farb RI, et al. Intracranial arterial wall imaging using high-resolution 3-tesla contrast-enhanced MRI. Neurology. 2009;72(7):627-634.

15. Sébire G. Transient cerebral arteriopathy in childhood. Lancet. 2006;368(9529):8-10. 16. Wintermark M, Hills NK, Deveber GA, et al. Arteriopathy diagnosis in childhood arterial ischemic stroke. Stroke.

2014;45(12):3597-3605.17. Stence NV, Pabst LL, Hollatz AL, et al. Predicting progression of intracranial arteriopathies in childhood stroke with

vessel wall imaging. Stroke. 2017;48(8):2274-2277.

Figure 5. Sagittal postcontrast 3D T1-weighted magnetic reso-nance vessel wall imaging (MR-VWI) demonstrates both diffuse circumferential and eccentric wall enhancement in the anterior cerebral arteries in an individual with a history of radiation therapy, consistent with radiation-induced vasculitis.

Mitchell Barnes, DOResident PhysicianDepartment of RadiologyChristiana Care Hospital Newark, DE

Parham Moftakhar, MDNeuroradiologistDepartment of RadiologyChristiana Care Hospital Newark, DE

DisclosuresMB and PM report no disclosures