Background/Purpose:

Magnetic resonance imaging (MRI) and ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) may provide unique or redundant information in large vessel vasculitis (LVV). The study objective was 1) to assess agreement between interpretation of MRA and PET for disease activity and disease extent and 2) to determine MRA features associated with PET activity.

Methods:

An observational cohort of patients with giant cell arteritis (GCA) or Takayasu’s arteritis (TAK) were prospectively recruited, along with a comparator group (patients with vasculopathy or healthy controls). Subjects underwent clinical assessment, MRA, and PET within 24 hours. Imaging and clinical assessments were performed blinded to each other. A radiologist and two nuclear medicine physicians with vascular imaging expertise evaluated the MRA and PET studies for evidence of active vasculitis. To evaluate disease extent, the aorta and primary branches were divided into 15 vascular territories. Vascular involvement within each territory was defined on MRI as presence of wall thickness (black blood sequences), edema (STIR sequences), stenosis, occlusion, or aneurysm. Vascular involvement on PET was defined as visual FDG uptake in each arterial territory > liver. Agreement was assessed by percent overall agreement, Cohen’s kappa, and McNemar’s test. Multivariable logistic regression was used to test which factors on MRA were associated with PET interpretation of disease activity.

Results:

68 patients (GCA=26; TAK=24; Comparator=18) contributed 115 paired PET/MRA studies. A total of 1398 vascular territories were evaluated. Scans were interpreted as active disease in 76 PETs and 77 MRAs. 80 studies showed agreement (70%, Cohen’s kappa=0.32) between PET and MRA. In 35 studies with disagreement, PET demonstrated disease activity in 17 studies and MRA in 18 studies (McNemar’s p=1.00). Clinical disease status was associated with PET scan interpretation (p=0.01) but not MRA interpretation (p=0.52). More comparators were interpreted as active vasculitis by MRA versus PET (50% vs 11%, p=0.03). 782 territories showed agreement (56%, Cohen’s kappa=0.17) for disease extent between PET and MRA. Of the 608 territories with disagreement, MRA demonstrated disease in more territories than PET (513 vs 95, McNemar’s p<0.01). Territories with PET disease activity were positively associated with edema (OR=1.36, 95%CI=1.10-1.70, p<0.01) and wall thickness (OR=1.17, 95%CI=1.01-1.37, p=0.04) but not associated with stenosis (OR=0.07, 95%CI=0.33-0.96, p=0.33).

Conclusion:

There was fair agreement in the interpretation of PET and MRA findings for disease activity, but PET interpretation, and not MRA interpretation, was associated with clinical assessment. MRA detects disease activity and damage, thus identifying a greater extent of vascular involvement compared to PET. These data suggest that PET and MRA provide complementary information in LVV. In situations where PET is not available, increasing number of arterial territories with edema and wall thickness on MRA could be a surrogate for PET scan activity.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-of-magnetic-resonance-angiography-mra-and-18f-fluorodeoxyglucose-positron-emission-tomography-pet-in-large-vessel-vasculitis/