Comparative effectiveness of 18F-FDG PET-CT and contrast-enhanced CT in the diagnosis of suspected large-vessel vasculitis

Objective: Large-vessel vasculitis (LVV) is a serious illness with potentially life-threatening consequences. ((18)Fluorine) fluorodeoxyglucose positron emission tomography-computed tomography (F-18-FDG PET-CT) has emerged as a valuable diagnostic tool in suspected LVV, combining the strengths of functional and structural imaging. This study aimed to compare the accuracy of FDG PET-CT and contrast-enhanced CT (CECT) in the evaluation of patients with LVV. Methods: A retrospective database review for LVV patients undergoing CECT and PET-CT between 2011 to 2016 yielded demographics, scan interval and vasculitis type. Qualitative and quantitative PET-CT analyses included aorta:liver FDG uptake, bespoke FDG uptake distribution scores and vascular maximum standardised uptake values (SUVmax). Quantitative CECT data were assessed for wall thickness and mural-lumen ratio. Receiver operating characteristics (ROC) curves were constructed to evaluate comparative diagnostic accuracy and a correlational analysis was conducted between SUV,, ex and wall thickness. Results: 36 adults (17 LVV, 19 controls) with a mean age (range) 63 (38-89) years, of which 17 (47%) were males were included. Time interval between CT and PET was mean [standard deviation (SD)] 1.9 (1.2) months. Both SUVmax and wall thickness demonstrated a significant difference between LVV and controls, with a mean difference [95%confidence interval (CI)] for SUVmax 1.6 (1.1, 2.0) and wall thickness 1.25 (0.68, 1.83) mm, respectively. These two parameters were significantly correlated (p < 0.0001, R = 0.62). The area under the curve (AUC) (95% CI) for SUVmax, was 0.95 (0.88-1.00), and for mural thickening was 0.83 (0.66-0.99). Conclusion: FDG PET-CT demonstrated excellent accuracy whilst CECT mural thickening showed good accuracy in the diagnosis of LVV. Both parameters showed a highly significant correlation. In hospitals without access to FDG PET-CT or in patients unsuitable for PET-CT (e.g. uncontrolled diabetes) CECT offers a viable alternative for the assessment of LVV. Advances in knowledge: FDG PET-CT is a highly accurate test for the diagnosis of LVV. Aorta:liver SUVmax ratio is the most specific parameter for LVV. In hospitals without PET-CT or in unsuitable patients e.g. diabetics, CECT is a viable alternative.