Assessment of Large-Vessel Involvement in Giant Cell Arteritis with ¹⁸F-FDG PET: Introducing an ROC-Analysis–Based Cutoff Ratio

Abstract

In the diagnosis of giant cell arteritis (GCA) with aortic involvement, 18 F-FDG PET has been demonstrated to be a powerful tool. No other imaging method is able to directly detect acute inflammation within the aortic wall. However, because GCA is a rare PET indication, the assessment of GCA with 18 F-FDG PET remains difficult and highly dependent on the experience of the investigator. This study aimed to semiquantify the relationship between aortic and liver uptake and to introduce a receiver operating characteristic (ROC)-based cutoff ratio to allow investigator-and experience-independent GCA diagnosis with optimal sensitivity and specificity. Ratios of aortic wall uptake versus liver uptake were calculated in a group of GCA patients and a control group. These data were assessed in an ROC analysis, and finally, a cutoff-ratio-optimizing strategy was applied. Methods: Twenty-three patients with initially suspected GCA (18 positive for GCA criteria, 5 negative) and 36 matched controls were included. The control subjects underwent PET for oncologic diagnostics. None had intrathoracic or hepatic disease or therapy-related tracer accumulation. Additionally, physiologic liver metabolism was ensured by the presence of normal liver enzymes. After defining regions of interest over the thoracic aorta and the liver, we calculated maximal standardized uptake value ratios. Sensitivities and specificities for cutoff ratios from 0.1 to 2.5 were estimated and were ultimately used to assess an optimal cutoff ratio for separating GCA patients from controls. To further investigate the usefulness of the resulting cutoff ratio, we tested it in a second control group with changed hepatic metabolism and elevated liver enzymes. Results: ROC analysis revealed optimal selectivity for a cutoff ratio of 1.0. This ratio led to a sensitivity of 88.9%, a specificity of 95.1%, and an accuracy of 94.4%. When this aorta-to-liver ratio was applied to the control group with pathologic liver metabolism, the resulting specificity was 95.6%. Conclusion: The 18 F-FDG PET regionof-interest analysis with aorta-to-liver maximal standardized uptake value ratios is a reliable, investigator-independent indicator of GCA not affected by minor inflammation-associated changes in hepatic metabolism. Our results for a cutoff ratio of 1.0 prove that 18 F-FDG PET is a method of high sensitivity and specificity for GCA-related large-vessel inflammation.

18F-Fludeoxyglucose PET/CT in the evaluation of large-vessel vasculitis: diagnostic performance and correlation with clinical and laboratory parameters

“…A pattern of high-grade (equal to or higher than liver activity) 18 F-FDG uptake in the vessel wall of the thoracic aorta and/or its major branches (carotid and subclavian arteries) was observed in these patients (Tables 1 and 3, Figure 2). This is in accordance with a recent study which, by applying receiver operator curve analysis in GCA patients and healthy control subjects, calculated an aortic wall/liver 18 F-FDG uptake ratio of .1.00 to be highly sensitive (89%) and specific (95%) for diagnosing vasculitis [12]. In the series of Walter et al [9], who applied a similar scoring system to our study, a vessel score $2 was not found to be sensitive (60%) but still demonstrated high specificity (99%).…”

“…Yet the accuracy of this technique has not been defined, nor has its exact clinical role been established with respect to initial diagnosis, evaluation of the response to therapy, monitoring of disease activity or follow-up. The 18 F-FDG PET studies that have been performed demonstrate notable variability regarding the diagnostic criteria (visual scoring systems for 18 F-FDG uptake, semi-quantitative standardised uptake values (SUVs) and target to background ratios) [9][10][11][12] used for differentiation between affected and unaffected vessels and for assessment of disease activity.…”

Positron Emission Tomography-Computed Tomography for Imaging of Inflammatory Cardiovascular Diseases

“…(c) Positive 67 Ga uptake in the heart. 25 In 2006, the joint committee of the Japan Society of Sarcoidosis and Other Granulomatous Disorders, and the Japanese College of Cardiology published a revised version (see Table 1).…”

Aortitis and aortic aneurysm in systemic vasculitis

“…Currently, conventional angiography is basically used to guide endovascular intervention procedures or to combine imaging with the detection of central blood pressure in patients with significant limb artery stenoses. Systematic evaluation of patients with large-vessel vasculitis with imaging studies such as color duplex ultrasonography (US), CTA, FDG-PET, angiography, and magnetic resonance imaging (MRI) or MR angiography (MRA) has been performed by several investigators (Agard et al, 2008;Andrews et al, 2004;Andrews & Mason, 2007;Blockmans et al, 2008;Blockmans et al, 2009;Both et al, 2008;Hautzel et al, 2008;Henes et al, 2008;Narvaez et al, 2005;Pipitone et al, 2008;Prieto-Gonzalez et al, 2009;Walter et al, 2005;Webb & Al-Nahhas 2006). These techniques offer different but complementary information to assess large vessel involvement with relative advantages and disadvantages which are summarized in Table 3 (Tso E et al, 2002;Blockmans et al, 2009;Cid et al, 2009;).…”