Assessment of large-vessel involvement in giant cell arteritis with 18F-FDG PET: introducing an ROC-analysis-based cutoff ratio.
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%.


CONCLUSIONS
The (18)F-FDG PET region-of-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.
Department of Nuclear Medicine, Heinrich-Heine-University of Düsseldorf, Düsseldorf, Germany. h.hautzel@fz-juelich.de
Hubertus
H
Hautzel
Oliver
O
Sander
Alexander
A
Heinzel
Matthias
M
Schneider
Hans-Wilhelm
HW
Müller
D000368:Aged; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000378:metabolism; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics; D013700:Giant Cell Arteritis / Q000000981:diagnostic imaging*; D006801:Humans; D008099:Liver / Q000000981:diagnostic imaging / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods; D012372:ROC Curve; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012680:Sensitivity and Specificity
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18