Improving Infective Endocarditis Diagnosis by Combining Semi-Quantitative and Visual Findings Obtained from Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Imaging

Objective: The aim of this study was to assess visual and semi-quantitative outputs of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) for diagnostic purposes in infective endocarditis (IE) and determine whether increased spleen or bone marrow FDG uptake secondary to infection can aid in the diagnosis of IE.
Method: Patients who underwent F-18 FDG PET/CT examinations for a preliminary diagnosis of IE between July 2020 and January 2024 were analyzed. IE diagnostic criteria were used to confirm diagnoses, categorizing patients into an IE-positive group and a control group (IE excluded). Demographics and imaging-related data, including mean standardized uptake value (SUVmean) and/or SUVmax for lesions, liver, spleen, and lumbar vertebrae, were recorded. Spleen hypermetabolism and bone marrow hypermetabolism (BMH) were defined as spleen-to-liver or bone marrow-to-liver ratios exceeding 1, respectively. Visually assessed FDG uptake was scored from 0 to 3, forming the uptake score, which was dichotomized into low and high uptake groups.
Results: The study included 48 IE patients and 21 control patients. Lesion SUV, uptake score, spleen hypermetabolism, and BMH demonstrated significant differences between the groups. For distinguishing IE, a high uptake score showed a sensitivity of 85.42% and an overall accuracy of 84.06%, while lesion SUVmax (> 3.5) achieved the highest specificity (95.24%) and positive predictive value (96.77%).
Conclusion: Visual detection of uptake exceeding blood pool values on F-18 FDG PET/CT images, coupled with an SUV greater than 3.5, appears to distinguish IE patients with high accuracy. Additionally, increased bone marrow FDG uptake was strongly associated with IE.

Keywords: F-18 fluorodeoxyglucose positron emission tomography, infective endocarditis, standardized uptake value