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.