Physiological skin FDG uptake: A quantitative and regional distribution assessment using PET/MRI

Area of Science:

• Nuclear Medicine
• Radiology
• Medical Imaging

Background:

• Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI) is an advanced imaging technique.
• F-18 fluorodeoxyglucose (FDG) is a radiotracer used to measure metabolic activity.
• Understanding physiological FDG uptake in normal tissues is crucial for accurate disease detection.

Purpose of the Study:

• To assess the repeatability of physiological F-18 FDG uptake in the skin using PET/MRI.
• To investigate the regional distribution of skin FDG uptake.
• To explore the relationship between skin FDG uptake and patient demographics (sex and age).

Main Methods:

• Retrospective analysis of 562 whole-body PET/MRI examinations with normal FDG distribution.
• Evaluation of 74 repeated examinations for repeatability assessment.
• Comparison of 224 examinations to analyze differences based on sex and age.
• Skin segmentation using MR-based attenuation correction maps and off-line reconstruction software.
• Statistical analysis including Bland-Altman plots and Kruskal-Wallis test.

Main Results:

• Skin FDG uptake demonstrated good repeatability with limits of agreement <30% for SUVmean and SUVmax.
• The highest maximum standardized uptake value (SUVmax) was observed in the face (3.09±1.04), followed by the scalp (2.07±0.53).
• Facial FDG uptake was significantly lower in younger individuals (boys 0-9 and 10-20 years, girls 0-9 years) compared to adult men and older girls (p<0.001).
• In women, facial SUVmax was lower in those ≥70 years compared to 30-39-year-olds (p<0.05).

Conclusions:

• PET/MRI allows for repeatable quantitative analysis of physiological skin FDG uptake.
• Skin FDG uptake is highest in the face and shows significant variations based on sex and age.
• Age-related differences in body habitus should be considered when interpreting skin FDG uptake.