The study titled "Study to determine interaction patterns of different organs in healthy volunteers as a basis for better patient diagnostics using PET/CT imaging" is designed to investigate the interaction patterns of different organs in healthy volunteers. The information gathered is intended to be leveraged to enhance patient diagnostics using PET/CT imaging techniques.

In the study titled "Study to determine interaction patterns of different organs in healthy volunteers as a basis for better patient diagnostics using PET/CT imaging," the investigators will utilize the Biograph Quadra from Siemens Healthineers. This clinically approved PET-based imaging platform enables the acquisition of emission data across an extended axial field of view (axFOV) of 106 cm.

The objective is to leverage the Quadra PET/CT's capabilities, which can perform quantitative functional examinations of an extended axFOV, large enough to cover an imaging range from the head to the thighs. This range is typically scanned in standard oncology re/staging scenarios using multiple, overlapping bed positions.

The aim is to convert the Quadra PET's higher volume sensitivity into a higher signal-to-noise ratio and image quality, and significantly reduce the injected radioactivity while maintaining the diagnostic quality of the PET images. Notably, all organs within the extended axFOV are covered synchronously by the PET measurement, allowing the examination of inter-organ signalling, a key factor in disease onset and progression.

It is understood that diseases like cancer cause deviations from normal inter-organ communication (homeostasis). To depict such deviations in the future, the aim is to establish a reference standard. This involves building a voxel-wise normative database of glycolytic activity across organs covered in the axFOV imaging range, which requires the acquisition of dynamic FDG-PET data of normal, disease-free individuals.

Additionally, the investigators seek to pair the FDG-PET image readouts with continuous physiological signals from an Apple i-watch wearable for identifying relationships between lifestyle and glucose uptakes during the scan. The objective is to build a normative database of voxel- and organ-based glycolytic uptake in 50 healthy volunteers. Subjects will be scanned twice for reproducibility standards and will wear a smartwatch for 3 months prior to the first PET scan and up to 3 months after the 2nd PET scan.

The hypothesis is that an atlas of normative glycolytic activities can be built with a test-retest variability of <15% (measured as organ-based standardized uptake value). The methodology involves using the Siemens Quadra PET/CT. Subjects come for test-retest within a month. Each time they will be injected 100MBq [18F]FDG and examined for 60 min (dynamic scan). An ultra-low-dose CT scan will be acquired to estimate mandatory attenuation correction factors.

No risks or adverse device effects are expected as the Quadra PET/CT is approved for clinical use.

Inclusion Criteria:

- Adult subjects

Exclusion Criteria:

• Age < 18, common exclusion criteria for PET/CT scans
• known presence of cancer
• pregnancy or breastfeeding
• On-site blood glucose level > 150mg/dL
• Not able to lie still for 65 min