Figure 1. Study protocol.

The thermoneutral experiment started in the morning on day one. After one hour a blood sample was taken and subsequently the [¹⁸F]FDG tracer was injected followed by the PET-CT scan one hour later. In the afternoon of day one, the shivering experiment was conducted, which started with a baseline period of 45 minutes during 31°C followed by 90 minutes of mild cold exposure (31°C) to determine the ambient temperature at which shivering occurred. The mild cold experiment on day two consisted of 45 minutes baseline (31°C) followed by 150 minutes of cold exposure. Blood samples were taken at the end of the baseline period and 90 and 150 minutes after the onset of cold exposure. The [¹⁸F]FDG tracer was injected 90 minutes after the onset of cold exposure, followed by the PET-CT scan one hour later.