Effect of insulin on FDG-PET

Last revised by Rohit Sharma on 19 Feb 2023

Insulin administration has an effect on FDG-PET by affecting the biodistribution of the radiotracer, F-18-fluorodeoxyglucose (FDG), the FDG organic ligand being an analog of glucose, posing a challenge for imaging those with diabetes mellitus.

FDG-PET-CT is a hybrid imaging modality commonly used in the investigation of oncology patients, inflammatory, infectious and neurodegenerative disorders 1. Insulin promotes the uptake of glucose from the blood to cells of end organs in response to elevated blood glucose levels. FDG PET-MRI is becoming increasingly more common as centers adopt the technology and this article is also pertinent for this hybrid modality.

In the context of FDG-PET, increased insulin secretion will affect the biodistribution of FDG to tissues sensitive to insulin. This leads to altered deposition of FDG, resulting in suboptimal image quality and introducing potential errors in achieving accurate SUV measurement 2,3. Common areas for increased tracer deposition include skeletal and cardiac muscle, as well as adipose and liver tissues 3,4.

Patient preparation

The type and route of administration of insulin will have different impacts on the FDG PET, with guidelines and protocols for insulin administration and imaging diabetic patients variable across sites. 

The European Association of Nuclear Medicine recommends 5

  • injection of FDG no sooner than 4 hours after subcutaneous administration of rapid-acting insulin

  • injection of FDG no sooner than 6 hours after subcutaneous administration of short-acting insulin

  • intermediate or long-acting insulin should not be administered on the day of the scan, with insulin administered no earlier than the evening before

  • patients on a continuous infusion should have their pump switched off for a minimum of 4 hours prior to FDG injection

Patients with a continuous insulin pump or those on rapid or short acting-insulin regimen often have their scans scheduled later in the morning or in the middle of the day to allow time between an early breakfast and latest insulin administration. Patients on intermediate or long acting insulin often have scans scheduled in the early morning to avoid administering insulin on the same day as the scan. 

Depending on the local site, insulin administration prior to FDG PET-CT may be used to manage high blood sugar levels, which can also adversely affect the quality of the study. 

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