Estimating the amount of FDG uptake in physiological tissues

Area of Science:

• Nuclear medicine
• Radiochemistry
• Medical imaging

Background:

• Physiological uptake of 2-deoxy-2-[(18)F]fluoro-D-glucose (18FDG) in certain tissues can reduce tracer availability for target tissues.
• Understanding this phenomenon is crucial for accurate Positron Emission Tomography (PET) imaging interpretation.

Purpose of the Study:

• To estimate the magnitude of 18FDG uptake in physiological tissues with potentially intense uptake.
• To develop a method for quantifying tracer redistribution in PET studies.

Main Methods:

• A mathematical formula was derived to estimate the percentage of injected 18FDG molecules irreversibly trapped in a tissue.
• The formula considers factors like physical decay, injection-acquisition time delay, total lesion glycolysis (TLG), and patient weight (W).

Main Results:

• The formula derived is P ≅ 0.17*exp(-λt(acq))*TLG/W.
• Calculations in two patients showed intense brown fat, myocardium, and bowel uptake ranging from 0.5% to 4.2%.

Conclusions:

• A practical formula is now available for estimating 18FDG tissue uptake.
• Significant physiological uptakes can influence Standardized Uptake Value (SUV) quantification in target tissues, impacting diagnostic accuracy.