The “Sponge Effect”

Describes the common phenomenon whereby circulating FDG available for tumoral uptake is decreased due to excessive FDG uptake in non-target tissues.

This “Sponge Effect” (soaking up of available FDG by non-target tissues) leads to false negative assessment of tumors — decreasing both visual appreciation and SUV assessment of lesions.

The most common etiologies for this phenomenon include:

• Poor Patient Preparation (non-fasting state, vigorous exercise, insulin administration) [Fig. 1]
• FDG Extravasation [Fig. 2]
• Extensive Brown Fat Activity
• Metformin-Induced Bowel Uptake [Fig. 3]
• Marked Reactive Marrow Uptake
• Extensive Tumor Uptake [Fig. 4] [Fig. 5]

In each of these situations, excessive non-target uptake of FDG decreases available FDG uptake by tumors in the body.

The left MIP image demonstrates marked skeletal muscle uptake due to vigorous exercise the morning of the exam.  The excessive muscle activity results in decreased available FDG for uptake throughout the remainder of the body (“Sponge Effect”), as evidenced by an abnormally low liver SUV. The one year follow up exam (right images) demonstrates a normal liver SUV, after proper patient preparation.