Should We Just Abandon the SUV?

Given the many factors that can significantly influence SUV calculations, the different formulas that are used to calculate SUV, the wide variations in threshold indicators for malignancy, and the very real problems of comparing SUV’s on sequential exams, should we just throw out the SUV altogether?

There are many respected radiologists who do advocate abandoning the SUV, arguing that the dangers arising from its imprecise nature and misuse exceed its utility.

These opponents of the SUV argue, rather convincingly, that qualitative assessment of a lesion’s metabolic activity (by visually comparing the lesion to background activity) is far more useful and far less prone to error.

Some advocates of this approach generally prefer describing the avidity of lesions as being:

• “Mild”:             Uptake less than liver activity,
• “Moderate”: Uptake ≈ liver (“Liverish”)
• “Intense”:             Uptake clearly greater than liver uptake

Unfortunately, there is little consensus even on these most basic definitions (there are those who define “mild” as any lesion with an SUV less than 2.5).

As a consequence, some advocate even a more basic approach for describing an FDG-avid lesion:

1. Simply call it “FDG-avid”; and
2. Describe its avidity relative to a reference (either the liver or mediastinal blood pool).
3. SUV values can be included, if so desired.

Example:

A 2.3 x 2.1 cm right upper lobe pulmonary nodule is present, with an SUV of 3.6 (this is greater than background reference uptake within the right lobe of the liver, which demonstrates an SUV mean of 2.0).

Final Recommendations:

• Like the cabinet members of the President, a radiologist serves “at the pleasure of his/her referring docs…” so keep them happy. If they want SUV’s, give them SUV’s. If they prefer descriptive terms, make it so.
• Always state the “type” of SUV at the beginning of the report: “All SUV’s are maximal and based on lean body mass.”
• Always include reference SUV’s for liver and/or mediastinal blood pool uptake at the beginning of every report. This way, if you are calling an FDG-avid node “active lymphoma”, your clinician knows the node’s SUV is greater than liver uptake (addressed in detail, here).
• If No Prior Exams: We recommend trying to limit the use of SUV’s, instead using descriptive terms to compare the relative activity of the lesion to the activity of the liver or mediastinal blood pool. A few SUV’s should be reported for representative lesions.
• Comparison Exams: Unless the background metabolic activity between the two exams is very different (discussed in detail, here), include a few comparison SUV’s for a few representative lesions.

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