On staging FDG PET-CT for oesophageal cancer, a 5 mm coeliac lymph node appears intensely avid visually yet records an SUVmax of only 2.1. Which phenomenon best accounts for this unexpectedly low quantitative value?
- A Partial volume effect: activity spills out of objects smaller than roughly twice the scanner resolution ✓
- B Attenuation correction overestimates activity in small structures
- C Dead-time losses during high count-rate acquisition suppress recorded counts
- D Respiratory motion artefact averages the node with adjacent gastric activity
Correct answer: A. Partial volume effect: activity spills out of objects smaller than roughly twice the scanner resolution
Explanation
The partial volume effect causes measured SUVmax to fall progressively when a lesion approaches or falls below about twice the system resolution, typically under 10 to 15 mm for modern PET scanners, because recovered counts spill into surrounding tissue. Visual avidity remains striking while the number underestimates true concentration. Attenuation correction errors and dead time affect large fields, and respiratory blurring would smear rather than selectively depress this small focus.
Reference: Physics in Nuclear Medicine (Cherry, Sorenson, Phelps), 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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