On a CT-based attenuation-corrected PET image, an intense linear band of apparent activity appears across the thorax in a patient whose uncorrected images show no corresponding focus. The patient has spinal instrumentation from prior surgery. What explains this?

• A Overcorrection artefact from CT beam hardening by metal, misassigned as high activity ✓
• B True metastatic deposit along the hardware tract
• C Residual anaesthetic gas in the lungs
• D Physiological brown adipose tissue activation

Explanation

Metallic implants cause beam-hardening streaks on CT. When these CT values are used for attenuation correction, the algorithm overestimates attenuation along the metal and applies excessive correction, creating spuriously intense apparent uptake on corrected PET images. Comparing corrected with non-corrected images resolves the issue: true lesions appear on both, artefacts only on corrected images. Metastasis would show on uncorrected images too, and brown fat has a characteristic supraclavicular and paraspinal distribution unrelated to hardware.

Reference: Brant and Helms Fundamentals of Diagnostic Radiology, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.