Artefacts, Pitfalls & Classic Signs

Artefacts arise from physics (attenuation, scatter, septal penetration), from hardware fusion (misregistration), from physiology (brown fat, muscle, bowel), and from technique. “Signs” are named, reproducible patterns that aid — or trap — interpretation.

Physics artefacts

• Attenuation (breast, diaphragm) causes apparent MPI defects — use attenuation correction or prone/upright imaging.
• Scatter and septal penetration (e.g. star artefact around intense foci).
• Partial-volume effects reduce apparent uptake in small structures.

Hybrid-imaging artefacts

• SPECT/CT and PET/CT misregistration from breathing/motion — check fusion before localising.
• CT-based attenuation-correction artefacts from contrast, metal or truncation.
• Respiratory motion at the lung bases/diaphragm.

FDG-specific pitfalls

• Brown fat and muscle uptake — patient preparation and warming reduce these.
• Hyperglycaemia lowers tumour uptake and degrades images.
• Inflammation and recent surgery/therapy cause false positives.

Classic signs

• Superscan: diffusely intense skeletal uptake with faint kidneys (extensive metastases or metabolic bone disease).
• Flare phenomenon: increased intensity or apparent new bone-scan lesions in the first months after effective therapy — not progression; PCWG3 requires a confirmatory scan at least 6 weeks later before progression is called.
• Doughnut/rim and photopenic patterns; “cold” lesions (e.g. avascular or purely lytic disease).
• Star artefact from septal penetration around a very hot source.