High-density materials do not always induce artifacts on PET/CT: what is responsible for the difference?

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiopharmacology

Background:

• Positron Emission Tomography/Computed Tomography (PET/CT) imaging often reveals increased radiotracer uptake at sites of high-density materials.
• However, certain materials, such as those used in hip prostheses, typically show minimal or no increased uptake on PET/CT.
• This discrepancy suggests that factors beyond material density may influence imaging artifacts.

Purpose of the Study:

• To investigate the hypothesis that motion of high-density materials is a critical factor in causing false increased uptake artifacts on PET/CT.
• To validate this hypothesis through controlled phantom studies.

Main Methods:

• A phantom cylinder filled with 18F-based activity was prepared with a pacemaker attached.
• PET/CT scans were performed under two protocols: static positioning (protocol 1) and repositioning after transmission CT but before emission scan (protocol 2).
• The effect of motion on radiotracer distribution around the high-density material (pacemaker) was analyzed.

Main Results:

• In protocol 1 (static), no increased uptake was observed at the pacemaker site, and the cylinder showed homogenous activity.
• In protocol 2 (motion), a distinct hotspot appeared at the pacemaker site, with inhomogeneous uptake in the surrounding cylinder.
• This indicates that motion significantly alters apparent radiotracer distribution around dense objects.

Conclusions:

• False increased uptake on PET/CT associated with high-density materials is not solely due to the material's density.
• Motion of these materials, particularly when adjacent to radioactive areas, plays a significant role in inducing these imaging artifacts.
• Understanding motion artifacts is crucial for accurate interpretation of PET/CT scans involving implants or dense foreign bodies.