Effects of MR surface coils on PET quantification.

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiology

Background:

• Combined PET/MRI systems face challenges with MRI surface coils affecting PET attenuation correction (AC).
• MRI surface coils can cause artifacts in CT-based AC, impacting PET data accuracy.
• Independent PET/CT systems may encounter CT artifacts from MR coil materials.

Purpose of the Study:

• To investigate the impact of MRI surface coils on attenuation-corrected PET emission data.
• To evaluate PET artifacts and quantification errors in scenarios with and without MR coils during AC.
• To compare CT-based AC (CT-AC) and MRI-based AC (MR-AC) in the presence of MR coils.

Main Methods:

• PET phantoms with MR surface coils were scanned using a clinical PET/CT system.
• CT-AC was used for reconstruction, with and without MR coils included in the AC data.
• Scenarios included varying coil presence (full, partial, absent) and phantom types (cylinder, anthropomorphic).
• Analytic simulations were performed for initial scenarios.

Main Results:

• MR coils introduced streak artifacts in CT images, persisting after conversion for PET AC.
• CT scans overestimated the linear attenuation coefficient of metal components in MR coils.
• PET emission images showed subtle artifacts outside phantoms; activity was underestimated by 19% without the head coil and overestimated by 28% with the head coil in CT-AC.
• Artifacts were reduced when half of a separable torso coil was removed.

Conclusions:

• MR coils can cause subtle artifacts and significant quantification errors in PET imaging.
• Improved CT techniques are needed to mitigate artifacts and enhance AC accuracy.
• Removing MR coil segments before PET/CT scans is recommended; coil redesign could further reduce artifacts.