[Relationship between CT Numbers and Artifacts Obtained Using CT-based Attenuation Correction of PET/CT]

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiology

Background:

• Computed tomography (CT)-based attenuation correction (CTAC) is essential for accurate positron emission tomography (PET) imaging.
• Image misregistration between CT and PET can lead to artifacts, particularly in regions with no radioactive tracer uptake (non-activity signals).
• Understanding these artifacts is critical for reliable quantitative analysis in PET scans.

Purpose of the Study:

• To investigate and characterize artifacts arising from CTAC errors due to image misregistration.
• To clarify the impact of varying CT numbers on the non-activity signal in PET images after CTAC.

Main Methods:

• A cylindrical phantom with a central tube served as the non-activity signal region.
• PET images were acquired using 18F-fluoro-2-deoxy-d-glucose (18F-FDG) in the background and water in the non-activity region.
• CT scans were performed with contrast agents to simulate various CT numbers, and PET images were corrected using these altered CT datasets.

Main Results:

• A direct correlation was observed between increasing CT numbers in the CT images and the magnitude of CTAC artifacts in PET.
• Distinct linear correlations were established for CTAC performed with CT numbers above zero (water) and below zero (air).
• Significant positive artifacts were detected in PET images post-CTAC, especially when CT numbers deviated from the original values (e.g., air).

Conclusions:

• Discrepancies in CT numbers used for CTAC, compared to the original scan, alter PET values.
• Image misregistration during CTAC can introduce significant artifacts, impacting quantitative accuracy.
• CTAC procedures require careful execution and validation to mitigate potential misregistration errors and ensure diagnostic integrity.