Motion artifacts occurring at the lung/diaphragm interface using 4D CT attenuation correction of 4D PET scans

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiology

Background:

• Fast CT acquisition in PET/CT can lead to attenuation correction errors, particularly at the lung/diaphragm interface.
• Gated 4D PET reduces motion artifacts, but residual artifacts may persist based on the CT dataset used for attenuation correction.

Purpose of the Study:

• To evaluate 4D PET images of targets near a density interface using different attenuation correction methods.
• To compare the effectiveness of 3D CT attenuation correction (3D CTAC), averaged 4D CT attenuation correction (CINE CTAC), and fully phase-matched 4D CT attenuation correction (4D CTAC) in reducing motion artifacts.

Main Methods:

• Phantom studies were conducted using a GE Discovery DVCT-PET/CT scanner with a custom phantom simulating lung/diaphragm density interfaces.
• An 18F-FDG loaded sphere phantom represented a lung tumor, with motion patterns sin(x) and sin4(x) applied.
• Image metrics, including normalized recovery coefficient (NRC) and fixed activity volume (FAV), were compared against a 3D PET scan with no motion (3D STATIC).

Main Results:

• 3D CTAC showed significant variations in FAV and NRC values over the motion cycle.
• Both 4D CTAC and CINE CTAC reduced motion artifacts, with greater reduction observed for targets in lower density material and with sin4(x) motion.
• 4D CTAC generally outperformed CINE CTAC in artifact reduction, though CINE CTAC was comparable for targets in water-equivalent material with sin(x) motion.

Conclusions:

• Attenuation correction using 4D CTAC or CINE CTAC effectively reduces motion artifacts at tissue interfaces like the lung/diaphragm border.
• 4D CTAC offers superior artifact reduction compared to CINE CTAC in several scenarios, improving image quality in dynamic PET/CT studies.