Respiration-Related Artifacts in PET/CT Imaging

Abstract

Discrepancy between the diaphragm position in PET and CT during PET/CT studies can lead to artifacts in the PET images due to improper attenuation correction. This artifact is an artificially depleted region at the liver dome that can potentially obscure lesions. We are developing a framework for quantifying the degree of mismatch and severity of artifacts on patient images and have performed phantom studies to illustrate the effect. A phantom was built with semi-cylinder lungs and 2 cm spheres below the lungs. The phantom was scanned with no motion, and then with incremental 1 cm shifts up to 5 cm in the axial direction to achieve PET/CT mismatch and blurring of PET. The spheres were filled with 6:1 and 3:1 radioactivity concentrations compared to the background. PET images were acquired and reconstructed using two different scanners with (AC) and without (NAC) attenuation correction and with and without time of flight (TOF) information. Additionally, patient images from FDG and PSMA studies were anonymized and evaluated for the presence of the artifact and the difference in diaphragm position. The location of the apex of the diaphragm was determined in each image. These patients were instructed to hold breath at end tidal volume. NAC PET images were used since the AC images are affected by the CT. A total of 168 FDG studies and 84 PSMA studies were evaluated.