Respiration-Related Attenuation Artifacts In PET/CT
Abstract
Purpose
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.
Methods
A phantom was built with semi-cylinder lungs. The phantom was scanned with no motion, and then with incremental 1 cm shifts up to 6 cm in the axial direction to achieve PET/CT mismatch and blurring of PET. PET images were reconstructed with (AC) and without (NAC) attenuation correction and with and without time of flight (TOF) information. Patient images from 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. Thus far 84 PSMA studies have been evaluated. Additional PSMA and FDG cases will be evaluated.
Results
Phantom images demonstrated that this artifact is present when the PET/CT mismatch is ≥2 cm. The artifact is lessened with TOF PET. Of the 84 prostate cancer cases, 26 definitively showed this artifact. All cases with displacements >1.12 definitively showed this artifact. The patients are breathing during PET acquisition but a distinct diaphragm location is determined since much of the respiratory cycle is spent at end tidal volume.
Conclusion
The severity of the respiratory artifact corresponds strongly to the displacement between CT and PET scans. Disclosures: One author consults for Data Spectrum Corporation.