The Influence of PET and CT Misalignment due to Respiratory Motion on the Cardiac PET/CT Imaging: a Simulation Study

Potential causes of misalignment between anatomical and functional images incardiac PET/CT imaging include respiratory and cardiac motion as well as bulk motion. In this study we evaluated the impact of respiratory and cardiac motion between CT and corresponding CT-based attenuation corrected (CTAC) PET images on apparent myocardial uptake. PET projection data of the 4D XCAT phantom were analytically generated using an analytic simulator considering the effect of photon attenuation and Poisson noise. Theassessment of PET images was performed through qualitative interpretation by an experiencednuclear medicine physician and a volume of interest based quantitative analysis. Moreover,Box and Whisker plots were calculated and bull’s eye view analysis performed. PET imageswere also reoriented along the short, horizontal and vertical long axis views for a betterqualitative interpretation. The simulation study showed that using the attenuation map at end-exhalation of therespiratory phase consistently overestimated the activity concentration in all segments of themyocardial wall as opposed to using the end-inhalation attenuation map image which resulted inunderestimation CT images acquired at end-exhalation could introduce larger errors compared toend-inhalation. These errors decrease significantly when the attenuation map was acquired atmid-inhalation or mid-exhalation phases of the respiratory cycle.