Dynamic cardiac PET motion correction using 3D normalized gradient fields in patients and phantom simulations

Abstract

This work expands on the implementation of three‐dimensional (3D) normalized gradient fields to correct for whole‐body motion and cardiac creep in [N‐13]‐ammonia patient studies and evaluates its accuracy using a dynamic phantom simulation model. Methods A full rigid‐body algorithm was developed using 3D normalized gradient fields including a multi‐resolution step and sampling off the voxel grid to reduce interpolation artifacts. Optimization was performed using a weighted similarity metric that accounts for opposing gradients between images of blood pool and perfused tissue without the need for segmentation. Forty‐three retrospective dynamic [N‐13]‐ammonia PET/CT rest/adenosine‐stress patient studies were motion corrected and the mean motion parameters plotted at each frame time point. Motion correction accuracy was assessed using a comprehensive dynamic XCAT simulation incorporating published physiologic parameters of the heart's trajectory following adenosine infusion as well as corrupted attenuation correction commonly observed in clinical studies. Accuracy of the algorithm was assessed objectively by comparing the errors between isosurfaces and centers of mass of the motion corrected XCAT simulations. Results In the patient studies, the overall mean cranial‐to‐caudal translation was 7 mm at stress over the duration of the adenosine infusion. Noninvasive clinical measures of relative flow reserve and myocardial flow reserve were highly correlated with their invasive analogues. Motion correction accuracy assessed with the XCAT simulations showed an error of <1 mm in late perfusion frames that broadened gradually to <3 mm in earlier frames containing blood pool. Conclusion This work demonstrates that patients undergoing [N‐13]‐ammonia dynamic PET/CT exhibit a large cranial‐to‐caudal translation related to cardiac creep primarily at stress and to a lesser extent at rest, which can be accurately corrected by optimizing their 3D normalized gradient fields. Our approach provides a solution to the challenging condition where the image intensity and its gradients are opposed without the need for segmentation and remains robust in the presence of PET‐CT mismatch.

Clinically viable myocardial CCTA segmentation for measuring vessel-specific myocardial blood flow from dynamic PET/CCTA hybrid fusion

“…As previously described (Piccinelli et al 2020 ), our methodology to calculate flow along vessel centerlines relies on the fusion of dPET and anatomy. Importantly, the dPET sequence was first corrected for inter-frame motion (Nye et al 2021 ) and the resulting images were used for the remainder of the processing. The registration procedure consisted of the following steps (performed for rest and stress separately): (1) a summed PET image (PET sum ) was created from the dynamic frames of the second half of the acquisition interval; (2) the LVs segmented from the CCTA and PET sum were rigidly registered; and (3) mutual information-based techniques were used to align PET sum with the CCTA-derived biventricular mask using LV and RV structures from both modalities.…”