Aortic valve imaging using ¹⁸F-Sodium Fluoride: Implications of triple motion correction on test-retest reproducibility

Objectives: ¹⁸F-Sodium fluoride (¹⁸F-NaF) PET permits the quantification of microcalcification activity in the aortic valve. Currently, assessments are based on evaluations of end-diastolic or cardiac motion-corrected (ECG-MC) images which are affected by both patient and respiratory motion; each capable of shifting the heart by up to 3 cm. We aimed to develop a triple-motion correction technique (3xMC) that corrected for cardiorespiratory and patient motion, and evaluate its impact on maximum standardized uptake value (SUVmax), target-to-background ratios (TBR) and test-retest aortic valve ¹⁸F-NaF reproducibility.

Methods: The study population comprised of fifteen patients who underwent repeated ¹⁸F-NaF (124±6MBq) aortic valve scans within (29±24) days. All patients underwent 30-min PET acquisitions with targeted injection-to-scan delay of 60 min. To obtain anatomical information, the patients had a CT angiography (CTA) immediately after each of the PET acquisitions. The PET-acquisitions were obtained with ECG-triggering, while information on respiratory and patient motion was extracted from the PET raw data (listmode data). In brief, both motion patterns were detected using center-of-mass based analyses of single-slice rebinned sinograms (compressed 3D sinograms) created with a temporal resolution of 200 ms. Detection of respiratory motion was obtained from the diaphragm only, while patient reposition events were detected using the full PET field of view. Using the extracted motion patterns, 3 different image-reconstruction protocols were considered; an end-diastolic reconstruction protocol (standard) utilizing 25% of the acquired data, an ECG-gated reconstruction (ECG-MC) employing all the acquired data (4-ECG gated) and a triple motion-corrected (3xMC) dataset which is corrected for both cardiorespiratory and patient motion employing 4 ECG gates and 4 respiratory gates per patient position. SUVmax of ¹⁸F-NaF PET uptake was measured in a 3-dimensional polyhedron (6-mm thickness in the valve plane) encompassing the valve. TBR values were obtained by normalizing the valvular SUVmax value to the mean standardized uptake value obtained in the center of the right atrium.

Results: Increases were observed for the SUVmax and TBR measurements obtained with 3MC when compared to standard and ECG-MC reconstructions (SUVmax: Standard= 2.8±0.7, ECG-MC= 2.6±0.7 and 3xMC= 3.2±0.9, all p-values ≤0.002; TBR = Standard= 2.7±0.7, ECG-MC= 2.5±0.6 and 3xMC= 3.3±1.2, all p-values ≤0.001) (Figure 1). 3xMC improved test-retest reproducibility of both SUVmax and TBR when compared to the standard technique, measured as coefficients of variability (CV) (SUVmax : Standard = 8.7%, ECG-MC = 7.4% and 3xMC =7.5%); TBR: Standard =7.8%, ECG-MC = 7.8%, 3xMC =5.1%)

Conclusions: 3xMC improves test-retest reproducibility and increases SUVmax and TBR assessments of the aortic valve.

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