Triple-gated motion and blood pool clearance corrections improve reproducibility of coronary 18F-NaF PET

Abstract

Purpose: To improve the test-retest reproducibility of coronary plaque ¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) uptake measurements.

Methods: We recruited 20 patients with coronary artery disease who underwent repeated hybrid PET/CT angiography (CTA) imaging within 3 weeks. All patients had 30-min PET acquisition and CTA during a single imaging session. Five PET image-sets with progressive motion correction were reconstructed: (i) a static dataset (no-MC), (ii) end-diastolic PET (standard), (iii) cardiac motion corrected (MC), (iv) combined cardiac and gross patient motion corrected (2 × MC) and, (v) cardiorespiratory and gross patient motion corrected (3 × MC). In addition to motion correction, all datasets were corrected for variations in the background activities which are introduced by variations in the injection-to-scan delays (background blood pool clearance correction, BC). Test-retest reproducibility of PET target-to-background ratio (TBR) was assessed by Bland-Altman analysis and coefficient of reproducibility.

Results: A total of 47 unique coronary lesions were identified on CTA. Motion correction in combination with BC improved the PET TBR test-retest reproducibility for all lesions (coefficient of reproducibility: standard = 0.437, no-MC = 0.345 (27% improvement), standard + BC = 0.365 (20% improvement), no-MC + BC = 0.341 (27% improvement), MC + BC = 0.288 (52% improvement), 2 × MC + BC = 0.278 (57% improvement) and 3 × C + BC = 0.254 (72% improvement), all p < 0.001). Importantly, in a sub-analysis of ¹⁸F-NaF-avid lesions with gross patient motion > 10 mm following corrections, reproducibility was improved by 133% (coefficient of reproducibility: standard = 0.745, 3 × MC = 0.320).

Conclusion: Joint corrections for cardiac, respiratory, and gross patient motion in combination with background blood pool corrections markedly improve test-retest reproducibility of coronary ¹⁸F-NaF PET.

Keywords: 18F-sodium fluoride; Cardiac PET; Data-driven motion detection; Motion correction; PET/CT; Vulnerable plaque.

Figure 1:. Overall scheme for comprehensive motion detection and correction of coronary PET images.

A fixed number of respiratory and electrocardiogram (ECG) gates were used. The number of gross patient motion (GPM) gates depended on the number of repositioning events the patient had during the acquisition. A 3D-mesh of gated reconstructions were obtained, which were registered to generate the 3×MC image set. Following the co-registration, the MC images (MC, 2×MC and 3×MC) were obtained by averaging all the gated images.

Figure 2:. Reproducibility of coronary ¹⁸F-NaF uptake measurement with motion correction.

Bland-Altman plots of the target-to-background (TBR) evaluations for all the lesions with and without motion correction. (A) Standard, (B) cardiac motion corrected (MC), (C) cardiac and gross patient motion corrected (2×MC) and, (D) cardiorespiratory and gross patient motion corrected (3×MC). Significant reductions in the 95% confidence intervals (orange lines) were observed for all motion corrected datasets in comparison to the standard evaluation (Table 2). The green line shows mean difference for all measurements. Standard = end-diastolic imaging.

Figure 3:. Reproducibility of coronary ¹⁸F-NaF uptake measurements and adjustments for blood pool clearance.

Bland-Altman plots of the TBR assessment for all lesions observed in the study. Standard images without and with corrections for injection-to-scan delay (Standard+BC) are shown in panels A and B respectively. The fully corrected dataset (cardiorespiratory and gross patient motion corrected with BC (3×MC+BC)) is shown in panel C. Significant reductions in the 95% confidence interval (orange lines) were observed for each incremental correction step (Table 5). The green line shows average TBR values across all measurements. BC = background blood pool correction. Standard = end-diastolic imaging.

Figure 4:. Reproducibility of coronary ¹⁸F-NaF uptake measurement in patients with substantial gross patient motion.

Bland-Altman plots of the target-to-background (TBR) assessment for ¹⁸F-NaF-avid lesions with gross patient motion >10 mm. Standard evaluations of the lesions without (Standard) and with correction for variances in the blood pool activity (Standard +BC) are shown in panels A and B. Panel C demonstrates the fully corrected dataset (cardiorespiratory and gross patient motion with BC (3×MC+BC)). Significant reductions in the 95% confidence interval (orange lines) were observed for each incremental correction step (Table 5). The green line shows average TBR values across all measurements. BC = background blood pool correction. Standard = end-diastolic imaging.

Figure 5:. Test-rest coronary PET reproducibility before and after corrections.

Patient 1. Patient with significant respiratory and gross patient motion during the first scan (10.3 mm) and a 20-minute difference in the injection-to-scan delay leading to discrepant evaluations in the test-retest scans. Patient 2. Patient with several repositioning events (gross patient motion) during the acquisition, which in combination with the cardiorespiratory motion reduced the appearing tracer-uptake in the lesion. Both patients. In both cases 3×MC+BC reduced the intra-scan variability TBR evaluation of the lesion. Following 3×MC+BC the test-retest lesion evaluation was concordant (18F-NaF-avid) in comparison to discordant test-retest evaluations obtained from the standard images in both cases. TBR = target to background value, BC = blood pool correction. Standard = end-diastolic imaging, 3×MC = cardiorespiratory and gross patient motion corrected.