Significant differences of MRμMaps generated for the same subjects but different PET/MR systems resulted in differences in attenuation correction factors, particularly in the thorax. These differences currently limit the quantitative use of PET/MR in multi-center imaging studies.

To improve the test-retest reproducibility of coronary plaque 18 F-sodium fluoride (18 F-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 using all the data (no-MC), (ii) end-diastolic PET (Standard), (iii) cardiac motion corrected (MC), (iv) combined cardiac and gross patient motion corrected (2xMC) and, (v) cardiorespiratory and gross patient motion corrected (3xMC). 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), 2xMC+BC = 0.278 (57% improvement) and 3xMC+BC = 0.254 (72% improvement), all p<0.001). Importantly in a sub analysis of 18 F-NaF-avid lesions with gross patient motion >10mm following corrections reproducibility was improved by 133% (coefficient of reproducibility: standard= 0.745, 3xMC= 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 18 F-NaF PET.

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Background We assessed the feasibility of utilizing previously acquired computed tomography angiography (CTA) with a subsequent PET-only scan for the quantitative evaluation of 18F-NaF PET coronary uptake. Methods & Results Forty-five patients (age 67.1±6.9 years, 76% males) underwent CTA (CTA1) and combined 18F-NaF PET/CTA (CTA2) imaging within 14[10,21] days. We fused CTA1 from visit one with 18F-NaF PET (PET) from visit two and compared visual pattern of activity, maximal standard uptake values (SUVmax) and target to background (TBR) measurements on (PET/CTA1) fused versus hybrid (PET/CTA2). On PET/CTA2, 226 coronary plaques were identified. Fifty-eight coronary segments from 28(62%) patients had high 18F-NaF uptake (TBR>1.25), whil 168 segments had lesions with 18F-NaF TBR ≤1.25. Uptake in all lesions was categorized identically on co-registered PET/CTA1. There was no significant difference in 18F-NaF uptake values between PET/CTA1 and PET/CTA2 (SUVmax: 1.16±0.40 vs. 1.15±0.39, p=0.53; TBR:1.10±0.45 vs. 1.09±0.46, p=0.55). The intraclass correlation coefficient for SUVmax and TBR was 0.987 (95%CI 0.983 to 0.991) and 0.986 (95%CI 0.981 to 0.992). There was no fixed or proportional bias between PET/CTA1 and PET/CTA2 for SUVmax and TBR. Cardiac motion correction of PET scans improved reproducibility with tighter 95% limits of agreement (±0.14 for SUVmax and ±0.15 for TBR vs. ±0.20 and ±0.20 on diastolic imaging;p<0.001). Conclusions Coronary CTA/PET protocol with CTA first followed by PET-only allows for reliable and reproducible quantification of 18F-NaF coronary uptake. This approach may facilitate selection of high-risk patients for PET-only imaging based on results from prior CTA, providing a practical workflow for clinical application.