Three-hour delayed imaging improves assessment of coronary ¹⁸F-sodium fluoride PET

Abstract

Coronary ¹⁸F-sodium fluoride (¹⁸F-NaF) PET imaging identifies ruptured plaques in patients with recent myocardial infarction and localizes to atherosclerotic lesions with active calcification. Most studies to date performed the PET acquisition 1-hour (1h) post-injection. Although qualitative and semi-quantitative analysis is feasible with 1h images, often residual blood pool activity makes it difficult to discriminate plaques with ¹⁸F-NaF uptake from noise. We aimed to assess whether delayed 3-hour (3h) post-injection PET scan improves image quality and uptake measurements. Methods: Twenty patients (67±7years old, 55% male) with stable coronary artery disease underwent coronary CT angiography and PET/CT both 1 h and 3 h after the injection of 266.2±13.3 MBq of ¹⁸F-NaF. We compared the visual pattern of coronary uptake, maximal background (blood pool) activity, noise, standard uptake values (SUV_max), corrected SUV (cSUV_max) and target to background (TBR) measurements in lesions defined by CTA on 1h vs 3h post injection ¹⁸F-NaF PET. Results: On 1h PET 26 CTA lesions with ¹⁸F-NaF PET uptake were identified in 12 (60%) patients. On 3h PET we detected ¹⁸F-NaF PET uptake in 7 lesions which were not identified on the 1h PET. The median cSUV_max and TBR values of these lesions were 0.48 [interquartile range (IQR) 0.44-0.51] and 1.45 [IQR, 1.39-1.52] compared to -0.01 [IQR, -0.03-0.001] and 0.95 [IQR, 0.90-0.98] on 1h PET, both p<0.001. Across the entire cohort 3h PET SUV_max values were similar to 1h PET measurements 1.63 [IQR, 1.37-1.98] vs. 1.55 [IQR, 1.43-1.89], P = 0.30 and the background activity was lower 0.71 [IQR, 0.65-0.81] vs. 1.24 [IQR, 1.05-1.31], p<0.001. On 3h PET, the TBR values, cSUV_max and the noise were significantly higher (2.30 [IQR, 1.70-2.68] vs 1.28 [IQR, 0.98-1.56], p<0.001; 0.38 [IQR, 0.27-0.70] vs 0.90 [IQR, 0.64-1.17], p<0.001 and 0.10 [IQR, 0.09-0.12] vs. 0.07 [IQR, 0.06-0.09], P = 0.02). The median cSUV_max and TBR values increased by 92% (range: 33-225%) and 80% (range: 20-177%). Conclusion: Blood-pool activity decreases on delayed imaging facilitating the assessment of ¹⁸F-NaF uptake in coronary plaques. The median target to background ratios increase by 80% leading to the detection of more plaques with significant uptake compared to the standard 1h protocol. A greater than a 1h delay may improve the detection of ¹⁸F-NaF uptake in coronary artery plaques.