Assessment of Arterial Wall Calcification with CT and Micro-Calcification with 18F-NaF PET

The calcification of arterial wall is a process linked to osteogenesis, thus, the PET radiotracer Fluorine-18F-NaF (18F-NaF) is capable of identifying micro-calcification in atherosclerotic plaque. In the present work, we assessed the relationship of calcification seen on CT images and 18F-NaF uptake measured in PET image. Calcification was classified based on its intensity (IC), area ratio (RCA) and scores (ACS) and each group was clustered using Hierarchical K-means algorithm (AHK) with the use of silhouette-coefficient. 18F-NaF uptake was quantified as tissue to background ratio by using superior vena cava for blood pool correction. TBR values corresponded to IC clusters were 2.52, IQR (1.70 – 2.76), 2.40, IQR (1.93 – 2.68), 2.11, IQR (1.95 – 2.27) and 1.86, IQR (1.36 – 2.33) for CI1, CI2, CI3 and CI4 respectively and 2.68 IQR (2.14 – 2.73), 2.20 IQR (1.52 – 2.46) and 2.26 IQR (1.40 – 2.43) for RCA1, RCA2 and RCA3 respectively. For ACS clusters, TBR values were 2.53 IQR (1.64 – 2.69), 2.31 IQR (2.13 – 2.55) and 2.25 IQR (1.60 – 2.38) for ACS1, ACS2 and ACS3 respectively. There was a reverse association of 18F-NaF uptake as a function of area, where large area (RCA3) was statistically significantly different (p=0.027) compared to small area (RCA1). No statistical difference was observed among CI and ACS clusters. In conclusion, there is a reverse correlation of calcification area as a function of 18F-NaF uptake. No statistical association of calcification intensity and 18F-NaF uptake. 18F-NaF may be a useful marker for the detection of plaque vulnerability. Multi-spot of calcification (MSCS) has higher 18F-NaF uptake compared to single spot of calcification (SSCS), and the difference was statistically significantly different