Arterial tissue-to-psoas muscle ratio: A novel metric for quantifying fluorodeoxyglucose uptake in predicting the association between atherosclerotic inflammation and arterial calcification

Atherosclerosis is one of the leading causes of death worldwide. Computed tomography (CT) and positron emission tomography (PET) are valuable tools for assessing atherosclerotic plaque burden and associated physiological processes. The objective of this study is to evaluate the arterial tissue-to-psoas muscle uptake ratio (TMR) as a metric for assessing the relationship between inflammation and arterial calcification. Thirteen atherosclerotic patients were scanned using fluorodeoxyglucose (FDG)-PET/CT. The descending aorta, femoral, and iliac arteries were delineated on PET images and co-registered with corresponding CT slices. Arterial calcium was determined in arterial regions of interest with CT numbers above 130, and calcium level, area, and score were measured and classified into four clusters. FDG aggregation in PET images was assessed using mean TMR, with two cut-off points (1.8 and 2.3). Normality of the FDG signal in the psoas muscle was observed for all participants (p = 0.23). No significant differences in TMR values were observed (TMR, TMR >1.8, and TMR >2.3) across calcium density clusters (p > 0.05). However, a higher calcium area was positively associated with TMR values (p < 0.05) compared to a lower calcium area. The same pattern was observed for calcium score clusters, where higher calcium scores were associated with higher TMR values compared to lower calcium scores (p < 0.05). Using the psoas muscle as a background correction strategy for quantifying FDG uptake is feasible and may help reduce variation seen with a blood-based normalization approach, thus improving the reproducibility of measurements. TMR is a sensitive metric for assessing the relationship between arterial calcification and inflammation. Calcium area is a comparable method to calcium score for quantifying arterial calcium burden.