Metabolic characteristics of patients with myocardial visualization in fasting whole body F-18 FDG PET

When we would like to find a lesion in the chest malignant or benign, increased myocardial metabolic rate of glucose is so disturbing that bright myocardium obscures nearby lesions in F-18-FDG PET. This study aimed at finding metabolic characteristics of myocardial visualization when we tried not to make myocardium shining by fasting our patients. Plasma insulin, free fatty acid (FFA) and glucose were measured before injection of F-18-FDG in 36 cancer patients who had performed F-18-FDG PET in fasting state. F-18-FDG PET images were grouped in two according to the presence (group I) or absence (group II) of myocardial visualization. When the myocardium was visualized, we measured myocardium to backgroud (lung) count ratio using regions of interest on the segmented attenuation-corrected whole body PET coronal images. We examined the characteristics of metabolic mileu of group I and II. We correlated myocardium to background (M/B) ratio and metabolic indices in group I. Myocardium was visualized in 21 cases (58%) and not in 15 (42%) during fasting. Plasma glucose concentration was 98.5±13.3 and 91.4±9.1 mg/dl in group I and II, respectively (P <0.05). Plasma insulin concentration was 10.5±5.0 and 8.1±3.2mIU/L in group I and II(P >0.05). Plasma FFA concentration was 0.62±0.23 and 0.92±0.17 mEq/L in group I and II (P<0.05). Among the correlation between M/B ratios and metabolic factors, FFA concentration was negatively correlated with M/B ratio (r=0.3, p<0.05). In conclusion, free fatty acid concentration could be a determining factor to let myocardium show up and shine in fasting state. Artificial increase of free fatty acid could help myocardium not to appear in fasting whole body F-18-FDG PET