Background: To investigate whether acute coronary syndrome resulting from coronary plaque instability is associated with widespread vascular inflammation, we assessed the vascular plaque inflammation activity using delayed whole body 18 FDG-PET imaging, better imaging protocol for active plaque detection, in patients with acute myocardial infarction (AMI) or chronic stable angina (SA).Methods: In a total 75 (male 39, 64.1 yrs) patients who were newly diagnosed as AMI (36 patients, male 18, 60.2 yrs) or SA (39 patients, male 21, 66.3 yrs), the 3-dimensional PET scanner together with a 16-slice Brilliance CT scanner using Gemini TF PET/CT (Philips Medical Systems) was performed within 1 week after disease onset. For the comparison of images acquired at 1 h and 2 h, the original axial slices were re-sliced to coronal images and images acquired at 1 h and 2 h were displayed simultaneously using the same windowing and leveling. The maximum standardized uptake values (SUVs) and standardized uptake ratios (SURs) were estimated in active plaques. Results: Age and gender-adjusted SUV and SUR of FDG was significantly higher in the carotid or aortic plaques of AMI patients than in those of SA patients (p<0.001, Figure 1 and 2). There were no differences of risk factors between two groups.Conclusions: The patients presenting with AMI have the increased inflammation activity in the vascular plaques. Our findings suggest that inflammation could contribute to widespread atherosclerotic plaque instability associated with ACS.