Histopathologically-validated Virtual Histology (VH) intravascular ultrasound (IVUS) is able to assess plaque composition, but not thrombus. Conversely, radiofrequency based-integrated backscatter (IB) IVUS can assess thrombus as well as plaque composition. Methods. We used pre- and post-stent impantation IB-IVUS to assess 23 intra-stent plaque prolapse and 33 intracoronary thrombus. Results. Pt age was 61짹9.9 yrs; 85% were males. The lesion length was 25.4짹12.45 mm and prolapsed plaque area measured 0.73짹0.61mm². The main component of prolapsed plaque was fibrosis and small lipid pool. Similarly, fibrosis was the dominant component of intracoronary thrombus. However calcification was higher in prolapsed plaque(p=0.053). The % of IB values (range -29% ~ -35%) was higher in intracoronary thrombus(p=0.0004) vs prolapsed plaque showed higher % of IB values (range -49% ~ -130%)(p=0.001). The frequency of mean IB values (> -40dB) was lower in thrombus [25/33(76%) of intracoronary thrombus vs 22/23(96%) of prolapsed plaque, p=0.046]. Overall, the mean IB values(dB) was higher in plaque prolapse (p=0.001)(Table). Conclusion. The fibrosis was a dominant component in both of prolapsed plaque and intracoronary thrombus, however, IB values may comparable to differentiate the intracoronary thrombus