Look at the plaque burden. There is some plaque, but it's not occluding or obstructing the vessel. There is an arc of calcium. You can see calcium very well by IVUS, because it reflects more echo and it is brighter. This arc of calcium gave us the false image of a severe lesion.
Calcified plaque reflects echo a lot, so it works like a shield.
We see a shadow behind the calcium, but we don't see any of the vessel structure behind the calcium. IVUS is also helpful in diagnosing unstable plaque. In Figure 7, you can see a lipid lake, prone to rupture, and in the second image, you can see that the plaque is ruptured. This is a very dangerous situation, because the patient can have an acute MI and can die. Measuring Lesion Length and Vessel Size Lesion length.