Cross-sectional imaging of how balloon inflation in a three-layer phantom mimics a coronary artery. These images show different balloon inflation pressure: a.) partially folded balloon without pressure, b.) partially inflated balloon, c.) an inflated balloon, and d.) OCT probe rotating within a balloon (no phantom), the red dot indicates where the light beam exits the probe. Note: Imaging is performed with infrared light, but visible light is coupled in the system to ease identifying probe location.