The presence of calcified and rigid lesions makes PCI challenging. Adjuvant techniques are often required to achieve satisfactory stent results. Angiography has low sensitivity (48%) for calcium detection, except for severe calcification. Optical coherence tomography (OCT) is a tool that precisely detects calcium as a signal poor an heterogeneous region with sharply defined borders. OCT estimates the area of calcification more accurately than intravascular ultrasound (IVUS) as the light penetrates calcium without shadowing. OCT also helps the operator to distinguish between superficial and deep calcium with accurate measurement of the minimum distance from the lumen, the thickness of the calcium, and arc of calcium. OCT could thus be a more useful clinical tool for quantifying calcified lesions. Total calcium arc >180° and increased calcium thickness of >0.5 mm are associated with greater risk of stent underexpansion. OCT is the ideal method to capture these parameters and indicate or defer the use of atherectomy before stent implantation and guide optimization of PCI.