Background Severe calcium in lesion segment is always with bad Percutaneous coronary intervention (PCI) outcomes or many complications including dissection,vessel loss,and imposes a rigid obstacle to optimal and symmetric stent expansion.Therefore,adequate plaque modification (PM) prior to DES implantation is the key of calcified lesion treatment.The usage of the cutting balloon for severely calcified lesions has been reported in single case and achieved satisfied results.This intravascular ultrasound (IVUS) study was designed to compare the efficacy and safety of cutting balloon angioplasty for severely calcified coronary lesions with the conventional balloon angioplasty.