The proposed study aims to compare (a) volume contrast administered for Optical Coherence Tomography (OCT) Imaging, (b) length of clear OCT images, and (c) electrocardiographic changes immediately after contrast injection between iso-osmolar and low-osmolar contrast agents. The proposed study is a prospective, single-centered, randomized controlled, study that will compare an iso-osmolar vs. a low-osmolar contrast agent in patients undergoing clinically indicated coronary OCT imaging. Each patient will be randomized to OCT acquisition.

Patients referred to the Cardiac Catheterization laboratory for clinically indicated coronary angiography and coronary OCT imaging will be identified by a study team member and screened for eligibility. The proposed study is a prospective, single-center, randomized, controlled, study that will compare an iso-osmolar vs a low-osmolar contrast agent in patients undergoing clinically-indicated coronary OCT imaging. Each patient will be randomized to OCT acquisition. Eligible patients will be approached to obtain informed consent by a member of the study team. Once consent is obtained and inclusion and exclusion criteria are verified, patients are randomized to undergoing OCT image acquisition with iso-osmolar contrast media(IOCM) first or with low-osmolar contrast media first (LOCM).

Then the patients undergo coronary angiography and OCT imaging as per clinical standard of care. However, during the OCT imaging acquisition based on their randomization assignment the patient will undergo the 1st OCT imaging run with either iso-osmolar contrast media or with low-osmolar contrast media. Following this a 2nd OCT imaging run of the same coronary vessel will be done using the other contrast media that was not used during the first run. Therefore, each patient will serve as a comparator to themselves, but also to each other. The electrocardiogram will be recorded during and for 30 seconds after each injection and analyzed offline for detection of any changes

Inclusion Criteria:

1. Age 18 years or greater
2. Willing and able to give informed consent. The patients must be able to comply with study procedures
3. Undergoing clinically-indicated coronary angiography and OCT

Exclusion Criteria

1. Baseline electrocardiographic changes hindering interpretation (such as left bundle-branch block, and >1 mm ST segment depression)
2. Emergency cardiac catheterization (for example in patients with ST-segment elevation acute myocardial infarction)
3. Inability to provide symptomatic assessment
4. Known allergy to contrast