The purpose of this study is to investigate and compare the images obtained from coronary imaging catheters used in the treatment of coronary blockages both in a clinical setting with patients and in models.

Inclusion Criteria:

• ≥18 years of age
• Scheduled for a coronary angiogram at the Royal Adelaide Hospital.
• Women must be non-lactating or not of childbearing potential (1 year post menopausal or surgically sterilized [total hysterectomy, bilateral tubal ligation, bilateral oophorectomy]).
• Target artery must be >2 mm to accommodate the IVUS catheter.
• IVUS must be clinically indicated or indeterminate angiographic lesion in the artery (40%-70% angiographic stenosis)

Exclusion Criteria:

• Cardiogenic shock
• Contraindications to intracoronary nitroglycerin (hypertrophic obstructive cardiomyopathy; cerebral hemorrhage, head trauma; concomitant sildenafil, tadalafil or vardenafil use)
• Known coronary artery spasm
• Significant bleeding risk (i.e. previous hemorrhagic stroke, active peptic ulcer disease)
• Bleeding diathesis
• Significant renal impairment (patients will be excluded if their calculated creatinine clearance is < 30 mL/min)