Intravascular ultrasound (IVUS) or intravascular echocardiography is a combination of echocardiography and a procedure called cardiac catheterization. IVUS uses sound waves to produce an image of the coronary arteries and to see their condition. The sound waves travel through a tube called a catheter. The catheter is threaded through an artery and into your heart. This test helps the cardiologists to look inside your blood vessels. The instantaneous wave-free ratio (iFR, sometimes referred to as the instant wave-free ratio or instant flow reserve) is a diagnostic tool used to assess whether a stenosis is causing a limitation of blood flow in coronary arteries with subsequent ischemia.(restriction of blood to tissues). iFR is performed during cardiac catheterisation (angiography) using invasive coronary pressure wires which are placed in the coronary arteries that are to be assessed.