Intravascular ultrasound

It is also used to assess the effects of treatments of stenosis such as with hydraulic angioplasty expansion of the artery, with or without stents, and the results of medical therapy over time.

IVUS enables accurately visualizing not only the lumen of the coronary arteries but also the atheroma (membrane/cholesterol loaded white blood cells) "hidden" within the wall.

[5] Perhaps the greatest contribution to understanding, so far, was achieved by clinical research trials completed in the United States in the late 1990s, using combined angiography and IVUS examination, to study which coronary lesions most commonly result in a myocardial infarction.

However the average or typical stenosis at which myocardial infarctions occurred were found to be less than 50%,[8] describing plaques long considered insignificant by many.

Only 14% of heart attacks occurred at locations with 75% or more stenosis[citation needed], the severe stenoses previously thought by many to present the greatest danger to the individual.

This research has changed the primary focus for heart attack prevention from severe narrowing to vulnerable plaque.

Compared to IVUS, intravascular OCT offers an order of magnitude improved resolution for a better visualization of vessel lumen, tissue microstructure and devices (e.g., intracoronary stents).

The guide wire is kept stationary and the ultrasound catheter tip is slid backwards, usually under motorized control at a pullback speed of 0.5 mm/s.

Heavy calcium deposits in the blood vessel wall both heavily reflect sound, i.e. are very echogenic, but are also distinguishable by shadowing.

Heavy calcification blocks sound transmission beyond and so, in the echo images, are seen as both very bright areas but with black shadows behind (from the vantage point of the catheter tip emitting the ultrasound waves).

This has been important given that atherosclerosis is the single most frequent disease process for the greatest percentage of individuals living in first world countries.

When using IVUS to determine whether an individual's left main disease is clinically significant, in terms of the desirability of physical intervention, the two most widely used parameters are the degree of stenosis and the minimal lumen area.

Intravascular ultrasound image of a coronary artery (left), with color-coding on the right, delineating the lumen (yellow), external elastic membrane (blue) and the atherosclerotic plaque burden (green). The percentage stenosis is defined as the area of the lumen (yellow) divided by the area of the external elastic membrane (blue) times 100. As the plaque burden increases, the lumen size will decrease and the degree of stenosis will increase.
An IVUS image of the ostial left main coronary artery (left). The blue outline delineates the cross-sectional area of the lumen of the artery (A1 in the upper right corner), measuring 6.0 mm 2 . A two-dimensional mapping of the proximal LAD and left main coronary arteries is shown on the right.