IVUS is a medical imaging methodology using a specially designed catheter with a ultrasound probe attached to the distal end of the catheter. It allows the application of ultrasound technology to see from inside blood vessels out through the surrounding blood column, visualizing the endothelium (inner wall) of blood vessels in living individuals.

The arteries of the heart (the coronary arteries) are the most frequent imaging target for IVUS. IVUS is used in the coronary arteries to determine the amount of atheromatous plaque built up at any particular point in the epicardial coronary artery. The progressive accumulation of plaque within the artery wall over decades is the setup for vulnerable plaque which, in turn, leads to heart attack and stenosis (narrowing) of the artery (known as coronary artery lesions). IVUS is of use to determine both plaque volume within the wall of the artery and/or the degree of stenosis of the artery lumen. It can be especially useful in situations in which angiographic imaging is considered unreliable; such as for the lumen of ostial lesions or where angiographic images do not visualize lumen segments adequately, such as regions with multiple overlapping arterial segments. 

Arguably the most valuable use of IVUS is to visualize plaque, which cannot be seen by angiography. 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. Current clinical uses of IVUS technology include checking how to treat complex (difficult) blockage before angioplasty and checking how well a stent has been deployed within a coronary artery after angioplasty. If a stent is not expanded, flush against the wall of the vessel, turbulent flow may occur between the stent and the wall of the vessel which might create a nidus for acute thrombosis (clogging) of the artery.

                                          Fibrous plaque                  Plaque rupture                     Thrombus                      Calcification

Virtual Histology

The term “virtual histology” is a concise term used to describe a technique complementary to IVUS, called ‘radiofrequency backscatter spectral analysis’. 

Virtual histology IVUS is a catheter-based technology where IVUS is generated from the transducer on the catheter tip and the reflected signals from the artery wall produce a color-coded map of the arterial disease. Different histological constituents of the plaque produce different reflected signals and these are assigned different colors (dark green, fibrous; yellow/green, fibrofatty; white, calcified; red, necrotic lipid core plaque). This color-coded map assists the interventionalist in understanding more fully how the lesion/blockage will behave at the moment of treatment, whether it will resist complete stent deployment or be liable to embolization.