ORIGINAL ARTICLE Original Article Virtual Histology: A Window to the Heart of Atherosclerosis J. Layland, FRACP a,b,∗ , A.M. Wilson, PhD, FRACP a,b,c , I. Lim, FRACP c and R.J. Whitbourn, FRACP a,b a Cardiovascular Research Centre, St. Vincent’s Hospital, Melbourne, Victoria, Australia b University of Melbourne, Parkville, Melbourne, Victoria, Australia c Epworth Heart Centre, Richmond, Melbourne, Victoria, Australia Intravascular ultrasound has done much to improve our understanding of atherosclerosis and the impact of percuta- neous intervention on the coronary artery. However, subjectivity in interpreting the acoustic reflection of the ultrasound signal has spawned the development of other progressive technologies. Virtual histology intravascular ultrasound (VHIVUS) utilises the ultrasound backscatter signal in order to colour code plaque into four pre-specified subtypes based on their histological composition. We review the background behind traditional grey scale intravascular ultrasound (IVUS) and examine the current evidence for VHIVUS and its potential for use in clinical interventional practice. (Heart, Lung and Circulation 2011;20:615–621) © 2011 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved. Keywords. Intravascular ultrasound; Percutaneous intervention; Plaque; Atherosclerosis Introduction A therosclerotic cardiovascular disease remains the leading cause of morbidity and mortality in the western world and is responsible for up to one third of total global deaths [1]. Post mortem studies have shown that rupture of an atherosclerotic plaque is the predomi- nant cause of acute myocardial infarction, and that a thin fibrous cap atheroma (TCFA) may represent a precursor to plaque rupture [2]. Moreover, victims of sudden car- diac death, secondary to ruptured TCFA, have a higher prevalence of thin-cap fibroatheroma elsewhere in the coronary circulation, that have not ruptured compared to victims who died of fibrocalcific plaques [2]. Clearly being able to recognise the presence of TCFA and other plaque subtypes in vivo, ante mortem would be advanta- geous and may allow for a more refined individualised risk assessment when patients present for coronary angiog- raphy. Conventional grey scale intravascular ultrasound (IVUS) revolutionised the field of percutaneous coronary intervention emphasising the shortcomings of fluoro- scopic coronary angiography in identifying previously unrecognised atheroma and serves as a benchmark in the evaluation of coronary plaque and vessel dimensions [3]. However its ability to distinguish plaque sub-types are limited by inter and intra-observer subjectivity as Available online 26 January 2011 ∗ Corresponding author at: Department of Cardiology, St. Vin- cent’s Hospital, Melbourne, Victoria 3065, Australia. Tel.: +61 3 9288 2211; fax: +61 3 988 4422. E-mail address: Jamie.LAYLAND@svhm.org.au (J. Layland). well as its axial resolution. Virtual histology intravascular ultrasound (VHIVUS) has moved the goal posts a little fur- ther utilising similar principles to IVUS but allowing real time quantification of plaque into differing subtypes. This review will look at the role of VHIVUS in interventional cardiology and review its clinical utility. Grey Scale IVUS Intravascular ultrasound like any ultrasound modality uses the transmission and reflection of high frequency lon- gitudinal mechanical waves in tissues in order to generate an image. At the tip of the IVUS catheter, a transducer emits and receives an ultrasound signal. The charac- teristics of the reflected ultrasound signal are primarily determined by the different acoustic properties of the tissue. In grey scale IVUS the backscattered signal is pro- cessed real time into a 2D video image that permits an accurate determination of vessel lumen dimensions and the distribution, morphology and severity of atheroscle- rotic plaque. In the normal artery, the IVUS image largely reflects the two acoustic impedances of the vessel wall, namely the border between blood and the leading edge of the intima and a second at the external elastic membrane located at the media adventitia border [4] (Fig. 1). Clinical Use of Grey Scale IVUS Following its introduction into clinical practice, IVUS led to marked changes in the practice of interventional © 2011 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved. 1443-9506/04/$36.00 doi:10.1016/j.hlc.2010.12.002