ORIGINAL PAPER Non-calcified coronary atherosclerotic plaque visualization on CT: effects of contrast-enhancement and lipid-content fractions Wisnumurti Kristanto • Peter M. A. van Ooijen • Marcel J. W. Greuter • Jaap M. Groen • Rozemarijn Vliegenthart • Matthijs Oudkerk Received: 27 June 2012 / Accepted: 21 December 2012 Ó Springer Science+Business Media Dordrecht 2013 Abstract Computed tomography (CT) may characterize lipid-rich and presumably rupture-prone non-calcified coronary atherosclerotic plaque based on its Hounsfield- Unit (HU), but still inconclusively. This study aimed to evaluate factors influencing the HU-value of non-calcified plaque using software simulation. Several realistic virtual plaqueburdened coronary phantoms were constructed at 5 lm resolution. CT scanning was simulated with settings resembling a 64-row multi-detector CT (64-MDCT) and reconstructed at 64-MDCT (0.4 mm) and MicroCT (48 lm) resolutions. Influences of lumen contrast- enhancement, stenosis-grades, and plaque compositions on plaque visualization were analyzed. Lumen contrast- enhancement and mean plaque HU-value were positively correlated (R 2 [ 0.92), with approximately the same slopes for all plaque compositions. Percentage lipid-content and mean plaque HU-value were negatively correlated (R 2 [ 0.98). Stenosis-grade and noise had minimal influ- ence on the correlations. Influence of lumen contrast- enhancement on plaque HU-value was following a specific exponentially declining pattern (y = Ae -kx ? c) from the lumen border until 2-pixel radius. Outside 2-pixel radius, plaque HU-values deviated maximally 5 HU from non- contrast-enhanced reference. Thus, to avoid lumen con- trast-enhancement influence, plaques should be measured outside 2-pixel radius from the lumen border. Based on the patterns found, a lumen influence correction algorithm may be developed. HU-based plaque percentage lipid-content determination might serve as an alternative plaque char- acterization method. However, its applicability is still hindered by many inherent limitations. Keywords Coronary artery disease  Non-calcified atherosclerotic plaques characterization  Computed tomography angiography  Software phantoms  Simulation study Introduction Computed-tomography (CT) is currently the preferred modality to assess the extent of coronary artery disease (CAD) in a non-invasive manner. CT not only excels in stenosis detection [1, 2] but also in measurement of cal- cified plaque burden [3–5]. The amount of coronary cal- cification quantified by CT is a strong predictor of coronary heart disease [6–8], although it does not accurately predict the site of stenosis [9]. In contrast, non-calcified plaque characterization and quantification by CT so far has been anything but conclusive. Differentiation between types of non-calcified plaques may allow identification of plaques which are more vulnerable to rupture and which, conse- quently, could cause an acute coronary syndrome. Gener- ally, lipid-rich plaques are considered to be more prone to rupture than fibrous plaques [10–12]. Several studies [13–15] reported various Hounsfield Unit (HU)-based criteria to distinguish lipid-rich from fibrous plaque, but the criteria have so far been discordant. Moreover, the HU values for distinguishing these two plaque types are overlapping, which makes distinction so far inaccurate. The main causes of the problem are the small size of plaques combined with the low CT contrast W. Kristanto  P. M. A. van Ooijen (&)  M. J. W. Greuter  J. M. Groen  R. Vliegenthart  M. Oudkerk Department of Radiology, Center for Medical Imaging-North East Netherlands, University Medical Center Groningen, University of Groningen, PO Box 30001, 9700RB Groningen, The Netherlands e-mail: p.m.a.van.ooijen@umcg.nl 123 Int J Cardiovasc Imaging DOI 10.1007/s10554-012-0176-4