Multidetector-row computed tomography and magnetic resonance imaging of atherosclerotic lesions in human ex vivo coronary arteries - ScienceDirect

Atherosclerosis

Volume 174, Issue 2, June 2004, Pages 243-252

Atherosclerosis

https://doi.org/10.1016/j.atherosclerosis.2004.01.041 Get rights and content

Abstract

In the present study, we tested the ability of multidetector-row computed tomography (MDCT) and magnetic resonance imaging (MRI) to identify and retrospectively characterize atherosclerotic lesions in human ex vivo coronary arteries. Thirteen ex vivo hearts were studied with MDCT and MRI. MDCT-images were obtained with an isotropic voxel size of 0.6 mm³. MR images were obtained with an in-plane resolution of 195 μm and 3 mm slice thickness. All images were matched with histopathology sections. For both modalities, the sensitivity for the detection of any atherosclerotic lesion was evaluated, and a retrospective analysis of plaque morphology according to criteria defined by the American Heart Association (AHA) was performed. At histopathology, 28 atherosclerotic lesions were found. 21 and 23 of these lesions were identified by MDCT and MRI, respectively. Both modalities detected a small number of false-positive lesions. After retrospective matching with histopathology, MDCT as well as MRI were able to differentiate typical morpholocigal features for fatty, fibrous or calcified plaque components. Using the information presented in this study, in vivo coronary artery wall imaging using MDCT as well as MRI could be facilitated and supported for future investigations on this subject.

Introduction

Currently available imaging techniques for the diagnosis of coronary artery disease are subject to several limitations. Conventional coronary angiography, widely accepted as the gold-standard for the detection of coronary artery disease, demonstrates the degree of luminal narrowing, but fails to visualize the coronary artery wall. It has been shown that plaque composition rather than the severity of an actual stenosis predicts the risk of plaque rupture and acute clinical complications of coronary artery disease [1], [2], [3]. Thus, new imaging techniques that can image the artery wall and characterize different lesion types may allow for identification and follow-up of patients at risk and for selecting appropriate therapeutic strategies [4].

Magnetic resonance imaging (MRI) has been shown to be capable of imaging vessel wall structures and differentiate various stages of atherosclerotic wall changes. MRI has been applied in several human in vivo studies to image atherosclerotic plaques in carotid [5], [6] and aortic [7] arterial disease. In vivo imaging of the coronary artery wall is challenging due to a combination of cardiac and respiratory motion artefacts, the tortuous course, small size and location of the vessels. Initial in vivo studies in human coronary arteries used non-invasive black-blood spin-echo techniques with breath-holding [8] or a real-time navigator for respiratory gating [9]. Diseased coronary artery wall was identified by wall thickening, but due to small cohort numbers and the technical difficulties mentioned above, the composition of coronary artery plaques was not systematically assessed. CT has become an established method for non-invasive and highly-sensitive detection of coronary artery calcifications [10]. Recently, with the introduction of multidetector-row CT systems, it was shown that CT also has the potential to in vivo identification of earlier stage, non-calcified plaques in carotid arteries [11] and coronary arteries [12], [13]. These first reports give rise to the perspective that MDCT might become an important tool for fast and non-invasive detection of various atherosclerotic lesions.

The general purpose of this study was to analyze atherosclerotic vessel wall lesions with MDCT and MRI in an ex vivo setting in the same cohort, and to verify the CT and MR findings with the corresponding histopathology. The specific purpose of the study was two-fold. First, both modalities were compared concerning sensitivity for the prospective detection of any atherosclerotic lesion, blinded to the results of histopathology. Second, after retrospective matching with histopathology, the typical appearance of various stages of coronary artery disease as depicted by MDCT and MRI was described, according to the criteria set forth by the AHA Committee on Vascular Lesions.

Section snippets

Specimen preparation

This study was approved by the institution’s internal review board. The hearts of 13 patients who had died for various reasons (malignant tumors, inflammatory diseases, and others) were investigated. There were five female and eight male patients with an age range between 34 and 87 years. After explantation the specimens were washed in water without further fixation or staining and imaged immediately. A mixture of methylcellulosis (73%), MR contrast agent (iron oxide particles, Lumirem^®,

Methodical results

In all 13 cases, data acquisition with MDCT and MRI was successful. All images were interpretable. Using the above described mixture of methylcellulosis, iron particles and iodine contrast agent, a constant lumen opacification in the CT images could be obtained ( $242±28 HU$ , 13 hearts, mean and standard deviation). In all MR images, signal intensity within the lumen was suppressed sufficiently by the iron-particle containing MR contrast agent, enabling clear delineation of the vessel wall.

Results of histopathology

In the

Discussion

Atherosclerotic coronary artery plaque rupture is the key trigger event for acute coronary syndromes. The in vivo identification of different plaque components in coronary arteries remains a major challenge due to the small size, fast motion and tortuous course of these vessels. Therefore, in our study, we tested the feasibility of MDCT and MRI to image coronary artery wall lesions in an ex vivo setting.

Acknowledgements

The authors want to thank Bernd J. Wintersperger, MD and Armin Huber, MD from the Department of Radiology, University of Munich, for their assistance in the experimental setup for the MDCT and MRI examinations. The authors also want to thank Joseph U. Schoepf from Harvard Medical School for additional review of the paper and for discussing the results.

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Although we did not quantify the grade of luminal obstruction it is generally accepted that early stage plaques show only minor luminal narrowing when compared to advanced AHA lesions [18]. Similar to previous studies performed on 4-detector slice CT we could demonstrate the ability of all investigated CT techniques to accurately differentiate between type IV (atheroma), type Va (fibroatheroma) and type Vb (calcific) plaque types [8]. All three CT modalities showed a sensitivity of 97% (30 of 31 plaques) for the correct characterization of calcified type Vb plaques which is explained by the high inherent sensitivity of CT for the detection of calcifications [25].
To compare different CT acquisition techniques regarding for attenuation-based characterization of coronary atherosclerotic plaques using histopathology as the standard of reference.
In a post mortem study 17 human hearts were studied with dual-source CT (DSCT) and dual energy CT (DECT) mode on a DSCT as well as with 16-slice single-source CT (SSCT). At autopsy, atherosclerotic lesions were cut at 5 μm sections. Histopathologic classification of the plaques according to the American Heart Association (AHA) criteria was performed by two pathologists. Attenuation values of all plaques were measured in DSCT, DECT and SSCT studies, respectively and classified based on attenuation according to modified AHA criteria.
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