Rationale and Objectives
We investigated if 16-slice multidetector row computed tomography (MDCT) allows correct classification of coronary plaques into calcified or noncalcified and further subclassification of noncalcified plaques into either lipid-rich with a necrotic core or fibrous.
Materials and Methods
Coronary arteries of 30 isolated hearts were filled postmortem with a contrast medium and scanned with a 16-slice MDCT imager (Light Speed 16 pro, GEMS, Milwaukee, WI). Imaging parameters: collimation 16 × 0.625 mm, pitch 0.325, tube voltage 120 kV, tube current 250 mA, and gantry rotation time 500 milliseconds. The images were reformatted perpendicular to the axis of the coronary arteries (AW 4.2 software, GEMS) and analyzed by establishing attenuation profiles of the coronary cross sections (ImageJ 1.33n software, NIH, Bethesda, MD). Results were compared with the correlating histopathologic sections of the arteries.
Results
Analysis of 195 CT cross-sections showed a sensitivity and specificity for the correct classification of calcified plaques of 100% and 97.3% and for noncalcified plaques of 80.8% and 95.1%, respectively. The attenuation of epicardial fat ranged from –119 Hounsfield units (HU) to 23 HU (median –71 HU), and from 93 HU to 625 HU (308 HU) for the contrast medium. Calcified plaques showed an attenuation between 333 HU and 1944 HU (1,089 HU), noncalcified plaques between 26 HU and 124 HU (52 HU). Further subclassification of noncalcified plaques showed attenuation values between 26 HU and 67 HU (median 44 HU) for lipid-rich plaques with a necrotic core and from 37 HU to 124 HU (median 67 HU) for fibrous plaques.
Conclusions
Coronary atherosclerotic plaques can be reliably identified and classified as either calcified or noncalcified by 16-slice MDCT in postmortem studies. Further differentiation of noncalcified plaques in either lipid-rich or fibrous is not reliably feasible because of substantial overlap of the attenuation.
The pathologic mechanism that triggers acute coronary syndromes is in most cases (60%–75%) the rupture of a coronary plaque and as a consequence the formation of thrombus ( ). Plaques that are prone to rupture are called vulnerable plaques. Recent studies show that the major precursor lesion of acute coronary syndromes is the “thin-cap fibroatheroma,” a noncalcified plaque with a lipid-rich, necrotic core that is separated from the arterial lumen by a thin fibrous cap with a thickness below 65 μm ( ). Therefore the structure and composition of atherosclerotic plaques seem to be more important factors in the pathogenesis of acute coronary syndromes than the degree of stenosis caused by the lesion. To gain further information about morphologic features of arterial vessel wall lesions in patients with coronary heart disease, new imaging modalities need to be developed and established in clinical practice. One of these modalities could be multidetector row computed tomography (MDCT). Rumberger and colleagues conducted one of the first studies characterizing plaques by CT. The results of this histopathologic study showed a close relation between whole heart, coronary artery, and segmental coronary atherosclerotic plaque area and electron beam CT coronary calcium area ( ). The potential of MDCT to detect calcified and noncalcified coronary plaques has been shown in various other studies ( ). By defining certain attenuation values for the components of coronary plaques, characterization of different types of plaques, and thus detection of vulnerable plaques could be possible ( ). Kunimasa et al showed in a clinical study that 16-slice MDCT can detect noncalcified plaques in remote arteries of patients with acute coronary syndrome and that those have lower attenuation values than patients without acute coronary syndrome ( ). The search for the vulnerable plaque is supported by the results of the courage trial ( ). The latter showed medical treatment to be equal to angioplasty in stable angina. Treating only the vulnerable plaques is likely to improve the results of coronary stenting.
We therefore investigated if 16-slice MDCT allows reliable classification of coronary plaques into either calcified or noncalcified and further classification of noncalcified plaques into either lipid-rich with a necrotic core or fibrous.
Materials and methods
Material
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Computed Tomography
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Attenuation Profile Analysis
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Histopathology
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Statistical Analysis
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Results
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Table 1
Type-by-Type Analysis for Plaque Types IV–VIII
Minimum (HU) Maximum (HU) Median (HU) Type IV ( n = 4) 33 59 50 Type V ( n = 24) 26 63 44 Type VI ( n = 5) 36 67 40 Type VII ( n = 82) 333 1,944 1,089 Type VIII ( n = 21) 37 124 67
HU: Hounsfield unit.
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Table 2
Cross Table Calcified Plaques
Histology Calcification+ Calcification− Total Computed tomography Calcification+ 82 3 85 Calcification− 0 110 110 Total 82 113 195
Table 3
Cross Table Noncalcified Plaques
Histology NCP+ NCP− Total Compute tomography NCP+ 59 6 65 NCP− 14 116 130 Total 73 122 195
NCP: noncalcified plaque.
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Table 4
Attenuation Values of the Examined Components
Attenuation (HU) Epicardial Fat Lipid-rich NCP Fibrous NCP Contrast Agent Calcified Plaque X ⁎ <24.5 300/300 (100%) 0 0 0 0 24.5< X ⁎ <59.1 0 30/33 (90.9%) 6/21 (28.6%) 0 0 59.1< X ⁎ <101.5 0 3/33 (9.1%) 14/21 (66.7%) 2/182 (1.1%) 0 101.5< X ⁎ <494.5 0 0 1/21 (4.8%) 174/182 (95.6%) 4/82 (4.8%) 494.5< X ⁎ 0 0 0 6/182 (3.3%) 78/82 (95.1%)
NCP: noncalcified plaque.
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Discussion
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Attenuation Profile Analysis
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Limitations of CT
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