CT Attenuation of Pericoronary Adipose Tissue in Normal Versus Atherosclerotic Coronary Segments as Defined by Intravascular Ultrasound.

BACKGROUND: The factors influencing genesis of atherosclerosis at specific regions within the coronary arterial system are currently uncertain. Local mechanical factors such as shear stress as well as metabolic factors, including inflammatory mediators released from epicardial fat, have been proposed. We analyzed computed tomographic (CT) attenuation of pericoronary adipose tissue in normal versus atherosclerotic coronary segments as defined by intravascular ultrasound (IVUS). PATIENTS AND METHODS: We evaluated the data sets of 29 patients who were referred for invasive coronary angiography and in whom IVUS of 1 coronary vessel was performed for clinical reasons. Coronary CT angiography was performed within 24 hours from invasive coronary angiography. Computed tomographic angiography was performed using dual-source CT (Siemens Healthcare; Forchheim, Germany). A contrast-enhanced volume data set was acquired (120 kV, 400 mA/rot, collimation 2 × 64 × 0.6 mm, 60-80 mL intravenous contrast agent). Intravascular ultrasound was performed using a 40-MHz IVUS catheter (Atlantis; Boston Scientific Corporation, Natick, Mass) and motorized pullback at 0.5 mm/s. Sixty corresponding coronary artery segments within the coronary artery system were identified in both dual source computed tomography and IVUS using bifurcation points as fiducial markers. In dual source computed tomography data sets, 8 serial parallel cross sections (2-mm slice thickness) were rendered orthogonal to the center line of the coronary artery for each segment. For each cross section, pericoronary adipose tissue within a radius of 3 mm from the coronary artery and enclosed within the epicardium (excluding coronary veins and myocardium) was manually traced and mean CT attenuation values were obtained. Intravascular ultrasound was used to define coronary segments as follows: presence of predominantly fibrous atherosclerotic plaque (hyperechoic), presence of predominantly lipid-rich atherosclerotic plaque (hypoechoic), and absence of atherosclerotic plaque. RESULTS: In IVUS, 20 coronary segments with fibrous plaque, 20 segments with lipid-rich plaque, and 20 coronary segments without plaque were identified. The mean CT attenuation of pericoronary adipose tissue for segments with any coronary atherosclerotic plaque was -34 ± 14 Hounsfield units (HU), as compared with -56 ± 16 HU for segments without plaque (P = 0.005). The density of pericoronary fat in segments with fibrous versus lipid-rich plaque as defined by IVUS was not significantly different (-35 ± 19 HU vs -36 ± 16 HU, P = 0.8). CONCLUSIONS: Mean CT attenuation of pericoronary adipose tissue is significantly lower for normal versus atherosclerotic coronary segments. This supports a hypothesis of different types of pericoronary adipose tissue, the more metabolically active of which might exert local effects on the coronary vessels, thus contributing to atherogenesis.

Association of systemic inflammation with epicardial fat and coronary artery calcification.

BACKGROUND: Increased epicardial fat volume (EFV) has been shown to be associated with coronary atherosclerosis. While it is postulated to be an independent risk factor, a possible mechanism is local or systemic inflammation. We analyzed the relationship between coronary atherosclerosis, quantified by coronary calcium in CT, epicardial fat volume and systemic inflammation. METHODS: Using non-enhanced dual-source CT, we quantified epicardial fat volume (EFV) and coronary artery calcium (CAC) in 391 patients who underwent coronary computed tomography for suspected coronary artery disease. In addition to traditional risk factors, serum markers of systemic inflammation were measured (IL-1α, IL-2, IL-4, IL-6, IL-7, IL-8, IL-10,IL-12, IL-13, IL-15, IL-17, IFN-γ, TNF-α, hs-CRP, GM-CS, G-CSF, MCP-1, MIP-1, Eotaxin and IP-10). In 94 patients follow-up data were obtained after 1.9 ± 0.5 years. RESULTS: The 391 patients had a mean age of 60 ± 10 years, and 69 % were males. Mean EFV was 116 ± 50 mL. Median CAC was 12 (IQR 0; 152). CAC and EFV showed a significant correlation (ρ = 0.37; P < 0.001). EFV and CAC were significantly correlated with the traditional risk factors like age, male gender, diabetes, smoking and hypertension. With regard to biomarkers, CAC was significantly associated (negatively) to G-CSF and IL-13. EFV (median binned) was significantly associated (positively) with IP-10 (P = 0.002) and MCP-1 (ρ = 0.037). In follow-up, EFV showed a mean annualized progression of 6 mL (IQR 3; 9) (P < 0.001); CAC progressed by a mean of six Agatston Units (IQR 0; 30). The progression of CAC was significantly correlated with the extent of EFV (P < 0.001) while there was no significant correlation between progression of EFV or CAC with systemic inflammation markers. CONCLUSION: Epicardial fat volume and the baseline extent as well as progression of coronary atherosclerosis-measured by the calcium score-are significantly correlated. While both baseline EFV and CAC displayed significant correlations with systemic inflammation markers, biomarkers were not predictive of the progression of CAC or EFV.

Interobserver agreement for the detection of atherosclerotic plaque in coronary CT angiography: comparison of two low-dose image acquisition protocols with standard retrospectively ECG-gated reconstruction.

BACKGROUND: We compared the interobserver variability concerning the detection of calcified and non-calcified plaque in two different low-dose and standard retrospectively gated protocols for coronary CTA. METHODS: 150 patients with low heart rates and less than 100 kg body weight were randomised and examined by contrast-enhanced dual-source CT coronary angiography (100 kV, 320 mAs). 50 patients were examined with prospectively ECG-triggered axial acquisition, 50 patients with prospectively ECG-triggered high pitch spiral acquisition, and 50 patients using spiral acquisition with retrospective ECG gating. Two investigators independently analysed the datasets concerning the presence of calcified and non-calcified plaque on a per-segment level. RESULTS: Mean effective dose was 1.4 ± 0.2 mSv for axial, 0.8 ± 0.07 mSv for high-pitch spiral, and 5.3 ± 2.6 mSV for standard spiral acquisition (P < 0.0001). In axial acquisition, interobserver agreement concerning the presence of atherosclerotic plaque was achieved in 650/749 coronary segments (86.8%). In high-pitch spiral acquisition, agreement was achieved in 664/748 segments (88.8%, n.s.). In standard spiral acquisition, agreement was achieved in 672/738 segments (91.0%, P < 0.0001). Interobserver agreement was significantly higher for calcified than for non-calcified plaque in all data acquisition modes. CONCLUSION: Low-dose coronary CT angiography permits the detection of coronary atherosclerotic plaque with good interobserver agreement. KEY POINTS: • Low-dose CT protocols permit coronary plaque detection with good interobserver agreement. • Image noise is a major predictor of interobserver variability. • Interobserver agreement is significantly higher for calcified than for non-calcified plaque.

Assessment of coronary artery remodelling by dual-source CT: a head-to-head comparison with intravascular ultrasound.

BACKGROUND: While it is widely assumed that coronary CT angiography permits detection and quantification of 'positive remodelling' of coronary atherosclerotic lesions, there is a paucity of data comparing CT with established reference methods. OBJECTIVE: To assess the accuracy of dual-source CT for detecting positive versus absent or negative coronary artery remodelling of coronary atherosclerotic lesions as compared with intravascular ultrasound (IVUS). METHODS: The datasets were evaluated of 38 patients referred for invasive coronary angiography and in whom an IVUS study of one coronary vessel was performed. Coronary CT angiography was performed within 24 h before invasive coronary angiography. Using dual-source CT (Siemens Healthcare, Forchheim, Germany), a contrast-enhanced volume dataset was acquired (120 kV, 400 mA/rot, collimation 2×64×0.6 mm, 60-80 ml contrast agent, intravenous). IVUS was performed using a 40 MHz IVUS catheter (Atlantis, Boston Scientific Corporation, Natick, Massachusetts, USA) and motorised pullback at 0.5 mm/s. 48 corresponding non-calcified and partially calcified plaques within the coronary artery system were identified in both CT and IVUS using bifurcation points as fiducial markers. In CT datasets, multiplanar reconstructions orthogonal to the centre line of the coronary artery were rendered and cross-sectional vessel area was measured at the site of maximal narrowing as well as at a reference segment proximal to the lesion for each of the 48 plaques. The remodelling index (RI) was calculated by dividing the vessel area at the site of maximal narrowing by the area of the reference segment. Corresponding vessel areas and RIs were also determined in IVUS. RESULTS: CT classified 41 plaques as positively remodelled (RI≥1.05) and seven as having either absent or negative remodelling (RI<1.05). In IVUS 29 plaques demonstrated positive remodelling, while 19 did not. Mean cross-sectional vessel areas measured by CT at the lesion and at the reference segment were 19±5 mm(2) and 17± 5 mm(2), respectively, versus 18±5 mm(2) and 17±5 mm(2) for IVUS (mean difference 1±2 mm(2) and -0.2±1 mm(2), p<0.0001 and 0.8, respectively). The mean RI in CT was significantly larger than in IVUS (1.2±0.2 vs 1.1±0.2, p<0.0001). Correlation between CT and IVUS was higher for vessel area measurements (r>0.9, p<0.0001) than for remodelling indices (r=0.7, p<0.0001) with Bland-Altman analysis showing a systematic overestimation of vessel areas and RI in CT. Interobserver agreement was moderate for CT and IVUS measurements. Receiver operating characteristic curve analysis showed that a RI of 1.1 in CT identified positively remodelled plaques in IVUS with a sensitivity of 83% and a specificity of 78% (area under the curve=0.8, 95% CI 0.7 to 1.0). Using the standard cut-off point of 1.05 to identify positively remodelled plaques in CT resulted in a sensitivity of 100%, and a specificity of 45%. CONCLUSION: Coronary CT angiography allows analysis of coronary artery remodelling. The degree of positive remodelling is typically overestimated by CT. A threshold of 1.1 for the RI may be optimal to classify plaques as 'positively remodelled' in coronary CT angiography.