Carotid Stenosis Evaluation by 64-Slice CTA: Comparison of NASCET, ECST and CC Grading Methods Poster No.: C-1583 Congress: ECR 2011 Type: Scientific Exhibit Authors: G. KILICKAP, E. ergun, E. Ba#bay, P. Kosar, U. Kosar; Ankara/TR Keywords: CT-Angiography, Cardiovascular system DOI: 10.1594/ecr2011/C-1583 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 11
Purpose Purpose of the present study is to evaluate the intraobserver and interobserver variability of the NASCET, ECST and CC methods, which are used to measure the degree of ICA stenosis, using 64-slice CT angiography and to compare the measurements made by these three methods. Methods and Materials 88 cases (111 carotid arteries) in which carotid bulb stenosis was detected by CTA were included in the study.all CT examinations were performed by a 64-slice CT scanner (Aquillon 64, Toshiba Medical Systems, Tochigi, Japan). CT parameters were as follows: section thickness: 3mm, matrix 512x512, FOV: 320mm, pitch: 0.641, mas: 440, kv: 120. CT raw data were transformed to a remote work station (Vitrea 2, Vital Images Inc., Minnetonka, Minn. USA) for further image processing and analysis. Two independent observers who were unaware of the patient`s clinical status assessed all 111 carotid arteries according to NASCET, ECST and CC methods. Each measurement was performed three times and stenosis degree was determined by taking the aritmetical mean of these measurements. To determine the intraobserver variability one of the observers repeated the mesurements 1 week later. Measurements were performed on an oblique axial plane perpendicular to the lumen center line. The ratio between the diameter of the residual lumen at the site of the maximal stenosis and the diameter of normal ICA distal to the stenosis was calculated for the NASCET method. The denominator was the diameter of normal CCA in CC method and estimated normal lumen diameter at the site of the stenosis for the ECST method (figure1). Statistical Analysis: Continuous variables were expressed as arithmetic mean ± standard deviation, and frequency of categorical variables were expressed as number (%). The relation between measurements made by each of the three methods (i.e: ECST, NASCET and CCA) was assessed by correlation coefficient. Both linear and quadratic models were used for correlation analyses. Intraclass correlation coefficient (ICC) and Bland-Altman plots were used to assess the intraobserver and interobserver variabilities of the stenosis measurements for each method (i.e: ECST, NASCET and CCA). Also, degree of stenosis was categorized as Page 2 of 11
<50%, 50-69% and #70%, then intra- and interobserver agreement were assessed using and linear-weighted statistics (along with their standard errors). In Bland-Altman analysis difference in two measurements (bias) are plotted against the mean of two measurements to assess the intra- and interobserver agreement for each method. Therefore, bias (and 95% confidence interval) can be evaluated across the mean stenosis; and the less agreement (i.e: the greater bias), the wider the dispersion of the scatterplot at a given mean measurement. The analyses were performed using the Statistical Package for the Social Sciences (SPSS 11.5; SPSS Inc., Chicago, IL, USA) and MedCalc statistical software version 9.2.0.1 (MedCalc Software, Mariakerke, Belgium). Images for this section: Fig. 1: Figure shows the 3 different measurement methods of ICA stenosis. The residual lumen diameter (A-arrow)at the site of the maximum stenosis is used in all three methods however the denominator in the equation changes. Normal distal ICA (B-open arrow)is taken as the reference point in the NASCET method, the estimated normal lumen diameter at the site of the stenosis (C-curved arrow) is used in the ECST method and finally CC method uses the normal common carotid artery diameter (D- double arrows). Page 3 of 11
Fig. 2: Figure shows the 3 different measurement methods of ICA stenosis. The residual lumen diameter (A-arrow)at the site of the maximum stenosis is used in all three methods however the denominator in the equation changes. Normal distal ICA (B-open arrow)is taken as the reference point in the NASCET method, the estimated normal lumen diameter at the site of the stenosis (C-curved arrow) is used in the ECST method and finally CC method uses the normal common carotid artery diameter (D- double arrows). Page 4 of 11
Fig. 3: Figure shows the 3 different measurement methods of ICA stenosis. The residual lumen diameter (A-arrow)at the site of the maximum stenosis is used in all three methods however the denominator in the equation changes. Normal distal ICA (B-open arrow)is taken as the reference point in the NASCET method, the estimated normal lumen diameter at the site of the stenosis (C-curved arrow) is used in the ECST method and finally CC method uses the normal common carotid artery diameter (D- double arrows). Page 5 of 11
Fig. 4: Figure shows the 3 different measurement methods of ICA stenosis. The residual lumen diameter (A-arrow)at the site of the maximum stenosis is used in all three methods however the denominator in the equation changes. Normal distal ICA (B-open arrow)is taken as the reference point in the NASCET method, the estimated normal lumen diameter at the site of the stenosis (C-curved arrow) is used in the ECST method and finally CC method uses the normal common carotid artery diameter (D- double arrows). Page 6 of 11
Results 88 cases were included in the study. Mean age of the cases was 67,3 ± 9,6 year (min.42- max. 85), 48 (54,5%) were male and 40 (45,5%) were female. Stenosis of various degrees (including both non-significant and significant stenosis.) were detected in 111 carotid arteries. In 41 cases (46.6%) the stenosis was on the right carotid artery, in 24 cases (27.3%) it was on the left carotid artery and in 23 cases (26.1%) it was bilateral. The plaque that caused the stenosis was soft in 35 (31.5%) arteries, calcified in 59 (53.2%) and mixed in 17(15.3%). Correlation between the Methods: Correlation coefficients showed linear relationships among all three methods, i.e. between the NASCET and ECST, NASCET and CC, and CC and ECST methods. Quadratic expressions to fit the data points, did not improve the accuracy of the fitting curves. The following equations can be generated from the linear regression: NASCET= -42,05 + 1,34xCC, i.e., 70% NASCET stenosis is equal to 83.6% CC stenosis. ECST= 11,6 + 0,86xCC, i.e., 70% CC stenosis is equal to 71.8% ECST stenosis. ECST= 41,91 + 0,56xNASCET, i.e., 70% NASCET stenosis is equal to 81.1% ECST stenosis. The degree of stenosis measured with the NASCET method had the lowest value, while the corresponding values measured with the ECST and CC methods were close to each other Reproducibility When intra class coefficients were considered intraobserver and interobserver agreements were good for each of the three measuring methods (Table 1). However, both intra and inter observer agreement was better with CC method when compared to ECST and NASCET methods. The agreement was found to be better for non-calcified lesions when compared with the calcified ones. Table 1: ICC statistics Method Agreement Intraclass correlation coefficient (ICC) (95% CI) Overall Non-calcified Calcified Page 7 of 11
ECST Intraobserver 0,89 (0,85-0,93) Interobserver 0,83 (0,74-0,89) NASCET Intraobserver 0,92 (0,88-0,94) Interobserver 0,79 (0,71-0,85) CC Intraobserver 0,93 (0,90-0,95) Interobserver 0,87 (0,81-0,91) 0,92 (0,86-0,95) 0,88 (0,78-0,93) 0,93 (0,89-0,96) 0,87 (0,78-0,92) 0,95 (0,91-0,97) 0,91 (0,84-0,95) 0,85 (0,76-0,91) 0,76 (0,60-0,85) 0,87 (0,80-0,92) 0,64 (0,46-0,77) 0,91 (0,85-0,94) 0,80 (0,69-0,88) Kappa statistics has shown that intra and interobserver agreements were moderatesubstantial with each of the three methods (Table 2). Similar to the ICC values, the reproducibility of CC method was higher when compared to ECST and NASCET methods and agreement was less with calcified plaques. Table 2: Kappa (Standard error) statistics Method Agreement Statistics Plaque type Overall Noncalcified Calcified ECST Intraobserver Kappa 0,59 (0.07) 0,65 (0.11) 0,52 (0.10) Weighted 0,64 (0,07) 0,70 (0.11) 0,57 (0.10) Interobserver Kappa 0,58 (0.07) 0,60 (0.10) 0,56 (0.10) Weighted 0,65 (0.07) 0,66 (0.10) 0,61 (0.10) NASCET Intraobserver Kappa 0,71 (0.07) 0,73 (0.10) 0,65 (0.12) Weighted 0,78 (0.08) 0,81 (0.12) 0,68 (0.12) Interobserver Kappa 0,52 (0.09) 0,60 (0.10) 0,34 (0.12) Weighted 0,61 (0.08) 0,69 (0.11) 0,40 (0.12) CC Intraobserver Kappa 0,70 (0.06) 0,72 (0.10) 0,66 (0.10) Page 8 of 11
Weighted 0,74 (0.07) 0,77 (0.11) 0,71 (0.10) Interobserver Kappa 0,62 (0.07) 0,78 (0.11) 0,46 (0.10) Weighted 0,68 (0.07) 0,81 (0.11) 0,53 (0.10) Bland-Altman plots demonstrated a good value for CC, ECST and NASCET methods. When Bland-Altman graphics are visually assessed (the spread of measurements depict the extent of disagreement) it is seen that the agreement is highest with CC method (the spread of measurements is least with CC method) and, the highest level of disagreement is observed in the NASCET method. The disagreement increased with calcified plaques. Inter and intraobserver agreements were free of the degree of stenosis. Conclusion NASCET, and ECST methods which are used to measure ICA stenosis have been the subject of various studies (1-8), however unlike the other two, there is only a limited amount of published data on the CC method(9-11). We evaluated the mathematical relations between these three methods and compared their reproducibility. Our measurements show linear relationships among all three methods. Rothwell et al. (9) suggested a linear relationship between the ECST, NASCET and CC methods, Eliasziw et al. (10) suggested a linear relationship between the NASCET and CC methods, and a quadratic relationship between the NASCET and ECST, and the CC and ECST methods. Similarly, Saba et al. (12) suggested a quadratic relationship between the NASCET and ECST methods. In line with the other studies our results show that the degree of stenosis measured with the NASCET method has the lowest value, while the corresponding values measured with the ECST and CC methods are close to each other (9-13). We found that all methods have an acceptable level of reproducibility, however the most reproducible is the CC method and the least is NASCET method. The three other studies that compared the reproducibility of the three methods also observed that, compared to the NASCET and ECST methods, the CC method has the highest level of reproducibility(9-11). Similar to Saba et al (14), we observed that reproducibility of each method decreases with calcified lesions. We believe that the CC method is the best candidate for being the worldwide standard for the measurement of carotid stenosis on angiograms, as well as for being the basis for the measurement of stenosis through non-invasive techniques. However, although the prognosis of the cases treated according to the degree of stenosis calculated by the Page 9 of 11
NASCET and ECST methods have been prospectively investigated with large trials, there is lack of data about the CC method in this regard. Therefore, before adapting the CC method as the standard method for clinical practice, more research is needed regarding the prognostic value of this method, including the follow-up results of the patients treated according to the CC stenosis. References References: 1- North American Symptomatic Carotid Endarterectomy Trial Collaborators. Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med 1991; 325:445-453 2. European Carotid Surgery Trialists' Collaborative Group. Randomised trial of endarterectomy for recently symptomatic carotid stenosis: final results of the MRC European Carotid Surgery Trial (ECST). Lancet 1998; 351:1379-1387 3-Hirai T, Korogi Y, Ono K, et al. Maximum stenosis of extracranial internal carotid artery: effect of luminal morphology on stenosis measurement by using CT angiography and conventional DSA. Radiology 2001; 221:802-809 4-Rothwell PM, Gutnikov A,WarlowCP, for the European Carotid Surgery Trialists Collaborator. Reanalysis of the final results of the European carotid surgery trial. Stroke 2003;34:514-23. 5- Gagne PJ, Matchett J, MacFarland D, Hauer-Jensen M, Barone GW, Eidt JF, et al.can the NASCET technique for measuring carotid stenosis be reliably applied outside the trial? J Vasc Surg 1996;24:339-56. 6- Vanninen R, Manninen H, Kovisto K, Tulla H, Partanen K, Puranen M. Carotid Stenosis by digital subtraction angiography: reproducibility of the European carotid surgery trial and the North American Symptomatic Carotid Endarterectomy Trial measurement methods and visual interpretation. Am J Neuroradiol 1994;15:1635-41. 7-Rothwell PM, Warlow CP. Making sense of measurement of carotid stenosis of carotid stenosis. J Stroke Cerebrovasc Dis. 1995;5:83-87. 8. Saba L, Mallarini G. MDCTA of Carotid Plaque Degree of Stenosis: Evaluation of Interobserver Agreement. AJR 2008; 190:W41-W46 Page 10 of 11
9- Rothwell PM, Gibson RJ, Slattery J, Sellar RJ, Warlow CP. Equivalence of measurements of carotid stenosis. A comparison of three methods on 1001 angiograms. European Carotid Surgery Trialists' Collaborative Group. Stroke 1994;25;2435-2439. 10- Eliasziw M, Smith RF, Singh N, Holdsworth DW, Fox AJ, Barnett HJ. Further comments on the measurement of carotid stenosis from angiograms. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group. Stroke 1994;25;2445-2449 11- Staikov IN, Arnold M, Mattle H, Remonda L, Sturzenegger M, Baumgartner RW, et al. Comparison of the ECST, CC, and NASCET grading methods and ultrasound for assessing carotid stenosis. J Neurol 2000;247:681-6. 12- Saba L, Mallarini G. A comparison between NASCET and ECST methods in the study of carotids Evaluation using Multi-Detector-Row CT angiography. European Journal of Radiology. 2010; 76: 42-47. 13-Rothwell PM, Gutnikov A,WarlowCP, for the European Carotid Surgery Trialists Collaborator. Reanalysis of the final results of the European carotid surgery trial. Stroke 2003;34:514-23. 14- Saba L, Mallarini G. MDCTA of Carotid Plaque Degree of Stenosis: Evaluation of Interobserver Agreement. AJR 2008; 190:W41-W46 Personal Information Dr. Elif Ergun Instructor in Radiology Department Ankara Training and Research Hospital Ankara, Turkey E-mail: elifergun72@gmail.com Page 11 of 11