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093 multi slice fast ct


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093 multi slice fast ct

  1. 1. Multi-slice fast CT and Electron Beam Tomography: the first screening step in imaging coronary atherosclerosis? Stephan Achenbach, MD Department of Cardiology, University of Erlangen, Germany
  2. 2. Coronary artery disease events such as myocardial infarction or coronary death frequently occur in previously healthy individuals without prior symptoms. Tests which permit identification of individuals at increased risk may thereore be beneficial. Since coronary events are in most cases caused by plaque rupture, imaging methods which permit the identification and quantification of coronary atherosclerotic plaque are potentially useful for risk stratification. Most non-invasive imaging techniques, however, lack the combination of high temporal and spatial resolution which is necessary to reliably visualize the coronary arteries. Electron beam tomography (EBT) and, more recently, multi-slice spiral CT have been shown to permit visualization and quantification of coronary calcium in a non- invasive fashion. Coronary calcium is always caused by coronary atherosclerosis and the amount of coronary calcification correlates to the overall atherosclerotic plaque burden. Numerous clinical studies conducted by electron beam tomography have proven the method´s potential to identify individuals at increased risk for coronary events through detection and quantification of coronary calcifications. Most (but not all) studies have demonstrated a higher predictive value of coronary calcifications as compared to traditional risk factors. Even though some smaller studies have shown that mulit-slice CT (MSCT) in conjunction with ECG-gated reconstruction techniques permits the detection and quantification of coronary calcium with accuracies similar to electron beam tomography, no clinical outcome data have so far been published using MSCT. In conclusion, the detection and quantification of coronary calcification my be a useful tool for the identification of individuals at increased risk for coronary events. Abstract:
  3. 3. Coronary events - such as myocardial infarction - are usually caused by plaque rupture and frequently occur in previously asymptomatic individuals Introduction
  4. 4. Traditional risk factors frequently do not permit satisfactory identification of individuals who are at increased risk for coronary artery events Introduction
  5. 5. Imaging techniques for the non- invasive detection of atherosclerotic plaque in the coronary arteries may be helpful to identify individuals at increased coronary event risk. However, both high temporal and high spatial resolution are necessary to visualize the corornary arteries in a non-invasive fashion. Introduction
  6. 6. Electron beam tomography is a cross-sectional x- ray imaging technique with a temporal resolution of 100 ms. Introduction
  7. 7. Electron beam tomography permits the sensitive detection and quantification of coronary artery calcification. Calcium in LAD & LCX Calcium in RCA Introduction
  8. 8. Aquisition protocols and methods for quantification of coronary calcium by EBT are standardized and large reference data bases are available1, 2 . Severe calcification in LAD Abscence of coronary Introduction
  9. 9. Recent pre-clinical work has shown that multi-slice spiral CT using the last hardware generation and sophisticated ECG-correlated image reconstruction software also permits coronary calcium detection4,5 . LAD calcifications in retrospectively ECG-gated multislice CT Introduction
  10. 10. Introduction However, care has to be taken in order to avoid motion artifacts which may be more frequent due to the longer acquisition window as compared to EBT Same patient: prospectively triggered (left) and retrosplectively triggered MSCT
  11. 11. What is the rationale behind the detection of coronary artery calcification? Discussion
  12. 12. Why detect coronary calcium? Coronary calcification is always caused by artherosclerosis 6 Discussion
  13. 13. Why detect coronary calcium? The amount of calcium correlates to overall plaque burden 7,8 However: no close relationship between calcium in a vessel segment and degree of luminal stenosis. Discussion
  14. 14. Even though calcium does not permit to specifically detect vulnerable plaque, it is wrong to assume that calcified plaques are stable or more frequently stable than non-calcified plaques9 . erosion stable vulnerable healed rupture acute rupture Presence of Calcium Discussion
  15. 15. Discussion Coronary calcium does not permit to detect the „vulnerable plaque“, but it permits to detect the patient with high coronary atherosclerotic plaque burden in an asymptomatic stage.
  16. 16. A number of clinical trials have evaluated the predictive value of coronary calcium detection by electron beam tomography in symptomatic and asymptomatic individuals. Discussion
  17. 17. Raggi et al10 : 632 asymptomatic patients 32 +/- 7 months follow-up myocardial infarction and death Annual event rate: 0.1% for calcium score of 0 2.1% for calcium score 1-99 4.1% for calcium score 100-400 4.8% for calcium score > 400 Raggi et al, Circulation 2000 Discussion
  18. 18. Arad et al11 : 1173 asymptomatic patients 1 year and 3.5 year follow-up Risk ratio for coronary events: 23 for calcium score > 160 Discussion
  19. 19. Meta analysis by O´Malley et al12 : Calcium score above median: All events: RR 8.6 „Hard“ events: RR 4.2 Discussion
  20. 20. Discussion In most studies, coronary calcium by EBT was more predictive than conventional risk Arad et al 1996: ROC 0.91 for calcium, 0.74 for RF 1173 asymptomatic subjects (mean age: 53 years) Raggi et al 2000: OR 22 for calcium, 7.0 for RF 632 asymptomatic subjects (mean age: 52 years) Detrano et al 1999: ROC 0.65 for calcium, 0.67 for RF 1196 asymptomatic high-risk subjctes (mean age: 67 years)
  21. 21. Keelan et al13 : 288 patients with CAD who underwent coronary angiography. Follow-up 6.9 years. Event-free survival was significantly higher for patients with calcium score < 100 than for those with scores > 100. Discussion
  22. 22. In summary, a number of studies have proven the prognostic value of coronary calcium detection by electron beam tomography in asymptomatic and symptomatic populations. Study results are not completely unanimous concerning the superiority of coronary calcium over traditional risk factors, but most studies found coronary calcium to have a higher predictive value. No clinical outcome studies have so far been performed using multi-slice CT. Discussion
  23. 23. What is the potential clinical role of coronary calcium detection? AHA/ACC statement14 : „A positive EBCT confirms the presence of coronary atherosclerotic plaque.“ „Total amount of calcium correlates ... total amount of atherosclerotic plaque.“ „A negative EBCT test makes the presence of atherosclerotic plaque, including unstable plaque, very unlikely.“ „A high calcium score may be consistent with a moderate to high cardiovascular event risk within 2-5 years.“ „A negative test ... low risk of a cardiovascular event in the next 2 to 5 years.“ Discussion
  24. 24. What is the potential clinical role of coronary calcium detection? In clinical practice, cleary low-risk and clearly high-risk individuals probably do not need further testing for risk stratification. Intermediate risk patients, however, might profit: ACC/AHA14 : „selected use of coronary calcium scores when a physician is faced with the patient with intermediate coronary artery disease risk may be appropriate“ Discussion
  25. 25. What is the potential clinical role of coronary calcium detection? Discussion
  26. 26. Role of EBT and MSCT in risk stratification? Coronary calcium, even though it does not permit to detect the „vulnerable plaque“, permits to identify the patient with high plaque burden. The detection of coronary calcium therefore permits identification of patients at increased risk for coronary artery events. It may be beneficially applied in patients who seem to be at „intermediate“ risk. Conclusion
  27. 27. Initial results have shown that EBT and especially MSCT - after i.v. injection of contrast agent - also permit visualization of non-calcified plaque: Partly calcified plaque in the proximal right coronary artery visualized by multi- slice CT MSCT Conclusion
  28. 28. Non-calcified plaque in EBT: EBT EBT Conclusion
  29. 29. Non-calcified plaque in MSCT: Conclusion
  30. 30. Some authors have compared plaque morphology in MSCT to intravascular ultrasound15 , but the clinical implications and the exact meaning of non-calcified plaque in MSCT or EBBT currently are not clear. Conclusion
  31. 31. SUMMARY: EBT and MSCT have sufficient spatial and temporal resolution for coronary artery visualization. Clinical studies have shown a high prognostic value of coronary calcium for identification of asymptomatic individuals at increased coronary artery disease risk. The meaning of non-calcified plques which can also be detected (after injection of contrast agent) is not yet clear. Conclusion
  32. 32. SUMMARY: Future clinical studies, some are currenty being conducted, will help to define the role of coronary calcium detection in the clinical work-up of patients ín whom risk stratification for coronary artery events may be beneficial. Conclusion
  33. 33. Conclusion
  34. 34. References 1. Hoff JA, et al: Age and gender distributions of coronary artery calcium detected by electron beam tomography in 35246 adults. Am J Cardiol 2001;87:1335-1339 2. Raggi P: Introduction. Am J Cardiol 2001:88(2A);1E-3E. 4. Carr JJ, et al: Coronary artery calcium quantification with retrospectively gated helical CT: protocols and techniques. Int J Card Imaging 2001;17:213-220 5. Becker CR, et al: Coronary artery calcium measurement: agreement of multirow detector and electron beam CT. Am J Roentgenol 2001;176:1295-1298 6. Blankenhorn DH: Coronary arterial calcification. Am J Med Sci 1961; 41-50 7. Rumberger JA, et al: Coronary artery calcium area by electron-beam computed tomography and coronary atherosclerotic plaque area. A histopathologic correlative study. Circulation 1995:92:2157-2162.
  35. 35. References 8. Sangiorgi G, et al: Arterial calcification and not lumen stenosis is highly correlated with atherosclerotic plaque burden in humans: a histologic study of 723 coronary artery segments using nondecalcifying methodology. J AM Coll Cardiol 1998;31:126-133 9.Burke et al: Coronary calcification: insights from sudden coronary death victims. Z Kardiol 2000;89(Suppl. 2):49-53 10. Raggi P et al: Identification of patients at increased risk of first unheralded acute myocardial infarction by electron-beam computed tomography. Circulation 2000;101:850-855 11. Arad Y et al: Prediction of coronary events with electron beam computed tomography. J Am Coll Cardiol 200:36:1253-1260 12. O´Malley et al: Prognostic value of coronary electron-beam computed tomography for coronary heart disease events in asymptomatic populations. Am J Cardiol 2000;85:945-948 13. Keelan PC et al: Long-term prognostíc value of coronary calcification detected by electron beam computed tomography in patients undergoing coronary angiography. Circulation 2001;104:412-417 14. ACC/AHA expert consensus document on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease. Circulation 2000;102:126- 140 15. Kopp AF et al: Non-invasive characterization of coronary lesion morphology and composition by multislice CT: first results in comparison with intracoronary ultrasound. Eur Radiol 2001:1607-1611