What every radiologist should know about cardiac CT: A case-based pictorial review

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1 What every radiologist should know about cardiac CT: A case-based pictorial review Poster No.: C-0555 Congress: ECR 2010 Type: Educational Exhibit Topic: Cardiac Authors: C. M. Capuñay, P. Carrascosa, A. Deviggiano, J. Vallejos, J. Carrascosa; Vicente López/AR Keywords: coronary CT angiography, computed tomography, cardiac CT DOI: /ecr2010/C-0555 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. Page 1 of 28

2 Learning objectives To describe the current multidetector CT technique for evaluation of coronary arteries and review different strategies for radiation dose reduction. To review cardiac and coronary artery anatomy, according to AHA criteria. To illustrate the spectrum of MDCT findings of coronary artery disease as well as other cardiac and coronary congenital and acquired abnormalities based on our series of 1250 cardiac CT studies performed between 2002 and Background Coronary artery disease is a major cause of morbidity and mortality worldwide. Early detection is important to identify potentially modifiable risk factors and to avoid the progression or even promote the regression of the disease. Coronary angiography is considered the diagnostic standard for determining the presence and severity of coronary artery stenosis. Coronary CT angiography with multidetector systems has been shown to be a highly accurate method for the non-invasive diagnosis of coronary artery disease as well as for the identification of coronary anomalies and other cardiac disorders. This is a relatively novel technique, with constant changes in CT equipment, scan protocols and post-processing softwares. The radiologist or cardiologist are obliged to be familiar with those advances to assure the best performance of the method. Page 2 of 28

3 Imaging findings OR Procedure details In this case-based pictorial review we focus the attention on the normal cardiac and coronary artery anatomy, the CT imaging findings on coronary artery disease, quantification of coronary stenosis and plaque characterization. Also we reviewed the CT findings on other cardiac and coronary abnormalities. Description of different CT acquisition protocols is also another topic for discussion, with debate of their pros and cons and the best scenario for each one. The patient selection is decisive to obtain a diagnostic CT scan. Prescan considerations Knowledge of the clinical history of the patient Discard iodine contrast contraindications Evaluation of previous cardiac exams Page 3 of 28

4 A regular, sinusal heart rate is necessary for reliable imaging of the coronary arteries by MDCT. The heart rate is predictive of image quality. A low heart rate < 60 b.p.m. substantially improves image quality, rate of assessable coronary segments and accuracy for stenosis detection. Proposed premedication protocols: Betablockers orally, min prior to scan (atenolol, mg; metoprolol, mg). The same betablockers can also be given orally the night before the exam. If necessary, i.v. betablockers (metoprolol, 5-20 mg) are used in the CT room before the scan. Monitoring of vital signs is essential. Scan acquisition Once the desired heart rate is achieved, sublingual nitrates isosorbide dinitrate (2.5-5 mg) or nitroglycerin ( mg) are given to dilate the coronary arteries and avoid vasospasm. After a scout scan, a volume data set covering the entire heart is acquired in inspiratory breath-hold. Page 4 of 28

5 Optimal coronary artery opacification is crucial. Dual-source injectors are mandatory. Contrast medium with high iodine concentrations (370 to 400 mg iodine/ml) are recommended. Using 64-slice MDCT scanners usually the injection of ml of contrast agent at 5-6 ml/s followed by 25 ml saline solution at 2.5 ml/s are sufficient. To assure that the scan will be during the peak of opacification of the coronary tree, image acquisition are triggered when the concentration of contrast media reaches an attenuation value of 110 UH in the descending aorta. Different ECG-synchronized scanning techniques. The retrospective ECG-gated helical scan mode can be performed with or without tube current modulation. The first provides a typical dose range on the order of 8-20 msv. Using dose modulation, depending on the heart rate, may reduce radiation dose 30-50%, with a dose range on the order of 8-12 msv. A recent strategy is the prospective ECG-gated axial scans mode. In selected patients, with stable, low heart rate it is the better alternative to reduce the radiation esposure. Typical dose range on the order of 2-4 msv, or even lesser (< 1 msv) (Fig. 1). Image analysis and post-processing Along the evaluation of the axial images, interactive post-processing software in 2D and 3D facilitates the interpretation of the complex data. Multiplanar reformats (MPR), thin maximum intensity projections (M.I.P.) and curvedmpr of a selected vessel are useful 2D tools to evaluate the coronary arteries and also allow the depiction of a curved vessel as a stretched MPR image. Page 5 of 28

6 Analysis of the artery lumen for stenosis include evaluation of the artery cross sections along its length to determine the plaque morphology and the effective free lumen diameter. Coronary anomalies Normal coronary anatomy The LMCA arises from the left sinus of Valsalva and usually bifurcates into the left anterior descending (LAD) artery and the left circumflex (LCX) artery. A third branch, the intermediate ramus branch can be present. In 0.4o% of the population, the LMCA is absent. The LAD artery runs in the anterior interventricular groove and gives origin to septal branches that supply the anterior two thirds of the septum, and diagonal branches that travel along the lateral left ventricular wall. The LCX artery travels in the left atrioventricular groove, gives origin to lateroventricular branches and usually terminates as a small branch in the atrioventricular groove. In a left dominant coronary artery circulation (10%-20%), supplies both the posterior descending coronary artery and the posterior left ventricular artery. The RCA arise from the right coronary sinus of Valsalva and runs into the right atrioventricular groove. It usually gives off the conus branch as its first branch and acute marginal branches to the lateral walls of the right ventricle. In 70%-80% of the patients, a right dominant coronary artery circulation is present, supplying the posterior descending artery and the posterior left ventricular artery. Figures 2-4 illustrate normal coronary arteris by coronary CT angiography. Page 6 of 28

7 Coronary anomalies Congenital anomalies of the coronary arteries are infrequent, affecting approximately 0,5-1% in the general population. Coronary anomalies can be isolated or associated with major congenital heart diseases. The majority of these anomalies are clinically insignificant; however they were associated with chest pain, dyspnoea, myocardial ischemia, myocardial infarction, syncope, arrythmias or sudden cardiac death. Coronary CT angiography is very useful in evaluating the origin and course of coronary anomalies, and can easily determine their relationship with the aorta and pulmonary trunk. They are divided in two groups: Benign or Minor coronary anomalies; Malignant or Major coronary anomalies. Examples are shown in Figures 5-9. Plaque characterization and Stenosis Quantification The complete analysis includes evaluation of the plaque morphology, the remodelling index, and the stenosis severity. Based on the density in HU, the atherosclerotic plaques can be classified as: Non-calcified plaques: the atherosclerotic plaque shows lower density than the enhanced lumen; Calcified plaques: the atherosclerotic plaque shows higher attenuation than the enhanced lumen; Mixed plaques (Fig, 10). According to the plaque morphology, they can be classified as concentric or eccentric. Page 7 of 28

8 The burden plaque is calculated measuring the luminal area and vessel area [1 - (lumen area / vessel area)] x 100. The remodelling index express the ratio between the area, including both plaque and vessel lumen at the site of maximal luminal narrowing and the mean area of the proximal coronary segment. Cross-sectional orthogonal images of the selected vessel are essential for a correct quantification of the coronary stenosis (Figs ). Evaluation of stents and bypass grafts. There is a high variability of artifacts and lumen visibility when evaluating the stents (Fig. 16). Two main factors should be considered: the type of stent (material) and the stent diameter. Current 64-slice and 256 CT scanners with high spatial and temporal resolutions improved the assessment of the stent lumen (Figures 17 and 18). MDCT-CA allows the assessment of coronary artery bypass grafts with high diagnostic accuracy and can be used in clinical routine as a reliable non-invasive method for patients with suspected CABG dysfunction (Figures 19 and 20). Functional analysis Retrospective ECG-gated helical scan allows functional evaluation of the LV (Fig. 21). Page 8 of 28

9 Images for this section: Fig. 1: Different ECG-synchronized scanning techniques. Page 9 of 28

10 Fig. 2: Consecutive axial CT images displaying the localization and course of each coronary artery. Page 10 of 28

11 Fig. 3: Curved multiplanar reformation images by prospectively gated axial coronary computed tomography angiography of the left anterior descending (LAD) artery, the left circumflex artery (LCX) and the right coronary artery (RCA). Fig. 4: Maximum intensity proyections and volume rendering image of the coronary tree. Left anterior descending (LAD) artery, the left circumflex artery (LCX), right coronary artery (RCA), diagonal branches (DG), lateroventricular branches (LV), posterior descending artery (PDA), posterior left ventricular artery (PLVA). Page 11 of 28

12 Fig. 5: Absence of LMCA. Page 12 of 28

13 Fig. 6: Myocardial bridging in the middle segment of the LAD artery. Page 13 of 28

14 Fig. 7: Intracavitary course of the RCA. Fig. 8: Double RCA. Page 14 of 28

15 Fig. 9: RCA arising from the LMCA. The anomaly artery runs between the aorta and the pulmonary trunk. Page 15 of 28

16 Fig. 10: Types of coronary plaques on coronary CT angiography. Page 16 of 28

17 Fig. 11: Moderate coronary stenosis in the proximal segment of the LAD due to a mixed plaque with large calcified component (yellow arrows). There is also a mild stenosis secondary to a small, excentric calcified plaque (red arrows). Fig. 12: Extense coronary artery disease en the LAD artery. There is a severe stenosis secondary to a mixed, predominantly non-calcified plaque (arrows). Page 17 of 28

18 Fig. 13: Large, concentric, predominantly non-calcified plaque in the proximal and middle segments of the LAD artery generating a severe stenosis (large arrow). The red arrow marks a small peripheric calcification, while the yellow arrow the non-calcified component. Page 18 of 28

19 Fig. 14: Excentric, non-calcified plaque at the level of the LMCA (blue arrow) generating a < 50% lumen stenosis. There is also an excentric, calcified plaque at the proximal segment of the LAD artery generating a mild stenosis (re arrow). Page 19 of 28

20 Fig. 15: Focal non-calcified plaque at the proximal segment of the LAD artery generating a severe stenosis (arrow). Page 20 of 28

21 Fig. 16: High variability of artifacts and lumen visibility in the evaluation of the stents. Page 21 of 28

22 Fig. 17: Permeable stent in the proximal LAD artery. The stent lumen is clearly visualized. Page 22 of 28

23 Fig. 18: Intra-stent thrombosis. The stent lumen in the area of thrombosis is hypodense, without contrast enhancement. Page 23 of 28

24 Fig. 19: Venous coronary artery bypass graft to the LAD artery. There is a severe proximal stenosis (blue arrows) and a mild to moderate stenosis (yellow arrow) in the middle of the graft. The other grafts to the LCX is normal. Page 24 of 28

25 Fig. 20: Total oclussion of a venous coronary artery bypass graft (arrows). There is also a permeable LIMA bypass graft. Page 25 of 28

26 Fig. 21: Left ventricular functional analysis. Page 26 of 28

27 Conclusion Nowadays, coronary CT angiography performed in a prospectively-gated axial mode using a 64-channel CT system provides an accurate, low-dose alternative for the evaluation of coronary and cardiac anatomy as well as the diagnosis of coronary artery disease. Personal Information Carlos Capuñay MD Sub-Head of CT and Research Departments at Diagnóstico Maipú Av Maipu 1668 (1602) Vicente López, Buenos Aires, Argentina. TE: carloscapunay@diagnosticomaipu.com.ar References Achenbach S. Computed tomography coronary angiography. J Am Coll Cardiol 48: , Achenbach S. Current and future status on cardiac computed tomography imaging for diagnosis and risk stratification. J Nucl Cardiol 12: , Carrascosa P, Capunay C, Garcia-Merletti P, et al: Characterization of coronary atherosclerotic plaques by multidetector computed tomography. Am J Cardiol 97: , Page 27 of 28

28 Carrascosa P, Capunay C, Parodi JC, et al: General utilities of multislice tomography in the cardiac field. Herz 28:44-51, Hoffmann MH, Shi H, Schmid FT, et al: Noninvasive coronary imaging with MDCT in comparison to invasive conventional coronary angiography: a fast-developing technology. AJR Am J Roentgenol 182: , Page 28 of 28