THE ROLE OF HIGH END MULTI DETECTOR CT IN CORONARY IMAGING ESSAY

Transcription

1 THE ROLE OF HIGH END MULTI DETECTOR CT IN CORONARY IMAGING ESSAY Submitted for partial fulfillment of Master degree in Radiodiagnosis By Ahmed Yehia Ahmed (M.B.B.Ch., Cairo University) Supervisors Prof. Dr. Seif EL Dien Abaza Abdel Monaem Professor of radiodiagnosis Faculty of Medicine Cairo University Dr. Mohamed Ali Salem Lecturer of radiodiagnosis Faculty of Medicine Cairo University Faculty of Medicine Cairo University 2012

2 Abstract Abstract Prospective gating on 256-slice CT therefore provides a temporal resolution of 135 ms compared with 210 ms on 64-slice CT, the improvement in temporal resolution results in significantly improved image quality for all coronary vessels and reduction of the motion artifacts. The significant difference between 256-slice MDCT and 64-slice MDCT is that 256-slice MDCT requires only two image acquisition to be combined so reduces the stair-step artifact compared five to eight with 64 MDCT),so, the potential for stair-step artifacts is reduced with prospectively gated axial 256-slice CTCA even with higher heart rates. Key word: MDCT- RCA- DSCT- DETECTOR- CT - CORONARY

3 Acknowledgments I wish to express my great indebtedness and deep gratitude to Prof. Dr. Seif El Dien Abaza Abd El Monaem, Professor of Diagnostic Radiology, Faculty of Medicine, and Cairo University for accepting the idea of this work, his kind assistance and efforts, which helped me in accomplishing this essay. I also extend my thanks and appreciation to Dr. Mohamed Ali Salem Lecturer of Radiology, Cairo University for her invaluable guidance and great help in supervising this work. No words can express my feelings, respect and gratitude to him as regards his continuous encouragement and constructive criticism given to me at every stage of this work. To my father, my mother and all my family, my wife, to whom I am overwhelmingly indebted to, thank you and GOD bless you.

4 Contents Page Introduction Aim of work 1 5 Chapter 1: Anatomy of the coronary arteries 6 Chapter 2: Basic principles of CT. 18 Chapter 3: Physics of post 64 MSCT era 42 Chapter 4: Advantages of post 64 MSCT in coronary imaging Summary References Summary in Arabic

5 List Of Figures Page FIG.1 Diagrammatic course of dominant right coronary artery 7 FIG.2 CT Axial images of the coronary arteries 8 FIG.3 CT anatomy of the right coronary artery 9 FIG.4 CT anatomy of the dominant right coronary artery (a&b) axial. (C) 3D images 10 FIG.5 Diagrammatic course of dominant left main coronary artery 13 FIG.6 CT anatomy of the left main coronary artery 14 FIG.7 CT anatomy of the ramus intermedius artery (a) right anterior oblique (b) axial.(c) 3D images 15 FIG.8 Non dominant left circumflex artery (a) axial. (b) left anterior oblique. 16 FIG.9 Dominant left circumflex artery (a) left anterior oblique 3D. (b) axial 3D 17 FIG.10 Generations of CT (a) first (b) second (c) third (d) fourth FIG.11 Principles of helical CT 22 FIG.12 Slip ring technology 23 FIG.13 The difference between single-row detector and multiple-row detector CT design 24 FIG.14 Various detector array designs used in multiple-row detector CT scanners 25 FIG.15 The necessity of low pitch in imaging of the cardiac cycle 28 FIG.16 Cardiac pulsation artifact (a) left anterior oblique. (b) anterior MPR 30 FIG.17 Banding artifact (a) coronal (b) sagittal 30

6 FIG.18 Streak artifact in the presence of stent 31 FIG.19 Contrast-enhanced retrospectively ECG-gated transverse coronary CT angiograms monophasic, biphasic and dual flow 38 FIG.20 CTA for noninvasive assessment of coronary artery stent patency (a&b) without edge-enhancing algorithm (c&d) with edge-enhancing algorithm. 41 FIG.21 Image quality of the right coronary artery using 4, 16 and 64 MSCT 43 FIG.22 Effects of the filter selection and window settings on image contrast and noise at 64-section CT coronary angiography 49 FIG.23 Visibility of low-contrast structures with different convolution filters 50 FIG.24 In-stent occlusion in a patient with recurrent angina pectoris 18 months after implantation of two stents in the right coronary artery (a-d) MSCTA. (e&f) conventional coronary angio. 51 FIG.25 Schematic illustration of the acquisition principle of dualsource CT by using two tubes c 53 FIG.26 Schematic diagram of a Dual Source CT unit showing the two images acquired by using two tubes with different energy spectrums 54 FIG.27 Images obtained using dual source 64- multislice computed tomography scanner 56

7 FIG.28 Improvement of image quality of the RCA using 256 MSCT in two patients examined with a retrospectively CTA without (a d) and with (e h) dose modulation 62 FIG.29 Curved multiplanar (cmpr) at 70% of the RR cycle in a male patient with a heart rate of 75/min using DSCT 68 FIG.30 Curved multiplanar (cmpr) at 45% of the RR cycle in a male patient with a heart rate of 102/min using DSCT 68 FIG. 31 Calculation of the ESTW. 69 FIG.32 CT angiography of 72-year-old woman with AF and no significant coronary artery stenosis. 71 FIG.33 CT angiography of 67-year-old man with AF and three-vessel disease. 72 FIG.34 DSCTA versus CCA in a patient with atrial premature beats and mean heart rate of 89 beats per minute 75 FIG.35 DSCTA and CCA in a patient with mean heart rate of 105 beats per minute (b) 76 FIG.36 DSCTA and CCA in a patient with atrial fibrillation and mean heart rate of 90 beats per minute. 77 FIG.37 DSCTA and CCA for evaluation of the stent patency in a patient with mean heart rate of 68 beats per minute. 79 FIG.38 DSCTA and CCA for evaluation of the stent patency in a patient with mean heart rate of 92 beats per minute. 80 FIG.39 DSCTA and CCA for evaluation of the stent patency in a patient with mean heart rate of 76 beats per minute 81 FIG.40 DSCTA and CCA for evaluation of the stent patency in a patient with mean heart rate of 82 beats per minute 82

8 FIG.41 Curved-planar reconstruction of the right coronary artery and volume-rendered images (insets) demonstrating the image quality of the three DSCTA protocols for dose modulation 85 FIG.42 Prospective-gated axial CTCA on 64-slice (a) and 256-slice (b) CT representing typical yet infrequent stair-step artifacts on 64-slice 89 FIG.43 Prospective gated CCTA using 256 slice MSCT and its effect on the image quality and dose reduction. 92 FIG.44 Prospective gated CCTA using 256 slice MSCT and its effect on the image quality and dose reduction. 93 FIG.45 Schematic diagram illustrating different protocols for dose reduction using 320 MSCT in coronary imaging 98 FIG.46 Prospective ECG gated 320-row detector CT coronary angiography showing normal left anterior descending coronary artery 99 FIG.47 Prospective ECG-gated 320-row detector CT coronary angiography using multi-segment acquisition and reconstruction showing non calcified plaque at the proximal segment of the left anterior descending coronary artery 99 FIG.48 Non-invasive coronary angiography using 320-row computed tomography angiography revealing the absence of significant coronary artery disease and the results are confirmed using conventional coronary angiography. 100

9 FIG.49 Non-invasive coronary angiography with 320-row computed tomography angiography revealing three-vessel disease the results are confirmed using conventional coronary angiography 101 FIG Row detector CT arrhythmia rejection protocol 103

10 List Of Abbreviation AF AV CAD CAS CCA CNR CT CTA CTCA D DSCT DSCTA ECG ESTW FOV HRV HU LAD LCA LCX LM LV NPV MDCT Arial fibrillation Atrio-ventricular Coronary artery disease Coronary artery stenosis Conventional coronary angiography Contrast to noise ratio Computerized tomography Computerized tomography angiography Computerized tomography coronary angiography Diagonal artery Dual source computerized tomography Dual source computerized tomography angiography Electrocardiography End-systolic temporal window Field of view Heart rate variability Hounsfield unit Left anterior descending Left coronary artery Left circumflex artery Left main Left ventricle Negative predictive value Multi detector computerized tomography

11 MRI MSCT OM PDA PL PPV RCA RV S µ Magnetic resonance imaging Multi slice computerized tomography Obtuse marginal Posterior descending artery Postero-lateral Positive predictive value Right coronary artery Right ventricle Septal Average attenuation coefficient

12 Introduction and Aim of the Work INTRODUCTION The global burden of cardiac disease has continued to rise as the average life span has increased and dietary and health patterns have changed. Indeed, coronary heart disease is now the leading cause of death worldwide, accounting for over 17 million deaths annually (Mackay & Mensah 2004) The unique demands of imaging the beating heart require optimal spatial, temporal, and contrast resolution. Excellent spatial resolution is necessary to evaluate the fine anatomic detail of the coronary arteries, which may harbor plaque that is clinically significant at a submillimeter level. Sufficient temporal resolution is also necessary to evaluate coronary arteries without motion artifacts finally, contrast resolution is critical for determining coronary plaque composition, which may greatly influence patient prognosis and management. (Pohle, et al, 2007) Although invasive coronary angiography remains the standard of reference for the evaluation of CAD, multidetector computed tomography coronary angiography (CTA) has recently emerged as a robust imaging modality for the non-invasive evaluation of CAD. With submillimetre spatial resolution, this technique allows detailed visualization of luminal narrowing as well as atherosclerotic changes within the coronary vessel wall. Advances in CTA technology have led to continuous improvements in image quality as well as reduction in radiation dose and contrast material. (Fleur et al, 2010) 1

13 Introduction and Aim of the Work A 64-slice MDCT technology is widely used for the assessment of coronary atherosclerosis and its accuracy has been recently confirmed in multi-center clinical trials (Miller et al, 2008) Despite promising results, 64-slice MDCT has important limitations for cardiac applications related to detector coverage, which leads to longer scan times, image artifacts, increased radiation and the need for higher contrast doses. (Sang et al, 2009) The temporal resolution was limited by single-cycle reconstruction and dependence on predictive gating algorithms; prospectively gated acquisitions require appropriate patient selection with aggressive heart rate control and are typically only indicated for patients with stable heart rates below 65 bpm on 64-slice CT (Klass et al, 2008) The recently introduced dual-source CT (DSCT) scanner is characterized by two x-ray tubes and two corresponding detectors mounted onto the rotating gantry with an angular offset of 90.Regarding cardiac imaging capabilities, the new scanner system offers a high temporal resolution of 83 ms in a mono-segment reconstruction mode. Temporal resolution is independent of the heart rate, which is a major difference from single-source (Flohr, 2006) The recently introduced dual-source CT (DSCT) scanner offers a higher temporal resolution and consequently, DSCT has been considered more useful than 64-slice CT in coronary artery angiography regarding image quality of coronary arteries, cardiac valves, and left ventricular myocardium at variable heart rates (Dikkers et al, 2009) 2

14 Introduction and Aim of the Work The faster gantry rotation speed (270 ms) of the 256-slice CT results in a single cycle temporal resolution of 135 ms compared with ms, depending on the 64-slice CT system used for prospectively gated axial CTCA. Initial evidence suggests that this improved temporal resolution enable prospective gating to be applied to patients with higher heart rates (Weigold et al, 2009) The additional number of detector elements in the 256 CT extends its coverage in the z-axis. As compared to 4-MSCT (2 cm) and 64-MSCT (4 cm), and the 256- MSCT prototype provides 12.8 cm of coverage. The 256-MSCT allows for comprehensive anatomic imaging of the whole heart. It also allows for functional cardiac images, including regional wall motion, systolic thickening, and ventricular volume and ejection fractions, to be obtained in slightly more time than required for a single gantry rotation. Thus, patients with rapid or irregular heart beats, including atrial fibrillation, can be imaged without administering medication to control their heart rate (Gregory et al, 2009) Prospectively gated axial CT coronary angiography performed with 256-slice CT provides significantly improved and more stable image quality at an equivalent effective radiation dose compared with 64-slice CT. (Oliver et al, 2010) Initial experience with 320-slice CT with a detector coverage of 16 cm have also demonstrated encouraging results with a general tendency towards further improvements in achievable image quality (Rybicki et al, 2008) 3

15 Introduction and Aim of the Work A 320-row CTA systems were introduced, with enhanced craniocaudal volume coverage when compared with 64-row systems. With 16 cm anatomical coverage (0.5 mm X 320 detectors), this new generation of CTA scanners allows image acquisition of the entire heart within a single gantry rotation and heart beat. Accordingly, wide volume CTA, in combination with prospective image acquisition, allows for a marked decrease in scan time and time of breath-hold, resulting in decreased radiation dose and contrast material when compared with retrospective helical imaging requiring multiple heart beats. Improved temporal resolution and scan time result in an overall reduction of cardiac motion artifacts and eliminate the problem of stair-step artifacts, observed during step-and-shoot acquisition techniques and helical imaging (Fleur &Joanne 2010). 4

16 Introduction and Aim of the Work AIM OF WORK The aim of this study is to highlight the advantages of the new generations of multidetectors CT ( dual source) in coronary imaging over the 64 detector CT regarding the image quality, radiation dose exposure and heart rate control. 5

17 Review of Literature NORMAL ANATOMY OF THE CORONARY ARTERIES The right and left coronary arteries originate from the right and left sinuses of Valsalva of the aortic root, respectively. The posterior sinus rarely gives rise to a coronary artery and is referred to as the non coronary sinus. The locations of the sinuses are anatomic misnomers: The right sinus is actually anterior in location and the left sinus is posterior. The myocardial distribution of the coronary arteries is somewhat variable, but the right coronary artery (RCA) almost always supplies the right ventricle (RV), and the left coronary artery ( LCA) supplies the anterior portion of the ventricular septum and anterior wall of the left ventricle (LV). The vessels that supply the remainder of the LV vary depending on the coronary dominance. (Kini et al. 2007). RCA Anatomy: The RCA arises from the right coronary sinus somewhat inferior to the origin of the LCA. After its origin from the aorta, the RCA passes to the right of and posterior to the pulmonary artery and then emerges from under the right atrial appendage to travel in the anterior ( right) atrioventricular (AV) groove ( Figs. 1 and 2). In about half of the cases, the conus branch is the first branch of the RCA. In the other half, the conus branch has an origin that is separate from the aorta. The conus branch always courses anteriorly to supply the pulmonary outflow tract. Occasionally the conus branch can be a branch of the LCA, have a common origin with the RCA, or have dual or multiple branches. In 55% of cases, the sinoatrial nodal artery is the next branch of the RCA, arising 6

18 Review of Literature within a few millimeters of the RCA origin. In the remaining 45% of cases, the sinoatrial nodal artery arises from the proximal left circumflex (LCx).In either case, the sinoatrial nodal artery always courses toward the superior vena cava inflow near the cephalad aspect of the interatrial septum. As the RCA travels within the anterior AV groove, it courses downward toward the posterior (inferior) interventricular septum. As it does this, the RCA gives off branches that supply the right ventricular (RV) myocardium; these branches are called RV marginals or acute marginals. They supply the RV anterior wall. After it gives off the RV marginals, the RCA continues around the perimeter of the right heart in the anterior AV groove and courses toward the diaphragmatic aspect of the heart (Kini et al. 2007). Figure. 1 Anterior schematic diagram of heart shows course of dominant right coronary artery and its tributaries. AV = atrioventricular, PDA = posterior descending artery, RCA = right coronary artery, RV = right ventricular, SA = sinoatrial (Kini et al. 2007). 7

19 Review of Literature A B C Figure. 2-CT images of normal heart in 53-year-old man. Ao = aortic root, CS = coronary sinus, LA = left atrium, LAD = left anterior descending artery, LCx = left circumflex artery, LM = left main coronary artery, LV = left ventricle, PDA = posterior descending artery, RA = right atrium, RCA = right coronary artery, RV = right ventricle, RVOT = right ventricular outflow tract. (A) Axial 5-mm maximum-intensity-projection (MIP) image shows left main coronary artery as it arises from left coronary cusp. (B) Axial 5-mm MIP image shows right coronary artery as it arises from right coronary cusp inferior to level of beginning of left main coronary artery. (C) Axial 5-mm MIP image shows course of right coronary artery within anterior atrioventricular groove. and Left anterior descending artery is shown within anterior interventricular groove, and left circumflex artery is shown in posterior atrioventricular groove. (D) Axial 5-mm MIP image shows origin of posterior descending artery from distal right coronary artery (Kini et al. 2007). D 8

20 Review of Literature Figure. 3-Distal right coronary artery anatomy in 34-year-old man. Left anterior oblique 20-mm maximum intensity-projection image shows course of entire right coronary artery. Distally, posterior descending artery and posterior lateral branch are shown, as is atrioventricular node branch. Ao = aortic root AVN = atrioventricular node, IMB = inferior marginal branch, LCx = left circumflex artery, LV = left ventricle PDA = posterior descending artery, PLB = posterior lateral branch, RCA = right coronary artery RVOT = right ventricular outflow 9