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18-09-2020 CT CORONARY ANGIOGRAM Dr.Sowmya.Dr.BGJ.pptx.pptx
- 1. CT CORONARY ANGIOGRAM MODERATOR- DR B G JAGATH KUMAR SIR PRESENTER- DR SOWMYA S
- 2. OVERVIEW • INTRODUCTION • TECHNICAL ASPECTS • ANATOMY • PROTOCOL • POST PROCESSING • PATHOLOGIES • ARTIFACTS
- 3. EBCT
- 4. TECHNICAL ASPECTS Challenges of coronary imaging: • Small arteries • Mobility of vessels & underlying heart • Need to assess the lumen & wall • Variable & Fast Heart rate • Tilt & rotation of heart away from body axes Solutions: • Increased Temporal resolution • Increased Spatial resolution • Multiplanar reconstruction
- 5. TEMPORAL RESOLUTION • Implies scan time (msec) required to obtain data needed for image reconstruction. • Lower the temporal resolution; better the images with least motion being captured. • For motion free imaging TR 250 msec for heart rates up to 70 beats/min and up to 150 msec for heart rates greater than 100 bpm. • Ideally conventional invasive coronary angiography has TR of 1-10 msec
- 6. Factors influencing temporal resolution Heart rate Gantry rotation time Acquisition mode Reconstruction method
- 7. HEART RATE • Cardiac cycle consists of systole and diastole. • Least amount of cardiac motion occur during diastolic phase, when ventricles are passively filling. • As the heart rate increases, the period of diastole narrows down requiring a machine with resolution of less than 100ms
- 8. ECG GATING
- 9. GANTRY ROTATION TIME • Amount of time required to complete one full rotation (360°) • Faster the gantry rotation, the greater the temporal resolution • To date, fastest gantry rotation time is 280msec
- 10. Acquisition mode Prospective ECG Triggering Retrospective ECG Gating
- 11. Prospective ECG Triggering • ECG is continuously monitored • X rays are turned on at predetermined portion of R-R intervals • Always sequential • Lower patient dose • Used in calcium scoring • Drawbacks: No functional evaluation Patients having irregular Heart rate
- 12. Retrospective ECG Gating • ECG is continuously monitored & the patient table moves through the gantry • X-rays are on continuously • Scan data are collected throughout the heart cycle • Retrospectively, data from select points within R-R interval are selected for image reconstruction • High radiation dose
- 14. Partial scan reconstruction Multiple segment reconstruction
- 16. SPATIAL RESOLUTION • Detector size in the longitudinal direction • Reconstruction algorithms • Patient motion.
- 17. Reconstruction interval • The reconstruction interval defines the degree of overlap between reconstructed axial images • Independent of x-ray beam collimation or image thickness and has no effect on scan time or patient dose • Improves the resolution especially in 3D & MPR images • For cardiac images, at least 50% overlap is desirable (0.5-mm section thickness with 0.25-mm reconstruction interval)
- 18. 5mm Recon interval 0.3mm Recon interval
- 19. Pitch • The ratio of table increment per gantry rotation to the total x-ray beam width • If the table feed becomes greater than the beam width, it results in a data gap, which is detrimental for image reconstruction. • Pitch for cardiac imaging is 0.2 to 0.4 for higher spatial resolution
- 20. ANATOMY OF CORONARY ARTERIES
- 23. LCA LAD LCx Diagonal Septal Course laterally Supplies LV Course Medially Supplies IV Septum AV Bundle Proximal bundle branch Left posterior coronary sinus NORMAL ANATOMY
- 24. LCA LAD LCx Course along AV groove Obtuse marginal branches Supplies LV free wall Anterolateral papillary muscle
- 26. DIAGONAL AND SEPTAL BRANCHES
- 31. Right anterior Coronary sinus Posterior descending artery and posterior left ventricular branch SA Nodal artery(58%) Acute marginal artery RCA (42%) Arises from LCx Supplies RV
- 32. RCA
- 33. AV NODAL ARTERY Axial and oblique MPR images showing the AV nodal branch arising at the level of crux (arrow)
- 34. Dominance • The coronary artery that gives rise to the PDA and posterolateral branch is referred to as the “dominant” artery, with the RCA being dominant in approximately 70% of cases. • The LCA is dominant in approximately 10% of cases, supplying the entire LV, accompanied by the PDA and posterolateral branches from the LCx artery.
- 36. Venous system Coronary sinus Great cardiac vein Middle cardiac vein
- 37. Myocardial bridging or tunneled coronary artery
- 38. TECHNIQUE Patient preparation: • No solid food for 4 hours • No stimulants like coffee • Explain the procedure to reduce anxiety • History of pacemakers and previous bypass surgery • 18G IV access in antecubital vein • ECG Leads- Just below right & left clavicle and left lower chest • Beta blockers and calcium channel blockers are given to reduce the heart rate <60
- 39. Parameters Gantry rotation time - 280 msec Pitch - 0.2 to 0.5 Collimation - 128 × 0.6 mm Tube voltage - 120 kV Tube current - 528mAs (Effective mAs) Acquisition mode - Retrospective ECG Gating
- 40. Contrast administration • 80ml of non ionic contrast (350 mgI/ml) followed by 30ml of saline (3.5-5ml/sec). • Scanning is triggered after the contrast reaches the ascending aorta • Triggering can be done in two ways one is using a test bolus technique and the other is using a bolus tracking technique.
- 41. Scan area CTA Graft evaluation Triple R/O
- 42. Post processing Reconstruction filter Kernel - B26f smooth Reconstruction FOV - 275mm Matrix - 512×512 Slice thickness - 0.6mm Reconstruction increment - 0.5mm Reconstruction ECG intervals - 40% and 70%
- 43. Axial veiw • Initial image evaluation • Review of Extra cardiac structures • Limitation - Tortuous course of vessels
- 44. Multiplanar reconstruction • Evaluation of cardiac chambers, Aorta and Pulmonary arteries • Selective evaluation of a short segment if narrowing is suspected on axial views. Limitations • Difficulty in visualizing coronaries in single oblique MPR; angle of the reconstruction plane must be changed constantly to follow the vessel • Stenosis grading impossible due to partial averaging
- 45. Curved MPR • Done by Manual or Automatic method • To identify and quantify the degree of stenosis Disadvantages: • Optimal contrast opacification is needed • Correct centerline placement
- 47. Maximum-intensity projections Advantages • Reduced noise • Good resolution between vessels and adjacent tissues • ‘’Angiographic” representation of coronary arteries, less dependent on their course. Limitations • Potential distortion of coronary arteries and the sensitivity of the technique to wall calcification, which can hinder vascular assessment. • Overestimation of stenosis • MIP images should be interpreted with original axial and MPR and not be assessed alone to avoid misinterpretations.
- 48. Volume rendering Advantages: • Display tissues with intact spatial relationships • Define complex anatomy of the heart and coronary arteries Disadvantages: • Operator dependent • Stenosis can’t be evaluated
- 49. PATHOLOGIES • Calcium scoring • Plaque morphology/assessment • Stenosis evaluation • Anomalies • Post CABG Graft evaluation
- 50. •Quantitative assessment of atherosclerotic burden of the patient Indications: • Atypical chest pain • Asymptomatic patients with other cardiovascular risk factors • Done routinely during coronary CT angiography • Prospective sequential scan • Agatston scoring commonly used CORONARY CALCIUM SCORING
- 51. AGATSTON SCORE • A constant attenuation threshold minimum of 130 HU is used to distinguish noncalcified from calcified coronary artery lesions. • Weighted density score given to the highest attenuation value (HU) X Area of the calcification speck (400 X 8sqmm=32). • Summed up for all lesions – final score HU Per Lesion Score 130-199 1 200-299 2 300-399 3 >400 4
- 52. Grading of coronary artery disease (based on total calcium score) • No evidence of CAD: 0 calcium score • Minimal: 1-10 • Mild: 11-100 • Moderate: 101-400 • Severe: >400
- 56. Plaque attenuation and pattern • <30 HU is widely used cut-off to differentiate between lipid-rich and fibrous plaques. • Types of plaque Non calcified/ Lipid-rich plaques 42 HU (+/- 22) Partially calcified/ Intermediate plaques 70 HU (+/- 21) Calcified plaques (>130 HU on non-enhanced CT). • Intra plaque calcification destabilizes the plaques and causes plaque rupture. • Microcalcifications- PET imaging using 18F- sodium fluoride
- 57. Vulnerable plaques STABLE PLAQUES UNSTABLE/VULNERABLE PLAQUES • Large calcifications • Fibrotic tissue and • Smaller lipid pools. • Spotty calcifications • Large-lipid pool (necrotic core), which is covered by a thin fibrous cap [thin-cap fibroatheroma (TCFA)].
- 58. Positive remodelling • Growth of plaque outwards without significant luminal stenosis. • No flow limitation caused as the lipid starts accumulating in the plaques. • More frequent in ACS patients compared to stable angina.
- 59. Spotty calcifications • Defined as calcifications < 3 mm. Small (< 1 mm), associated with high- risk plaques Intermediate (1-3 mm) and Large (> 3 mm) calcifications.
- 60. Napkin-ring sign • NRS plaques are characterized by a central low attenuation area (<130HU), which is apparently in touch with the lumen, encompassed by a higher attenuation ring-like peripheral area • NRS plaques had greater area of lipid-rich necrotic core which is a key feature of rupture prone TCFA’s • Qualitative high-risk plaque feature on CTA and is strongly associated with major adverse cardiovascular events. • On histology Low-attenuation central area- large necrotic core, Ring-like high attenuation outer area- fibrous plaque tissue.
- 63. Stenosis assessment Degree of coronary stenosis: • Normal • Minimal <25% stenosis • Mild 25-49% • Moderate 50-69% • Severe/High grade stenosis >70-99% • Complete occlusion 100% 50% stenosis of LMCA is considered very significant
- 70. ALCAPA • Anomalous origin of the LCA from pulmonary artery. • Results in the left ventricular myocardium being perfused by relatively desaturated blood under low pressure, leading to myocardial ischemia. • 0.25-0.5% of all CHD • Symptoms of CHF within the first 1- 2 months of life.
- 71. • Evaluation of CABGs in both the early and late postoperative settings • Provides valuable information for the planning of repeat bypass surgeries • Sometimes difficult - metal clip artifacts • Sensitivity-100% specificity-99% for detecting bypass graft occlusion Coronary Artery Bypass Grafts
- 72. Types: Saphenous vein Grafts IMA Grafts Radial and Gastro epiploic artery Grafts
- 73. Early Complications Thrombosis Graft malposition Graft Kinking Graft spasm Pericardial effusion Sternal infection Pleural effusion Pulmonary embolism Iatrogenic complications Late complications Stenosis and Occlusion Graft aneurysm
- 74. Limitations of coronary CT angio • Artifacts • Radiation • Contrast reaction & toxicity • Non co operative patients • Arrhythmias • HR control needed (<64 slice)
- 75. Artifacts Motion related Beam hardening Technical error or limitations
- 77. Step ladder artifacts Respiratory motion
- 79. Air Stent Calcification Beam hardening artifacts
- 80. Technical errors
- 81. • Dose is highly dependent on the protocol used • ECG Modulation – Tube current is reduced during systole and 10-40% reduction in dose. RADIATION RISKS
- 82. CONCLUSION • Coronary CTA is a noninvasive diagnostic modality to visualize the coronary arteries and to detect significant coronary stenosis • Best modality to rule out disease, bypass graft and arterial anomalies evaluation • Has a high sensitivity and negative predictive value for coronary stenosis detection • Higher temporal resolution and reduced dose are necessary for wider applications in future
- 83. 1. Webb: Pulmonary and cardiovascular imaging 2. Coronary artery disease in young Indians. JIACM 2001.Vol. 2, No. 3 3. Physics of cardiac imaging with MDCT Radiographics 2007; 27:1495–1509 4. Predictive value of EBCT. Circulation 1996 ,93(11)1951-1953 5. Plaque imaging with CT—a comprehensive review on coronary CT angiography based risk assessment; cardiovascular diagnosis and therapy, Vol 7, no 5 6. The Napkin-Ring Sign: CT Signature of High-Risk Coronary Plaques Pál MaurovichHorvat, Udo Hoffmann, Marc Vorpahl, Masataka Nakano, Renu Virmani, Hatem Alkadhi, J Am Coll Cardiol Img. 2010 Apr, 3 (4) 440-444. REFERENCES
Editor's Notes
- Coronary artery disease represents a major cause of morbidity and mortality in the world. In India, compared to the western population there is 2-4 fold higher prevalence of CAD & mortality. By the end 21st century, India would account for more than half of the total heart patients in the world (WHO) . Gold standard to evaluate and treat CAD is conventional coronary angiography.
- In1982, specifically for cardiac imaging, able to acquire an image in 100 msec, suited for cardiac imaging at that time. Electrons accelerated in a vacuum funnel and are precisely focused towards and swept across a 210º tungsten ring anode placed under the patient. A cone beam of X-ray photons is emitted which go through the patient and are captured by two 240º detector rows above the patient. Slice collimation is 3 mm, so 40 slices needed to cover the entire heart (12 cm),for a total imaging time of 30 sec. One breath-hold. ECG-based triggering used for motion-free imaging during diastole. Significant motion artifacts still remain. the spectrum of applications limited, and its physical setup cumbersome. Mostly used for noninvasive evaluation of coronary artery calcium but other applications including assessment of coronary artery stenosis have been reported in limited cases. Expensive and widely not available
- Cardiac imaging with multiple-row detector computed tomography (CT) has become possible due to rapid advances in CT technologies.
- the demand for high temporal resolution implies decreased scan time required to obtain data needed for image reconstruction and is usually expressed in milliseconds.
- The coronary arteries generally fills in with blood during the diastolic phase, when the heart is relaxed and this is the right time to take images of the coronaries using cardiac scanner. As you know to image any fast moving structure we should use the fastest mode of gantry rotation and should use the multi-sector reconstruction.
- ECG represents the contraction and relaxation of heart, called as systole and diastole respectively. In cardiac scanners we couple the ECG waveform with that of image acquisition and reconstruction, known as ECG-gated cardiac scanning. The ECG shows a very distinct electrical peak called as R-wave the immediate time gap after this peak is the systole followed by diastole. Thus, for a patient having 60 beats per minute the interval between one R-R wave is 1 second or 1000 ms.
- However, with increasing gantry rotation speed, there is also an increase in the stresses on the gantry structure, since rapid movement of heavy mechanical components inside the CT gantry results in higher G forces, making it harder to achieve a further reduction in gantry rotation time. since the currently available gantry rotation time is not in the desired range for obtaining reasonable temporal resolution, various methods have been developed to compensate, such as different types of scan acquisitions or image reconstructions to further improve temporal resolution.
- the patient’s ECG is continuously monitored but the x-rays are turned on at predetermined R-R intervals to acquire sufficient scan data for image reconstruction. The table is then moved to the next location for further data acquisition. These types of scans are always sequential and not helical and result in a lower patient dose because the x-rays are on for a limited period. Calcium scoring scans are typically performed in this scan mode.
- In partial scan reconstruction, sufficient data from prescribed time range within the R-R interval of one cardiac cycle are selected for image reconstruction. Both prospective triggering and retrospective gating acquisitions In Multiple segment reconstruction sufficient data segments of the same phase from multiple cardiac cycles are selected for image reconstruction. Possible only with a retrospective gating technique and a regular heart rhythm Data required for a partial scan reconstruction are selected from various sequential heart cycles
- The minimum amount of data required to reconstruct a CT image is at least 180° plus the fan angle of data in any axial plane. This determines the scan time to acquire projection data needed for partial scan reconstruction and also limits the temporal resolution that can be achieved from an acquisition. If the gantry rotation time is 500 msec, the time required to obtain the minimum scan data is slightly greater than half of the gantry rotation time. This means that, for a gantry rotation of 500 msec, the scan time for acquiring data for partial scan reconstruction is around 260 to 280 msec. This value represents the limit of temporal resolution that can be achieved through partial scan reconstruction. The multiple-segment reconstruction method selects small portions of projection data from various heart cycles, so that when all the projections are combined, they constitute sufficient data to perform partial scan reconstructions. For example, if one chooses to select half of the data set required for partial scan reconstruction from one heart cycle and the rest from another heart cycle, this results in temporal resolution that is about one-fourth of the gantry rotation time. This is done by using projection data from two separate segments of the heartbeat cycle for image reconstruction. Further improvement in temporal resolution can be achieved by cleverly selecting projection data from three or four different heart cycles, resulting in temporal resolution as low as 80 msec.
- Effect of temporal resolution on reconstructed images from the same patient. (a) Partial scan reconstruction with temporal resolution of approximately 250 msec. (b) Multiple-segment reconstruction (two segments) yields a temporal resolution of approximately 105 msec. The stair-step artifacts are less visible and the structures in the sagittal plane have a smooth edge compared with the appearance of partial scan reconstruction.
- axial spatial resolution has been very high from the beginning and is dependent on the scan field of view (SFOV) and image reconstruction matrix. On the other hand, the longitudinal or z-axis resolution mainly depends on the image thickness. The z-axis spatial resolution (image thickness) ranges from 1 to 10 mm in conventional (nonhelical) and in helical single-row detector CT. With multiple-row detector CT, the z-axis detector size is further reduced to submillimeter size
- Overall, spatial resolution in the axial or x-y plane has always been quite high and is on the order of 10–20 line pairs per centimeter. The z axis spatial resolution is influenced by the detector size, reconstruction thickness, and other factors such as pitch and is around 7–15 line pairs/cm
- Pitch values less than 1 imply overlapping of the x-ray beam and higher patient dose; pitch values greater than 1 imply a gapped x-ray beam and reduced patient dose (18). Cardiac imaging demands low pitch values because higher pitch values result in data gaps (Fig 10), which are detrimental to image reconstruction. Also, low pitch values help minimize motion artifacts, and certain reconstruction algorithms work best at certain pitch values, which are lower than 0.5 in cardiac imaging
- The aortic valve consists of three semilunar cusps, the right and the left, from which arise the right and left coronary arteries, and the posterior or non-coronary cusp. The cusps are pouch-shaped and flexible. When blood moves out of the left heart during systolic contraction, the pliable valve cusps are forced outwards towards the wall of the aorta, allowing for free flow of blood. Upon diastole, however, the elastic walls of the aorta, no longer pushed outward by the force of ventricular contraction, will recoil. This sends a backflow of blood towards the valve cusps, producing valve closure. Blood then fills the aortic sinuses (Sinuses of Valsalva) from which the coronary arteries arise and is projected down the right and left main branches.
- Axial MPR image (superoinferior view) demonstrates the aortic valve and its cusps in relation to the LA. These cusps are the right coronary cusp (white *), the left coronary cusp (black *), and the noncoronary cusp (box).
- The LAD artery courses anterolaterally in the epicardial fat of the anterior interventricular groove and supplies the majority of the LV
- Axial MPR image displays the origin of the coronary arteries from the aorta. The LCA (black arrow) bifurcates into the left anterior descending (LAD) artery (white arrowhead) and the left circumflex (LCx) artery (black arrowhead). White arrow indicates the right coronary artery (RCA). (b) VR image shows the LCA (black arrow) arising from the aorta and bifurcating into the proximal LCx artery (arrowhead) and the proximal LAD artery (white arrow). Oblique axial (a)and vertical long-axis (b)MPR images show the normal LAD artery (arrows) coursing in the epicardial fat of the interventricular groove toward the LV apex.
- Oblique axial MPR (a) and VR (b) images show the septal branches (black arrowheads) and diagonal branches (white arrowheads) of the LAD artery. The septal branches quickly reach and penetrate the myocardium, whereas the diagonal branches course laterally to the LV free wall.
- Figure 4. Oblique axial MPR (a) and VR (b) images show the LCx artery (black arrow) and obtuse marginal branches (white arrows). The LCx artery is the other major branch of the LCA. It courses in the left AV groove, giving rise to obtuse marginal branches, sometimes referred to as lateral branches. It variably gives rise to posterolateral and posterior descending artery (PDA) branches supplying the diaphragmatic portion of the LV
- 3D VR images showing the septal and diagonal branches of LAD 3D VR image showing left circumflex and obtuse marginal branch in green
- Show variation in the number and size of the circumflex and its obtuse marginal branches Axial section at the mid ventricular level showing the distribution of all the main branches
- In approximately 15% of patients, a third branch, the ramus intermedius (RI) branch, arises at the division of the LCA, resulting in a trifurcation. When present, the RI branch courses laterally toward the LV free wall. Its course is similar to that of a diagonal branch of the LAD artery. (a) Oblique axial MPR image shows the RI branch (arrow) arising between the LAD artery (black arrowhead) and the LCx artery (white arrowhead), resulting in a trifurcation of the LCA. (b) VR image shows the RI branch (arrow) arising from the trifurcation. Black arrowhead indicates the LAD artery, white arrowhead indicates the LCx artery.
- The RCA normally arises from the right coronary sinus (CS) and courses in the right AV groove toward the crux of the heart (the point on the posterior surface of the heart where the AV groove transects the line of the interventricular septum and interatrial septum, forming a cross).
- In approximately 50%–60% of patients, the first branch of the RCA is a conus artery. The conus artery can also arise directly from the aorta (30%–35% of patients). The conus artery supplies the RV outflow tract and forms the circle of Vieussens, an anastomosis with the LAD arterial circulation. In approximately 58% of patients, the SAN artery arises from the RCA; in the remaining patients (42%), it arises from the LCx artery. Multiple ventricular branches arise from the RCA, the largest of which is called the acute marginal branch. MPR images (a, c) and VR image (b) show the RCA (black arrow in a) and its branches. In this case, the conus artery (arrowhead in a) arises from the aorta. White arrow in a and arrow in b indicate the acute marginal branch, arrowhead in c indicates the sinoatrial nodal branch.
- In 80% of patients, the right coronary artery supplies the atrioventricular (AV) node via an AV nodal artery. This branch arises near the origin of the posterior descending artery (PDA) at an area known as the crux of the heart, where the two ventricles and two atria meet.
- This is a coronary segmentation diagram of the Society of Cardiovascular Computed Tomography is used to indicate where the stenoses are located
- Coronary sinus is the wide vein which courses in the posterior part of coronary sulcus from the left side to the right side accompanying the circumflex artery. It opens into the right atrium. It receives the great cardiac vein at its left, and the middle and small cardiac veins at its end on the right side. Tributaries • The great cardiac vein is located in the anterior interventricular sulcus, alongside the anterior interventricular (descending) artery. It courses upwards from the apex and drains into the coronary sinus. • The middle cardiac vein also begins at the apex but it courses upwards in the posterior interventricular sulcus, alongside the posterior interventricular (descending) artery.
- The main coronary arteries habitually follow an epicardial route. On occasion the epicardial arteries penetrate into the myocardium for part of their route and finally occupy their habitual epicardial position, popularly known as myocardial bridging or tunneled coronary artery. Bridging is charecterized by systolic compression of the tunneled segment which may remain clinically silent in most cases. In some cases it may present with symptoms of myocardial ischemia. Several mechanisms are postulated for the occurrence of ischemia including vasospasm, systolic kinking of the artery, exercise induced high heart rate, shortened diastolic perfusion time. The likelihood of ischemia increases with the depth of the tunneled segment.
- Oral Metoprolol– If baseline > 60 bpm give metoprolol 50 mg orally. – If baseline > 65 bpm give metoprolol 50-100 mg orally. – If baseline > 70 bpm give metoprolol 100-150 mg orally. – If baseline > 80 bpm give metoprolol 100-200 mg orally.
- Images showing bolus triggering of contrast
- BETA-BLOCKER USE FOR CCTA Purpose: To decrease patient’s heart rate and reduce r-r interval variability for improved image quality of coronary artery CTA Contraindications • Congestive heart failure (CHF) • Significant asthma or bronchospasm who have used an inhaler within the past 2 weeks • Severe aortic stenosis • Known hypersensitivity to metoprolol • Systolic blood pressure less than 100 mm Hg • Heart rate less than 60 bpm
- Triple Rule-out The unique and simple noninvasive tool for managing these patients with a single 10-12s scan, rules out these 3 potentially life threatening conditions. There are three important causes for acute chest pain: • Aortic dissection • Pulmonary embolism • Acute coronary artery blocks.
- a window width of 800 –900 and a level of 350 –400 is an acceptable starting point to display MDCT-CA images,
- Orthogonal standard MPR are of limited value in MDCT-CA due to the complex anatomy of the heart and coronary arteries, but on the contrary, oblique MPR images are most useful to follow the tortuous course of the vessels, especially if interactively performed during the assessment on a workstation.
- Representation of the vasculature by the selection of the highest attenuation voxels along directions projected through the acquired volume, rendered as a 2D image
- Based on classification of voxels according to their density correlated to their representation in terms of colour and transparency
- For example, if a calcified speck has a maximum attenuation value of 400 HU and occupies 8 sq mm area, then its calcium score will be 32.
- Coronary calcium scoring correlates with extent of atherosclerosis but underestimates the total coronary plaque burden. Intravascular US is the gold standard technique which is invasive and expensive
- ROI is used to define plaque attenuation and pattern Mean CT attenuation is measured and further categorized as low/ high attenuating plaque. Low-attenuation plaque (HU=14) with severe (70-99%) stenosis in the LAD.
- The advances in cardiac CT imaging now enable the noninvasive visualization of the coronary lumen and atherosclerotic plaques. Moreover, CT studies investigating patients with ACS described high-risk plaque features characteristic to culprit lesions, such as low plaque attenuation (<30 Hounsfield units [HU]), positive remodeling, and spotty calcification Lipid plaques more vulnerable than calcified plaques Vulnerable plaques are those which have large lipid core, spotty Ca, napkin ring lesions & positive remodeling.
- On histology plaques with positive remodeling show a higher lipid content and abundance of macrophages. Patients with positive remodeled plaques can present with an acute coronary syndrome without any prior cardiac history. An example of positive remodeling of a non-calcified plaque in the mid RCA. There is outward growth of the plaque with minimal stenosis of the lumen.
- Spotty calcification in the LAD and D1
- Overall, although the napkin-ring sign indicates increased vulnerability and subsequent adverse cardiovascular events, it is not specific to TCFA. HISTOPATHOLOGY HAS DEMONSTRATED THAT RUPTURE OF CORONARY ATHEROSCLEROTIC PLAQUES WITH subsequent intraluminal formation of thrombi is the most frequent cause of acute myocardial infarction (1). Furthermore, it has been shown that plaque ruptures resemble plaques that are histologically classified as thin cap fibroatheroma (TCFA). TCFAs have distinct histological characteristics, including a large necrotic core with an overlying thin intact fibrous cap, macrophage infiltration, and often increased number of intraplaque vasa vasorum (2). These lesions have been designated as vulnerable plaques indicating the increased probability of rupture
- The lesion is characterized by a necrotic core (star), which is consistent with the low attenuation core of the plaque and a significant amount of fibrous plaque tissue, which is consistent with the high attenuation rim on the CT images (red dashed line). The arrowheads indicate the vasa vasorum.
- Both axial and MPR images permit the visualization of the coronary arteries in multiple orientations. However, original axial images remain the cornerstone of the evaluation, as virtually all pathologies can be recognized.
- Anomalous origin High takeoff, Multiple ostia, Single coronary artery, Anomalous origin from pulmonary artery, Origin of coronary artery or branch from opposite or noncoronary sinus and an anomalous course(retroaortic, interarterial, prepulmonic, septal) Anomalous course Myocardial bridging, Duplication of arteries Anomalous termination Coronary artery fistula, Coronary arcade, Extracardiac termination
- The illustration in the left upper corner is the most common and clinically significant anomaly. There is an anomalous origin of the LCA from the right sinus of Valsalva and the LCA courses between the aorta and pulmonary artery. This interarterial course can lead to compression of the LCA (yellow arrows) resulting in myocardial ischemia and sudden death. The other anomalies in the figure on the left are not hemodynamically significant.
- cardiac pulsation Banding artifacts due to increased heart rate incomplete breath holding. These types of artifacts are not observed on axial images
- Banding artifacts due to an increased heart rate from 51 to 69 beats per minute. Coronal (a) reformatted images of the heart obtained from CT data show banding artifacts (arrowheads). Artifacts due to incomplete breath holding. (a) Axial images show no motion artifacts. (b, c) Coronal (b) and sagittal (c) reformatted images show banding artifacts.