CT ANGIOGRAPHY IN CARDIOLOGY

CT ANGIOGRAPHY

• Computed tomography angiography (CTA) is a computed tomography technique used to visualize arterial and venous vessels throughout the body.

• Coronary computed tomography angiography (CCTA) is a heart imaging test that helps determine if plaque buildup has narrowed a patient's coronary arteries, the blood vessels that supply the heart.

CT ANGIOGRAPHY (CONTD...)

• Noninvasive coronary imaging requires a system capable of acquiring motion-free, high spatial resolution images within less than 20 seconds, while patients are holding their breath.

• Current generation 64-channel multidetector row computed tomography (MDCT) fulfills these requirements reasonably well.

• The basic principle of CT technology harnesses ionizing radiation within a gantry rotating around the patient in which x-rays are detected on a detector array and converted through reconstruction algorithms to images.

• Physical limits to spatial and temporal resolution are recognized, based on minimum detector width for detection of radiation signals and the speed at which the gantry can physically rotate.

• Each row is a narrow channel, approximately 0.625 mm in width for “standard” width detectors, through which x-rays are detected on scintillation crystals.

• The number of detector rows aligned in an array has increased from one in single-detector units to 4, 16, 64, and ultimately 256 to 320 rows in “wide-area” detectors.

• The increase in the number of rows leads to wider coverage, with more of the heart viewed simultaneously—up to 16 cm in a single gantry rotation for 320 detector rows at a width of 0.625 mm each leading to shorter scan acquisition times and consequently reduced radiation exposure and contrast requirements.

Abbara S, Arbab-Zadeh A et al: J Cardiovasc Comput Tomogr 3:190, 2009.

RADIATION DOSE

• Radiation exposure : Radiation doses of cardiac CT scans vary greatly depending on the scan parameter settings, scan range (cranial-caudal length of the scan), gender (women receive more radiation due to breast tissue), and patient body habitus (obesity increases exposure).

• Chest x-ray is 0.04 to 0.10 mSv,

• Average annual background radiation 3 to 3.6 mSv.

• Invasive diagnostic coronary angiography 2.1 to 4 mSv.

• Coronary CT angiography 4 to 11 mSv.

• This study showed that the effective dose for cardiac MSCT scanning in daily practice is estimated to be 6.4± 1.9 and 11.0 ±4.1 mSv with 16- and 64-slice CT, respectively.

• The increase in dose estimates with the 64-slice technology is explained by the higher spatial and temporal resolution achieved with current CT scanner technology.

• Image quality of coronary CTA is improved by– Achieving a slow, regular heart rate, excluding very obese

patients,

– Selecting patients able to cooperate with instructions to be motionless and to hold their breath during imaging, and

– By assessing the presence and distribution of coronary calcification.

PATIENT PREPARATION AND SCANNING SEQUENCE

Dewey M, Vavere AL, et al. CORE-64 Multicenter International Trial. AJR Am J Roentgenol 2010; 194:93.

CT ANGIOGRAPHY PROCEDURE

• For maximum enhancement CTA should start when contrast agent arrives in the ascending aorta ( 15-25 sec. after i.v injection).

• A standard three-phase injection protocol consists of administration of undiluted contrast, 40 to 60 mL, at a rate of approximately 5 mL/sec through an antecubital 18 to 20 gauge intravenous line, followed by a smaller volume of dilute contrast (50:50 contrast-to-saline ratio, for a total of 10 to 20 mL), and then a bolus of saline (40 mL).

• The intent is to maximize contrast enhancement of the left side of the heart and arterial structures, with mild contrast enhancement of the right side of the heart and pulmonary artery.

• Timing of the scan in relationship to the contrast bolus is commonly performed using the triggered bolus method, in which contrast attenuation in the pulmonary artery or aorta is monitored, followed by automated scan initiation once an adequate CT attenuation value (110 to 180 Hounsfield units [HU]) is achieved.

SCAN MODES• There are two basic scan modes in cardiac CT:

• Helical (spiral) scanning : Most current MDCT scanners use spiral, retrospectively gated acquisition techniques.

• Helical scanning involves continuous radiation exposure and table movement (the patient is moved through the rotating x-ray beam), during which the detector arrays receive projection data from multiple contiguous slices of the patient.

• Axial (sequential, step & shoot) scanning : axial imaging involves sequential scanner “snapshots,” in between which the x-ray tube is turned off and the table is moved to a different position for the next image to be acquired.

Abbara S, Arbab-Zadeh A et al: J Cardiovasc Comput Tomogr 3:190, 2009.

ECG GATING

a. PROSPECTIVE TRIGGERING: The trigger signal is derived from the patient’s ECG based on a prospective estimation of the RR interval.

The scan is usually triggered to begin at a defined point after the R wave, usually allowing image acquisition to occur during diastole.

Advantage: ● dose efficient (80% reduction in x-ray exposure) Disadvantage : ● limited portion of cardiac cycle data set

obtained ● greatly depends on the regularity of patient’s heart rate

A diagram showing the division of the cardiac cycle into 10% intervals. The two ovals cover the two regions of the cardiac cycle where the motions are the most still. The light blue oval covers the mid- to end-systolic phase, and the red oval covers the mid- to end-diastolic phase.

Hurst’s The Heart

b. RETROSPECTIVE GATING : Collects data during the entire cardiac cycle. Once scan is complete , data from specific periods of the cardiac cycle are used for image reconstruction by retrospective referencing to the ECG signal.

Advantage : allows assessment of cardiac function via four-dimensional reconstruction.

Disadvantage : higher radiation dose exposure.

TECHNICAL LIMITATIONS

• Cardiac motion artifacts.• High spatial resolution is required to image relatively smaller

vessels e.g. Coronary arteries.• Current MDCT scanner provide a spatial resolution of 0.4mm

compared to 0.2mm for invasive angiography .

TECHNICAL LIMITATIONS

• Blooming Artifacts ： High-attenuation structures, such as calcified plaques or stents, appear enlarged (or bloomed) because of partial volume averaging effects and obscure the adjacent coronary lumen, the main cause of false-positive results in coronary CTA because of overestimation of the degree of stenosis.

CARDIAC COMPUTED TOMOGRAPHY ANATOMY

CARDIAC COMPUTED TOMOGRAPHY ANATOMY

1. This noninvasive acquisition does not use IV contrast material and is performed at a relatively low radiation dose compared with coronary CTA.

2. It is used to detect and quantify coronary artery calcification (CAC).

3. Although CAC is a specific indicator of the presence of coronary artery atherosclerosis, it represents only the calcified or healed plaque, not the full burden of plaque.

COMPUTED TOMOGRAPHY FOR DETECTING CORONARY ARTERY CALCIUM

4. CAC is estimated to represent approximately 10–20% of the total atherosclerotic plaque burden.

5. Patients who have CAC are more likely to have noncalcified plaque that is prone to rupture, leading to acute thrombosis, than patients without CAC .

(From Burke AP, Taylor A, Farb A, et al: Coronary calcification: Insights from sudden coronary death victims. Z Kardiol 89[suppl 2]:49, 2000.)

• The AGATSTON-JANOWITZ SCORE was the initial method for calcium quantification and is the most widely used.

• To be included in the Agatston-Janowitz score, CAC must reach a threshold of 130 HU and cover an area of at least 1 mm2; calcifications that are lower in attenuation or smaller in size are not included in the score.

Agatston AS, Janowitz WR, Hildner FJ, Zusmer NR, Viamonte M, Jr., Detrano R. Quantification of coronary artery calcium using ultrafast computed tomography. J Am Coll Cardiol. 1990;15:827-832

• The score of each calcification is calculated by multiplying the area of the CAC by an attenuation-weighting factor based on the highest HU value of the CAC, a score ranging from 1 to 4.

• 1 for 130-199 HU, • 2 for 200-299 HU, • 3 for 300-399 HU, • 4 for 400 HU.

• The CAC score can be classified into five groups:

• 1) zero, no coronary calcification;• 2) 100, mild coronary calcification; • 3) > 100 to 399, moderate calcification;• 4) >400 to 999, severe calcification; • 5) > 1000, extensive calcification.

CORONARY CALCIUM SCORING

A, Data from MESA for the distribution of CAC scores among men relative to age and ethnicity

B, Major cardiovascular outcomes observed in MESA in association with higher thresholds of coronary calcium scores

CORONARY CALCIUM COVERAGE SCORE

• Higher clinical risk is associated with multivessel CAC

• The number of calcified lesions (the more lesions, the worse the prognosis)

• Diffuse spotty calcified lesions (small foci <3 mm in size).

Distribution of coronary calcium on cardiac CT in four different patients: A, no detectable coronary calcium; B, coronary calcium in all three epicardial coronary arteries including (clockwise) the right coronary artery (arrow) and the left anterior descending and left circumflex coronary arteries; C, a “spotty” or diffuse pattern with multiple small (<3 mm) foci of coronary calcium; and D, a large calcified lesion in the left anterior descending coronary artery.

Williams M, Shaw LJ et al: J Am Coll Cardiol Img 1:61, 2008.

• In comparison with a CAC score of zero, the presence of any CAC is associated with a fourfold risk of coronary events over 3 to 5 years.

• In patients at intermediate clinical risk for coronary events (e.g., by Framingham score), the CAC score can help to reclassify patients to a higher or lower risk group.

• For instance, a CAC score of zero confirms low risk of events. Conversely, a CAC score of greater than 400 is observed with a significant cardiac event rate (greater than 2 %/year) in patients who appear to be intermediate risk by Framingham score.

Kronmal RA, McClelland RL, Detrano R, et al: Risk factors for the progression of coronary artery calcification in asymptomatic subjects: Results from the Multi-Ethnic Study of Atherosclerosis (MESA). Circulation 115:2722, 2007.

• However, not every atherosclerotic plaque is calcified, and even the detection of a large amount of calcium does not imply the presence of significant stenoses.

• Therefore, it adds only incrementally to traditional risk assessment and should not be used in isolation.

• The test is most useful in intermediate risk populations,in which a high or low score may reclassify individuals to a higher or lower risk group. Unselected screening is not recommended.

CT ANGIOGRAPHY : INDICATIONS

• Suspected CAD with symptoms

• Intermediate pre-test probability of CAD with uninterpretable ECG or unable to exercise.

• Acute chest pain with intermediate pre-test probability of CAD and no ECG changes and negative serial enzymes.

• Chest pain syndrome with uninterpretable or equivocal stress test (exercise, perfusion, or stress echo).

PRE TEST PROBABILITY FOR CAD

Modified from Gibbons RJ, Balady GJ, Bricker JT, et al: ACC/AHA 2002 guideline update for exercise testing: Summary article. A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). J Am Coll Cardiol 40:1531, 2002.

CT ANGIOGRAPHY : INDICATIONS ..)

• Evaluation of suspected aortic dissection or thoracic aneurysm.

• Evaluation of suspected pulmonary embolism.

• Evaluation of pulmonary vein anatomy prior to invasive radiofrequency ablation for atrial fibrillation.

• Evaluation of coronary arteries.

CT ANGIOGRAPHY : INDICATIONS• Assessment of complex congenital heart diseases including

anomalies of coronary circulation, great vessels, and cardiac chambers and valves.

• Noninvasive coronary arterial mapping, including internal mammary artery, prior to repeat cardiac surgical revascularization.

• Evaluation of coronary artery anomalies.

• Coronary artery bypass grafts.

CORONARY CT ANGIOGRAPHY

• The primary clinical application of cardiac CT is the performance of noninvasive coronary CT angiography among patients with symptoms suggestive of myocardial ischemia.

• The overall accuracy of 64-row CT angiography included a sensitivity of 87% to 99% and specificity of 93% to 96%.

• Coronary CT angiography for evaluating CAD is most useful in low- to intermediate-risk patients with angina or anginal equivalent.

• The negative predictive value of coronary CT angiography is uniformly high in studies, approaching 93% to 100%; in other words, coronary CT angiography is an excellent modality for ruling out coronary disease.

GRADING

• 0 Normal: Absence of plaque and no luminal stenosis• 1 Minimal: Plaque with <25% stenosis• 2 Mild: 23%-49% stenosis• 3 Moderate: 50%-69% stenosis• 4 Severe: 70%-99% stenosis• 5 Occluded

Raff GL, Abidov A, Achenbach S, et al: SCCT guidelines for the interpretation and reporting of coronary computed tomographic angiography. J Cardiovasc Comput Tomogr 3:122, 2009.

Coronary artery lesions of differing severity and grade as depicted on cardiac CT. A, Large mixed plaque without significant stenosis in the proximal left anterior descending coronary artery (curved multiplanar reformat), with outward arterial remodeling (arrow), as shown in the cross-sectional image (inset). B, Large noncalcified plaque with outward arterial remodeling in the right coronary artery with mild luminal stenosis (<25%). C, Moderate stenosis (50%) in the proximal left circumflex coronary artery with a mixed plaque (arrow). D, High-grade (>70%) stenosis of the mid–left anterior descending coronary artery with a noncalcified plaque (arrow). E, Total occlusion (arrow) of the distal left circumflex coronary artery.

Motoyama S, Kondo T, et al:J Am Coll Cardiol 50:319, 2007.

CLINICAL APPLICATIONS OF CORONARY CT

• In emergency department. • Detection of non calcified plaque.• Evaluation after CABG• Imaging of coronary stents

ROLE IN EMERGENCY DEPARTMENT

• Because of the High negative predictive value of cardiac CT, it has been used to exclude CAD among patients presenting with acute chest pain.

• There was improved efficiency of clinical decision making for triage in the emergency department, with a shorter length of stay in the hospital and more direct discharges from the emergency department.

• This improvement appeared to be accomplished safely, without putting patients at greater risk for undetected acute coronary syndromes.

• There was increased diagnostic testing and higher radiation exposure in the CCTA group, with no overall reduction in the cost of care.

• On the basis of the clinical trials evidence, coronary CT angiography received a recommendation as “appropriate” for patients at low and intermediate likelihood for having CAD.

DETECTION OF NON CALCIFIED PLAQUE

• Defined as any coronary arterial wall lesion with an x-ray attenuation detectably below that for the iodine contrast medium but higher than for surrounding tissue, noncalcified plaque is difficult to quantify, with limited accuracy and reproducibility for the techniques in use.

• Detection requires maximal spatial and temporal resolution and minimized image noise through higher radiation exposures.

• Among asymptomatic patients, noncalcified plaque frequently is found along with CAC but is present in only 5% to 10% of patients as the sole finding, and very infrequently in an obstructive pattern.

• For this reason, screening CT angiography is not advocated in asymptomatic patients for the purpose of detecting noncalcified plaque.

Hausleiter J, Meyer T, Hadamitzky M, et al: Prevalence of noncalcified coronary plaques

by 64-slice computed tomography in patients with an intermediate risk for significant coronary artery disease. J Am Coll Cardiol 48:312, 2006.

• Among symptomatic patients, noncalcified plaque tends to be a common finding.

• Plaques with low attenuation values (15 to 50 HU) tend to be morphologically classified as lipid-rich, and those with attenuation values of approximately 100 HU tend to be fibrous plaques.

• Plaques associated with greater risk for plaque rupture or ACS include:

a) low-attenuation plaque (plaque with attenuation values <30 HU),

b) outward arterial remodeling (artery diameter ratio of the involved segment to a proximal reference of 1.1 or greater)

c) and a spotty pattern (<3 mm in size) of calcification.

Motoyama S, Kondo T, et al:J Am Coll Cardiol 50:319, 2007.

CORONARY CT ANGIOGRAPHY OF NON-CALCIFIED PLAQUE

CORONARY CT ANGIOGRAPHY OF CALCIFIED PLAQUES

A significant stenosis ofLAD is confirmed on coronary angiography

Extensive calcified plaques arenoticed in the proximal and middle segments of left anterior descending (LAD) on curved multiplanar reformatted

Extensive calcified plaques are noticed in volume rendering images

CORONARY CT ANGIOGRAPHY OF MIXED PLAQUES

Coronary CT angiography of mixed plaques. Mixed plaques are observed in the proximal segment of the left anterior descending (LAD) artery with > 50% stenosis (a, arrow). Coronary angiography confirms the significant stenosis of the LAD (b, arrow).

BYPASS GRAFT IMAGING

• 1. Graft location : MDCT can accurately characterize the origin, course, and touchdown of prior bypass grafts

• 2. Graft patency : Patency of both arterial and venous bypass grafts can be assessed.

• Recent studies have suggested that the sensitivities and specificities of MDCT for detecting stenosis or occlusion of bypass grafts, when compared with invasive angiography, approaching 100%.

• Before reoperative CABG, cardiac CT is considered an appropriate indication, defining the relationship of sternal wires to cardiac and graft structures for the purpose of planning surgical reentry techniques.

• High-risk findings on cardiac CT include cardiac structures adjacent to or adherent to the sternum and coronary bypass grafts that extend into the midline.

• CT images also guide the surgical team on optimal locations for aortic crossclamping, to avoid regions with extensive CAC or atheroma .

• Occasionally, artifacts related to metallic clips can interfere with assessment of the distal anastomosis of an arterial graft (internal mammary or radial artery graft).

Maluenda G, et al: Perioperative outcomes in reoperative cardiac surgery guided by cardiac multidetector computed tomographic angiography. Am Heart J 159:301,

2010.

Cardiac CT provides high accuracy for evaluation of coronary bypass grafts owing to their large size, often limited extent of calcified atherosclerosis, and limited mobility, as shown in the oblique multiplanar reformat (A) and three-dimensional volume-rendered reformat (B).

High-risk substernal reoperative anatomy in a patient with previous coronary bypass surgery including a coronary bypass graft (arrow)

immediately beneath the sternum, shown in axial (A) and sagittal (B) views. The right ventricle is immediately adjacent and adherent to the

sternal wire (C, arrow).

Three-dimensional rendering image shows the adhesion of the mid-portion of the left internal mammary artery graft to the sternum. Fuster V, Walsh RA Hurst’s The Heart

Noncontrast CT showing extensive aortic calcification (“porcelain aorta”). A, In the coronal plane, calcification extends from the aortic sinotubular junction to the aortic arch. B, C, Cross-sectional images (at levels indicated by arrows extending from A) from the upper (B) and lower (C) ascending aorta show the circumferential nature of the calcification

STENT PATENCY• Image artifact from metallic stents limits the application in

patients with prior coronary stent procedures. • Small stents are difficult to evaluate .• However, 90% accuracy can be obtained in stents 3 mm or

greater in diameter with the use of sharp kernel and wide display window.

• Quantitative assessment of within-stent contrast density may assist in the diagnosis.

• A contrast density ratio of 0.81 between the stent (proximal, mid-, and distal portions) and the aorta showed a sensitivity of 90.9% and a specificity of 95.2% in-stent stenosis for stents down to 2.5 mm in size.

Abdelkarim MJ, Ahmadi N, Gopal A, et al: J Cardiovasc Comput Tomogr 4:29, 2010

CORONARY CT ANGIOGRAPHY OF A PATENT STENT

A patent coronary stent is noticed in the proximal left anterior descending (LAD) artery on a curved multiplana reformatted (MPR) image with clear demonstration of the intrastent lumen without in-stent restenosis.

Stent imaging with cardiac CT. A, A large stent with uniform contrast attenuation in the lumen, indicating patency. B, A small stent in the left anterior descending artery with another stent in the proximal diagonal branch. Three reconstruction/display settings are shown: a medium-soft kernel, a sharp kernel, and sharp kernel reconstruction displayed with a wide window width. Visualization of in-stent restenosis in the diagonal branch is optimized with the third approach (i.e., sharp kernel, wide window display width).

CORONARY CT ANGIOGRAPHY OF IN-STENT RESTENOSIS

An in-stent restenosis is present at the distal part of the right coronary artery (RCA) stent which is demonstrated as the low-attenuating area on longitudinally straightened (a), curved multiplana reformatted (b) and cross-sectional images (c).

SCAN ARTIFACTS

• High heart rate (>65 beats/min for single-source scanners) can lead to CORONARY MOTION ARTIFACT, particularly within the mid–right coronary artery .

• Respiratory motion artifact can be minimized by holding breath during image acquisition.

• Misalignment of axial image slices arises from positional changes of the heart with patient motion (particularly respiratory motion), ectopic heart beats, or abrupt changes in heart rate during scanning.

• Highly attenuating objects (metallic objects or CAC) can produce an artifact called beam hardening, created by alteration in the energy spectrum of the x-ray beam.

• This artifact can particularly hamper interpretation of coronary plaques with highly dense calcified atherosclerosis.

Multiphase axial images of the right coronary artery showing motion artifact throughout the cardiac cycle including systole (0 to 40% phases) and diastole (50% to 90%). The most motion-free images of the right coronary artery (arrow) are at 40% (end-systole) and 70% (mid-diastole), when cardiac motion is minimized.

Cardiac motion artifact. Top left panel: Three-dimensional (3D) rendering image of a heart with significant motion artifact affecting the interpretation of the distal right coronary artery (RCA). This patient was scanned with a dual-source computed tomography (CT) (temporal resolution of 83 ms), and the heart rate in the time of the scan was 105 beats/min. Top right panel: Maximum-intensity projection (MIP) image of the same patient showing significant transitional motion artifact in the proximal and mid RCA. Bottom left panel: 3D rendering image of a heart without motion artifact showing the distal RCA. The heart rate was 75 beats/min, and the patient was scanned with a dual-source CT. Bottom right panel: MIP image of the same patient showing only slight transitional motion artifact in the mid RCA.

Common imaging artifacts or nondiagnostic imaging on cardiac CT. A, Registration error seen as horizontal lines (arrow) in the image. B, Respiratory motion seen as discontinuity of the sternum. C, Poor contrast opacification of the coronary artery. D, Coronary duplication artifact caused by an ectopic beat. E, Poor signal-to-noise ratio (grainy image) caused by obesity. F, Severe coronary calcification. G, Streak artifact from an implanted biventricular pacemaker .

VENTRICULAR AND VALVULAR MORPHOLOGY AND FUNCTION

• Helical scan acquisitions, allow reconstruction of cardiac CT data from both systolic and diastolic phases enabling evaluation of ventricular systolic function.

• Myocardial morphology also can be reliably assessed for findings of previous MI such as wall thinning, calcification, or fatty myocardial replacement (indicated by negative HU densities within the myocardium).

van der Vleuten PA, Willems TP, Gotte MJ, et al: Quantification of global left ventricular function:. Acta Radiol 47:1049, 2006.

• Cardiac ct also provides highly accurate detection of LV MURAL THROMBI.

• Mural thrombi typically have an attenuation value ranging between 25 and 80 HU (mean, approximately 40 HU) which is below that of surrounding myocardium (typically 70 to 200 HU)

LaBounty TM, Glasofer S, Devereux RB, et al: Comparison of cardiac computed tomographic angiography to transesophageal echocardiography for evaluation of patients with native valvular heart disease. Am J Cardiol 104:1421, 2009.

• ANATOMIC EVALUATION OF CARDIAC VALVES and their motion also is feasible for both native and prosthetic valves.

• Aortic stenosis is characterized by CT in terms of both the extent of valvular calcification and orifice area by planimetry.

• Valve area planimetry is closely related to other invasive and noninvasive determinations in aortic stenosis.

• Cardiac CT performed before TRANSCATHETER AORTIC VALVE REPLACEMENTprovides a more accurate assessment of the aortic annulus area with its oblique nature, determination of optimal angiographic angulations, and detection of potential hazards such as severe aortic root calcification.

• In AORTIC REGURGITATION, malcoaptation of the valve leaflets by greater than 0.75 cm2 is associated with severe aortic regurgitation .

• Prosthetic valve malfunction including size mismatch, tissue ingrowth, or valve thrombosis can be identified.

• Increasingly, cardiac CT imaging in patients with prosthetic valve endocarditis identifies paravalvular leaks , and can provide a preoperative coronary arteriographic assessment when cardiac surgery is anticipated.

• The weakness of cardiac CT for evaluation of valve disorders is the inability to assess hemodynamics, so complementary imaging should include Doppler echocardiography.

LaBounty TM, Agarwal PP, Chughtai A, et al: Hemodynamic and functional assessment of mechanical aortic valves using combined echocardiography and multidetector computed tomography. J Cardiovasc Comput Tomogr 3:161, 2009.

CORONARY ARTERY ANOMALIES

• The diagnosis of coronary artery anomalies has previously required invasive coronary angiography; however, in up to 50% of patients, the coronary artery anomalies may be incorrectly classified during invasive angiography.

• This misclassification may result from the difficulty in delineating the precise vessel path within a complex 3D geometry using a relatively restricted two-dimensional view.

• Coronary CTA has been shown to accurately depict the anomalous vessel origin, its subsequent course, and the relationship to the great vessels.

• Two studies comparing CCTA and invasive coronary angiography found that invasive angiography was able to detect 80% of the anomalous origins but only 53% of the anomalous coronary courses and resulted in a precise anatomic diagnosis in only 55% of patients.

• In a multicenter coronary artery CT registry, CCTA was able to unequivocally demonstrate the origin and the course of the anomalous artery in all patients with equivocal findings on invasive coronary angiography.

Shi H, Aschoff AJ, Brambs HJ, et al. Multislice CT imaging of anomalous coronary arteries. Eur Radiol. 2004;14(12):2172-2181.

Schmitt R, Froehner S, Brunn J, et al. Congenital anomalies of the coronary arteries: imaging with contrast-enhanced, multidetector computed tomography. Eur Radiol. 2005;15(6):1110-1121

Datta J, White CS, Gilkeson RC, et al. Anomalous coronary arteries in adults: depiction at multi-detector row CT angiography. Radiology. 2005;235(3):812-818.

Evaluation of coronary anomaly. A. Three-dimensional (3D) rendering image showing an anomalous left circumflex arising from the right coronary sinus and coursing between the aorta and the left atrium. B. 3D rendering image showing a coronary aneurysm involving the LM, the proximal LAD, and a diagonal branch. LAD, left anterior descending (coronary artery); LM, left main.

PERICARDIAL DISEASES

• The pericardium appears as a thin line (1 to 2 mm) surrounding the heart, usually visible with a small amount of adjacent pericardiaI fat.

• The pericardium normally enhances with contrast administration; hyperenhancement of the pericardium in the appropriate clinical setting is characteristic of pericarditis.

• A pericardial thickness of >4 mm in a patient with abnormal rapid early LV diastolic filling is diagnostic of pericardial constriction.

Diffuse pericardial thickening surrounding the entire heart in a patient with pericardial constriction.

Baim RS, MacDonald IL, Wise DJ, et al. Computed tomography of absent left pericardium. Radiology. 1980;135(1):127-128

1. By CT, congenital absence of the pericardium is easily diagnosed.2. Findings of pericardial constriction on CT include irregular pericardiaI

thickening and calcification, conical or tubular compression of one or both ventricles, enlargement of one or both atria, dilation of the IVC, and a characteristic diastolic bounce of the interventricular septum.

3. Pericardial effusions can be reliably detected by CT. 4. A pericardiaI cyst will appear as a well circumscribed paracardiac mass

with characteristic water attenuation (H.U. = 0), usually in the right costophrenic angle.

5. Both primary neoplasms and, more commonly, metastatic neoplasms can be visualized in the pericardium.

CONGENITAL HEART DISEASE• Cardiac CT and MRI have been increasingly used for the assessment of

congenital heart disease.• Both modalities can be rendered into 3D images that are useful in

clarifying the often complex anatomic relationships in patients with congenital heart disease.

• MRI has limited use in critically ill patients, metallic implants and often mri requires significant sedation .

• Anomalies of the aortic arch, patent ductus arteriosus, tetralogy of Fallot, and abnormal arteriovenous connections can all be carefully evaluated with cardiac CCTA .

• The high spatial resolution of MDCT also permits the evaluation of the atrioventricular valves in conditions such as Ebstein anomaly and tricuspid and mitral valve atresia.

• MDCT can also be used to accurately quantify intracardiac shunts, as well as cardiac masses.

Rius T, Goyenechea M, Poon M. Combined cardiac congenital anomalies assessed by multi-slice spiral computed tomography. Eur Heart J. 2006;27(6):637.

A patient with tetralogy of Fallot with large ventricular septal defect (black arrows), overriding aorta (Ao), and thickened right ventricle (RV).

• Three-dimensional rendering (B) and corresponding maximum-intensity projection (C) images of a patent ductus arteriosus

DISEASES OF AORTAContrast-enhanced MDCT is nearly 100% sensitive and specific forevaluating acute aortic syndromes. 1. Acute aortic dissection is characterized by visualization of a dissection flap

(i.e., separation of the intima from the media) that forms true and false lumens. The CT study can characterize the origin and extent of the dissection, classify it as Type A or B, assess for concomitant aneurysmal aortic dilatation, and identify branch vessels involvement.

2. Aortic intramural hematomas are believed to be caused by spontaneous hemorrhage of the vaso vasorum into the medial layer. They appear as crescent-shaped areas of increased attenuation with eccentric aortic wall thickening. Unlike dissections, hematomas do not spiral around the aorta.

3. Aortic aneurysm is a permanent dilation of the normal aortic caliber(usually greater than 5 cm in the thoracic aorta and greater than 3 cm in the

abdominal aorta). Litmanovich D, Bankier AA, Cantin L, et al. CT and MRI in diseases of the aorta. AJR Am J

Roentgenol. 2009;193(4):928-940.

An aortic dissection starting in the descending thoracic aorta

A, Dissection of the descending aorta (white arrow) in a patient with previous ascending aorta dissection repair (black arrow). Graft material surrounds the aortic root. First-pass contrast attenuation is seen in the true lumen of the descending aorta. B, Aortic intramural hematoma, seen as low-attenuation material in the wall of the ascending and descending segments of the aorta (upper and lower arrows).

PULMONARY EMBOLISM• MDCT can diagnose acute and chronic pulmonary

thromboembolism.• It has replaced nuclear ventilation/perfusion scans as the

primary imaging study in the diagnosis of acute pulmonary embolism.

• The cross-sectional view of the main and proximal right and left pulmonary arteries provides clear delineation of the proximal extent of the thrombi, which is essential for successful surgical treatment.

• Accuracy for the diagnosis of pulmonary embolism using multidetector CT is high, with a negative predictive value of 99% among patients with low to moderate pretest likelihood, although accuracy for the detection of subsegmental pulmonary emboli may be limited.

Quiroz R, Kucher N, Zou KH, et al: Clinical validity of a negative computed tomography scan in patients with suspected pulmonary embolism: A systematic review. JAMA 293:2012, 2005.

Patient with both an aortic dissection evidenced in a dilated aorta and a small pulmonary embolism (black arrow) in the left pulmonary artery (PA).

TRIPLE RULE OUT(TRO) CTA

• Triple rule-out (TRO) CTA can evaluate the coronary arteries, pulmonary arteries, aorta, and intrathoracic structures in selected patients presenting with acute chest pain of unclear etiology.

• The new 64-slice MDCT scanners can provide high-quality TRO CTA studies by tailoring the injection of iodinated contrast to provide simultaneous high levels of arterial enhancement in the coronary arteries and aorta (>300 HU) and in the pulmonary arteries (>200 HU).

Halpern EJ. Triple-rule-out CT angiography for evaluation of acute chest pain and possible acute coronary syndrome. Radiology. 2009;252(2):332-345

• Radiation exposure is minimized by limiting the imaging window to include from the aortic arch down through the heart, rather than encompassing the entire chest.

• In addition, the same imaging parameters, such as prospective gating and current modulation, used in CCTA are incorporated into the TRO CTA to limit ionizing radiation doses to between 5 and 9 mSv.

• When used in the emergency department on appropriately selected patients, TRO CTA can eliminate the need for further diagnostic testing in >75% of patients.

EVALUATION OF PULMONARY VEINS

• In the context of electrophysiology interventions such as pulmonary vein isolation (PVI), preprocedural MDCT can be used to define pulmonary venous anatomy and identify supernumerary veins, and postprocedural MDCT can be used to evaluate for pulmonary vein stenosis.

• Additionally, in the setting of congenital heart disease, CT can be used to identify anomalous pulmonary venous return.

Taylor AJ, Cequeira M, Hodgson J, et al. ACCF/SCCT/ACR/AHA/ASE/ASNC/SCAI/SCMR 2010 appropriate use criteria for cardiac computed tomography. J Am Coll Cardiol. 2010;55

VIABILITY AND PERFUSION IMAGING WITH CT

• Myocardial attenuation reflects relative coronary blood flow on first-pass imaging .

• First-pass CT stress perfusion imaging includes contrast-enhanced CT angiography both at rest and during the administration of adenosine agonists.

• The sensitivity for the detection of significant coronary stenosis ranges from 72% to 98%, with specificity ranging from 71% to 92%, with radiation doses as low as 2.5 mSv using high-pitch helical CT.

• A meta-analysis found an overall pooled sensitivity of 81% and specificity of 93% for this method.

Tashakkor AY, Nicolaou S, Leipsic J, et al: The emerging role of cardiac computed tomography for the assessment of coronary perfusion: A systematic review and meta-analysis. Can J Cardiol

28:413, 2012.

• Late myocardial enhancement imaging with infusion of additional contrast medium and a delay of approximately 10 minutes can be done.

• The kinetics of iodinated contrast material is similar to that of gadolinium, with accumulation within the interstitial space of myocardial fibrosis.

• Under delayed imaging, contrast preferentially accumulates within areas of scarring and can be detected on delayed imaging.

• Delayed enhancement on cardiac CT indicates regions of myocardium with reduced likelihood of functional recovery and patients whose ejection fraction will remain lower after myocardial infarction, particularly when a transmural pattern of delayed enhancement is present.

Sato A, Hiroe M, Nozato T, et al: Early validation study of 64-slice multidetector computed tomography for the assessment of myocardial viability and the prediction of left ventricular remodelling after acute myocardial

infarction. Eur Heart J 29:490, 2008.

• MDCT has the ability to differentiate prior and recent MI based on the tissue density expressed in HU. Prior infarctions have lower CT densities, or more hypoenhancement, compared with recently infarcted areas (44 ± 17 HU vs 63 ± 19 HU).

• As a result of the high spatial resolution of MDCT, it is also possible to distinguish subendocardial from transmural MIs, which provides additional prognostic information.

Wada H, Kobayashi Y, Yasu T, et al. Multi-detector computed tomography for imaging of subendocardial infarction: prediction of wall motion recovery after reperfused anterior myocardial infarction. Circ J. 2004;68(5):512-514.

• Another newer technique is the application of COMPUTATIONAL FFR from resting coronary CT angiographic images.

• Measured from standard first-pass coronary CT angiography its accuracy has been compared with that for invasive measurement of FFR of 0.80 or less.

• In a multicenter trial in 252 patients, overall accuracy was limited at 73%, with sensitivity of 90% and specificity of 54%.

• The technique, still in development, currently requires off-site analysis but has the potential advantage of assessment from routine coronary CT angiograms acquired with the patient at rest. CT fractional flow reserve (FFR) using computational fluid

dynamics. From the invasive coronary angiogram (A), coronary lesions assessed by invasive FFR (B) are correlated with CT-derived FFR (C).

the DeFACTO study. Circ Cardiovasc Imaging 6:881, 2013.

CONTRAINDICATIONS

Absolute Contraindications• Pregnancy• Hypersensitivity to

iodinated contrast agent

Relative Contraindications• H/o allergy to medicines

• Hyperthyroidism

• Renal function impairment

• Congestive heart failure

• H/O thromboembolism

• Atrial Fibrillation

Cardiac arrhythmias, coronary artery stents and tachycardia may result in a reduced image quality

CTA LIMITATIONS

• Rapid (>80 bpm) and irregular HR

• High calcium scores (>800-1000)

• Contrast requirements (Cr > 1.6 mg/dl)

• Small vessels (<1.5 mm) and collaterals

• Obese and uncooperative patients

• Radiation Exposure

WHAT ARE THE BENEFITS VS. RISKS?

• Benefits– CCTA is not invasive. – Able to view bone, soft tissue and blood vessels all

at the same time.– Provides detailed images of many types of tissue.– Fast and simple.

BENEFITS VS. RISKS (CONTD..)

– Less sensitive to patient movement than MRI.– CT can be performed if patient has an implanted

medical device of any kind, unlike MRI.– No radiation remains in a patient's body after a CT

examination.– X-rays used in CT scans doesnot have no

immediate side effects.

• Risks– In patients with abnormal kidney function, the dye

used in CT scanning may worsen kidney function.– Skin damage or damage to blood vessels and nerves

if leaked out from injected vessels.– Slight chance of cancer from excessive exposure to

radiation.– Not recommended for pregnant women unless

medically necessary because of potential risk to the baby in the womb.

BENEFITS VS. RISKS (CONTD..)

– Mothers should not breastfeed their babies for 24-48 hours after contrast medium is given.

– The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare.

BENEFITS VS. RISKS (CONTD..)

CAG VS MDCT

GUIDELINE RECOMMENDATIONS

ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR2010 Appropriate Use Criteria

for Cardiac Computed Tomography. JACC Vol. 56, No. 22, 2010

SUMMARY AND CONCLUSION

• Coronary CT angiography represents the most rapidly developed imaging modality in cardiac imaging.

• Demonstrates high diagnostic accuracy.

• Utilization of coronary CT angiography must be defined in terms of whether it leads to the greatest benefit and whether the radiation risk may be greater than the benefit expected from the CT examinations.

THANK YOU