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DR RAJESH K F. Cardiac CT and CCTA has emerged as promising noninvasive imaging modality for coronary artery and cardiac structural and functional evaluation.

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Presentation on theme: "DR RAJESH K F. Cardiac CT and CCTA has emerged as promising noninvasive imaging modality for coronary artery and cardiac structural and functional evaluation."— Presentation transcript:

1 DR RAJESH K F

2 Cardiac CT and CCTA has emerged as promising noninvasive imaging modality for coronary artery and cardiac structural and functional evaluation

3 Formation of CT image Three phase process Scanning phase -scan data Reconstruction phase - processes acquired data and forms digital image(pixels) Digital to analog conversion phase - Visible and displayed analog image (shades of gray- Hounsfield units)

4 Sequential mode First scanning mode Scan and step Prospective triggered One complete scan around body while body is not moving Spiral or helical scanning Retrospective gating Body moved continuously as x-ray beam scan around Higher radiation dose

5 SDCT Single detector row helical/spiral CT MDCT Electronically acquire multiple adjacent sections simultaneously

6 Full Scan Reconstruction Full rotation (360 0 ) reconstruct one image Half-scan reconstruction Commonly used in cardiac CT Data from sweep Temporal resolution- half gantry rotation time Multisegment reconstruction For multidetector systems Use <180 0 rotation

7 Temporal resolution Gantry rotation time decreased Temporal resolution correspond to half rotation time Maximum gantry rotation time to 330 msec Temporal resolution is approximately 83 to 165 msec - half- scan reconstruction techniques Image acquisition or reconstruction during periods of limited cardiac motion (end systole to mid-late diastole)

8 Spatial resolution Decreased slice collimation (thickness) Approximately 0.5 mm3 Strengthened X-ray tubes - Reduce image noise Multislice Data in more slices simultaneously From 4 to 64 to 320 per rotation Decreases overall duration of data acquisition, breath hold duration and amount of contrast

9 64-slice scanners High temporal and spatial resolution Gantry rotation times of 420 ms or shorter Spatial resolution of 0.4 by 0.4 by 0.4 mm “state-of-the-art” equipment for CTA Breath hold is 6 to 12 s

10 256 slice CT Spatial and temporal resolution remain unchanged Approx 0.5-mm collimation Increase volume coverage (number of slices) Image heart in single beat Less vulnerable to arrhythmia

11 4-ROW16-ROW64-ROW320-ROW Temporal resolution (half-scan reconstruction) 250 msec210 msec165 msec175 msec Spatial resolution1.25 mm1 mm0.4 mm Volume coverage0.5-3 cm1-2 cm2-4 cm15 cm Breath-hold30-40 sec20 sec10 sec2 sec

12 Dual-source CT Number of slices X-ray tubes and detectors in single gantry at 90° One-quarter rotation of gantry collect data from 180° of projections Temporal resolution is twice of single X-ray tube and detector Reduce motion artifact

13 Thin-slice cardiac CT reconstructions Displayed in any imaging plane

14 Multiplanar imaging Oblique planar views Images displayed in orthogonal planes (axial, coronal, sagittal) or nonstandard planes Analysis of cardiac chambers

15 Maximal intensity projection Thick-slice projections Pixel within slab volume with highest Hounsfield number is viewed Ability to view more structures in single planar view Can obscure details when high-density structures are present (coronary artery calcium)

16 Curved multiplanar reformations Curved structures can be viewed in planar oblique multiplanar reformats Can be used to evaluate entire coronary tree in one view

17 Volume rendered reconstructions Useful for revealing general structural relationships but not for viewing details of coronary anatomy

18 Non-contrast study Refine clinically predicted risk of CHD beyond that predicted by standard cardiac risk factors Used in asymptomatic patients Coronary calcium Present in direct proportion to extent of atherosclerosis Minority (20%) of plaque is calcified

19 3 mm non overlapping thick tomographic slices Average about 50–60 slices From coronary artery ostia to inferior wall of heart Calcium score of every calcification in each coronary artery for all of tomographic slices is summed

20 Hn x-factor (Agatston Scoring) >400 4 Area = 15 mm 2 Peak CT = 450 Score = 15 x 4 = 60 Area = 8 mm 2 Peak CT = 290 Score = 8 x 2 = 16 AGATSTON SCORE = Sum CALCIUM VOLUME SCORING

21 4 calcium score categories Calcium score correlates directly with risk of events and likelihood of obstructive CAD Interscan variability of 10% to 20% 0none 1–99mild 100–400moderate >400severe

22 Coronary calcium presence and extent are dependent on age, gender, ethnicity, and standard cardiac risk factors Calcium scores are higher for age and male gender among whites

23 Data from 13 studies (75,000 patients) during 4 years - calcium score of 0 is associated with a very high event-free probability (99.9% per year)

24 Shaw et al. Radiology 2003; 228: * * * *p<0.001

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26 Helical scan Provide CT data from systole and diastole Can be displayed in cine-loop format Estimation of RVEF, LVEF, volumes and RWMA EF highly accurate

27 Myocardial morphology - wall thinning, calcification or fatty replacement (negative HU densities) Atrial morphology and volume

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29 Anatomic evaluation of cardiac valves and their motion Both native and prosthetic Lack of physiologic valve flow evaluation Prosthetic valve malfunction- size mismatch, tissue ingrowth, and valve thrombosis

30 Severe AR- malcoaptation of leaflets >0.75 cm2 AS- extent of valve calcification and planimetry Planimetry equalent to other invasive and noninvasive methods Aortic valve calcification is directly related to valve area and quantitated by area-density methods

31 Less information concerning tissue type than CMR Lipomas-low CT numbers (< 50 HU) Cysts – water like density (0 to 10 HU) Intracardiac thrombi – (20 to 90 HU) Density values overlap with myocardium Identify thrombi in LAA Poor enhancement of LAA- false-positive result common

32 Embedded in epicardial and pericardial fat-can be delineated in CT Normal thickness-1to 2mm Can clearly delineate pericardial calcification

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34 Visualization of coronary arteries and lumen Excellent tool to investigate coronary artery anomalies Problems Rapid motion Small dimensions of coronary arteries Temporal and spatial resolution of CT

35 Lower heart rate to 60 beats/min - Oral or intravenous BBs Metoprolol 25 to 100 mg orally 1 hour before or IV 5 mg rpt doses Dilate coronary arteries Sublingual nitrates immediately before scanning Nitroglycerin 400 to 800 Microgm Breath hold of 6 to 20 s Depend on scanner generation and dimensions of heart 50 to 120 ml of contrast IV

36 3 to 15 mSv, depending on scan protocol ECG-correlated tube current modulation Reduction of tube current in systole Can reduce radiation exposure by 30% to 50%

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38 Transaxial image

39 2D image reconstruction Maximum intensity projections Facilitate data interpretation Only maximal density values at each point in 3-D volume are displayed

40 2D image reconstruction Curved multiplanar reconstruction Evaluate entire coronary tree in one view

41 3 Dimensional display Visually pleasing Rarely helpful to evaluate data

42 Motion artifact Irregular and fast HR Respiration Limit temporal and spatial resolution Blurr contours of coronaries RCA - most frequently affected

43 Partial volume effect e.g., metal, bone, calcifications Appear bright on image Lead to overestimation of dimensions of high-intensity objects Accuracy for detection of coronary stenoses is lower

44 Streaks and low-density artifacts Adjacent to regions of very high CT density e.g., metal or calcium

45 64-row CTA Overall accuracy Sensitivity of 87% to 99% Specificity of 93% to 96% NPV -93 to 100% ~4% uninterpretable Specificity reduced in calcium scores > 400 to 1000 or obesity (excess image noise) Best for ostial and first centimeter lesions

46 Most studies are limited by selection of patients optimized for cardiac CT and analysis involves only more proximal coronary segments down to 1.5 mm

47 Compared with grading by CAG, CT CAG stenosis severity tends to be worse and correlation is Correlates very well with IVUS (better visualization of arterial wall) >50% stenosis on cardiac CT has 30% to 50% likelihood of demonstrable ischemia on MPI

48 Identification of obstructive CAD did not successfully identify individuals with abnormal MPS Measures of perpatient coronary artery plaque burden, proximity, and location predictive of identifying individuals with abnormal MPS

49 Rapid (>80 bpm) and irregular HR High calcium scores (> ) Stents Contrast requirement Small vessels, distal vessels (<1.5 mm) and collaterals Obese Radiation exposure

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51 2%-6% of patients are erroneously discharged with missed MI CCTA useful in this patient subgroup Highlighting the NPV of CCTA A successful triage tool that may allow safe early discharge of low-risk patients

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54 Sensitivity and specificity - nearly 100% Large size and limited mobility of grafts Limitation in native coronary artery evaluation (metallic clips and calcium) Cardiac structures adjacent or adherent to sternum and grafts cross midline can be seen

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56 Image artifact limits application Accuracy of 90% in stents >3 mm Small stents are difficult to evaluate Dependent on stent design Optimization of reconstruction techniques (sharp kernel) and display characteristics (wide display window)

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