1. Cardiac CT and CT Angiography: Techniques & Clinical Applications
Ethan J Halpern, MD
Director, Cardiac CT
Thomas Jefferson University

2. Cardiac Imaging Technique
Patient Preparation
Contrast Injection
Scan Positioning
mAs and kVp
ECG Gating
Multicycle Reconstruction
Editing of ECG Gating
ECG Gated Dose Modulation
Image reconstruction

3. Patient Preparation Prior to CT
Ask patient to refrain from stimulants (i.e. coffee) on the day of the scan
No solid food for 4 hours prior to the study
Premedicate for asthma & allergic history
Medrol 32mg po 12hrs and 2 hrs prior to study
Patient should have good IV access (18G antecubital)
Adequate EKG tracing – good contact
Patient prep guidelines.
Bullet 1 – Increase heart rate with coffee, the funny story from Wake Forest and the free cappuccino
Bullet 3 – Motivation
Bullet 4 – Decrease the chance of miscommunication
Bullet 5 – Use the right basilic vein is preferred

4. Patient Preparation - Heart Rate
IV Beta Blockade (preferred)
2.5 – 30 mg Metoprolol
Titrate to heart rate of 55-60
Monitor BP while giving metoprolol
If asthmatic, consult physician
No more than 10mg metoprolol
Consider calcium channel blockers
Diltiazem (bolus 0.25mg/kg)
Oral Beta Blocker
50 – 100 mg Metoprolol
1 hour prior to examination
Who will monitor the patient ?

5. Objective of the Contrast Injection
Uniform enhancement of the left heart to greater than 300 HU
Minimize streaking due to contrast in SVC and RV

6. Impact of Iodine Concentration
140cc injection
HU in aorta
Cademartiri F et al. Intravenous Contrast Material Administration at Helical 16–Detector Row CT Coronary Angiography: Effect of Iodine Concentration on Vascular Attenuation. Radiology 236: , 2005

7. Contrast Injection Use high iodine density contrast  350 mgI/mL
We use Optiray 350 (Mallinckrodt Inc.)
16 detector system (25-30 second scan)
cc 4 cc/s
40 4 cc/s
40 detector system (15-20 second scan)
100 cc cc/s
40 cc 5 cc/s
64 detector system (15 second scan)
75 cc cc/s
Start scan 5 seconds after the contrast reaches the left heart
Contrast volume = scan duration * injection rate
Want sufficient contrast to enhance PDA at end of scan

8. Scan Start Position Native coronary arteries Bypass Grafts
Begin above carina
Tortuous aorta or prominent upper left heart border – begin scan 1-2cm higher
Bypass Grafts
Veins: top of arch
LIMA: above clavicles

9. Scan Ending Position Need to image PDA
Note overlap of heart & diaphragm
Observe contour of heart
Extend scan ~2cm below the caudal extent of the heart
Position of heart will change with inspiratory effort

10. Center the Scan on the Heart
Maximize spatial resolution for coronaries
CT resolution is greatest in the center of scan field
Set left-right position on AP scout view
Move table up-down to center on aortic root and Left ventricle

11. Voltage kV 90 kV, 120 kV, 140 kV Cardiac protocols
These values determine the Peak value of X-ray photons.
The effective energy is about half of these values
A higher voltage means:
Lower contrast
Less noise
Higher Patient dose: dose proportional to ~ kV 2.7
Longer recovery time between scans (shorter life)

12. Tube Current: mA/mAs Axial: mAs = mA x Rotation-time/slice
Helix: mAs = mA x (Rotation-time/360°)/ Pitch
For most scanners: tube provides mA
A higher mAs means:
Less noise: noise proportional to 1/(mAs)0.5
Higher Patient dose: dose proportional to mAs
Larger X-ray tube damage/scan
Longer recovery time between scans

13. Scan Parameters kVp mAs Pitch Generally set at 120kVp
For heavy patients (>200lbs) use 140kVp
For patients with calcified arteries and stents also use 140kVp
mAs
Effective mAs = mA x (rotation time / pitch)
Effective mAs in the range of
Increase for heavy patients to minimize noise
Pitch
Generally , but adjust for heart rate

14. EKG Gating Coronary CTA requires EKG gating to overcome cardiac motion
Heart is most quiescent in mid-diastole and end-systole
Best time for reconstruction
70-80% of R-R interval for LAD, CRX
70-80 or 40% for RCA
Single cycle vs. multicycle

15. EKG Based Techniques Fixed time offset Percentage of R-R interval
Example: 500 ms after R peak
Window centered at 500 ms
Percentage of R-R interval
Example: 60% of R-R interval
For 60 bpm, R-R interval = 1000 ms
Window centered at 600 ms
500
600

16. Heart rate variation during CTA Diastole varies in length
58 bpm
r-r interval = 1021 msec
r-t interval = 258 msec
70%
79 bpm
r-r interval = 757 msec
r-t interval = 230 msec
Timing of Intervals in
Different Heart Rates
Systole remains stable
Changes in heart rate primarily effect diastole
104 bpm
r-r interval = 576 msec
r-t interval = 204 msec

17. Consistent Phase Selection Beat-to-Beat Variable Delay Algorithm
58 bpm
r-r interval = 1021 msec
r-t interval = 258 msec
70%
Fixed time and percent of R-R may not pick a consistent phase
Beat-to-Beat variable delay algorithm
Always pick same percentage delay in diastole
Improves image quality
79 bpm
r-r interval = 757 msec
r-t interval = 230 msec
104 bpm
r-r interval = 576 msec
r-t interval = 204 msec

18. Single Cycle Reconstruction
Single Heart beat
Uses 180o per heart beat
Temporal Res = (rot time)/2

19. Multi-Cycle Reconstruction
Combine a portion of projections from one heart cycle with a portion of projections from another to make the full 1800.
Improves temporal resolution, because each segment of data covers the same (smaller) region in time.

20. Single Cycle vs. Multicycle
Stenosis= 50%
Single Cycle
Multicycle
Nonassessable
21% (28/136)
2% (3/136)
Sensitivity
74% (31/42)
88% (37/42)
Specificity
71% (67/94)
91% (86/94)
PPV
84% (31/37)
NPV
94% (67/71)
95% (86/91)
Accuracy
72% (98/136)
90% (123/136)
Toshiba Aquilion 16-slice: 27/34 patients with HR>65
Dewey et al. Investigative Radiol 39: , 2004

21. Temporal Window & Heart Rate
% phase
____ 80% phase
+__+ multicycle
reconstruction
Hoffmann MHK: Radiology 234:86-97, 2005

22. Image Quality & Heart Rate
Hoffmann MHK: Radiology 234:86-97, 2005

23. Correction of Gating Errors

24. EKG Dose Modulation Best images obtained at mid-diastole
RCA sometimes is best at end-systole
Dose modulation can achieve dose reduction of 40-50%
Use only with stable heart rate
Limitations
Cannot review coronary anatomy at end-systole
Cannot correct for errors in gating

25. Image Reconstruction Reconstruction slice thickness
3mm for function
mm for coronary arteries
mm for photon limited scans
Reconstruction kernel
Sharper kernel: noisier image, but may be required to visualize coronary lumen with stents and calcified vessels

26. Slice thickness vs. noise
A thicker slice from 0.8mm to 1.0mm decreases noise and makes the images less grainy.
0.8mm
1.0mm

27. Reconstruction filter vs. noise
Filters vs. noise: CA is the smoothest.
CB gives you the higher standard deviation and noise. This filter is usually the best choice.
Girth is size of the patient in diameter.
Girth 0 = 32cm
Girth 1 = 37cm
Girth 2 = 42 cm
20 – 25 or below looks better visually with less noise for slice thickness and mAs. .

28. Reconstructions Choose appropriate filter
Sharper filter for patients with heavy coronary calcium or stents
Perform targeted reconstructions
3mm reconstruction of contiguous slices @ 10 phases for cardiac function analysis
0.8mm reconstruction of overlapping 40%, 70%, 75% and 80% for coronary anatomy. 1.0mm recons for heavy patients.

29. Clinical Application of Coronary CTA
Indications
Rendering & display modes
Characterization of Plaque
Grading of stenosis

30. Cardiac Indications
The MDCT angiography of the chest for cardiac assessment (0146T-0149T) is indicated for the following signs or symptoms of disease:
Emergency evaluation of acute chest pain
Cardiac evaluation of a patient with chest pain syndrome (e.g. anginal equivalent, angina), who is not a candidate for cardiac catheterization
Management of a symptomatic patient with known coronary artery disease (e.g., post-stent, post CABG) when the results of the MDCT may guide the decision for repeat invasive intervention
Assessment of suspected congenital anomalies of coronary circulation

31. Rendering Modes MIP & slab MIP Surface Display Vessel tracking
Curved MIP
Globe view

32. Plaque Characterization
Calcified vs. Soft
Positive remodeling
Irregularity
Ulceration

33. Grading of Stenosis
Leber AW et al. Quantification of Obstructive and Nonobstructive Coronary Lesions by 64-Slice Computed Tomography: A Comparative Study With Quantitative Coronary Angiography and Intravascular Ultrasound JACC 46(1):147-54, 2005

34. Bland-Altman Analysis of Stenosis Grading
Dashed lines % CI
Hoffmann: JAMA, Volume 293(20).May 25, –2478

35. Impact of Calcified Vessels on detection of stenosis >50%
Calcium score
Cutpoint = 55
CTA: 1310 segs
Low CS pts
Sens = 90%
Spec = 92%
High CS pts
Sens = 97%
Spec = 91%
Low CS
High CS
Age
57 +/-10
58 +/-11
Male/female
55/5
Heart rate
57 +/-7
58 +/-7
Calcium score
14 +/-16
578 +/-716
Weight (kg)
70 +/-6
72 +/-8
Cademartiri F et al. Impact of coronary calcium score on diagnostic accuracy for the detection of significant coronary stenosis with multislice computed tomography angiography. American Journal of Cardiology. 95(10):1225-7, 2005

36. Impact of Coronary Calcium
All segments
Ca Score < 1000
Patients 60 46
Segments
780
598
True positive 54 39
False positive 21 10
Sensitivity
72%
98%
Specificity
97%
PPV
80%
NPV
100%
Kuettner A et al. Noninvasive detection of coronary lesions using 16-detector multislice spiral computed tomography technology: initial clinical results. JACC 44(6):1230-7, 2004.

37. Proximal versus Distal Segments
All segments
Proximal segs
Patients 33
Segments
530
438
True positive 34 27
False positive 19 13
Sensitivity
63%
82%
Specificity
96%
93%
PPV
64%
68%
NPV
97%
Hoffmann F et al., Predictive value of 16-slice multidetector spiral computed tomography to detect significant obstructive coronary artery disease in patients at high risk for coronary artery disease patient-versus segment-based analysis. Circulation 110: 2638–2643.

38. Non-coronary Assessment
Valvular assessment
Cardiac morphology
Cardiac function
EP planning