This document discusses the evolution and advances in coronary CT angiography (CCTA) technology and its role in the assessment of coronary artery disease (CAD). Key points include: - CCTA has advanced from early CT scanners with 4-minute scan times to modern multi-detector scanners that can image the entire heart in a single heartbeat. - CCTA provides information on coronary artery anatomy, plaque characteristics, and has prognostic value when assessing coronary artery calcium scoring. - CCTA has good accuracy for detecting CAD compared to invasive coronary angiography, especially for ruling out disease, though its role in asymptomatic patients is still unclear. - CCTA is useful for evaluating coronary anomalies, bypass grafts,

1. Coronary CT Angiography
Role in CAD
Dr. Shashank Pandey
Dept of Cardiology SGPGI, Lucknow

2. Evolution of Coronary CT
# CT was first introduced by Sir Godfrey Hounsfield in the
1970s—a short 30 yr ago.(image time 4 min)
# In the early 1980s, EBCT scanners moved CT into
the realm of cardiac imaging.(image time 1 sec )
# In the late1990s, spiral CT scanners moved CT into
the coronary artery imaging.(image time 200ms)

3. Evolution of coronary
CT……
The coronary arteries move independently throughout the
cardiac cycle and even at slow heart rates
# Exhibit significant translational motion
- 60 mm/sec for the right coronary artery
- 20 to 40 mm/sec for the left anterior descending
- 20 to 50 mm/sec and circumflex coronary arteries
# Image acquisition < 50 msec is required to completely
avoid cardiac motion artifacts.

5. Advances in CT Technology
# Introduction of 64-row, 128 row 256-row and 320-row
single-source systems, and the use of 128 row DSCT.
- faster acquisition (< 200 ms)
- thinner slices(0.5- 0.6 mm)
- high-performance multiplane imaging
- Single-breath acquisition
- Reduction in radiation by 1-4 mSv
Dewey M, Zimmermann E, Deissenrieder F, et al. Circulation. 2009;120:867–875.

6. 4 to 64 Slice Scans
Five Heart Beats
10 mm detector
3 cm in 5 sec
20 mm detector
6.2 cm in 5 sec
40 mm detector
12.5 cm in 5 sec

7. Advances Continue......
• significantly reduce the amount of contrast agent
• 256 & 320-row can image the entire heart during a
single heartbeat.
• Does not improve spatial or temporal resolution above
that provided by 64-channel scanners.

8. Advances Continue......
# prospectively ECG-triggered data acquisition with the
application of radiation only during a predetermined
interval of the cardiac cycle (ordinarily diastole).
Vs
# Retrospective ECG-gating- Continuous CT acquisition
centred over the heart is synchronized with simultaneous
ECG recording and retrospective image reconstruction.
Earls JP, Berman EL, Urban BA, et al. Prospectively gated... circulation2008;246:742–753

9. Advances Continue......
# 3D postprocessing provides information on
- anatomy of coronary arteries
- 3-dimensional relations of the vessels

10. Coronary Artery Calcium (CAC)
• Non contrast image acquisition.
• Prospective ECG triggered scan.
• From bifurcation of MPA to apex.
• 2.5 – 3 mm slice thickness, 120 KVp tube voltage.
• No beta blockade.
• Scan time of 3-5 secs.
• Radiation dose 1-2 mSv.
• Agatston score: quantifies CAC, as a function of CAC
surface area and density (lesions > 130 HU).

11. Density converion
factor
130-199 HU 1
200-299 HU 2
300-399 HU 3
>400 HU 4
Area = 15 mm2
Peak CT = 450 HU
Score = 15 x 4 = 60
Area = 8 mm2
Peak CT = 290 HU
Score = 8 x 2 = 16
Total Score = S
Agatston Score
1-10: minimal, 11-100: mild, 101-400: moderate, >400: severe

12. Coronary Calcium Scoring
# The presence of CAC is clearly indicative of coronary
atherosclerosis.
# CACS severity extent of atherosclerotic plaque.
# Stenosis severity total CAC.
# CAC > 0 – definite atherosclerosis.
normal coronaries
# CAC 0
non calcified plaque.

13. CACS: Prognostic implications
• CACS – strong independent predictor of mortality, 43%
additional predictive value. (Shaw et al, Radiology, 2003)
• CAC Score = 0 provides a warranty period for CV events.
Warranty period relates to <1% annual mortality rate.
Valenti v et al, jacc cardiovasc imaging 2015;8;900-9

14. Slow progression of CACS 0 to greater than 0
predictable clinical outcomes
Warranty period
• More accurate risk assessment than traditional risk
factors in asymptomatic patients.
• Measure of overall vascular atherosclerotic burden.
• Independent predictor of cerebrovascular risk, AF,
stroke and CHF. (MESA study)
• Screening modality with excellent sensitivity and
negative predictive value.

15. CAC progression
• Can be used to see response to treatment.
• Shows effect of cholesterol lowering on atherosclerosis
progression.
Study groups Mean calcium volume score
No treatment +52% ± 36%
Statin (LDL >120) +25% ± 22%
Statin (LDL < 120) -7% ± 23%
Callister et al. Radiology, 1998
• Post hoc analysis of 8 IVUS based studies showed
paradoxical relation between coronary calcium and
atheroma volume in patients treated with statin therapy.
promotes coronary calification
• High intensity statin
regresses atheroma volume

16. Appropriate use criteria
ACC/ AHA 2013 AUC considers calcium scoring as may be
appropriate for
- asymptomatic patients with:
o intermediate/ high global CHD risk
o With or without interpretable ECG
o Able to exercise or not.
ACC/ AHA 2013 cholesterol and risk guidelines recommend
CAC as class IIB for adults, age 40-75 with no ASCVD, LDL
70-189 and 10 year ASCVD risk < 7.5% to determine need
for statin treatment.

17. CORONARY CT ANGIOGRAPHY

18. TECHNIQUE
• >64 slice CT is appropriate for coronary imaging.
• ECG gating can be prospective or retrospective
• In prospective gating, data is acquired at prespecified phase of
cardiac cycle (mid diastole or end systole), radiation exposure is
less (2-6 mSv) but functional assessment is not possible.
• In retrospective gating, data is acquired through entire cardiac
cycle and only data during least cardiac motion is used to
reconstruct images, radition exposure in high (6-20 mSv).
• Radioiodine contrast is used, 50-100ml.
• Bolus tracking is used to time acquisition after contrast injection.

19. Patient preparation
• Heart rate control (<60/min) with beta blockers or ivabradine.
• Caffeine/ nicotine to be restricted 12 hours before examination.
• No food intake 4 hrs before study.
• Clear fluids and water intake up until the study is promoted.
• Premedication for contrast allergy, if there is a history.
• Metformin to be discontinued for 48 hrs after examination.
• Sublingual nitrates few minutes before the study is
recommended in patients without contraindication, to improve
visualization of coronary arteries.

20. Suspected stable CAD
• Most obvious indication of CCTA- to exclude CAD in
symptomatic pts with low/ intermediate pretest probability.
• Also in patients with low/ intermediate pretest probablity of CAD
 With new onset heart failure.
 Patients undergoing noncoronary cardiac surgery.
• A meta-analysis of 30 studies (2005-2013), CCTA was
compared to ICA (invasive coronary angiography) as reference
gold standard, sensitivity- 93.9% and specificity- 79.2%
• It has excellent negative predictive value, but role in
asymptomtic patients is not clear.
• CCTA should not be used as 1st line investigation for exclusion
of CAD in patients with high pretest probability of CAD.

23. Suspected ACS
• Alternative to ICA in patients with suspected ACS having low/
intermediate pretest probability, when ECG is normal/
nondiagnostic and cardiac biomarkers are normal/ equivocal.
• CT-STAT, ACRIN-PA and ROMICAT II trials have confirmed
safety of negative CCTA study in identifying patients for
discharge from ED with very low rate of MACE.

24. Coronary plaque morphology
• Atherosclerotic plaque starts accumulating long before
development of luminal stenosis.
• Early stages are typically associated with outer expansion of
arterial wall (positive remodelling)
• This early stage is associated with increased risk of CV
events.
• CCTA assesses luminal dimensions as well as arterial wall.
Hence detects positive remodelling, usually not visualized by
ICA.
• Remodelling index EEM at the site of plaque
EEM at adjacent reference site
• Remodelling index > 1 suggests positive remodelling.

25. Positive arterial remodelling

26. • Coronary plaques are classified based on density:
>130 HU – calcified plaque
<130 HU – non calcified plaque.
• Non calcified plaque can be further subcategorised as
70-130 HU – fibrous rich
<70 HU – lipid rich
<30 HU – low attenuation plaque
• Low attenuation plaque (LAP) is seen more often in
patients with ACS than those with stable CAD.
• LAP is more often associated with ruptured fibrous cap
of culprit lesion and correlates to necrotic lipid core on
IVUS studies.
Coronary plaque morphology

28. • Effect of calcification on plaque instability is
controversial,
• Heavily calcified plaques are relatively stable
• Plaques with small (<1 mm) spotty calcification are
associated with accelerated disease progression.
Coronary plaque morphology

29. • Napkin ring sign- refers to specific CT feature of plaque
with large necrotic core and represents reliable marker of
plaque instability,
• Qualitative plaque feature defined in a non calcified plaque
cross section by two features:
1. Central area of low CT attenuation that is apparantly in
contact with lumen.
2. Ring like higher attenuation plaque tissue surrounding
this central area.
Coronary plaque morphology

30. Two large, predominantly non calcified plaques in proximal RCA
Napkin ring sign with histological evidence of necrotic core and spotty calcification

31. CCTA in coronary anomalies
• Clinically imoprtant, ACAOS with inter arterial course is the
coronary anomaly associated with SCD.
• Upto 50% of coronary anomalies can be incorrectly classified
using ICA alone (3D geometry in 2D view).
• CCTA accurately depicts anomalous vessel origin, its
subsequent course and relationship to great vessel.
• CCTA preferable to ICA for diagnosis of coronary anomalies,
given its superior efficacy.

32. Inter arterial course of anomalous RCA originating from left sinus

33. Assessment of bypass grafts
• Imaging of venous grafts is easy compared to native
coronary arteries because of larger diameter and less
mobility.
• IMA grafts can be difficult to image due to artefacts
caused by metal clips and smaller diameter.
• Diagnostic performance of graft stenosis/ occulsion by
CCTA is usually excellent with sensitivity and
specificity > 95%.
• Imaging of native coronaries in grafted patients is very
difficult due to pronounced atherosclerosis and severe
calcification.

34. Normal LIMA to LAD graft (arrow)
Normal venous graft to OM

35. Asssessment of coronary stent
• Several artefacts can complicate evaluation of coronary
stents:
 Beam hardening – virtual loss of CT density along the
stent and black streaks may occur in vessel lumen.
 Partial volume artefact- loss of sharp edge delineating the
stent and lumen.
• Thinner slice and shaper kernel reconstruction improves in
stent resolution.
• Overall, diagnostic accuracy is better in stents > 3 mm and
stents with thinner struts.
• A systematic review of CCTA with 16 slice or more MDCT
showed moderate sensitivity (85%) and high specificity (97%)
for detection of ISR compared to ICA.

37. COST-EFFECTIVENESS OF
CCTA
- CCTA is the most cost-effective approach for individuals
with low and intermediate pretest likelihood of CAD.
- For patients with a pretest probability of CAD greater than
60%, conventional coronary angiography remains more
cost-effective.
Carl et al ; CARJ Vol 58, No 2, April 2007

38. Limitations and Pitfalls of CT
Coronary Angiography
• Rapid (>80 bpm) and irregular HR
• High calcium scores (>400-1000)
• Stents
• Contrast administration in kidney disease.
• Small vessels (<1.5 mm) and collaterals
• Obese and uncooperative patients

41. Appropriate use criteria (AUC)
for CCTA
1 . Technical parameters
- performed on multidetector-row scanners include
CT equipment enabling 64 or more slices
- sub-millimeter spatial resolution
- gantry rotation time no greater than 420 msec.
- Appropriate computer software must be available
for image analysis
Taylor AJ, Cerqueira M, Hodgson J, et al:ACCF/SCCT/ACR/AHA/ASE/ASNC/SCMR 2010 AUC for cardiac CT. JACC 56:1864, 2010.

42. Appropriate use criteria (AUC)
- Regular heart rate and rhythm
- Body mass index below 40 kg/m2
- Normal renal function
- Ability to hold still and to follow breathing
instructions
- Tolerate beta blockers & sublingual nitroglycerin
- To lift both arms above the shoulders
2 . Patient selection
Taylor AJ, Cerqueira M, Hodgson J, et al:ACCF/SCCT/ACR/AHA/ASE/ASNC/SCMR 2010 AUC for cardiac CT. JACC 56:1864, 2010.

43. Appropriate use criteria
(AUC) ..
Diagnostic Impact of Coronary Calcium on the Decision
to Perform Contrast CT Angiography in Symptomatic
Patients
Coronary calcium score <100 A
Coronary calcium score 100-400 A
Coronary calcium score 401-1000 U
Coronary calcium score >1000 U

44. Appropriate use criteria (AUC)
Detection of CAD in Symptomatic Patients Without Known Heart Disease
Non-Acute Symptoms Possibly Representing an Ischemic Equivalent
1. ECG interpretable and able to exercise Intermediate A
2. ECG uninterpretable or unable to exercise Low A
3. ECG uninterpretable or unable to exercise Intermediate A
Taylor AJ, Cerqueira M, Hodgson J, et al:ACCF/SCCT/ACR/AHA/ASE/ASNC/SCMR 2010 AUC for cardiac CT. JACC 56:1864, 2010.

45. Appropriate use criteria (AUC)
..
Acute Symptoms with Suspicion of Acute Coronary Syndrome (Urgent
Presentation)
Normal ECG and cardiac biomarkers Low A
Normal ECG and cardiac biomarkers Intermediate A
ECG uninterpretable Low A
ECG uninterpretable Intermediate A
Nondiagnostic electrocardiogram or equivocal cardiac
biomarkers
Low A
Nondiagnostic electrocardiogram or equivocal cardiac
biomarkers
Intermediate A
Taylor AJ, Cerqueira M, Hodgson J, et al:ACCF/SCCT/ACR/AHA/ASE/ASNC/SCMR 2010 AUC for cardiac CT. JACC 56:1864, 2010.

46. Appropriate use criteria (AUC)
# CT angiography is appropriate-
: in heart failure, with reduced left ventricular ejection fraction
with low or intermediate pretest CAD probability.
: patients undergoing heart surgery for noncoronary
indications (e.g., valve replacement surgery ) when the
pretest CAD risk is intermediate.
: The evaluation of coronary stents is considered as a function of
patient symptom status, time from revascularization, and stent
size. Only with larger stents (≥3 mm in diameter) and only
with left main stents. after long time periods (≥2 years) is stent
imaging considered uncertain.
: Evaluation of graft patency after coronary bypass surgery in
symptomatic patients.
Taylor AJ, Cerqueira M, Hodgson J, et al:ACCF/SCCT/ACR/AHA/ASE/ASNC/SCMR 2010 AUC for cardiac CT. JACC 56:1864, 2010.

47. Physiologic assessment of CAD
• Anatomic and physiologic testing for CAD is
complimentary.
• Presence of lesions causing
 Ischemia without significant stenosis (IWOS)
 Significant stenosis without ischemia (SWOI)
• Important for identification and exclusion of actionable
CAD that may benefit from revascularization.

48. CT- MPI
• Requires 2 CT acquisitions:
1. Rest MPI and CCTA
2. Vasodilator induced stress MPI
• Heart rate lowering required only for rest scan.
• Both rest study after stress and stress after rest
feasible, but latter is cost effective.
• Adenosine, dipyridamole and regadenoson (single
injection) can be used for vasodilatation.

49. A 60 yr old man with diabetes, dyslipidemia, hypertension and a prior
LAD stent presented with chest pain.

50. CT-FFR
• Goal is to identify lesion specific ischemia i.e physiologically
significant stenosis.
• Non invasive calculation of FFR
 without modification of imaging acquisition protocols.
 without additional imaging/ radiation.
 without need of vasodilators.
• Coronary fluid pressure, velocity and flow is calculated.
• Application of computational fluid dynamics (CFD), based on
law of mass conservation and momentum balance.
• Simulated model of effect of adenosine is used, estimating
the maximal hyperemia state.

51. (A). CT- FFR in LAD was 0.72. Invasive coronary angiography and FFR
confirmed functionally significant stenosis. (B). CT-FFR demonstrates
no ischemia in LAD after virtual stenting, with computed value 0.86.
Invasive FFR after stent implantation 0.90

52. Important trials
 NXT trial
• FFR CT with CCTA Vs ICA, reference standard- invasive FFR
• 240 patients with CCTA stenosis 30-90%
• Area under ROC for FFR CT- 0.90 Vs CCTA- 0.81
• FFR CT was also superior in diagnostic accuracy for lesion specific
ischemia compared to diameter stenosis by ICA.

53. Limitations of FFR CT
• Significant motion, beam hardening from calcified
lesions and artefacts from irregular breathing can affect
image quality.
• Irregular/ high heart rate and high BMI can affect image
quality.
• Often takes several hours.
• Most literature is from data on intermediate risk
patients.