computed tomography coronary angiogram technique and physical aspect covered ,,,

1. CT - Coronary Angiography
Presenter :- Yashawant Kumar yadav
Bsc MIT 3rd year
National Academy of Medical Science (NAMS) (Bir Hospital )
1

2. Contents
• Glance on Technical advancements of CT .
• Anatomy of cardiac blood circulation .
• CT techniques and protocol for cardiac angiogram
• Radiation dose
• Artefacts in CCTA
• References
2

3. Abbreviation
• CCTA – Coronary computed tomography angiogram
• LCA – Left coronary artery
• LDA – Left descending artery
• LCx – Left circumflex artery
• RCA- Right coronary artery
• PDA- posterior descending artery
• PLA- posterior lateral artery
• CAD – coronary artery disease
• CABG-coronary artery bypass graft
• DSCT- dual source computed tomography
• ECG-CTCM – electrocardiogram controlled tube current modulation
• MPR – Multiplanar Reconstruction
• VR – volume rendered
• MIP – maximum intensity projection 3

4. Why CCTA???
4

5. Advancements
5

6. CT -Coronary Angiography
• Coronary computed tomography
angiography (CCTA) is a noninvasive
technique to detect coronary artery disease,
which is characterized by its high sensitivity
and negative predictive values .
There is significant pre-occlusive thrombotic stenosis at the proximal
short segment of the LAD.
6

7. Temporal resolution
• For motion-free cardiac imaging is 250
msec for heart rates up to 70 beats per
minute and
• up to100 - 150 msec for heart rates greater
than 100 beats per minute.
• Ideally, motion-free imaging for all phases
requires temporal resolution to be around
50 msec (???).
7

8. Anatomy
Left and right coronary artery main supply
Left coronary artery
The left coronary artery (LCA) normally arises
from the left posterior coronary sinus. However,
the LCA can arise from the right (P) coronary
sinus and follow anomalous courses.
The LCA gives rise to the left anterior
descending (LAD) and left circumflex (LCx)
arteries.
8

9. Contd…
• The LAD courses anterolaterally in the
anterior interventricular groove and
supplies the majority of the left
ventricle.
• The branches of the LAD are: ·
a. lateral diagonal branches that supply
the LV free wall ·
b. medial septal branches that supply
the interventricular septum.
• The LCx courses in the left
atrioventricular groove, giving rise to the
obtuse marginal branches.
9

10. Right coronary Artery
10

11. Area of distribution:
LCA
i. Left atrium
ii. Greater pert of left
ventricle & small part of
right ventricle.
iii. Anterior part of
interventricular septum
iv. Left branch of AV node.
RCA
i. Right atrium
ii. Greater part of right ventricle &
small part of left ventricle.
iii. Posterior part of interventricular
septum.
iv. Whole conducting system of
heart except left branch of AV
bundle.
v. SA node (60%) supplied by
RCA.
11

12. Venous drainage
12

13. Dominance
• Determined by the supply of (PDA ) Posterior
descending artery .
• Its also know as posterior interventricular
artery.
• Most hearts are right dominant (80%) where
the PDA is supplied by the RCA.
• However, up to 20% of hearts may be left
dominant, where the PDA is supplied by the
LAD or LCx, or codominant, where a single
or duplicated PDA is supplied by branches of
both the RCA and LAD/LCx (20%)
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15. 15

16. ECG Gating/Triggering
• The oldest and most straightforward way to reduce cardiorespiratory
artifacts is to synchronize CT data acquisition to the cardiac cycles.
• This process is known as gating or triggering. The two terms are often
used interchangeably.
• ECG gating refers to the monitoring, collection, and use of ECG data
before, during, and after the scan acquisition,
• ECG Signal is also used
to modulate tube current .
16

17. • CT of a 53-year-old woman with thymoma.
• The degree of motion artifacts was judged as
fair and good, respectively. The border
between the tumor and pericardium on non-
ECG-gated CT was not clear (open arrow)
because of motion artifacts, while that on
ECG-gated CT was clear (arrow). Blurring
border at the pericardium mimicked irregular
tumor contour on non-ECG-gated CT.
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18. 18

19. 19

20. Contd…
• In some cases, the real-time ECG events during the scan are also used to trigger
data acquisition and drive the scan.
• In other cases, the x-ray tube is turned on by arrival of contrast material in the
ROI.
20

21. ROI (REGION OF INTEREST )
• (ROIs) in the aorta have been adopted
to determine scan timing in CCTA.
• It is common for bolus-tracking
ROIs to be placed in the ascending or
descending aorta to avoid
displacement of the ROIs by breath
movement.(100-150-180HU)
• Increase in CT value in the ROI is
the trigger for the start of imaging.
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22. 22

23. ROI position
• 4-dimensional magnetic resonance imaging (4D-
MRI) studies using the phase contrast method
have revealed that arterial flow velocity is not
uniform along the same axial plane in the aorta.
• Dorsally placed ROI would shorten contrast
arrival time and potentially cause decreased
coronary artery enhancement.
• A new dual-ROI tracker technique has the
potential to improve consistent opacification.
After a first ROI with a threshold of 100 HU
initiates breathing commands, a second ROI with
a higher threshold closer to peak enhancement
(300 HU) triggers the CT scan .
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24. 24

25. C1
• A 46-year-old woman with a dorsally placed ROI. CT values of the proximal
and the distal RCA were 393.6 HU and 355.6 HU, respectively. Contrast arrival
time was 18.65 seconds.
25

26. • A 66-year-old man with a ventrally placed ROI. CT values of the
proximal and the distal RCA were 496.3 HU and 479.0 HU,
respectively. Contrast arrival time was 26.84 seconds. 26

27. 27

28. ECG gated Acquisition Mode
Retrospective ECG gating
• Coronary CT angiography is routinely performed with retrospectively ECG-gated
cardiac CT examination, which indicates that helical CT scanning is performed
while an ECG trace of heart movement is recorded simultaneously.
• Thus, volumetric data are acquired and the acquired data are selected for image
reconstruction based on ECG signal collected along with the attenuation data ,
• Thus ensuring the fewest motion artefacts present in the final reconstructed data.
28

29. Contd…
• Cardiac reconstruction algorithms use ECG data to parse out the data and reconstruct the
images at a single time point within the cardiac cycle, usually late diastole,
• when the heart briefly
comes to rest
( to occur 3/4th of cardiac cycle ).
• Diagram illustrating the
concept of retrospective
scanning.
During helical data
acquisition
29

30. Cond….
• Very low pitch values (0.2– 0.4/0.5) are
typically required for coronary data acquisition
to ensure continuous z-axis coverage between
consecutive cardiac cycles.
• X ray tube is triggered by Increment of CT no.
in ROI
30

31. Contd..
• After detection of the heart rhythm, the scan covers the whole heart during
multiple cardiac cycles.
• Therefore, information from different phases of the cardiac cycle is gained and
used for the reconstruction of still images .
• This is especially useful for cine-sequences which show the heart motion
throughout the cardiac cycle.
• This technique result in higher radiation dose even after dose reduction technique
as compare to prospective ECG gated CCTA .
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32. 32

33. Contd….
• The image reconstruction is performed either with data corresponding to partial
scan data or with multiple segmented reconstruction.
• This results in further improvements in temporal acquisition can range from 80 to
250 msec.
33

34. Prospective ECG Gating
• Prospective ECG-triggering with non-helical scan was used a long time ago with
electron-beam CT for calcium scoring;
• The principle of prospective ECG triggering is that data acquisition only takes
place in the selected cardiac phase.
• X ray tube is triggered by ECG Signal ((i.e., to turn the x-ray tube on at the
beginning of diastasis and off at the end of diastasis).
• Preferably in the mid-diastolic phase, when cardiac motion is minimal.
34

35. • Prospective triggering is also
referred to as sequential data
acquisition with an effective pitch
of 1.0
35

36. • However, it suffers from several limitations.
1. First, it is limited to heart rate less than 70 or
65 beats per minute (bpm).
2. Estimation of the next R-R interval may be
incorrect when heart rate changes are present
such as arrhythmia .
36

37. Contd…
• Temporal resolution with this type of acquisition can range from 200 to
250 msec.
• Prospective triggering is the mode of data acquisition used for calcium
scoring studies.
37

38. Contd…..
• Second, ECG-triggered sequential scan is usually
restricted to scanning with non-overlapping
adjacent slices, or slice increments with only
small overlap Consequently, prospective ECG-
triggering puts high demand on the z-axis
coverage,
• Presence of misalignment due to acquisition of
images in 4-5 heart beats to cover the entire heart
with 64-slice CT is an example of this limitation .
38

39. Reconstruction Method
• High temporal resolution images are obtained by reconstructing the data either
with partial scan reconstruction or with multiple-segment reconstruction.in both
type of technique .
Partial Scan Reconstruction.
• Among the methods of image reconstruction in cardiac CT,
the most practical solution is the partial scan.
• Partial scan reconstruction can be used for both
prospective triggering and retrospective gating acquisitions.
39

40. Multiple-Segment Reconstruction.
• The primary limitation to achieving high temporal resolution with the partial scan
approach is the gantry rotation time.
• To achieve even higher temporal resolution, multiple-segment reconstruction was
developed.
• The principle behind multiple segment reconstruction is that the scan projection
data required to perform a partial scan reconstruction are selected from various
sequential heart cycles instead of from a single heart cycle.
• This is possible only with a retrospective
gating technique and a regular heart rhythm.
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42. 42

43. 43

44. • (a,b) multisegment and (c,d) halfscan
reconstructions.
• Halfscan reconstruction is degraded
by so-called “stair-step” artefacts
(yellow arrows), resulting from an
insufficient temporal resolution of
200 ms.
• In multisegment reconstruction, the
reconstruction window is 93 ms in
width.
44

45. •Can we perform prospective helical scan??
45

46. High-pitch spiral acquisition
• Dual-source CT scanners allow for a gapless acquisition with a pitch of up to 3.4
which cannot be achieved with conventional single-source CT scanners.
• A high-pitch spiral acquisition can be performed in less than one second
(approximately 0.280 s) and thus information from a single heartbeat can be
generated.
• In combination with iterative reconstruction techniques, high-pitch spiral
acquisition allows for cardiac CT with sub-milli Sievert doses.
46

47. Contd…
• The following scan parameters were
used:
• 320 mAs per rotation,
• 100 and 120 kV,
• pitch 3.4 for prospectively ECG-
triggered high-pitch CTCA,
• scan range of 13.5 -14cm,
• collimation 64*2*0.6 mm with z-flying
focal spot,
47

48. Contd…
• The effective whole-body dose of the cardiac scan ranged from 1.1 mSv to
1.6 mSv and from 1.2 to 1.8 mSv for males and females,
48

49. DSCT
49

50. Importance of thin slice
• A, Axial (transverse) plane reconstruction using a
standard computed tomography (CT) slice thickness
(5 mm). Note blurring of edges and loss of detail,
particularly of the coronary arteries (arrow), a result
of volume averaging.
• B, Coronal reformat of the same image set,
demonstrating the stair steps and
blurring (arrows) indicative of a z-axis resolution
that is insufficient for such a reformat.
• C, Axial plane image reconstructed from the same
attenuation data set using 0.5-mm slice thickness and
combining 10 of these thinner cuts to generate a 5-
mm-thick slab (maximum intensity projection). The
same “slice” of anatomy is represented, but now with
improved z-axis resolution, which minimizes the
volume averaging
• D, Coronal reformat of the same, thin-cut image set,
demonstrating much improved z-axis resolution.
50

51. Contd…
• Analysis of coronary CT angiography requires the use of multiple nonaxial plane
reformats, and curved plane reformats, for which high z-axis resolution is an
absolute necessity.
• In multiplanar reformation a straight or curved plane is defined and only the data
in this plane are displayed; this can be used to ‘‘stretch out’’ a vessel and view it
from many angles.
• Volume rendering techniques produce visually pleasing images , but these are
generally only of clinical use in visualizing bypass grafts or coronary anomalies.
51

52. 52

53. • Curved MIP shows critical
stenosis (C) in the proximal LAD.
Further moderate-to-severe (M)
stenosis in the mid-LAD. A stent
(S) is also seen more distally.
53

54. Indications
• Noninvasive evaluation of coronary artery anomalies and other thoracic vessels
• Symptomatic patients with low/moderate probability of coronary artery disease (CAD)
• normal or uninterpretable/non-diagnostic ECG
• normal or equivocal cardiac biomarkers
• moderate risk non-acute symptomatic patients without known heart disease (may be able to
exercise)
• low risk non-acute symptomatic patients without known heart disease (if the patient cannot
exercise or undergo stress test)
• Evaluating the patency of a coronary artery bypass graft (CABG)
• New onset heart failure
• no prior history of CAD, low/intermediate probability
• decreased ejection fraction
54

55. Contd…
• Preoperative assessment of the coronary arteries before noncoronary cardiac
surgery if intermediate risk of CAD
• Discordant ECG and imaging results after stress imaging
• New or worsening symptoms with past normal stress imaging study
• Preoperative assessment for transcatheter aortic valve implantation (TAVI/TAVR)
Its utility is uncertain in some situations:
• High probability coronary artery disease
• Including non-acute symptomatic patients without known heart disease
• Acute chest pain of uncertain cause (angina )
• Evaluation of coronary artery stents >3 mm
55

56. Contraindications
• If the patient is having an acute myocardial infarction (heart attack)
• Screening of asymptomatic patients with low-to-intermediate risk of CAD
• Evaluation of coronary artery stents <3 mm
• Evaluation of asymptomatic patients post CABG (<5 years old) and post stent (<2
years old)
• Contrast related reaction
• Increased intracranial pressure
• calcium scoring either more or in severe range (400)
56

57. Pt. preparation
• Prior to the examination, the patients were asked about their disease history and
their general conditions, and the patients signed the informed consent for CT
angiography.
• Creatinine and urea should be in acceptable range.
• If pt. is on metformin recommend to continue medication after 48hr of
examination
• The most effective renal protection from IV contrast is adequate hydration both
before and after the scan.
• The patients were subjected to breathe training to maintain the heart rate below 80
beats/min.
• An 18 G or 20 G cannula is placed in the right cubital vein , and before the start
of the examination.
57

58. Contd….
• For patients with a rapid heart rate, 25-50 -100
mg metoprolol or atenolol administered under
the supervision of the physician.
• Nitroglycerine A potent vasodilator, which
dilates both normal and abnormal coronary
arteries by relaxing the vascular smooth muscle.
(0.4–0.6 mg) tablet or sublingual spray 2 puff (5
min prior )
• ECG leads are places properly .
58

59. 59

60. Contraindications are :-
• Sinus bradycardia,
• Allergy to the medication
or its constituents;
• Decompensated cardiac
failure; ‘
• Presence of asthma treated
with b-agonist inhaler;
• Active bronchospasm;
• Second - or third-degree
atrioventricular block.
60

61. Contrast media
• Contrast agent: 50-70 mL iopamidol (370 mgl/mL) was used as the contrast
agent. The dosage used was adjusted according to the body mass index (BMI)
(body weight/ height squared, kg/m²) of the patient.
• The intravenous bolus injection of the 50-70 mL contrast agent is administered
into the right cubital vein using a two-tube high-pressure injection syringe at a
flow rate of 5.0 mL/s.(??)
• Next, at the same rate a bolus injection of 20-30 mL saline was administered to
reduce the contrast agent artifacts in the right ventricle and to save the contrast
agent.
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62. 62

63. Multiphasic injection protocol
• Dual-head power injectors have separate reservoirs for
iodine CM and saline and allow injection of CM, saline
or a mixture of both.
• Biphasic protocols usually contain undiluted CM bolus
with volumes ranging from 50 to 120 mL providing
high contrast in the left cardiac chambers, ascending
aorta and coronary arteries followed by a 20–30 mL
saline chaser.
• But (RV) is almost entirely void of CM at the time of
scan acquisition.
• This has the advantage to suppress streak artifacts from
the RV. RV enhancement but during screening coronary
CTA as they hardly detected any RV pathology ..
63

64. Triphasic protocol
• Triphasic injection protocols contain an
undiluted CM bolus, followed by a diluted
contrast chaser and, finally, the saline chaser.
• The dilution of CM can be varied (e.g., 20%
iodine with 80% saline) and provides
diminished right heart cavity attenuation .
• That allows accurate and reproducible
assessment of the RV volumes, anatomic
structures, cardiac disease, and right
ventricular function.
64

65. Contd…
• Scan range: From tracheal bifurcation to the diaphragmatic surface of the heart.
• Scan Direction :- craniocaudal ,,, incase of CABG caudocranial is preferred .
• Scanning protocol: tube voltage 120-135 kV,
• tube current 400-450 mA,
• detector width 16cm (320*0.5 mm),
• field of view FOV-M,
• rotational speed 0.35 -0.275 s/r.
65

66. Contd..
• The CT monitoring level was set to the descending aorta (ROI ). Automatic trigger
of the scan is applied.
• If descending aorta contrast agent threshold 150 Hounsfield Unit (HU)is selected
and ; when this threshold is reached the scan is triggered.
• The patient held his/her breath for approximately 5 s. During the scanning process,
ECG was simultaneously recorded.
66

67. 67

68. Calcium scoring
• When evaluating the heart for potential CAD, usually a nonenhanced calcium scoring
sequence is first performed to assess for coronary artery calcification.
• This low-dose (40-80mAs) technique allows for a detection of calcifications of the
coronary arteries. Although this technique does not give any information about
potential hemodynamically relevant stenoses,
• Agatston score is a semi-automated tool to calculate a score based on the extent
of coronary artery calcification
• patients with a high Agatston score (>160) have an increased risk for a major adverse
cardiac event (MACE) . Although it does not allow for the assessment of soft non-
calcified plaques, it has shown a good correlation with contrast-enhanced CT coronary
angiography
68

69. 69

70. Method of calculation
• The calculation is based on the weighted density score given to the highest attenuation
value (HU) multiplied by the area of the calcification speck.
Density factor
• 130-199 HU: 1 , 200-299 HU: 2 , 300-399 HU: 3 , 400+ HU: 4
• 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.
• The score of every calcified speck is summed up to give the total calcium score.
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 70

71. Delay scan In Post MI ( myocardial infarction)
71

72. • Time course of contrast enhancement in an acute myocardial infarction after intravenous iodine
injection (150 ml )
• a | First-pass image during contrast-agent injection. The signal density of the infarct in the first pass is
substantially lower than that of the remote myocardium.
• b | 5 min after injection, the signal density of the damaged myocardial region is markedly greater than
that of the remote myocardium.
• c | The damaged myocardium still appears bright 10 min after contrast delivery, while signal intensity in
the remote myocardium and in LV chamber is lower.
• d–h | The washout of contrast can be visually appreciated 20 min after contrast injection and is most
apparent in the left ventricular chamber 72

73. Radiation dose in CCTA
• ECG controlled tube current modulation is one of the most effective approach for
dose reduction in CCTA.
• Early effective dose for CCTA is approx. 20-30 mSv reported and by the use of
ECG -CTCM dose was reduced up to 30-50% in 4 and 16 rows of detector system
.
• Later on in 64 rows, DSCT along with ECG - CTCM dose is significantly reduced
up to 10 mSv , radiation dose may vary with Pt. heart rate , low or high heart rate,
with the effective dose being 6.8 and 4.2 mSv, respectively.
• Appropriate use of lower peak kilovoltage values (80 or 100 kVp) for CCTA
examinations can further reduce radiation dose without compromising image
quality.
73

74. Contd…
• Recent studies utilizing DSCT compared a 100 kVp protocol with the routine 120
kVp for coronary CT angiography and demonstrated a dose reduction of 25–54%,
with an estimated effective dose as low as 4.4 mSv
• kVp needed to be correlated with Pt. BMI
• Lowering the tube voltage from 120 to 100 kVp is appropriate when the patient's
BMI is <25 kg m–2.
• Reduction of the tube voltage to 80 kVp should only be considered in children and
slim young adults with a BMI <20 kg m–2.
• Additional dose reductions can be achieved using prospective ECG triggering or
the step-and-shoot method.
• In prospective ECG gating dose is reduced upto80- 90% as compared with
retrospective ECG gating .
74

75. 75

76. On average for (320 RD) prospective 1.2-3mSv
Retrospective 4.4-5mSv 76

77. Artefacts in CCTA
• In cardiac imaging rapidly moving organ arise many unique artifacts ,among
them, the most common artifacts are due to cardiac pulsation …
shows disconnect in the lateral reconstructed image due to pulsation.
77

78. Contd…
These types of artifacts are not observed on axial images but are visible on coronal or sagittal views
78

79. 79

80. Appear on axial
images with no
streak artifact but
are very distinct
and disturbing in
coronal or sagittal
planes
80

81. References
• https://link.springer.com/chapter/10.1007/978-3-642-23508-5_151
• https://www.appliedradiology.com/articles/coronary-ct-angiography
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3479873/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3839169/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6531088/
• https://radiopaedia.org/articles/cardiac-ct-1
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294285/
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5716940/
• Radiopedia cardiac Ct article
• Ct for technologiest.
• https://pubs.rsna.org/doi/full/10.1148/rg.275075045
• https://www.digitmedicine.com/article.asp?issn=2226-
8561;year=2015;volume=1;issue=1;spage=28;epage=33;aulast=Lei
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