Paediatric cardiothoracic CTA
Indications,
Technique
And Relevant Anatomy
Gerhard van der Westhuizen
Medical officer, Radiology
3 Military hospital
12 October 2012
Introduction
• MDCT has revolutionised angiographic evaluation of the heart
and thoracic vessels.
▫ Faster scan times
▫ Increased anatomical coverage
▫ High quality reconstructions
• Previous scanning issues in children included:
▫ Breath-holding ability (motion artifacts)
▫ Slow scan times causing difficulties in administation of contrast
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Small gauge IV catheters
Difficult sites
Manual administration
Short distances between central line and heart.
Comparison of thoracic imaging techniques
• Echocadiography
▫ CTA more global assessment of cardiovascular structures
(pulmonary arteries, anterior mediastinum, thoracic aorta
etc).
▫ CTA also includes airway and lung parenchyma.
▫ Sedation needed with echocardiography, not always needed
with CTA.
▫ CTA is quicker, less operator dependent.
▫ Costs the same.
▫ CTA limited functional information, less portable, poorer
temporal resolution and RADIATION .
▫ IV access not required with echo.
Comparison of thoracic imaging techniques
• MR angiography
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Less need for sedation with CTA.
CTA is quicker.
Thermal stability (esp. Neonates – out of incubator).
CTA can be performed immediately post-op, no metal
issues.
▫ No radiation with MRI.
Comparison of thoracic imaging techniques
• Heart catheterisation
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Better physiologic and functional information.
Only intracardiac and intravacular anatomical detail.
Biplane compared to 3D options with CTA.
Radiation dose usually higher with catheterisation.
Sedation needed.
More expensive than CTA.
Technically more difficult.
Dose comparison
• Study compared conventional chest CT, CTA,
Gated CTA and conventional angiography:
(Frush, Yoshizumi; 2006)
• Average dose in children:
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Conventional chest CT
CTA
Gated CTA
Conventional angiography
1.0 to 4.0 mSv
1.0 to 4.0 mSv
7.0 to 25 mSv
5.0 to 20 mSv
Indications
• Detection of disease or pathology
▫ i.e. Diagnosis
• Improve clinical decision making
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▫ Need for other diagnostic testing
▫ Use of specific intervention
No role in defining normal anatomy
No role in assessing function
Not a screening tool
Specific disease states
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Extracardiac great vessel anomalies
Intracardiac shunt lesions
Post-operative anatomy
Most often used for congenital heart lesions
Trauma
CTA technique
• Preperation
▫ Ask clinician to list specific questions to adress
 ? Vascular anomalies
 ? Major airways, lung aeration
 ? Mediastinal abnormalities – Collections, infection
etc.
 ? Status of upper abdomen – situs abnormalities/
abscence of spleen
 Less frequent ‘protocol’ scanning than in adults
CTA technique
• Example: Scan onset differs for conditions like
caval-to-pulmonary artery connection compared
to systemic arterial-to-pulmonary artery
connection.
• Artifacts: Coils, stents, clips, valves, septal
occluders, pacing wires etc. Know about them
before the scan!
CTA technique
• Preperation
▫ Sedation
 Mostly needed for 1-2 year age group
 Can be performed by other health care providers
 If child is intubated – as quickly as possible during
inspiration
 Quiet breathing also acceptable
CTA technique
• IV access – Type
▫ 20 or 22 gauge peripheral
▫ 24 gauge can also provide adequate information
▫ Long extension tubing – small contrast volume
may remain in ‘dead space’ if not flushed.
▫ Contrast volume may be less than 5 ml and 1-2 ml
in ‘dead space’ is significant.
CTA technique
• IV access – Location
▫ Distance from heart – peripheral line in infant
same distance as central line in adults.
▫ Anterior mediastinum – use right arm or lower
extremity (less streak artifact from left
brachiocephalic vein).
▫ Difference in evaluating IVC inflow for Fontan
procedure (use lower limb or delayed scan) to
evaluating pulmonary stenosis.
CTA tecnique
• Avoid artifacts
▫ Remove leads and wires from chest surface
▫ Careful not to have watches/jewelry in gantry
when injecting manually.
CTA technique
• IV contrast
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Type
Volume
Rate
Route
Method
Onset of scanning
CTA technique
• Type
▫ Low or isosmolar
▫ 300mg I/ml concentration
▫ 370mg I/ml if total volume is an issue (rarely)
• Volume
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MDCT lower dose
1.5ml/kg
Max of 3 ml/kg
(Cardiac catheterisation uses 5-6ml/kg)
These doses are beneficial if repeat scanning is needed
CTA technique
• Rate
CTA technique
• Route
▫ Peripheral or central
 With central – opacification of pulmonary arteries almost
instantaneous.
 NB to know where tip of catheter is.
 Hardware delays may lead to missing peak opacification with
small contrast volumes.
• Method
▫ Contrast pump whenever possible
 Not with 24-G, positional lines, poor backflow or lines on distal
forearm, hands or feet.
▫ Manual
 Unpredictable enhancement, average rate of 1.5 ml/sec
 Extravation detectors not used due to low amount of contrast used.
CTA technique
• Onset of scanning
▫ MDCT has obviated much of the calculation required
▫ Possible to scan too early or too late
 Too early – Rapid scanning time
 Too late – Small volume of contrast, high cardiac
output (shot period of optimal enhancement)
▫ Three techniques:
 1. Empiric delay
 2. Bolus tracking
 3. Test bolus
CTA technique
• 1. Empiric delay
▫ Paeds: 10-20 sec
▫ Neonates: 4-10 sec
• 2. Bolus tracking
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“Smartprep”
Serial enhancement at a preselected level
10 mA (minimum tube mA)
At level of vessel/structure most critical for evaluation
Mostly at mid-ventricular level
Difference of 5-7 sec between actual enhancement and when
scanning begins (software and hardware delays)
▫ Counteract this by:
 Monitor interval of 1.0 sec
 Inject only after first monitoring image shows
CTA technique
• 2. Bolus tracking (cont.)
▫ Steps:
 1. Start bolus tracking display of monitoring images
 2. Start contrast injection after 1st monitoring image
appears
 3. Start diagnostic scanning when opacification of
desired structures begins or just prior to (more
guesswork required)
 4. Stop contrast injection if scanning is complete
before entire volume is given
CTA technique
• 3. Test bolus
▫ Small volume (0.5 – 1.0ml) given
▫ Time from injection to opacification of desired
structure then use with diagnostic scan with full
contrast bolus.
• Onset of scanning is a critical step in CTA!
▫ With evaluation of pulmonary arteries start
scanning when right ventricle starts opacifying.
▫ Start scanning when left ventricle starts opacifying
for evaluation of aorta.
CTA technique
• Scan parameters:
▫ Scan FOV
 Use large FOV if child may move
▫ Number of detector rows
 Use highest available - 64
▫ Detector thickness
 Thinnest width – 0.625mm
 NB for multiplanar recons and 3D volume rendering
▫ Tube current
 According to patient’s size
▫ kVp
 Reduced for small children (80kVp under 2 years, 100 kVp up to 6 years)
▫ Scan thickness
 Include all structures of interest
▫ Reconstruction algorithms
 Volume rendering and MIP projections usually sufficient when necessary
Parameters
Coronary artery CT angiography
• For adequate visualisation: Use isotropic in-plane and
through-plane spatial resolutions <1mm
(Equal voxel dimensions in x, y and z axes)
• Submillimeter collimation
• Pitch <1 (0.2 to 0.3)
• Higher milliamperage and kVp necessary to counter
increased noise.
• Bolus tracking/ test bolus used.
• ECG gating necessary for motionless images.
• Usually retrospective ECG gating – use diastole.
• Increased exposure!
• Online dose modulation programs – high mA only during
diastole.
Coronary artery CTA
Left
Right
Normal anatomy
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Thoracic aorta
Pulmonary arteries
Pulmonary veins
Superior vena cava
Azygous system
Thoracic aorta
• Five segments:
▫ Aortic root
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From base of heart
Includes aortic valve
Annulus
Sinus of Valsalva
▫ Ascending aorta
 From aortic root to right innominate artery
▫ Proximal aortic arch
 Right innominate artery to left subclavian artery
▫ Distal aortic arch/isthmus
 Left subclavian artery to ligamentum arteriosum
▫ Descending aorta
 Level of ligamentum arteriosum to hiatus in diaphragm
Thoracic aorta
• Normal branching pattern:
▫ Brachiocephalic trunk–R subclavian artery, R CCA
▫ Left CCA
▫ L subclavian artery
Pulmonary arteries
• Main pulmonary artery/pulmonary trunk lies within
the pericardium
• Devides into larger right and smaller left pulmonary
arteries
• Right passes posterior to AA, SVC, R upper lobe
pulmonary vein
• Then devides into 2 branches – upper lobe branch
and interlobar artery supplies middle and lower lobe
• The left is shorter and smaller
• Courses anterior to the descending aorta and left
main bronchus and divides into upper and lower
lobe branches.
Pulmonary arteries
Pulmonary veins
• Typically 4 pulmonary veins:
▫ Right and left superior and inferior
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R superior – Blood from R upper and middle lobes
R inferior – Blood from R lower lobe
L superior – Blood from L upper lobe + lingula
L inferior – Blood from L lower lobe
Pulmonary veins
• Variations:
▫ Conjoined – Sup and inf open into L atrium via
common ostium. More common on the left.
▫ Accessory – Extra veins seperate from pulm
veins. Occurs more commonly on the right.
Pulmonary veins
SVC and azygous system
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SVC formed by L and R brachiocephalic veins
Blood from upper extremities, head and neck.
Drains into R atrium
Azygous vein formed by ascending lumbar and
right subcostal veins.
• Blood from posterior chest and abdominal walls
• Arches over right hilum and drains into
posterior part of SVC.
• Hemiazygous and accessory hemiazygous veins
drain from the left into the azygous vein.
Azygous system
Normal anatomy of the heart
• Cardiac chambers
▫ Right atrium
 Larger posterior atrium proper and smaller anterior
atrial appendage. Devided by crista terminalis.
 Receives SVC and IVC.
▫ Left atrium
 Forms base of the heart.
 Valveless R and L pulmonary veins drain into L atrium
 Left auricle forms superior part of left border of heart.
Seperated by interatrial septum containing fossa ovale
Normal anatomy of the heart
Normal anatomy of the heart
• Cardiac chambers
▫ Right ventricle
 Forms largest part of anterior surface of the heart
 Contains coarse trabeculae and tapers into conus
arteriosus which leads to pulmonary trunk.
 Contains commonly identified muscle band- Moderator
band
▫ Left ventricle
 Forms apex of the heart and left border.
 Fine trabeculae, walls 3 x thicker than right.
 Two prominent papillary muscles
Seperated by interventricular septum – membranous and
muscular parts.
Normal anatomy of the heart
Normal anatomy of the heart
• Cardiac valves
▫ Aortic valve: Right, left and non-coronary cusps
▫ Pulmonary valve: Anterior, right and left cusps
▫ Mitral: Aortic (anterior) and mural (posterior)
leaflets
▫ Tricuspid: Septal, anterior and posterior leaflets
Normal anatomy of the heart
• Cardiac valves
Normal anatomy of the heart
• Coronary arteries
▫ Left coronary artery
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From left coronary sinus
Bifurcates into LAD ad left circumflex branches
LAD gives rise to diagonal branches.
Circumflex gives rise to left marginal artery.
▫ Right coronary artery
 From right coronary sinus
 Branches include: Sinuatrial nodal, AV nodal, right
marginal and most commonly posterior IV branch.
Normal anatomy of the heart
Normal anatomy of the heart
• Cardiac veins
▫ Great cardiac vein accompanies LAD
▫ Middle cardiac vein accompanies posterior IV
branch
▫ Small cardiac vein accompanies right marginal
branch of RCA.
▫ All larger branches drains into coronary sinus
and into right atrium
▫ Small anterior cardiac veins drain directly
into right atrium
Thoracic vascular anomalies
• Aortic anomalies:
▫ 0.5 to 3% of population
▫ Five groups:
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Left aortic arch
Right aortic arch
Double aortic arch
Cervical arch
Innominate artery
Left arch with abberant right
subclavian artery
• R subclavian artery is seen on CT as last of major
arterires from aortic arch.
• Most common anomaly of aortic arch
• 0.5 to 2% of population
Right aortic arch with aberrant left
subclavian artery
(Posterior view)
Double aortic arch
• Two arches from single ascending aorta
• Gives off own CCA and subclavian arteries
• Some patients may have persistent airway obstruction
related to tracheomalacia from external airway
compression
Double aortic arch
Cervical aortic arch
• Rare
• High-riding ascending aorta above level of clavicles
making a sharp downward turn.
Innominate artery compression of the
trachea
• Anterior compression of trachea by the
brachiocephalic trunk
Pulmonary artery anomalies
Abscence or interrruption of pulmonary artery
Pulmonary artery sling
• L pulm a. from posterior part of R pulm a.
• Crosses towards left between oesophagus and
trachea
Pulmonary venous anomalies
Partial anomalous pulmonary venous drainage
Stenosis of pulmonary veins
Left superior vena cava
Coarctation of the aorta
Interruption of aortic arch
Valve lesions
• Aortic valve stenosis
Pulmonary valve stenosis
Intracardiac shunts
• VSD
ASD
Secundum type
Primum type
Patent foramen ovale
Patent ductus arteriosus
Thank you
• References:
▫ 1. Frush DP, Herlong RJ (2005) Pediatric thoracic CT
angiography. Pediatric Radiology 35:11–5.
▫ 2. Frush DP, Yoshizumi T (2006) Conventional and CT
angiography in children: Dosimetry and dose
comparisons. Pediatric Radiology 36: 154-158
▫ 3. Pediatric body CT, 2nd ed. Siegel MJ, Marilyn J.
Lippincott Williams & Wilkins. Baltimore. 2008.
Chapter 8: Great vessels.
▫ 4. Clinically orientated anatomy, 5th ed. Moore KL,
Dalley AF. Lippincott Williams & Wilkins. Baltimore.
2006.