Paediatric cardiothoracic CTA

Paediatric cardiothoracic CTAIndications,TechniqueAnd Relevant Anatomy Gerhard van der Westhuizen

Medical officer, Radiology3 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

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

▫ 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

▫ 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:▫Conventional chest CT 1.0 to 4.0 mSv▫CTA 1.0 to 4.0 mSv▫Gated CTA 7.0 to 25 mSv▫Conventional angiography 5.0 to 20 mSv

Indications• Detection of disease or pathology

▫ i.e. Diagnosis• Improve clinical decision making

▫ 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

▫ 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

▫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▫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▫ “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•Thoracic aorta•Pulmonary arteries•Pulmonary veins•Superior vena cava•Azygous system

Thoracic aorta• Five segments:

▫ Aortic root 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 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•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 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:

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 anomaliesPartial 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.