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 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-topulmonary 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 patients 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 trunkR 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 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 anomalies Partial anomalous pulmonary venous drainage
Stenosis of pulmonary veins Left superior vena cava Coarctation of the aorta Interruption of aortic arch
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