Imaging of congenital heart disease (CHD) begins with fetal echocardiography in the intrauterine period and continues postnatally with transthoracic echocardiogram confirming anatomy and physiology. In cases of complex CHDs, further imaging is necessary to delineate anatomy for further management and surgical intervention.
How can cardiac magnetic resonance imaging (MRI) and computed tomography (CT) complement the role of transthoracic echocardiogram in delineating further details of anatomy and physiology in the neonatal period? In this review, a team from the Department of Pediatrics at the University of Iowa in the United States covered the indications, techniques, and safety of non-invasive advanced cardiac imaging in neonates.
An “important complementary role”
Echo is the first-line noninvasive imaging tool in pediatric and adult cardiology - offering multiple advanced features such as tissue Doppler imaging, strain imaging, speckle tracking imaging, and three-dimensional imaging. When echo cannot provide comprehensive details of relevant cardiovascular anatomy, the review highlighted that advanced non-invasive cardiac imaging techniques such as cardiac MRI and CT play an important complementary role.
MRI is frequently used for anatomical and functional evaluation of CHD, and fetal cardiovascular magnetic resonance imaging is showing promise as a clinical diagnostic tool in CHD when the cardiac anatomy is unresolved by ultrasound or when complementary quantitative data on blood flow, oxygen saturation, and hematocrit are required to aid in management. Advancements in CT - such as multi-detector CT and reconstruction methods, and lower radiation - have seen the modality emerge as a viable tool for CHD in newborns, children, and adults.
Goals and indications of advanced neonatal imaging
The review outlined the segmental approach that is used to delineate cardiac anatomy from images obtained from echo and advanced imaging modality. The physiologic status is assessed using physical examination, chest radiography, echo, advanced imaging, and if needed cardiac catheterization.
Indications for advanced neonatal cardiac CT or CMR were broadly categorized as the assessment of intra-cardiac anatomy (in patients with unusual complex CHD, cardiac tumors, cardiomyopathy or to help decide single vs biventricular repair in patients with borderline ventricular hypoplasia) or extra-cardiac vasculature (assessing vascular structures such as anomalous pulmonary veins, vascular ring, pulmonary sling, aortopulmonary collaterals, and aortic arch anomalies).
The review points out that “echocardiography remains the main diagnostic tool in the neonates for cardiovascular imaging” but that “there are certain instances where additional information needs to be obtained to confirm the diagnosis or add information when echocardiography has not been able to provide complete information”.
An advancement in CT and MRI technologies has almost completely negated the need for cardiac catheterization, an invasive procedure, for cases in which echocardiography has provided insufficient information.
Cardiac MRI in unborn children
Cardiac MRI plays an important part in the multimodality assessment of CHD, which is essential for anatomical and functional evaluation for diagnosis and planning. Cardiac MRI sequences highlighted by the review include anatomy delineation, flow quantification, magnetic resonance angiography (MRA), and tissue characterization.
The review set out several indications for cardiac MRI in the neonate:
Extracardiac vascular anatomy – for accurate delineation where an echocardiogram is unable to sort out intricate anatomy.
Airway issues - for assessment secondary to vascular malformation or chamber enlargement causing compression.
Patency of aortopulmonary shunt – for assessment in the postoperative period with patient instability.
Venous anatomy and abnormalities, including ensuring there is no superior vena cava (SVC) obstruction in patients with Glenn and after arterial switch operation.
Obtaining 3D data sets for 3D printing and virtual reality cardiac MRI techniques.
Cardiac CT in unborn children
The review described cardiac CT as a complementary modality to echocardiography or cardiac MRI for CHD evaluation in neonates, providing a fast approach to high-resolution images for defining the cardiac anatomy, and multi-detector technology that can acquire full anatomic coverage of the heart and chest.
Current indications for cardiac CT in neonates were picked out by the review:
Aortic arch anatomy - diagnosis and delineation of various aortic arch anomalies that can be present at birth.
Pulmonary artery anomalies – imaged with a similar technique as used for an aorta, but image acquisition timing may differ based on pulmonary arterial supply.
Abnormalities of great vessels – including congenital heart defects like d-TGA, congenitally corrected TGA, and tetralogy of Fallot (TOF) that usually require advanced imaging in neonatal life if early surgical intervention is required.
Congenital coronary artery anomalies – which may exist in isolation or with other CHDs.
Evaluation of pulmonary veins - depending upon the suspected defect.
Evaluation of systemic venous anomalies – such as interrupted inferior vena cava with azygous continuation or persistent left SVC.
Evaluation of single ventricle anatomy and estimation of ventricular volume
“A complex and exciting field”
The review concluded that “neonatal cardiac imaging is a complex and exciting field that provides a rapid and accurate diagnosis of neonatal anatomy and physiology to determine the optimal management”. It was summarized that while echocardiography provides the initial tools for delineating the complex anatomy, some cardiac lesions require advanced cardiac imaging for “successful medical management and surgical intervention”.