Neonatal indications of cardiac MR

Shi-Joon Yoo
Professor of Diagnostic Imaging and Paediatrics, University of Toronto
Section Head, Cardiac Imaging, The Hospital for Sick Children
Toronto, Canada

Magnetic resonance (MR) is not favorable for imaging the neonatal heart because of long examination time, a need for deep sedation or general anesthesia, an awkward room setting for emergency care and a high examination cost. However, MR does have a few important advantages over echocardiography and computed tomography. MR images are usually more objective than echocardiograms. There is no limitation in selection of imaging planes. Contrast-enhanced MR angiography is not complicated by significant side-effects when it is performed in patients without severe renal dysfunction. Contrast-enhanced angiography can also be performed repeatedly after a single injection of contrast medium, allowing time-resolved angiography. Cine MR imaging is widely accepted as the gold standard tool for ventricular volume studies. Phase-contrast velocity mapping at MR is the only accurate tool for quantification of flow volumes. With these advantages, MR is used when echocardiography is not able to provide complete information that is needed for medical and/or surgical treatments.
　Neonatal indications at the Hospital for Sick Children include:

1.　Borderline hypoplasia of the left ventricle
2.　Pulmonary venous pathologies
3.　Major aortopulmonary collateral arteries in tetralogy of Fallot with or without pulmonary atresia
4.　Other complex pulmonary arterial anatomy
5.　Cardiac tumors
6.　Complex intracardiac anatomy

　The main reasons for MR imaging in these indications are for measurements of ventricular volumes and systolic functions and for evaluation of hemodynamic parameters such as blood flow distribution, direction and amount of shunts and Qp/Qs. As the neonates who undergo MR are usually critically ill or hemodynamically unstable, it is crucial to minimize the examination time by having the procedure performed by the most experienced physicians and technologists available. In addition, the echocardiograms and other patient data should be thoroughly reviewed before the procedure so that the examination is focused on the issues in question.
　This presentation will show the utility of MR examination in the neonatal indications listed above.

References:
1.Kellenberger CJ, Yoo SJ, Buchel ER: Cardiovascular MR imaging in neonates and infants with congenital heart disease. Radiographics 2007; 27: 5-18.
2.Grosse-Wortmann L, Yun TJ, Al-Radi O, Kim S, Nii M, Lee KJ, Redington A, Yoo SJ, van Arsdell G: Borderline hypoplasia of the left ventricle in neonates: insights for decision-making from functional assessment with magnetic resonance imaging. J Thorac Cardiovasc Surg 2008; 136: 1429-1436.