Functional and morphological MR studies in congenital cardiovascular malformations

The aim of this study was to evaluate new MR techniques permitting qualitative and quantitative analysis of cardiac function and measurement of velocity and flow, and later on contrast-enhanced MR angiography, techniques largely unexplored in children with CHD. Infants with tetralogy of Fallot and pulmonary atresia with ventricular septal defect were examined pre-operatively. MRI was found to be a good alternative to angiocardiography for the pre-operative evaluation of the right ventricular outflow tract and the central pulmonary arteries, even in very young patients under one year of age. Contrast-enhanced MR angiography was adapted to and optimized for infants and children. MR velocity mapping was compared with first-pass radionuclide angiography for Qp/Qs determination in left-to-right shunts. MR velocity mapping measured shunts over the whole range of possible Qp/Qs values, with high accuracy and precision, in both adults and children. Thus, one may assume the technique to be accurate and precise also in other flow applications. In children and young adult conduit patients, MRI including MR velocity mapping and Doppler-echocardiography were compared. MRI provided complete morphological and functional information about the right ventricle and about the extra-cardiac ventriculo-pulmonary conduit. This may be extended to include right ventricular outflow tract obstruction and right ventricular dysfunction in general, both pre- and post-operatively. The value of combining morphological and functional MR information in assessing the haemodynamic importance of coarctation of the aorta was examined. It was found that the visual estimation of collateral vessels correlated reasonably well with collateral flow assessment using MR velocity mapping. MRI can replace cardiac catheterization in most pre-operative investigations, both in infants and older children. Adding CE-MRA to the MR protocol aids diagnosis and saves time. MRI is the method of choice for long-term post-operative follow-up, as it is accurate and reproducible. If MRI and echocardiography are in agreement, invasive catheter studies are not necessary for diagnostic purposes in the majority of patients.