Usefulness of MRI for the pre-operative evaluation of the pulmonary arteries in Tetralogy of Fallot.

Adequate pre-operative evaluation of patients with Tetralogy of Fallot (TF) includes cine-angiography to delineate the pulmonary vasculature and the coronary artery anatomy and to demonstrate the presence of multiple ventricular septal defects (VSDs). All other information is obtained from color-Doppler-echocardiography. Magnetic resonance imaging (MRI), using the spin-echo sequence and cine-angiography was employed on 18 patients with TF, four of whom had aorto-pulmonary shunts. Mean age at MRI was 12.9 m (SD 2.3 m) and 14.3 m (SD 2.8 m) at cine-angiography. To compare MRI and cine-angiography we measured the ascending aorta, the main, the left and right pulmonary arteries and each structure at three levels. Diagnostic agreement between the two imaging methods was found if, for each modality, one of the three measurements in one structure differed by more than 40% from the other two measured in case of a local stenosis, and the diameter of the main pulmonary artery was less than 60% of the aorta to diagnose hypoplasia of the main pulmonary artery. There was close agreement between cine-angiography and MRI. With regard to the intracardiac anatomy, MRI was superior to color-Doppler-echocardiography in the depiction of aortic override and of right ventricular hypertrophy. In three cases local stenoses in the pulmonary arteries were detected by MRI and cine-angiography. Hypoplasia of the main pulmonary artery was detected by MRI in six patients and by cine-angiography in five patients. Cine-angiography missed one case of hypoplasia. In the remaining 11 patients normal findings were found by MRI and cine-angiography. For the demonstration of shunts, gradient-recalled-echo MRI is expected to give better results than the spin-echo sequence which depicted two out of four shunts in this series. Cine-angiography can be substituted by MRI in delineating the pulmonary arteries. New developments in MRI indicate the feasibility of delineating the coronary arteries.