A magnetic resonance imaging method for evaluating atrial septal defects.

Excellent definition of anatomic structure, ability to provide detailed flow information, and a global field of view make magnetic resonance imaging (MRI) well suited as a tool for the noninvasive diagnosis of congenital heart disease. One of the most frequently encountered lesions is the atrial septa1 defect (ASD), which may be associated with important morbidity in the long term if unrecognized. The need for correction of the defect is most often defined by the magnitude of the trans-septa1 shunt flow. Increasingly, the evaluation also includes an assessment of the suitability of the lesion for percutaneous closure by new catheter-based techniques. This requires detailed knowledge of the size and location of the defect and of its proximity to other structures, such as the atrioventricular valves, the venae cavae, and the pulmonary veins. By far the most common form of ASD is the secundum type in which the defect is located at the fossa ovalis in the central part of the interatrial septum. Lesions in this region may be difficult to evaluate by MFU because of marked thinning of the normal septum (Fig. 1). The defect may involve only part of this thin membrane that is not imaged reliably by standard T1 spin-echo techniques because of its relatively low signal intensity and very narrow profile, particularly if the course of the septum through the slice thickness is somewhat oblique. These factors often result in signal “dropout” at the fossa ovalis, creating the appearance of an ASD, even when the septum is intact.