A n 8-year-old boy was referred to our department for evaluation of a heart murmur. There was no history of cardiac failure, cyanosis, or respiratory distress or illness. At echocardiography, an aberrant origin of the left pulmonary artery was demonstrated. The barium-enhanced esophagogram showed an anterior indentation at the level of the tracheal bifurcation. Bronchoscopy revealed a stenosis of the ventral and right lateral tracheal wall approximately 1 cm above the bifurcation, with no

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... ce of tracheomalacia. To assess the pulmonary vascular anatomy, we performed a time-resolved contrast-enhanced magnetic resonance angiography (MRA) using an ultrafast 3-dimensional gradient echo pulse sequence (3D FLASH, repetition time 2.3, echo time 0.9 ms, flip angle 40°, field of view 263ϫ350 mm, matrix 135ϫ265, reconstructed slice thickness 2.0 mm) with a scan time of 6.2 seconds per data set. In total, 5 data sets were acquired in a single breath hold, showing the transit of the contrast agent bolus through the pulmonary vasculature. Three-dimensional reconstructions (volume-rendering) of the contrast-enhanced MRA data sets were generated (Figure 1) . The dynamic acquired images demonstrated 5 phases of the vascular enhancement (venous, pulmonary artery, mixed, pulmonary venous, and aortal phase). The reconstructions of each phase were individually color enhanced and subsequently merged (Figure 2, Movie) . The time-resolved MRA confirmed the diagnosis of an abnormal origin of the left pulmonary artery that was passing posterior to the trachea to the left lung (pulmonary artery sling) and compressing the airway. Surgery with total cardiopulmonary bypass was performed, and the left pulmonary artery was attached to the pulmonary trunk ventrally to the trachea. Tracheoplasty was not necessary. Postoperatively recovery was uneventful. In patients with suspected pulmonary artery sling, conventional angiography is the current diagnostic standard. MRA is a novel imaging tool that provides good anatomic detail information, with the advantage of being noninvasive and free of ionizing radiation, and is therefore very useful for the diagnosis of pulmonary vascular anomalies in pediatric patients. Figure 1. Volume-rendering of timeresolved contrast-enhanced MRA data set in an early phase of the contrast bolus flowing. At that time, the isolated pulmonary artery phase is shown. A, anterior view; B, left lateral view; and C, posterior view. The arrows mark the abnormal origin of the left pulmonary artery. MP indicates main pulmonary artery; RPA, right pulmonary artery; LPA, left pulmonary artery; and *, position of the trachea.