Estimation of pulmonary vascular resistance by MRI in patients with congenital cardiovascular shunt lesions.

The intensity of the magnetic resonance signal in the pulmonary arteries was assessed in 15 patients with congenital left to right shunts and in 10 normal volunteers, using an ECG-gated multislice spin-echo technique. In normal subjects, magnetic resonance signal was only observed in great vessels of the thorax on images acquired near end-diastole; they disappeared in systole. Among the group of 15 patients, 10 had severe pulmonary hypertension (systolic pressures greater than 80 mm Hg) with severe elevation of pulmonary vascular resistances (greater than 787 dynes cm sec-1). The magnetic resonance signal persisted in systole in all 10 patients, and its intensity could be quantitatively assessed. On the other hand, in one other patient with high pulmonary artery pressure but only moderate elevation of pulmonary vascular resistance, and in patients with moderate pulmonary hypertension and normal pulmonary vascular resistance, the intravascular signal was minimal and no different from the signal recorded in normal subjects. A direct linear relationship was found between the pulmonary vascular resistance and the intensity of the magnetic resonance signal in the right pulmonary artery during systole (r = 0.84). An even closer correlation was found for the linear relationship between the ratio pulmonary vascular resistance/systemic resistance and the magnetic resonance signal in the right pulmonary artery (r = 0.93). Thus, magnetic resonance, with its sensitivity to slow-flow conditions, can potentially provide physiological information in congenital cardiovascular disease.