Differentiation between pulmonary thrombi and slow blood flow in the pulmonary artery by MR imaging

On electrocardiogram (ECG)-gated spin-echo magnetic resonance (MR) images, differentiation of thrombi from slow blood flow in the pulmonary arteries (PA) is sometimes difficult in such cases with prominent pulmonary hypertension (PH) as they show high signal intensity of intraluminal slow flow in not only diastole but also systole. ECG-gated, double spin-echo MR images were obtained in eight patients with PH accompanied by the high signal intensity of blood flow in the right main PA in both diastole and systole. These images were compared with those of five patients with chronic pulmonary thromboembolism (CPTE). Slow flow, but not thrombi, significantly increased signal intensity relative to other tissues from the first-echo to the second-echo image. In two patients with both CPTE and PH discrimination between slow flow and central thrombi was established by this imaging technique. This study suggests that ECG-gated, double spin-echo technique is useful for differentiating central thrombi from slow flow. MR imaging can play an important role in detection and repeated noninvasive examination of proximal pulmonary thromboemboli. (author)