Pulmonary circulation

Evaluation of the pulmonary vasculature is mainly indicated in patients with suspected pulmonary thromboembolism. The routine procedure so far is ventilation-perfusion scintigraphy alone or in combination with diagnostic assessment of the legs to rule out deep venous thrombosis. The results are still not reliable for the majority of patients. In the case of equivocal diagnosis, invasive conventional angiography is considered the gold standard. With steady improvements in tomographic imaging techniques, such as computed tomography (CT) or magnetic resonance imaging (MRI), non-invasive alternatives to the routine diagnostic work-up are given. Helical CT and CTA techniques are already in clinical use and estimated to sufficiently serve the demands for detection/exclusion of pulmonary thromboembolism. The disadvantages mainly concern peripheral disease and reconstruction artifacts. MRI and MR angiography have been implemented in the diagnosis of pulmonary vascular disease since the introduction of contrast-enhanced MRA. In breath-hold techniques, the entire lung vascularization can be delineated and thromboemboli can be detected. The clinical experience in this field is limited, but MRI has the potential to demonstrate its superiority over CT due to its improved delineation of the vascular periphery and the more comprehensive three-dimensional reconstruction.