Magnetic resonance imaging of the thorax: techniques, current applications, and future directions

Magnetic resonance imaging (MRI) has been used extensively to evaluate the central nervous and musculoskeletal systems. MRI provides excellent contrast between normal and pathologic tissues, identifies vascular structures without the need of intravenous contrast, and is able to image in multiple planes. Until recently, physiologic motion produced artifacts that markedly limited the use of MRI in the thorax. However, with the advent of cardiac gating and respiratory motion compensation, diagnostic images can now be readily acquired. The ability to distinguish between flowing blood and adjacent tissue allows for the detection of aortic aneurysms and dissections. Prominent vessels may be differentiated from hilar adenopathy without the use of contrast agents. Preliminary experience suggests MRI may be useful in assessing central pulmonary emboli and mediastinal venous obstruction. The ready identification of flow combined with the multiplanar capability of MRI provide a means of assessing congenital abnormalities and other anatomic information. Fast scan techniques provide a dynamic means of assessing cardiac function and are sensitive to valvular stenosis and insufficiency. Combined with spin-echo techniques, areas of myocardial infarction and focal wall motion abnormalities can be detected. Currently, MRI has little application in the assessment of pulmonary nodules, bronchogenic cancer, and diffuse parenchymal disease. Sagittal MR images may more clearly show tumor extension into the axilla, brachial plexus, and spinal canal in patients with superior sulcus neoplasms. Future applications may include faster imaging techniques, blood flow measurement, detection of thrombus using phase sensitive techniques, regional perfusion, and assessment of cellular energy metabolism.