The thorax

Computed tomography (CT) is becoming increasingly important for evaluation of thoracic diseases. The clinical role of MRI requires direct comparison of its advantages with those of CT. For imaging of the thorax, MRI has some intrinsic advantages in regard to other modalities. It also has some disadvantages at present, but these may be temporary, because MRI is still an immature and rapidly developing technology. The major advantage is maximum contrast between lesions and blood vessels at all tomographic levels. On the other hand, achieving such contrast with CT requires precise coordination between delivery of the bolus of contrast materials and exposure of the CT scan; this can generally be attained only at one or a few anatomic levels. Metallic surgical clips cause a signal void on MRI but do not cause the severe streak artifacts seen on CT scans. Another advantage of MRI results from the high MRI intensity of fat. This provides high contrast between lesions and hilar or mediastinal fat. The ability to obtain MR images in multiple planes can be critical for evaluating abnormalities in some locations, such as the aorticopulmonary window and the cervicothoracic junction. Coronal and sagittal reconstructions from transverse CT scans generally have not been useful because of markedly reduced spatial resolution in the reconstructed plane