CT and MR imaging in the evaluation and staging of lung cancer

Cancer of the lung is one of the most frustrating yet important challenges facing medicine today. Despite screening programs and education of the public concerning the established link of lung cancer and cigarette smoking, the overall incidence of lung cancer continues to rise. Improved imaging has led to more accurate staging. Expanded treatment has yielded improving survivals of certain specific tumors. Accurate diagnosis and staging of lung cancer is important in detecting therapy and prognosis. Computed tomography (CT) has been established as an important component of the staging process. More recently, applications of magnetic resonance imaging (MRI) are ideally suited to evaluate tumor extent and nodal disease. We reviewed the uses and limitation of CT and MRI. Compared with CT, the relatively low signal in the lung limits the detection of pulmonary nodules and other lung parenchymal diseases, and noise due to motion has been a frequent and significant problem in thoracic MRI. Because of its superior spatial resolution and ability to detect calcification, CT is better than MRI for the detection and evaluation of lung nodules and mediastinal adenopathy when assessing lung cancer. For the detection of mediastinal invasion or lymph node metastases, CT and MRI generally provide similar information. However, volume averaging problems, which may occur on trasaxial CT, can be avoided or clarified using MRI, and nodes can sometimes be more clearly distinguished from vessels using this technique. In the diagnosis of hilar masses or lymphadenopathy, CT and MR provide similar information in the majority of cases, but occasionally MR may more clearly indicate the presence or absence of a mass. Because of superb vascular imaging capability (without the need for exogenous contrast agents), exquisite soft tissue contrast, the ability to image the chest directly in multiple planes, and the potential to characterize certain tissues, MRI appears to be superior to CT in defining the extent of chest-wall invasion. In general, CT is superior to MRI as an all-around tool for imaging the wide range of thoracic abnormalities that can be present in patients with lung cancer. Limited availability, and longer examination time of MRI compared with CT has restricted the use of thoracic MRI. If MRI is used selectively as a secondary imaging study to answer specific questions raised or unanswered by CT, its value can be optimized.