DIAGNOSTIC TECHNIQUES AND THEIR INDICATIONS - IMAGING PROCEDURES



The standard chest roentgenogram comple­ments the history and physical exam as the start­ing point for the diagnosis of pulmonary disor­ders. The chest x-ray may demonstrate a density that only physical exam can differentiate between consolidation and loculated pleural fluid. Con­versely, the chest x-ray may show dramatic in­volvement of the lung by tuberculosis while the physical exam is not remarkable. Standard views include the posteroanterior and the left lateral projections; they reduce disproportionate mag­nification of the heart and anterior mediastinal structures. These films allow visualization of the air-containing lung, vascular markings, heart and mediastinal structures, pleura, lymph nodes, ribs, spine, and soft tissues of the thorax. Correct in­terpretation requires that the film be taken as close to total lung capacity as possible. A correctly exposed film allows the vertebral bodies to be barely visible behind the heart. A number of specialized views and procedures can be added to the stan­dard PA and lateral films.

Significant improvement in visualization of chest structures has resulted with computed tom­ography (CT), which provides excellent visibility of areas previously difficult to see and has ten times the contrast resolution of conventional ra­diography. Excellent evaluation of the medias­tinum makes it valuable in the work-up of bron­chogenic neoplasms. Differentiating pleural from parenchymal densities, a common problem on the routine film, has been improved. Computed tom­ography has virtually replaced the standard ra­diographs for evaluating the presence of early metastatic spread to the lung parenchyma; un­fortunately, specificity is low, and 20 to 60 per cent of nodules visualized on CT scan but not on x-ray are benign. In addition, CT is’ useful for de­tecting calcification in pulmonary nodules.

Ultrasound is useful in helping to differentiate pleural opacities into solids or fluid and to lo­calize loculated pleural effusions. Other imaging methods such as nuclear magnetic resonance and digital subtraction angiography are not generally available, and their superiority over available methods has yet to be proven.