Spiral computed tomography in the assessment of focal and diffuse lung disease

Conventional computed tomography (CT) processes the raw data of a single rotation at any given level to produce the image at that level. Scan collimation and interspacing are determined prospectively. Spiral CT combines longitudinal patient transport with continuous data acquisition. Interpolated projections are used for reconstructing any level inside the scanned volume. Therefore, spiral CT allows any number of images, their spacing, position, and field of view to be determined retrospectively. Technically, the only limiting factors of spiral CT are the load of the x-ray tube and the computation power of the scanner. Spiral CT is superior to conventional CT in detecting lung nodules, in imaging the representative slice of a small nodule by retrospective selection, and in its ability to reformat the image in any plane. It also allows rapid scanning and three-dimensional re-formation of images. It may reduce the dose of contrast agent required for optimal enhancement of the vascular structures, reduce the radiation dose, and eliminate motion artifacts.