This is the first in a series of axial (transverse) CT images of the thorax. The images have been "windowed" (contrast adjusted) in order to highlight soft-tissue structures, and consequently, the lungs appear mostly black. As you work through these images, it may be helpful to remember the structures in the previous "slice" in order to be able to trace those structures and maintain orientation. This first image will ask you to name several structures for reference, most of which will continue to be present in subsequent slices. In all of these images, vascular structures are bright due to the injection of contrast dye in the venous system (usually via the arm) of the patient. You can assume that black represents air.