Where Does Cardiopulmonary Imaging Begin?
The evaluation of the cardiopulmonary system begins with conventional radiography. In the clinic, the radiograph of the heart and lungs is commonly referred to as the chest radiograph, chest film, or chest x-ray.
The chest radiograph has always been and continues to be a mainstay of basic health care. The chest radiograph is a quick, inexpensive, and noninvasive tool for screening and diagnosis. Many pathologies are adequately diagnosed and treated based on the chest radiograph itself. The chest radiograph also yields valuable information on the adjacent structures of the thyroid gland, gastrointestinal tract, and bony thorax. Additionally, metastatic disease from the skeleton and viscera often manifests in the lung. For these reasons, the chest radiograph has long been known as the “mirror of health or disease.”
However, the chest radiograph has limitations. Modern cardiopulmonary imaging still begins with the static image of the chest radiograph but may extend to encompass images of organ motion, blood flow, ventilation, perfusion, even the molecular mechanisms of disease processes. Today, any physiological function can be observed noninvasively with the tools of advanced imaging.
A brief review of anatomy specific to viewing the chest radiograph follows.
First, it is a good idea to review the anteroposterior (AP) and lateral views of the thoracic spine in Chapter 9. Note a major difference between the thoracic spine radiograph and the chest radiograph is in exposure technique. Skeletal films are made in high contrast to see cortical margins. The chest radiograph is made in low contrast to see the soft tissues (see Fig. 1-22). Thus what you see of the bony thorax on a chest radiograph is incidental, but still useful. The bones help identify soft tissue anatomy and the location of lesions. For example, a lesion is reported to be located “at the seventh intercostal space.” This is accepted to mean between the seventh and eighth posterior ribs.
A second major difference is the thoracic spine radiograph is made as an AP projection, thus details of the spine are easily seen because the vertebrae are closest to the image receptor. The chest radiograph is made as a posteroanterior (PA) projection (see Fig. 1-16). The sternum (now closest to the image receptor) and spine are superimposed and difficult to separate.
A typical chest radiograph will show six anterior ribs and ten posterior ribs. How is it possible to tell them apart? The crosshatched image produced by the rib cage is very confusing for any beginner to decipher. Start by focusing on the posterior ribs. The posterior ribs are easiest to identify for two reasons: (1) they are furthest from the image receptor and so are magnified the largest and (2) ...