![]() This is because in the AP projection, the heart is farther from the detector plate and the x-ray beam diverges as it goes farther from the tube. įor interpretive purposes, the main difference is that the heart will be more magnified on the AP projection ( Fig. This is called an AP (or anterior to posterior) chest x-ray. If the patient is lying down, it is standard practice to take the image with the x-ray beam entering the front of the chest and have the detector plate behind the patient. This is referred to as a PA (posterior to anterior) projection. The x-ray tube is behind the patient, and the x-ray beam passes in from the back and exits the front of the chest. Posteroanterior Versus Anteroposterior Chest X-RaysĬhest x-rays of ambulatory patients are usually done with the subject’s chest up against the detector plate. These should be bilateral and sometimes can be seen in the anterior soft tissue of the chest on the lateral view. Prominent nipple shadows can be seen in men and women and are seen in the midclavicular line over the lower half of both the right and left lung (arrows). If only one nodule is found projecting over a lung in the PA projection and no nodule is seen on the lateral view, a small metallic BB can be taped over the nipple and the single PA view repeated to see whether it was the nipple that was being visualized. 3.3 ), but before you completely stop worrying, also look at the lateral image and make sure that the nodule is not seen projecting within the lung. If one does, usually you can stop worrying ( Fig. First, look at the opposite lung to see if a comparable nodule appears there. Nipple shadows are common in both men and women. Visualization on a PA or AP chest x-ray of a single well-defined nodule in the lower lung zone should raise the suspicion that you are seeing a nipple shadow and not a real pulmonary nodule. In contrast, the left lung appears darker than the right, and you might mistakenly think there is hyperinflation of the left lung. The right breast, which remains, causes the pulmonary vessels at the base of the right lung to be accentuated, and this can be mistaken for a right lower lobe infiltrate. In this circumstance, recognition of the mastectomy will prevent you from making an erroneous diagnosis of an infiltrate or effusion based on the relatively increased density on the side with the remaining breast ( Fig. The lung on the side of the mastectomy will appear darker than the lung on the normal side. In this circumstance, the lung density will be asymmetric. One common problem is encountered in the woman who has had a unilateral mastectomy. If the breasts are large, bilateral basilar lung infiltrates may appear to be present on the PA or AP projection. This results in the lung behind the breast appearing whiter and the pulmonary vascular pattern in the same area appearing more prominent. Breast tissue absorbs some of the x-ray beam, essentially causing underexposure of the tissues in the path. This is generally relevant only in interpretation of a posteroanterior (PA) or anteroposterior (AP) projection and not of the lateral projection. The major difference between male and female chest x-rays is caused by differences in the amount of breast tissue. Even with digital or computed radiography, nothing can be done to an underexposed image to improve the image. Underexposure also makes it impossible to see the detail of the mediastinal, retrocardiac, or spinal anatomy (see Fig. It will make the small pulmonary blood vessels appear prominent and may lead to thinking that there are generalized infiltrates when none are really present. This is a major problem for adequate interpretation. Underexposure causes the image to be quite white. (B) Underexposure accentuates the pulmonary vascularity, but you cannot see behind the heart or behind the hemidiaphragms. (A) Overexposure makes it easy to see behind the heart and the regions of the clavicles and thoracic spine, but the pulmonary vessels peripherally are impossible to see. If the image was obtained by using either digital or computed radiography, the image can be “windowed” lower on the computer, resulting in an interpretable image. ![]() Under these circumstances, the thoracic spine, mediastinal structures, retrocardiac areas, and nasogastric and endotracheal tubes are well seen, but small nodules and the fine structures in the lung cannot be seen ( Fig. Overexposure causes the image to be dark. A correctly exposed image should allow visualization of vessels to at least the peripheral one-third of the lung and, at the same time, allow visualization of the paraspinous margins and the left hemidiaphragm behind the heart. The range stretches from small vessels in air-filled lungs to dense bony structures located behind the heart. Making a properly exposed chest x-ray is much more difficult than making x-rays of other parts of the body because the chest contains tissues with a great range of contrast.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |