The Radiograph and Its Evaluation

The process for evaluating a radiograph can be broken down into several stages. The initial evaluation should verify all of the technical details of the scan; subsequent stages look at various aspects of the anatomy imaged.

Evaluation for Pathology

Overview

After verifying the technical aspects of the images, the diagnostic evaluation can begin. It will help to first review the different projections that have been taken (Table 11-1). There are special views that position the patient in such a way that a particular area of interest is oriented for optimal visualization.

Table 11-1

Standard Radiograph Projections

View	Description
AP (anteroposterior)	Frontal view, taken with the patient facing the x-ray tube, with the back toward the film
PA (posteroanterior)	Looks the same as the AP, but the patient is positioned facing the film
Right lateral	Side view, with the right side against the film
Left lateral	Side view, with the left side against the film
Oblique	A view taken at a 45-degree angle, between the AP and the lateral views

The standard chest radiograph is taken as a posteroanterior (PA) and a left lateral view, with the patient standing. These two views position the heart closest to the film; clinicians use the radiograph to judge the size of the heart, and the farther away from the film the heart is, the more it will appear magnified. This concept is easy to understand if you shine a light on your hand and view the resulting shadow on the wall. The closer your hand is to the wall, the more its shadow’s size is true to life. The farther away the hand gets from the wall, the larger and fuzzier the shadow appears. The evaluation of the heart and lungs is most accurate when these structures are positioned close to the film during imaging.

The next step in evaluating a chest radiograph is to do a quick scan of the entire image to look for obvious or life-threatening abnormalities. General anatomy should be identified, including:

 Spine

 Sternum

 Clavicles and ribs

 Right and left diaphragms

 Abdominal organs

 Heart

 Mediastinum and great vessels

 Trachea

 Main bronchi

 Lungs

At this point it is also important to assess the position of the patient by looking at the clavicles to ensure they are aligned. If they are rotated, this could distort images of the lungs, heart, and other important structures. The image should also be scanned for any nonanatomical findings such as pacemakers, tubes, electrical leads, staples, etc. If old films exist in the patient record, it is helpful to compare the current findings with the old. Once this is done, a more thorough evaluation is begun (Table 11-2).

Table 11-2

Summary of Chest X-Ray Evaluation

Focus	Findings
Patient information	Name, date of birth, social security number, sex, existence of any old films.
Nonanatomical findings	Pacemakers, ECG leads, buttons, surgical remnants (e.g., staples), foreign bodies.
General inspection	Check rotation of chest by evaluation of the clavicles. Does anything “jump out” at you? Is everything present that should be there?
Bones	Are the appropriate number present? Are they in normal anatomical position? Any fractures, lesions?
Trachea	Is it midline? Is it narrowed? Are there any foreign bodies?
Lungs	Assess inspiratory effort, diaphragms, lung tissue, full expansion of lungs, opacities, infiltrates.
Heart	Size, borders, shape.
Mediastinum	Is it widened?

Bony Skeleton

The bony skeleton (Figure 11-3) should be checked for signs of fracture, especially along the margins of the ribs. Fractures are seen as radiolucent lines within the bone or as disruptions of the smooth cortical line at the edges of the bone. Unexplained fragments of bone that are not in a normal anatomical position are another sign of fracture.

Inspiratory Effort

The inspiratory effort should be evaluated. Patients are asked to take a deep breath at the time of the radiograph, and this deep inspiration should make it possible to visualize 10 to 12 ribs within the thoracic cavity. If a radiograph is taken during expiration or during a poor inspiratory effort, the ribs will appear very close together and the lower ribs will be seen below the level of the diaphragm. It is important to take notice of this, as poor inspiratory effort can mask findings in the lungs, or make some findings appear more pronounced than they really are. Inspiratory effort is also important to note because it can provide a quick guide to your patient’s respiratory ability.

Position of the Diaphragm

The position of the diaphragm should be noted. Its position, shape, clarity, and the appearance of the costophrenic angles are important, remembering that anatomically, the left (L) diaphragm is usually lower than the right (R) diaphragm. The costophrenic angles are where the diaphragm meets the chest wall. In these thin, pointy areas at the base of the chest cavity, blood or fluid accumulations inside the chest can be seen on an upright film. Such accumulations can affect patient lung capacity and thus oxygenation.

Trachea

Another important structure to evaluate is the trachea, which should be visible at the upper portion of the CXR, with a more radiolucent density, similar to the lung fields. The trachea should be in the midline on the PA view, and the carina (where the trachea branches into the two main stem bronchi) should also be visible. A shift from midline can indicate tension in the chest wall such as that found with some pneumothoraces. Narrowing and/or any foreign objects in the trachea can indicate respiratory distress and must be evaluated immediately.

Lung Fields

Next, the lung fields should be evaluated for uniform density and vascular markings throughout. The hilar area, where the vascular and airway structures converge, is normally more dense and can be an area of importance when looking for masses or tumors. The peripheral lung fields, where the smallest vascular and airway structures are, appear the smoothest and least dense. Comparing them side by side for symmetry helps in the recognition of abnormal areas. Conditions such as pneumonia, tumor, effusion, or other disease processes lead to consolidation of lung tissue, making it more dense than tissue in the rest of the lung fields (Figure 11-4).

Full expansion of the lung fields is also important to evaluate. A pneumothorax causes part of the lung to collapse, creating a less dense empty space in the chest cavity that is devoid of any pulmonary or vascular markings (Figure 11-5). Conversely, a hemothorax or pleural effusion fills the chest cavity with fluid that is denser than normal lung tissue (Figure 11-6). Both of these abnormalities are evident on chest radiographs and can affect oxygenation, as discussed above.

Heart Size

Normally, the heart is about as wide as one-half of the chest cavity. Measuring the cardiac silhouette and then measuring the width of the hemithorax (from the center of the sternum to the outer edge of the ribs) for comparison helps to identify conditions such as cardiac hypertrophy due to chronic or acute heart failure. Next, the shape and the borders of the heart should be examined. For example a “boot shaped” heart can indicate congenital heart deformities in children, and the loss of a distinct heart border could indicate an infiltrate in the adjacent lung tissue.

Mediastinum

The width of the mediastinum is also important to evaluate. The mediastinal structures should be just wider than the thoracic spine. When the dense structures in this area are much wider than expected, a life-threatening aortic aneurism should be suspected. As the aortic arch widens, it projects a higher-density shadow over the upper left chest cavity that is visible on the radiograph (Figure 11-7).

Other Disease States

Other common disease states can have typical findings on chest radiographs. The hyperinflation caused by an acute asthma attack may present as increased bronchial markings throughout the lung fields, a flattened diaphragm, and a maximally expanded chest cavity. Chronic obstructive pulmonary disease (COPD) causes similar effects, including a barrel-shaped chest (increased anteroposterior [AP] diameter), a flattened diaphragm, and an overall decreased density of the pulmonary markings.

CT scans of the chest can be a useful diagnostic tool for certain diseases (Figure 11-8). Like standard radiographs, CT uses ionizing radiation, but it allows for rapid scanning in much more detail. The CT scan generates pictures that are “slices” through the patient in the axial plane (Figure 11-9). Although bone is visualized much better than soft tissues, a CT scan can still provide excellent images of the lungs, vascular structures, and heart. New software can produce three-dimensional images that show the anatomy beautifully (Figure 11-10), and the sensitivity of these machines can allow for the detection of very small amounts of calcification in the coronary arteries, which can be an indication of early heart disease. Newer “ultrafast” CT scanners can see more subtle changes in the coronary arteries because they take images so quickly that they seem to “stop” or “freeze” the action and movement of the heart. This results in clearer pictures and the ability to discern small details more accurately.⁴ Another modality, called spiral CT scan, provides higher resolution and more rapid images, making it very helpful in the diagnosis of pulmonary embolism, because it can visualize vessels with great precision. In certain cases, an iodine-based dye must be injected intravenously to enhance CT images. This dye can exacerbate renal disorders, and should thus be used with caution.

As CT scans become more and more precise, they are also used more frequently. This increased use raises a concern regarding the radiation exposure of patients undergoing these studies. Although radiation exposure is also a factor with conventional radiography of the chest, the level of exposure with computed tomography has been documented to be much higher. A typical chest CT will expose a patient to the radiation equivalent of 50 to 450 chest x-rays. This increase in radiation exposure had been linked to cancer development later in life, most notably in the pediatric population. Because of this risk, other chest imaging techniques may be considered if appropriate.5,6

Magnetic Resonance Imaging

Magnetic resonance imaging of the chest can be performed to evaluate the soft tissues of the chest cavity.⁷ MRI has the advantage of using magnetic energy rather than ionizing radiation, so there is no harmful exposure for the patient. MRI scans also provide much higher-quality views of soft tissues than can be achieved by CT scans, but MRI is more expensive and takes nearly an hour to complete. A chest CT can be done in less than a minute, making it a better choice for evaluation of trauma (Figure 11-11). MRI is most useful when evaluating heart function/wall movement, vasculature of the heart and lungs, tumor size and staging, and respiratory movement of the muscles and diaphragm.^4,8

Summary

There are a variety of ways to image the chest. The standard chest radiograph is still an important way to gather information quickly, inexpensively, and at low risk for the patient. A physical therapist should be familiar with the basic techniques of reading a chest radiograph and should be able to identify common abnormalities viewable by x-ray, as well as other imaging methods, in order to better adapt their therapy regimen to fit the patient’s needs and oxygen demands.