Emphysema, 492.8
Pericardial effusions, 423.9
Pneumonia, 486.
Pulmonary nodules (also called coin lesions), 793.1
GENERAL PRINCIPLES
I. Most common views
A. Anteroposterior (AP) films (back against film plate)
1. Usually obtained with a portable x-ray machine
a. Indicated when patient’s condition precludes prudent travel
b. Most often done supine unless specified as upright
2. May limit attainment of optimal image
a. More magnification, less sharp image
b. Supine position
i. May limit inspiration and lead to misinterpretation
ii. Unable to reveal free pleural fluid level
iii. Flattening of posterior surface of heart, causing lateral borders to be falsely widened
B. Posteroanterior (PA) films (chest against film plate)
1. Usually obtained in the x-ray suite
2. Most often done upright
3. May allow optimal image
a. Less magnification, more sharp image
b. Upright position
i. Deeper inspiration shows more of the lung.
ii. Dependent free pleural fluid level more evident
iii. Less distortion (widening) of cardiac silhouette
II. Adequacy of the film
A. Some portion of the x-ray beam is absorbed by the material(s) it passes through before reaching the film plate.
1. Air, fat, soft tissue (water), and bone (metal) absorb progressively more radiation.
B. Only the portion of the beam that penetrates the material (is not absorbed) will create an image on the film.
1. A high degree of penetration (low absorption) will create a black area on the film.
2. A low degree of penetration (high absorption) will create a white area on the film.
C. Sufficient detail in the image is largely determined by the intensity of the x-ray beam.
1. Optimal penetration is generally judged by the clarity of the vertebral bodies in the image.
a. Overpenetration: beam too intense, resulting in overly dark image with subtle details rendered invisible
b. Underpenetration: beam insufficiently intense, producing an overly white image; all detail is lost in the glare
D. The x-ray beam should be perpendicular to the film and/or anatomic plane so as to avoid distortion of structural relationships and sizes.
1. In the PA/AP view, clavicular symmetry is a general indicator of chest rotation from the perpendicular plane.
a. Clavicles should be approximately equal in length.
b. Clavicular heads should be in the chest midline.
E. The film should be exposed during a deep inspiration to produce good alveolar inflation and avoid diaphragmatic displacement of the heart.
1. A general indicator of adequate inspiration is the seventh rib visible at or above the diaphragm.
2. Inadequate inspiration flattens the inferior border of the heart, causing the lateral borders to falsely widen.
READING A CHEST X-RAY
I. Keys to consistent accuracy
A. Understanding of normal anatomic relationships in three dimensions (not covered in this chapter)
B. Understanding the impact of pathologic changes on image
D. Compare with previous films, when available.
II. Basic impact of disease on image
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A. Silhouette sign
1. Contrasting border between adjacent areas with normally dissimilar densities is obscured as area of least density acquires more water (becomes more dense).
2. Useful in localizing lesion. For example, if an area of increased density in the right lower lung (RLL) field obscures the borders of the heart and the hemi-diaphragm, the lesion is in the RLL; if only the border of the hemi-diaphragm is lost, the lesion is in the right middle lung (RML).
B. Interstitial pattern
1. As the pulmonary interstitium (bronchial tree and vasculature) acquires more water (more density), it becomes more distinct.
2. Appears as aerated lung with distinct linear or nodular markings
3. Diffuse interstitial patterns likely indicate chronic disease.
C. Alveolar pattern
1. As alveoli fill, consolidate, or collapse, interstitial markings become less distinct (similar to silhouette sign).
2. Remaining air-filled bronchi may show up in contrast against otherwise non-aerated lung (air bronchogram).
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