radiographs.Here is given a simplified approach to reading chest x -rays.
Most commonly the chest x rays are in a PA (posterio anterior) view in which the X-ray beam first
enters the patient from the back and then passes through the patient to the film that is placed anterior to the patient‘s chest. It uses 80–120 kV and focus film distance of 6 feet.
On a PA film, lung is divided radiologically into three zones:
1. Upper zone extends from apices to lower border of 2nd rib anteriorly.
2. Middle zone extends from the lower border of 2nd rib anteriorly to lower border of 4th rib anteriorly.
3. Lower zone extends from the lower border of 4th rib anteriorly to lung bases.
Radiological division does not depict anatomical lobes of the lung.
In a well-centered chest X-ray, medial ends of clavicles are equidistant from vertebral spinous process. Lung fields are of equal transradiance.
Apices are visualized free of ribs and clavicles on apicogram shown below:
The normal length of trachea is 10 cm, it is central in position and bifurcates at T4–T5 vertebral level. Left atrial enlargement increases the tracheal bifurcation angle (normal is 60°). An inhaled foreign body is likely to lodge in the right lung due to the fact that the right main bronchus is shorter, straighter and wider than left main bronchus
Normal heart shadow is uniformly white with maximum transverse diameter less than half of the maximum transthoracic diameter.
Cardiothoracic ratio is estimated from the PA view of chest. It is the ratio between the maximum transverse diameter of the heart and the maximum width of thorax above the costophrenic angles:
a = right heart border tomidline,
b = left heart border to midline,
C = maximum thoracic diameter above costophrenic angles from inner borders of ribs. Cardiothoracic ratio = a + b: c. Normal cardiothoracic ratio is 1:2
To detect any pulmonary pathology, it is important to remember the normal thoracic architecture, both lungs are compared for areas of abnormal opacities, translucency or uneven bronchovascular distribution in the lungs.
An abnormal opacity should be closely studied to ensure that it is not amalgamated opacity formed by superimposed normal structures such as bones, costal cartilages, vessels, muscles or nipple. Any opacity is evaluated by its extent, margins and location with presence or absence of calcification or cavitation. A general assessment survey is made to look for any other lesion or displacement of adjacent structures.