Do technical factors matter on interpretation of a Chest X-ray?
Yes, they do. Take the following examples.
This Xray looks Exceptionally dark. You may be confused there might be bilateral pneumothorax ( air in the pleural cavity) or emphysema by looking at the lungs. But actually, this is a technical default of over penetrated Xray. How I recognize this from pathology (emphysema) is that if I see both lungs very dark, I try to see for the vertebral bodies first to see if it is over penetrated.
A normally penetrated Xray is the Xray where the intervertebral discs of 7-8 thoracic vertebra are visible. In an over penetrated Xray, instead of the visualization of the intervertebral discs, the whole morphology of the thoracic vertebras will be visible. This will look like a Xray of the Thoracic Spine, instead of a Chest Xray.
An Underpenetrated Xray.
Here, the Xray is more opaque and appears white. You can’t see the intervertebral discs from behind the heart. This is a case of underpenetrated Xray. When you see exceptionally white lungs, ask the technician to repeat the Xray. Otherwise, you may miss pathologies. Small soft nodules may be missed because the Xray is too white.
In this Xray, The lower part of the right lung appears more opaque than the left lung. We can also see that the lower zone of both lungs is hazy near the costophrenic angle region.
In the first instance, one may think that this is a case of the infective process ( pneumonitis ) in the right lung. But the patient was asymptomatic.
There are two technical faults in this Xray.
1. The first fault in the chest Xray is the degree of inspiration. Only 5 anterior and 8 posterior ribs are visible. The patient didn’t inspire to his fullest. Normally, the anterior 6th rib should cross the right hemidiaphragm and the posterior 9-10 rib should cross the hemidiaphragm.
Note how the degree of inspiration changed the appearance of the same Xray taken some time afterward. Now it is normal.
2. Another fault in this chest Xray is rotation. The right clavicle ( yellow arrow) is shifted downward in comparison to the left clavicle. They should be almost at the same level and their medial ends should be near to the spinous process as much as possible. Take for example in this image-
This is a part of chest Xray with good centering. The medial end of both the clavicles are near the midline by an equal distance.