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Reading chest radiograph - Penetration

 PENETRATION 

Penetration is one of the five technical factors that help you in determining whether a radiograph is technically adequate.

 ADEQUATE PENETRATION 

If a frontal chest radiograph is adequately penetrated, you should be able to see the thoracic spine through the heart shadow.

In the radiograph above, we can see the thoracic spine through the heart shadow (solid white line).

 UNDER PENETRATION 
It means that the penetration is inadequate. The radiograph will appear as too white. We will not be able to see the thoracic spine through the heart. This can lead us into making interpretation errors.
1) The pulmonary markings may appear more prominent and these can be mistaken for being due to a congestive heart failure or pulmonary fibrosis.
2) The left lung base will appear opaque thus obscuring the left hemidiaphragm. This can mimic or hide a true disease in the left lower lung field e.g. left lower lobe pneumonia or left pleural effusion.

To avoid these misinterpretations always correlate clinically. Also if you are suspecting a congestive heart failure, look for other signs apart from increased pulmonary markings e.g. effusions, Kerley lines etc. A lateral radiograph will also help us when faced with these dilemmas.


In this frontal chest radiograph we can see that there is under penetration.

The solid black line shows that the thoracic spine cannot be seen through the heart shadow.

The broken black lines show that the left hemidiaphragm is not clearly visible.



 OVER PENETRATION 
In this case, the lung markings will appear decreased or absent. The patient may be mistaken of having a pneumothorax or emphysema. We may also miss a pulmonary nodule if the radiograph is too dark.


This is an example of an over penetrated chest radiograph.

At first glance we may suspect emphysema in this patient because of the increased lucency at the apices but when we look at the diaphragm we find that it is not flattened, which means there is no hyperinflation as expected for a case of emphysema.







First published on: 01 January 2016

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