How to look at a chest X-ray

CHAPTER 1 How to look at a chest X-ray



1.1 Basic interpretation is easy 2

1.2 Technical quality 4

1.3 Scanning the PA film 10

1.4 How to look at the lateral film 13


1.1 Basic interpretation is easy


Basic interpretation of the chest X-ray is easy. It is simply a black and white film and any abnormalities can be classified into:


1. Too white.

2. Too black.

3. Too large.

4. In the wrong place.

To gain the most information from an X-ray, and avoid inevitable panic when you see an abnormality, adopt the following procedure:


1. Check the name and the date.

2. If you are using a picture-archiving system, see whether previous X-rays are on the system for comparison. The patient may have had previous X-rays which are stored on film. If you cannot access previous films, look for old radiology reports, which may be helpful.

3. Check the technical quality of the film. (Explained in Chapter 1.2.)

4. Scan the film thoroughly and mentally list any abnormalities you find. Always complete this stage. The temptation is to stop when you find the first abnormality but, if you do this you may get so engrossed in determining what it is that you will forget to look at the rest of the film. Chapter 1.3 explains how to scan a film.

5. When you have found the abnormalities, work out where they are. Decide whether the lesion is in the chest wall, pleura, within the lung or mediastinum. Chapter 2 explains how to localize lesions within the lung and the heart, Chapter 8 the mediastinum and Chapter 9 the ribs.

6. Mentally describe the abnormality. Which category does it fall into:
I. Too white.

II. Too black.

III. Too large.

IV. In the wrong place.

Chapters 4 and Chapter 9 will take you through how to interpret your findings.


7. Always ensure that the film is reported on by a radiologist. Basic interpretation of the chest X-ray is easy, but more subtle signs require the trained eye of a radiologist. Seeking a radiologist’s opinion can often expedite a diagnosis or the radiologist may suggest further imaging.

8. Finally, do not forget the patient. It is possible and, indeed, quite common for a very sick patient to have a normal chest X-ray.


1.2 Technical quality



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The next four X-rays are examples of how the technical quality of a film can affect its appearance and potentially lead to misinterpretation. Above is an AP film which shows how the scapulae are projected over the thorax and the heart appears large. Compare this to the film opposite which is a standard PA projection showing how the scapulae no longer overlie the thorax and the heart size now appears normal.



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Films on pages 6 and 7 show the effects of respiration. The above film is taken with a poor inspiration, and page 7 with a good inspiration. Note how the lung bases look whiter, and the heart size appears larger.



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Always check the technical quality of any film before interpreting it further. To do this you need to examine in turn the projection, orientation, rotation, penetration and degree of inspiration. Problems with any of these can make interpretation difficult and unless you check the technical quality carefully you may misinterpret the film.



Projection


Look to see if the film is anteroposterior (AP) or posteroanterior (PA). The projection is defined by the direction of the X-ray beam in relation to the patient. In an AP X-ray the X-ray machine is in front of the patient and the X-ray film at the back. In a PA film the beam is fired from behind the patient and the film placed in front. The standard chest X-ray is PA but many emergency X-rays are AP because these can be taken more easily with the patient in bed. AP films are marked AP by the radiographer and PA films are often not marked since this is the standard projection. If you are not sure then look at the scapulae. If the scapulae overlie the lung fields then the film is AP. If they do not it is most likely PA. If the X-ray is AP you need to be cautious about interpretation of the heart size which will appear magnified on an AP film because the heart is anterior. The shape of the mediastinum can also be distorted. An AP film can be taken with the patient sitting or lying. The film should be marked erect or supine by the radiographer. It is important to note this since the appearance of a supine X-ray can be very different to that of an erect one.

Related posts:

The widened mediastinum The abnormal hilum Localizing lesions The hidden abnormality The CT scan The black lung field

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Sep 3, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on How to look at a chest X-ray

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