A Quick Guide to Chest X-Rays

Chest X-Ray by Tor Ercleve

A systematic approach to Chest X-Ray (CXR) interpretation is essential to avoid missing significant pathological changes. With time and practice, interpreting CXRs will become easier, but first you have to find an approach that works for you.

The Basics
Before we begin with our approach to CXR interpretation, there are some principles we need to understand. A chest radiograph uses ionising radiation (usually 0.06 mSv) to paint a picture of your internal chest anatomy. The dose of radiation from an individual X-Ray is typically of little concern. However if you're worried check out XKCD's Guide to Radiation.

It is important to note that not all chest structures will be seen on CXR, and some will only show up if an abnormality is present (e.g. pleura).

Adapted from Wikipedia

4 Main Radio-densities
When looking at a CXR it's important to get a grasp on anatomical & foreign structures will be presented. There are 4 main Radio-densities to be aware of;
◘  Gas = Black
◘  Fat = Dark grey
◘  Water = Light grey
◘  Bone/metal = White

Rule 1: The denser the tissue, the whiter it will appear on x-ray.

Views
The next thing to consider is what angle are you viewing the chest from. The most common view is the Posterior-Anterior, otherwise known as a PA film. Other views are;
◘  Anterior-posterior (AP)
- Exaggerates heart size. 
- For less mobile or emergency patients.
◘  Lateral CXR
◘  Decubitus
◘  Oblique
◘  Supine or standing?
 
Interpreting for Beginners
We will start with the most simple of interpretation methods that apply nearly to all radiological images.

Rule 2: Always check Patient Details & Film Type.
◘  Who: correct patient
◘  When: correct day
◘  Why: what is the indication for the test / what are we looking for?
◘  What: what is the image of?
These basic questions will set you in good stead before commencing on the intricacies of interpreting. Next consider, what systems are present in the image, and then identify and examine them.

Mnemonics can be a good way of making sure that you don't miss anything when your first starting out. I've included a number of examples below. At the end of the day, your approach to CXRs is basically what works for you.

Simple Interpretation
1. Check patient details & technical adequacy.    
2. ABC Method – Airways, breathing, circulation.

ABC Method
Airways
◘  Trachea
◘  Hilar
Breathing & Bones
◘  Lung fields, pleura. Costophrenic Angles.
◘  Bones – destruction, #s
Circulation & Soft tissues.
◘  Mediastinum – width.

Another option is the;

DCBAA Method
D ocuments
C hest
◘  Compare lungs
◘  Airway (right place, deviation)
◘  Mediastinum
◘  Diaphragm
◘  Pleura
B ones
◘  Look at all the bones.
◘  Pattern recognition.
A bdomen
◘  Frees gas - erect Chest X-Ray under diaphragm. 
A nd Areas
◘  Additional areas that you wouldn't normally look at.
Common Mistakes
This list of common mistakes comes courtesy of Duncan;
◘  Did I stop looking after I found one abnormal finding? Do I need to complete my system?
◘  What are the commonly missed things in this situation/imaging modality?
◘  Am I tired / bored / distracted?
◘  How do the clinical findings and the radiographic findings correlate?
◘  Have I examined the patient properly (ED juniors, a shoulder x-ray is not a substitute for an examination)
Beyond the Basics - ABCDEFGHI Method
Airway (midline, patent)
Bones (eg, fractures, lytic lesions)
Cardiac silhouette size
Diaphragm (eg, flat or elevated hemidiaphragm)
Edges (borders) of the heart (to rule out lingular and left middle lobe pneumonia or infiltrates)
Fields (lung fields well inflated; no effusions, infiltrates, or nodules noted)
Gastric bubble (present, obscured, absent)
Hilum (nodes, masses)
I   Instrumentation (eg, lines, tubes)


The DRSABCDE Method
Developed by Matthew Lumchee, the DRSABCDE method brings back the familiarity of the Basic Life Support algorithm whilst throwing in some additional features to CXR Interpretation. For more details on this method checkout Lifeinthefastlane.com.


Got any more tips for approaching Radiology?
Then Share Them Here.

Further Resources
  1. 1. Chest X-Ray Atlas - http://www.meddean.luc.edu/lumen/meded/medicine/pulmonar/cxr/atlas/cxratlas_f.htm
  2. 2. Medline: Chest X-Ray (info for patients) - http://www.nlm.nih.gov/medlineplus/ency/article/003804.htm
  3. 3. Radiology Masterclass - http://radiologymasterclass.co.uk/index.html
  4. 4. Radiopedia.org (an atlas)
  5. 5. The Radiology Assistant

Not quite sure how to interpret an ECG? 
Then have a look at A Quick Guide to ECG.
References
Crausman RS. The ABCs of chest X-ray film interpretation. Chest. 1998 Jan;113(1):256–7.

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