How to Read Chest X- Ray

Chest X-ray is the most commonly done radiographic investigation in hospitals. House officers MUST know how to interpret a Chest X-Ray in a systematic manner.

STEP 1

 No imaging can help you to come to a diagnosis without  the clinical information of the patient. So know your case first before looking at the X-Ray film.
* This is the reason why radiologist insist you to write patient’s history,  clinical findings and investigations on radiology imaging request forms.


STEP 2

As you look at the Chest X-Ray the very first thing that you need to do is verify details on the film.
1.     Name of the patient
2.     Identity / Hospital Reg. No
3.     Date and time of the imaging
4.     What view ? PA / AP / Lateral


STEP 3

The next step is to look for 1.Rotation, 2.Exposure and 3.Expansion

Rotation -  Bilateral medial clavicle ends have to be at an equal distant from the spinous process.

If the film is rotated, certain appearance may become misleading like :
a) Changes in the lung density due to asymmetry of overlying soft tissue may be incorrectly                     interpreted as lung disease.
b) If the patient is rotated to the Left the heart may appear enlarged and if rotated to the right its size       may be underestimated.

Example of a non- rotated film

Example of a rotated film

EXPOSURE - Exposure or level of penetration is assessment of degree to which X-rays have passed through the body. Assessment of penetration is a standard part of assuring chest X-ray quality.

A well penetrated chest X-ray - a) Vertebral bodies and spinous processes are just visible behind the heart with faintly visible intervertebral disc spaces.
 b) The left hemidiaphragm should be visible to the edge of the spine. 

CXR with adequate exposure

                                                 

Under penetrated chest X-ray -
a) Thoracic Vertebrae not visible behind the heart                                                                                  
b) The left hemidiaphragm not visible to the edge of the spine..
c) X ray looks fairly whitish



Over penetrated chest X-ray - 
a) Vertebral bodies and spinous processes are clearly visible behind the heart with distinctly visible intervertebral disc spaces.
b) The film looks blacked out


Expansion - Chest X-Rays are taken during deep inspiration - the patient has to hold his/her breath for few seconds when the X-ray is being done. Those who are dyspnoic and unable to follow instructions would not have taken good inspiration during X-ray which would produce a 'Poor Inspiratory' film (under expanded lungs).


Some patients might have obstructive lung diseases that causes air trapping in lungs that would result in 'Hyperexpanded' CXR.


So to assess adequate expansion it is conventional to count ribs down to the diaphraghm. The diaphragm should be intersected by the 5th to the 7th anterior ribs in the mi clavicular lines. Less is a sign of incomplete inspiration and more is a sign of hyperexpansion.

                       

Hyper expanded CXR

( Count the level of rib intersecting at diaphragm @ MCL)

STEP 4

 Analyzing anatomical structures Systematically

I use my own mnemonic to analyze the structures - A2 B2 C2 D S

A - Artifacts and Airway ( Large Airways )
B - Bones and bronchial tree
C - Cardiac shadow and Costophrenic angles
D - Diaphragm
S  - Soft tissue 


Artifacts in CXR
Abnormal shadows in the film or poor image quality produced by artificial means. Common artifacts theat are seen in CXR are caused by radio opaque objects that are found on or externally in a patient.

Artifacts that are commonly seen are - Ryle's Rube, Pacemaker and the wires, sternal pins in post CABG patients, orthopaedic implants like clavicular plate, spine implants, chain orn by the patient and etc.

Airway - Large Airways 
1. Examine trachea - look for deviation from central position, stenosis and Foreign body.
2. Trace the right and left main bronchus - look for deviation, stenosis and Foreign body.

Bones 
Examine the bony structures one by one - Clavicle, Ribs and Spine
Look for lytic lesions, fractures and deformity.

Bronchial Tree ( small Airways )
1. Examine the small airway from hilar region to  peripheries.
2. Look for opacification (mass/hepatization in penumonia/pulmonary edema), reticular shadowing (fibrosis), honeycombing (bronchiectasis).

Cardiac Shadow
1. Look at the borders of cardiac shadow - a poorly demarcated border could possibly due to pnemonic changes in the adjacent lung field.
2. Measure the Cardiothoracic ratio. CTR of more than 0.5 indicates Cardiomegaly.
* The cardiac shadow is usually appear bigger in AP films and may falsely indicate cardiomegaly. PA films are better to assess cardiomegaly.

How to measeure CTR ??
- Measure the distance from a centre point of the film (spine) to the lateral most point of the cardiac shadow on both sides. Add the distance and divede with Thoracic span length.

Cardiomegaly is present if CTR > 0.5  - If cardiomegaly is present look hard for Septal Kerley B lines and pleural effusion ( signs of pulmonary edema )