Chest (expiratory view)

The expiratory chest radiograph increases the attenuation of normal lung, thereby increasing the contrast between lung and pneumothorax or demonstrating unilateral air trapping.

Other effects include widening of the cardiac silhouette due to a more horizontal position and increased basal opacity which obscures the pulmonary blood vessels, mimicking lung disease ³. 

Indication

Expiratory radiographs are used to increase the conspicuity of small pneumothoraces, although sensitivity is not increased over inspiratory chest radiographs ¹.

A forced expiration chest radiograph or FEV1 exposure is used to assess unilateral air-trapping in Swyer-James syndrome or suspected inhaled foreign body ^2,3. The mediastinum typically shifts to the normal side on expiration.

Patient position

• PA projection

  • patient is erect facing the upright image receptor, the superior aspect of the receptor is 5 cm above the shoulder joints

  • the chin is raised as to be out of the image field

  • shoulders are rotated anteriorly to allow the scapulae to move laterally off the lung fields, this can be achieved by either:

    • hands placed on the posterior aspect of the hips, elbows partially flexed rolling anterior or

    • hands are placed around the image receptor in a hugging motion with focus on lateral movement of the scapulae 

  • shoulders are depressed to move the clavicles below the lung apices

• AP projection

  • patient is erect facing the x-ray tube, the superior aspect of the receptor is 5 cm above the shoulder joints

  • the chin is raised as to be out of the image field

  • the arms are internally rotated to attempt to remove superimposition of the scapulae over the lung fields, although this is not always possible on an AP projection

  • shoulders are depressed to move the clavicles below the lung apices

Patient position

• patient is erect facing the upright image receptor, the superior aspect of the receptor is 5 cm above the shoulder joints

• the chin is raised as to be out of the image field 

• shoulders are rotated anteriorly to allow the scapulae to move laterally off the lung fields, this can be achieved by either:

  • hands placed on the posterior aspect of the hips, elbows partially flexed rolling anterior or

  • hands are placed around the image receptor in a hugging motion with focus on lateral movement of the scapulae

• shoulders are depressed to move the clavicles below the lung apices 

Technical factors

• posteroanterior or anteroposterior projection

• suspended expiration

• centering point

  • the level of the 7^th thoracic vertebra, approximately the inferior angle of the scapulae  

• collimation

  • superiorly 5 cm above the shoulder joint to allow proper visualization of the upper airways 

  • inferior to the inferior border of the 12^th rib 

  • lateral to the level of the acromioclavicular joints

• orientation  

  • portrait or landscape 

• detector size

  • 35 cm x 43 cm or 43 cm x 35 cm

• exposure

  • 100-110 kVp

  • 4-8 mAs

• SID

  • 180 cm

• grid

  • yes

Image technical evaluation 

The entire lung fields should be visible from the apices down to the lateral costophrenic angles. 

• the chin should not be superimposing any structures

• minimal to no superimposition of the scapulae borders on the lung fields

• sternoclavicular joints are equal distant apart

• the clavicle are in the same horizontal plane

• the ribs and thoracic cage are seen only faintly over the heart 

• clear vascular markings of the lungs should be visible

Practical points

• ask the patient to practise suspended expiration or forced expiration as appropriate

• patient rotation causes unilateral hypertransradiacy of the lung and can mimic Swyer-James syndrome

• grid cut-off causes unilateral hypertransradiancy of all tissues, including lung

• Poland syndrome and mastectomy cause hypertransradiancy on the affected side