Abdominal radiography

Abdominal radiography can can be useful in many settings. Before the advent of CT, it was a primary means of investigating gastrointestinal pathology and often allowed indirect evaluation of other abdominal viscera.

Indications

Although abdominal radiography has lower sensitivity and specificity than a CT of the abdomen, it still serves a role as an adjunct or optional test. Current uses for abdominal radiography include:

• a preliminary evaluation of bowel gas in an emergent setting

  • a negative study in a low pretest probability patient may obviate the need for a CT study and therefore lower radiation dose

• evaluation of radiopaque tubes and lines

• evaluation for radiopaque foreign bodies

• evaluation for postprocedural intraperitoneal/retroperitoneal free gas

• monitoring the amount of bowel gas in postoperative ileus

• monitoring the passage of contrast through the bowel

• colonic transit studies

• monitoring renal calculi

Contraindications

• pregnancy is a relative contraindication to the use of ionising radiation

  • non-ionising studies (e.g. ultrasound or MRI) should be tried first

  • abdominal radiographs administer a much lower radiation dose than CT

Projections

Standard projections

• AP supine view

  • can be performed as a standalone projection or as part of an acute abdominal series

• PA erect view

  • often taken with the supine view, when used together it is a valuable projection in assessing gas-fluid levels, and free gas in the abdominal cavity.

• KUB view

  • used to visualise calculi within the urinary system (kidneys, ureters, bladder)

Additional projections

Generally, plain radiograph examination of the abdomen comprises an AP supine and PA erect view, supplemented by a number of additional views as clinically indicated. 

NB: please note that in the UK, a single supine abdominal radiograph is the norm, i.e. erect abdominal x-rays have not been routinely performed for decades ².

• lateral decubitus view

  • performed as an alternative to the PA erect view to assess for free gas in the abdominal cavity 

• lateral view

  • often used as a problem solving view during the identification and localisation of foreign bodies  

• PA prone view

  • performed if the patient is unable to lie supine

• dorsal decubitus view

  • used when it is unsafe to perform both a PA erect or a lateral decubitus view, this projection requires no patient movement.

• oblique views

  • used in barium studies and the location of foreign bodies and/or lines such as a Tenckhoff catheter 

Procedure

Preprocedural evaluation

The patient should be gowned with minimum clothing. Radiopaque materials (zippers, belts, etc.) should be removed.

If relevant, enteric tube suction should be avoided before the study. Ideally, the patient's bladder should be emptied as well.

Technique

Abdominal radiographs may be obtained in the radiology department or may be performed portably. Views should generally include either the diaphragm or inferior pubic ramus. Gonadal shielding may be provided for men.

Portable abdominal radiographs may be necessary due to patient immobility but are of much poorer quality. 

kVp

The kVp of the x-ray beam may be altered in order to bring out different aspects of the abdominal radiograph:

• lower kVp offers greater tissue contrast and better visualisation of gas, but there is decreased penetration of the x-ray beam

• higher kVp may be useful for evaluation of radiopaque objects (contrast, tubes, lines, etc.)