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Collimation (Rad specific)


Appropriate collimation is performed to optimize image quality and minimize radiation dose


+ Reducing patient exposure

  • MRTs have a responsibility to ensure patient exposure is as low as reasonably achievable (ALARA) (also see the Minimizing patient exposure guideline).
  • Using collimation to limit the beam at the source is the most effective radiation protection for the patient and personnel.
    • Collimation narrows the area that the radiation can strike and the volume of tissue that gets irradiated, as well as reducing scatter radiation1-3

+ Improving image quality

  • Image quality is improved by limiting the X-ray beam to the smallest field giving the required diagnostic information.2,3
    • Optimal collimation also reduces image noise caused by scatter radiation originating from outside the region of interest1,4
    • Over-collimation and under-collimation lead to data recognition errors that affect the histogram in digital imaging1,5

+ Image post-processing

  • Post-processing techniques, such as shuttering/masking, are not acceptable substitutes for collimation.6
    • Both are image modification techniques that only mimic collimation
    • Neither shuttering nor masking limits the dose of radiation given to the patient

+ References

  1. Pongnapang N. Practical guidelines for radiographers to improve computed radiography image quality. Biomed Imag Interv J 2005;1(2):e12.
  2. European Commission. European Guidelines on Quality Criteria for Diagnostic Radiographic Images. Available at: Accessed February 22, 2013.
  3. Carroll QB. Radiography in the digital age. Springfield, IL: Charles C Thomas Publisher Ltd.; 2011.
  4. Henry Ford Health System, Radiation Safety Office. Reducing Radiation Exposure. Available at: Accessed February 22, 2013.
  5. Carter CE, Veale BL. Digital Radiography and PACS. Revised Reprint, 1st Ed. St. Louis, MO: Mosby Elsevier; 2010.
  6. Herrmann TL, Fauber TL, Gill J, et al. Best practices in digital radiography. ASRT White Paper. Available at: Accessed February 22, 2013.



May 8, 2013


Canadian Association of Medical Radiation Technologists
85 Albert St, Suite 1000, Ottawa, ON, K1P 6A4
phone: 613 234-0012 / 800 463-9729
fax: 613 234-1097