02.02.04. Collimation
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) (see related guideline Minimizing patient exposure).
- 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 radiation1-4
Improving image quality
- Image quality is improved by limiting the X-ray beam to the smallest field giving the required diagnostic information2-4.
- Optimal collimation also reduces image noise caused by scatter radiation originating from outside the region of interest1,5
- Over-collimation and under-collimation lead to data recognition errors that affect the histogram in digital imaging1,6
Image post-processing
- Post-processing techniques, such as shuttering/masking, are not acceptable substitutes for collimation7.
- Both are image modification techniques that only mimic collimation
- Neither shuttering nor masking limits the dose of radiation given to the patient6
References
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Pongnapang N. Practical guidelines for radiographers to improve computed radiography image quality. Biomed Imag Interv J 2005;1(2):e12.
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European Commission. European Guidelines on Quality Criteria for Diagnostic Radiographic Images. www.sprmn.pt. 1996. Available from: https://www.sprmn.pt/pdf/EuropeanGuidelineseur16260.pdf. [Accessed 23 May 2018]
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Carroll QB. Radiography in the digital age. 3rd ed. Springfield, IL: Charles C Thomas Publisher Ltd.; 2018.
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Statkiewicz Sherer MA, Visconti PJ, Russell Ritenour E, et al. Radiation Protection in Medical Radiography. 8th ed. St. Louis, MO: Elsevier, 2018.
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Henry Ford Health System, Radiation Safety Office. Reducing Radiation Exposure. Available from: http://www.radiologyresearch.org/RadiationSafety/FluoroscopyTrainingChapter5.aspx. [Accessed 22 Feb 2013]
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Carter CE, Veale BL. Digital Radiography and PACS. 2nd ed. St. Louis, MO: Mosby Elsevier; 2013.
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Herrmann TL, Fauber TL, Gill J, et al. Best practices in digital radiography. ASRT White Paper. Available from: http://www.asrt.org/docs/whitepapers/asrt12_bstpracdigradwhp_final.pdf. [Accessed 22 Feb 2013]