With digital radiography, we are now able to electronically collimate images after acquisition. This may seem convenient, but there are also downsides to this technique. Post-processing collimation implies that the original field size should have been smaller, and that the patient has been exposed to unnecessary radiation. In addition, by using this process there is the potential of losing important information.
Before getting into some of these issues in further detail, I do want to note that the upgrade from screen-film radiography to digital imaging has provided us with many advantages. We can send images directly to the radiologist, and easily share images with the patient and other clinicians. Images can be archived and retrieved without loss of quality. Digital post-processing techniques can suppress artifacts and noise, and increase sharpness and contrast, improving image quality.
Issue #1: Reduced Field Size
Electronic collimation may be used to optimize contrast and suppress noise in the region of interest, but an image with the original field size should always be sent to the radiologist, since the radiologist is legally responsible for interpreting the entire image. Also note that the patient has the right to all information acquired during an X-ray examination.
Issue #2: Inadequate Collimation When Taking the Original Image
Since the implementation of digital radiology, there seems to be less motivation to properly collimate! This attitude is disturbing, to say the least. Adequate collimation reduces the amount of tissue irradiated and improves image quality by reducing scatter radiation. Inadequate collimation is responsible for the highest unnecessary integral dose to patients in diagnostic radiology.1
Issue #3: Increased Use / Exposure
The availability of digital imaging compared with screen-film radiography has also caused a tremendous increase in the use of imaging. Clinicians rely less and less on the clinical exam and become more dependent on imaging, increasing patient exposure to the harmful effects of radiation.2-3
Issue #4: Legal Issues Can Arise
Another issue with post-processing collimation: the legal ramifications, originating from the fact that the patient has the right to all the information acquired during an X-ray examination. If some of the patient's anatomy has been collimated post-processing, the radiologist can miss pathology.
Unfortunately, the practice of post-processing collimation occurs in many radiology departments across the country. When an X-ray series is performed without adequate collimation, the technician will use the software to improve the image. However, this process sometimes crops out anatomy that may have pathology. This can become a legal issue, especially if there is life-threatening pathology.
Cases in which this has occurred are noted in the material referenced at the end of this article; however, most of the time the lawsuit is settled out of court because the defense has no defense; the hospital settles for a huge sum and everyone involved is required to sign a gag order. The hospital sees it as money well-worth spending for not having the public find out that the imaging department makes these kinds of mistakes.4-5
Even in our profession, some may consider post-processing collimation a reasonable option. On occasion I have received three regions of the spine ( cervical, thoracic and lumbar) without the inclusion of the original AP full-spine image. This is not legal. We are legally responsible for reviewing the entire image, which on a full-spine X-ray includes the mandible, sinuses, chest, shoulders, abdomen, pelvis, etc.
Take-Home Points
- Post-processing collimation implies that the original field size should have been smaller, and that the patient has been exposed to unnecessary radiation.
- Post-processing collimation carries the risk of losing important information.
- The radiologist has the responsibility to evaluate the entire image.
- The patient has the right to all information that is obtained during an X-ray examination
References
- Okeji MC, Anakwue AM, Agwuna K. Radiation exposure from diagnostic imaging. Internet J Medical Update, 2010;5(2):31-3.
- Reza F, et al. Exposure to low-dose ionizing radiation from medical imaging procedures in the United States. New Engl J Med, 2009;361(9):849-857.
- European Society of Radiology: White paper on radiation protection by the European Society of Radiology. Insights Imaging, 2011;2:357-362.
- Bomer J, Wiersma-Deijl L, Holscher HC. Electronic collimation and radiation protection in paediatric digital radiography: revival of the silver lining. Insights Into Imaging, 2013;4(5):723-727.
- Bowman D. "The Trouble With Post-Processing 'Collimation.'" http://digitalradiographysolutions.com/the-trouble-with-post-processing-collimation/
