January 22, 2016
Article submission by Sharon Cheek BS RT (R) (M) Central Region Advisor
I chose a topic for this month that students and radiographers employ on a regular basis with all exams but may have a different understanding of the terminology. I thought it might be a good opportunity to discuss some basics. Let’s begin with collimation. All of us learned in our professional training that the restriction of the beam helps to protect the patient from unnecessary radiation and reduces the amount of scatter radiation that can reach the IR and reduce the contrast resolution.
With the introduction of DR (Digital Radiography) automatic collimation or (PBL) positive beam limitation isn’t possible except with the newer units that have preset collimation sizes. It is the responsibility of the radiographer to collimate to the correct field size to include only the anatomy of interest. As a reminder, it is a violation of the Code of Ethics to collimate larger than the required field size. Using the reasoning that “I don’t want to miss anything” is unacceptable. This is the purpose of being a professional and receiving proper training.
The software in the computer of the DR systems allows the radiographer to employ shuttering. Shuttering is a post processing technique that may be used to eliminate ambient light around an image for the sole purpose of improving the quality of the displayed image. It should not be used as a substitute for insufficient collimation of the irradiated field.
It is the position of the American Society of Radiologic Technologists that a digital image should not be cropped or masked such that it eliminates areas of exposure from the image that are presented for interpretation. Pre-exposure collimation of the x-ray beam is necessary to comply with the principle of as low as reasonably achievable (ALARA). To determine that exposed anatomy on an image is not significant or of diagnostic value is a medical decision and is therefore outside of the scope of practice for a radiologic technologist.
Adopted, Main Motion, C-14.10, 2014
Electronic Masking indicates electronic collimation or cropping of the digital radiographic image that occurs during post-processing of the acquired image and does not alter the size of the irradiated field.
Cropping is the term used mainly for the process of selecting and removing a portion of the image.
An example of this might be using the L5/S1 spot being cropped from the Lateral Lumbar image.
Cropping is also done post processing.
It is the position of the American Society of Radiologic Technologists that an image obtained for a prescribed projection in a digital imaging system or series be assigned only to that specific projection and not be altered by post-processing in order to be represented as another projection. Adopted, Main Motion, C-14.07, 2014
(Quality of Evidence: High) Scopes of Practice and Practice Standards Reference
With written permission of the ASRT, I have include a direct link to Practice Standards for Medical Imaging and Radiation Therapy / Advisory Opinion Statement.
ASRT Advisory Opinion Statement
Use of Post-Exposure Shuttering, Cropping and Electronic Masking in Radiography