You don't really need to collimate with CR... you can simply crop your images.
Unfortunately, this is a practice seen all too often. Most Technologists will not admit to it, but I know it happens. Just ask any Radiography Student. There are several reasons this is a poor habit to get into.
Radiation Protection - it should be a priority of every Technologist to maintain radiation dose ALARA. If you are knowingly including anatomy within your field that is not necessary for the sake of the exam you are performing, it is unethical to expose your patients in this manner. Pure laziness!
Unfortunately, this is a practice seen all too often. Most Technologists will not admit to it, but I know it happens. Just ask any Radiography Student. There are several reasons this is a poor habit to get into.
Radiation Protection - it should be a priority of every Technologist to maintain radiation dose ALARA. If you are knowingly including anatomy within your field that is not necessary for the sake of the exam you are performing, it is unethical to expose your patients in this manner. Pure laziness!
Reduction in image quality - the same basic principles of radiation physics apply during image production whether you are talking about film/screen, CR or DR imaging. If you are exposing a larger area of tissue than you need to for the body part you are imaging, you will be creating unnecessary scatter radiation. Knowing that digital systems are more sensitive to scatter and background radiation should influence the Technologist to be even more conservative on the collimation, and not the other way around. It's true that the image can be adjusted post-processing to make changes to image contrast, but not recommended. The raw data from the initial exposure will contain information from scatter radiation that degrades image quality even if you manipulate it later... garbage in, garbage out.
Increased risk of processing errors - we know that the initial data will be evaluated by the software to find the "values of interest" for each radiographic exposure. The idea is that the anatomical regions that you are attempting to obtain a diagnostic image of should be manipulated during the initial processing algorithm to be displayed to appear appropriately at the display after processing - the best way to accomplish this is to use the correct exposure factors and collimate. The more data included in your initial data set that does not need to be included in the image, the greater the risk that the "values of interest" will not be properly detected (see "Anatomy of a Histogram" for more detail). If a large number of dark (exposed) pixels are included in the VOI by mistake, the software assumes that there is an overexposure due to the average pixel value being on the darker side. Performing its function, the software will make the entire image display lighter than desired.
Legal concerns - I have not been able to reference any legal cases in which cropping anatomy that was recorded has ever caused a patient harm, but that doesn't mean the potential for such a situation does not exist. We will be required to report dose information in the near future for all exams. It's already starting with CT, and general radiology will be soon to follow. If the total dose administered for every type of exam that you perform is 30% greater compared to another technologist, you can see how your employer may consider you to be a liability.
I'm not sure that it's appropriate to say that this post is about a myth, but it does seem like a general assumption that many Technologists make. Perhaps we all need to be reminded that just because technology exists that help with sloppy practices, it doesn't mean we should become complacent about our imaging techniques... and I'm off my soap box.
Other posts in this series:
.
No comments:
Post a Comment