We have had hundreds of digital equipment training hours at my hospital in the past 10 years, but in all of that I don’t remember any time given in learning how to correctly critique the image. I have to imagine this is the same with everyone around the country, possibly the world.
Last month I wrote about how reliable the Exposure Index (EI) numbers are, especially when the collimation and centering were good. Today I am again to reiterate that these numbers have to be a huge part of the critiquing process. Without the actual phantom lateral skull images I use in all of my talks to prove my point, we are stuck with you just having to believe me.
I have taken my skull phantom and shot 9 different manufacturers to prove exactly how much mAs can be used and still have a passable image. Depending on the vendor one can use from 10 – 100 times too much mAs and still have a perfectly passable image, if a visual check is the only guideline being followed. This is why the EI numbers must be used.
Sometimes a radiographer will “post collimate” or “shutter” an image which depending on the vendor may change the EI number. As a huge side note, if any of the actual body is cropped out during this process, the image is now open for a lawsuit (see upcoming blog #4 on Feb. 15th).
Another “tool” to use is the magnification mode button. Quite often burn or mottle can only be seen with the image, or part of the image, being magnified.
The last “tool” to use is Level/Windowing. Whether your facility allows you to Level and Window the image and send it to PACS, all departments should allow a radiographer to Level and Window and then reset it before sending it to PACS. Whenever an image does not look perfect, one should always Level and Window it and see if the image can be made to look perfect (or at least much better). If after Level and Windowing the image does not look better, it is impossible to know if the radiologist can make it look better.
So as a quick synopsis, the 3 things that should be done to properly critique a digital image are:
- Check the EI number
- Use the magnification mode to check for burn and mottle
- Level and Window the image and either reset it or send it depending on your facility’s protocol