How much can you over-radiate and still get a perfect image?

I decided to write and post this blog on the same day I changed my current research on my website.  This subject is one of the most exciting and scary things that is happening in our profession at this time.   If you go to the Current Research section, you’ll see handfuls of images proving that 5, 10, 50+ times too much mAs can be used and the images all look the same.

When I first started going to lectures on digital radiography, I heard that using 3-4 times too much mAs would cause noticeable changes in the images contrast and resolution.  This didn’t seem to match what I was seeing with our CR and DR equipment, so after a year of pleading and begging, CHOMP bought four phantoms and digital dosimeter to go with our abdomen phantom.  And with that; the “game” to finally understand what we were doing was on in earnest.

The first blog I wrote was about Creeping mAs/Dose.  I explained that one the reason’s this is occurring is because the digital computers all have the remarkable ability to automatically rescale the image.   So now an unbelievable amount of mAs (meaning way too much) can be used and a prefect image is created almost every time.

Without a body phantom to experiment with, it is impossible to see how easy it is to over-radiate a patient and still have a perfect (or at least very passable) image.  I have now been able to use my skull phantom on nine different manufacturers to determine how much mAs can be used, and over-used.  Currently I have four CR and five DR vendors.

From the experiments I’ve performed, all of the CR manufacturers except Agfa have the ability to “fix” an exposure that has been over-radiated by more than 50 times.  That is automatic rescaling at its finest.  It is also why no human being can see if an image was only over-radiated 2 or 3 times too much.  This is why it is impossible for anyone to be able to look at a monitor and tell if the patient was over-radiated, unless enough radiation was used to create burn on the image.  This is also why the EI numbers are the only way a radiographer can tell if the technique was correct.

I could go on and on (and do when I get to this section of my lectures) but I just hope you have a few minutes to go to the Current Research section of my website and see the images for yourself.  If there ever was a time where a picture is worth a thousand words, it will be there.

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