There are only 5 reasons why a radiographer would change a technique (and 8 ways you could do it without using distance). As the how’s are not nearly as interesting as the whys, we’ll start with why you would change a given technique. Here are the 5 reasons:
- Increase kV, decrease mAs = you want to lower the dose.
- Increase kV, decrease mAs = you want to decrease the time. This is relevant with all portable machines that have a built in 100 mA station (which is most of them).
Even if your reason is to decrease the time, you are also decreasing the dose to the patient. If you remember from my blog “HOW LOW CAN YOU GO?” posted on 6/15/2013 that by adding 15% more kV and halving the mAs the entrance dose to the patient will be cut by almost 33%!!
- Increase mAs, kV stays the same = original image was underexposed.
This is the worst scenario concerning dose as it will proportionally increase as the mAs increases. The kV should stay the same only if you are using the highest kV possible.
- Decrease mAs, kV stays the same = original image was overexposed.
This is a great scenario concerning dose as it will proportionally decrease as the mAs decreases.
- Increase or decrease mAs, kV stays the same = decision made before exposure is taken because of visual clues taken from the patient’s body habitus, condition or disease or you don’t like the technique someone else already used.
Reasons 1,2 and 5 were made before the original exposure while 3 and 4 were made after (for a repeat).
Here is the list of the 8 ways you can change a technique using just mAs and/or kV:
- Increase kV, mAs stays the same
- Increase kV, increase mAs
- Increase kV, decrease mAs
- Decrease kV, mAs stays the same
- Decrease kV, decrease mAs
- Decrease kV, increase mAs
- Increase mAs, kV stays the same
- Decrease mAs, kV stays the same
I wrote this article for a few reasons.
1. I wanted to show how many things may need to be considered when choosing the perfect technique.
2. I wanted to show that both the how’s and the whys definitely matter.
3. I also wanted to put it out there once again that with higher kV and lower mAs the dose to your patient is always better.