Back in the film days I would always give my students a technique chart that had about 50 different body parts on it. When we went digital in 2002, our vendor told to use the same techniques, so we continued to use those charts. Four years later we had learned all about the new optimum kVs from Barry Burns (for more information on optimum kV or why you would want to use a higher kV and lower mAs see blog #7 from April 1st).
In addition, Barry had taught us that all the manufacturers used the same style of x-ray tube and all large facilities used the same high frequency generators. Most important was the fact that regardless of what the manufacturers called their Exposure Index (EI) number, they all got their perfect EI number if the image receptor received 1 mR (for more on EI numbers and their ranges see blog #2 from January 15th).
Because of this I had the idea that a universal technique chart could be created, but needed to talk it over with Barry first. He agreed that as long as the x-ray room had a modern high frequency generator (all hospitals and large facilities have used only these generators for the past 25 years) then a universal chart was absolutely feasible. So I took my film/screentechnique chart, had my student Callie DeGuzman sit at the computer with a blank Excel chart in front of her and I did the 15% and 7 ½% Rule changes to the old techniques and came up with the new ones using the higher kV and lower mAs. Then we did this over 190 times and when we were finished we had a fully functional CR Universal technique chart.
Soon after our radiologist’s let us cut the mAs in half for every exposure (except for abdomen’s which had too much mottle/noise). These new images had a tiny bit of noise, which our radiologist’s called “acceptable mottle”. When you go my website and go into All Charts, you will see many versions of the CR technique charts. The first one is titled “Least mAs”, and the next one is “33% More mAs”, then “66% More mAs” and finally “100% More mAs”. What this means is there are 4 sets of charts which will work for all manufacturers except Konica, which has its own set of 4. The first chart titled “Least mAs” has the lowest amount of mAs, or in other words, the lowest dose. It would also have the biggest possibility of having images with mottle/noise.
So what I suggest to everyone is to do the following: Start with the “100% More mAs” chart and see how it works in your department. If the images are coming up fine and the EI number shows that you can use even less mAs, go to the “66% More mAs” chart. If the EI number shows you can continue to drop the mAs, go to the “33% More mAs” chart. Lastly you might be able to drop the mAs/Dose all the way down and begin using the “Least mAs” charts. As I mention in the disclaimer, your radiologist should always the final word if your image is diagnostic.
A few years later two DR rooms were built into our new emergency department with third generation GE using Cesium based detectors. Immediately we noticed that the techniques were noticeably less than our CR techniques. Two years after that we had three Siemens DR rooms installed in our main department and from there I could now compare techniques between these two major manufacturers. The Siemens Rad room has two built in Cesium based detectors while the fluoro rooms use a tethered Canon detector (Gadolinium based). During this time I discovered how similar both the GE and Siemens techniques were. It took a full 6 months of studying, writing and comparing techniques before I was able to develop the Universal Cesium and Gadolinium DR technique charts.These charts are pretty self explanatory, other than you need to know if your detectors are Cesium or Gadolinium based. The Gadolinium detectors use just about 50% more mAs than the Cesium detectors.