The quality reference mAs is the mAs that we would give to a patient if we were to use a fixed technique for an average sized patient. CARE Dose4D defines an average sized patient as 75 kilogram.

CARE Dose4D is going to modulate up and down based on that midpoint. What you should be doing when you set your quality reference mAs is to set it for the mAs that you would give to an average patient for that specific protocol.

One of the other nuances to recognize with CARE Dose4D is that there’s no upper limit to the amount of mAs that you apply to the patient. The only limit is the power of the x-ray tube itself. With CARE Dose4D, you’re setting a midpoint and then modulating up and down from there. 

Looking at the prescan CTDI is really important because you could end up in a situation where you’re giving the patient a higher dose than what they should get. You should be able to tell by looking at the prescan CTDI if that looks normal for the size of patient. Develop a habit particularly on a Siemens scanner of looking at that prescan CTDI to make sure that your dose isn’t modulating too high or potentially too low as well.

The Siemens guidance documents on CARE Dose4D say that you don’t need to create large patient or obese patient protocols. The reason for this is because the tube current is going to modulate up based on what it’s seeing in the scout and the quality reference mAs. You don’t need to increase the quality reference mAs. You don’t need to create a different protocol for large patients because it should all be taken care of by just using CARE Dose4D the way that it is out of the box.  

So if you have a value that fails like this 3.19%, when the criteria is 3%, what do you do?

The first thing we recommend to people to do is to go through a tuning and peeking exercise on the equipment. Go through the tuning and peaking exercise, do all of the things that you can run before you get to the uniformity test and then rerun the flood.

Oftentimes that will correct the issue. If that doesn’t correct the issue, you can go back in and rerun and an intrinsic calibration. When you run an intrinsic calibration, we sometimes call that a high count flood. With the Siemens systems, you need to do at least 120 million counts. 

Oftentimes they’re set to 200 million counts, and this can be quite timely. But when you’re redoing that intrinsic calibration you’re going to smooth out any non uniformity that you see in the intrinsic verification. When you do the intrinsic calibration, there is a specific criteria associated with it that you can find in the manual.

For intrinsic calibrations, we say that they can compensate for values up to about 10%. If you exceed 7% for the calibration, then you need to contact service. If your intrinsic calibration passes and you don’t see any issues, you’re below the 7% on the intrinsic calibration. 

Now you can rerun your intrinsic verification or daily flood and see if you you pass those values. If you are still not passing those values, that’s the point that you should probably contact either service or contact your physicist to try to get some direction on what it is that you need to do in order to get your camera to pass the manufacturer stated specifications.