You probably already know that automatic exposure control (AEC) is an excellent way to help reduce the radiation dose to the patients you scan with your CT scanner. What may still be confusing you are all the different names for AEC systems.
In the case of GE CT scanners, the AECs are called AutomA and SmartmA. Cool names, huh? Everyone loves it when something is done for them AutomA-tically, and if SmartmA is half as smart as your smartphone, it's gotta be awesome too, right? Of course. But hi-tech sounding proprietary names won't tell us how these controls work and what makes them different from one another. So- let's break it down.
AutomA vs. SmartmA
AutomA and SmartmA are esentially two sides of the same radiation dose-reducing coin. Both controls adjust mA up or down over the course of a scan to optimize dose on a patient-by-patient basis. The biggest difference is what triggers adjustment from each of them.
AutomA changes dose based on the thickness and radiation attenuation of tissues along the length of the patient's body (Z axis). For example, bony areas, like the upper chest or around the hips and pelvis, will need a higher mA to get a clear image. AutomA will increase the mA in those areas. In areas like the abdomen, which are comprised of softer tissues, AutomA will turn the mA down. This results in a significantly lower overall radiation dose than leaving the mA at "bone level" for the entire scan.
SmartmA is the GE proprietary name for the more general AEC term, "rotational AEC". As far as the outcome of its use, SmartmA does very much the same thing as AutomA- adjusting dose up or down to the optimum level for any given point in a scan. However, instead of responding to thickness or attenuation, SmartmA changes dose based on angular variations of the position of the X-ray tube relative to the patient within each gantry rotation (X and Y axes).
Another notable difference is that you can't have SmartmA without AutomA. In fact, a GE CT system will only allow SmartmA to be activated after AutomA has already been activated. This is because SmartmA is informed in part by the information gathered by AutomA.
Just like the thickness of an area of tissue, a tube's angle relative to the patient is only part of the picture. With AutomA and SmartmA working together, the system is fully informed and able to lower doses while maintaining consistent image quality across all portions of a scan.
Both AutomA and SmartmA are available on GE's Lightspeed, Brightspeed, and VCT product lines. CT scanners from other manufacturers have these same functions, but they are known by other sets of proprietary names. Hopefully, for those of you considering a GE CT scanner, this explanation has lent some clarity to your pursuit of radiation dose reduction. AECs are only a piece of the puzzle, but a crucial one.