Patient Dose and AEC calibration in CR

Charlie · Joined: 01 Jul 2005 Posts: 2 Location: Swansea

I have just started a project looking at the optimisation of Automatic Exposure Controls (AEC) as used in CR applications. One of the aspects that I am interested in is the effect that the introduction of CR into radiology has had on patient dose. I'd be very interested in the forums' experience with CR and how, following conversion from film-screen to CR plates, you found your patient doses changing, if at all. Also, I am looking at possible AEC calibration procedures for CR systems and I wondered whether any forum members had experience in this field and what approach they had? Many thanks for any help you can give!

RadMaster · Site Admin Joined: 09 Aug 2004 Posts: 198

I've had experience in three different institutions and would say that the overall dose is way up. Most of this is due to techs overexposing and allowing the computer to fix the image. Please post your results for others to see.

dxraygirl · Guest

Most vendors have a calibration proceedure to calibrate the AEC. Check with your vendor to see what that proceedure is.

As for my expirerance, in general, when techs overexpose, then don't see a noticable change in the image, yet when underexpose, they see grainy image. So their thought is to "overexpose" which of course WRONG!

What is wrong with a correctly exposed image?! Lets all look at the exposure index numbers!

Just a reminder! Wink

ingvey · Joined: 01 Dec 2005 Posts: 1

We have a CR system by Fuji and when we put it in I could not believe how much dose it took to satisfy the detector plates. Quite simply are dose increased 3 fold. Yes 3 times higher than our Kodak film screen combo required. I dont know how the regulators overlook this but I think its a sad state for our powers that be to allow such a step backwards. So as I went around adjusting are Phototimers to give the amount they required I was sick. And oh yes No ONE wanted to hear about it. They simply asked is it legal? than if so SHUT UP. Never to ask is it ethical. So to this day I think that much less about myself for never making more of an issue about the very high doses we were now using , and all for what/??????????????Thanks
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iraydee8 · Power User Joined: 14 Oct 2004 Posts: 64 Location: AZ

I cant beleive some of these posts! We use about the same for our CR as we did for our extremity film/screen combo. Example Adult Wrist PA 60KVP @ 2 mas! How can others see an increase in 3 times or more when installing CR?

Puzzeled!
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MaBones · Guest

I worked at a hosp that also had Fuji CR and they collaborated with the radiologists on parameters for the "S" (sensitivity) numbers for specific body parts. Chests were in the range of 150 to 300, etc. They broke it down to spines, skull, extremities and abdomen. The rads were really anal about these numbers, too. If the number went over, which meant you underexposed the patient, you'd better repeat it before you sent it. Lower numbers meant you overexposed...made everyone crazy with that. And let's face it...not all films can be saved by the magic of "windowing."
We were also told to stay away from AEC...don't phototime! The Fuji rep explained that because of the CR cassettes, the PT cells can't tell when it was time to shut off, unlike the old metal cassettes that had some sort of sensor gizmo or maybe it was just the metal in it that the PT thing could tell when it should shut off.
Anyway, the first thing we noticed a difference on was the CXRs...with AEC they were grainey or gray. It took a little time, but after a while no one used the AEC and films were lookin' good!
Now I work at a hosp that uses AGFA CR and for the life of me I can't get a simple explanation on the sensitivity issue. The AGFA guy never heard that AEC shouldn't be used with CR. I think the images here are not as great, only because a lot of the techs do use the AEC and jack up the techniques. Plus you are expected to send over minimally crummy films per the rads...they will do the windowing.
I guess it's all up to your rads....!
BTW...I do a hand/wrist >>55kvp @ 2MaS

MaBones

moe6977 · Guest

We have been using Kodak CR for a year. The exposure for CR is the same as using Kodak fine lanax film screen. For our work with extremities this means patient dose has remained the same, however if you have used a faster film screen combination ie: Kodak reg lanax the exposure increase is 3x mas or euiv kvp. We have found that we can use higher kvp to make exposure conversion without degrading image quality. We now use 85-90 kvp for grid work. However, nongird you MUST use low kvp as scatter will destroy image quality.
Good luck,
Moe

moe6977 · Joined: 12 Oct 2006 Posts: 1

We have been using Kodak Cr for a year and a half. The CR takes the same exposure as a Kodak detail screen. Which means exposures need 3 times the amount that a Kodak Reg Lanex screen use. We have found that kvp can be used to compensate instead of mas as long as a grid is used. This does not help if you are using high kvp chests as you may not be able to set high enough kvp to compensate. Without grids low kvp Must be used.

lisajwp · Joined: 24 Jan 2007 Posts: 1 Location: Somerset, PA

We've had our Kodak CR for just about 6 months and are still dealing with controversy over using high KVP to minimize patient dose. As some of you mentioned; we've found that for extremity work, we are using about the same technique on CR as with film.

However, there is constant argument over technique on nearly anything done in the bucky. Some techs just manually set all techniques, keeping with our old-school KVs. Other techs jack up their KV to reduce mas. In general, the radiologists have complained that the techs who jack up the KV are turning in washed-out, gray looking images...ie ribs look like a chest x-ray, air in sinuses is not as defined, etc.

As PACS Admin, I've inherited the task of coming up with a chart that lists what KVs are acceptable with what mas range for each exam. Has anyone else done this? Anyone willing to share examples of such a chart?