Why not place AEC detectors behind the cassette in all X-ray machines?

[EeePC1005PR]

In mammography AEC (automatic exposure control) detectors are placed behind the cassette.

AEC detectors in front of cassette would contribute to additional scatter, uneven attenuation, and additional thickness which also results in distortions. In otherwords AEC detectors in front of cassette gives you poorer image quality, and further more, in order to push through these detectors a higher dose needs to be given. That means higher patient dose.

Moving AEC to behind cassette helps improve image quality (by removing all the things just listed above) and also helps reduce dose required (since the beam no longer needs to penetrate AEC before reaching cassette, so a lower dose will suffice).

My question is: so why don't we do this to all X-ray machines? Why not do this for normal chest and abdominal X-rays as well?

I appreciate the cassette itself attenuates away significant fraction of the beam, and so significantly reduced intensity reaches AEC detectors that are placed behind the cassette. But that shouldn't be a problem. We know the attenuation coefficient of the cassette and so the detector can factor that into its calculation. Suppose we change cassette, we can still feed the AEC the new coefficient.

So still comes back to the same question, if placing detectors behind cassette is so good (better resolution and lower dose), why not do it for all X-ray machines? why just mammography? Or asked differently, what's the benefit of keeping AEC detectors in front of the cassette in ordinary X-ray machines? 😕

Hope my questions are clear. Thanks 🙂 Feel free to correct any misconceptions.

(Again, this is a genuine question sincerely asking for explanations. I understand there are some unfriendly people on this forum who are quick to give advices about everything but can't seem to directly answer the question asked. Those clowns will be ignored.)

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[Bradstein]

I don't know but I can speculate wildly.

Mammography uses lower energy x-rays than many other imaging applications. That might have something to do with placement of the AEC. In a plain film machine maybe it doesn't make much of a difference where it goes because the higher energy photons are less likely to be absorbed or scattered by the AEC if it's in front of the cassette.

 

[EeePC1005PR]

Mammography uses lower energy x-rays than many other imaging applications. That might have something to do with placement of the AEC. In a plain film machine maybe it doesn't make much of a difference where it goes because the higher energy photons are less likely to be absorbed or scattered by the AEC if it's in front of the cassette.

Thanks. That makes sense.

 

[cowme]

we use them at our peds hospital for CXRs. I personally notice no difference