Digital x-rays and radiation

Do digital x rays use less radiation tham traditional ones? My child’s dentist says they do but I’m not sure I believe her.

But you’ll believe us?

This source claims less radiation is required to produce a digital X-ray image than one using traditional film methods.


The simple question is, what is the quantum conversion efficiency of the sensor? Traditional X-Rays used fairly conventional silver halide film, often in a sandwich with a sheet of a suitable phosphor material (which did the vast bulk of the detecting - converting the high energy X-Ray photons into a stream of visible light photons that the film was much more likely to detect.) A dental digital sensor is a solid state chip - really a big and expensive version of the same sensor technology used in a digital camera. These modern detectors are able to detect individual X-Ray photons, so from that point of view they may be regarded as close to 100% efficient. (Digital cameras don’t get this high, but may approach 50%) The old film/phosphor system was vastly less efficient at detecting X-Ray photons, and thus we can reasonable say that the modern systems will involve a substantially lower dose of X-Rays.

It’s certainly plausable. I know for sure that CCD cameras can be more sensitve than film at optical wavelengths. With a telescope, it’s possible to image much dimmer objects using a digital camera than using film.

My mother felt the same way but that was in the 90’s. And I asked the same question when I was at the dentist last time I was there and got a similar answer that was given by Francis Vaughan but not as technical. You should but more concerned if you go for an x-ray for say a broken leg which is why most doctors make sure you really need the x-ray first. That is where the real radiation comes from but if it medically necessary it needs to be done. And also most dentist only x-ray your teeth every 2yrs ( I believe). But I wouldn’t worry at all I had radiation treatment when I was 11 and it was blasted into me at full power and I still get dental x-rays.

Why would you take your child to a dentist who would lie to you on as basic and serious a matter as this?

it’s not a liar/truthful issue. dentists aren’t nuclear scientists. it’s entirely probable (in fact likely) that the dentist is merely parroting to his clients what he was told by the x-ray machine salesman.

OP is seeking independent confirmation, no big deal.

Sorry, but if I thought my dentist was that stupid and ill-informed about a tool used every day, I wouldn’t go there. That dentists know only what the salesperson says is a canard and a libel on the profession. If it’s ever true in any specific case, run like hell.

you think I’m libeling dentists when I claim that they don’t really know much about the scientific, technical functioning of an x-ray machine? surely you jest.

That you think they are so unconcerned about radiation, that they use x-rays every day but don’t know or care about dosages or the effects they might have is libel, yes. You don’t have to know how a machine functions. You have to know what its effects are.

Radiation is an enormous and controversial issue in the field. Any dentist who hasn’t been keeping up with the medical journals on this is a disgrace. But I doubt the majority is this careless about the lives of their patients.

Dental X-ray detectors are not simple CCDs. CCDs are thin pieces of silicon; any X-ray powerful enough to go through human tissue would also pass through the CCD without being detected. So the sensor is actually a scintillator, read out by a CCD or CMOS detector. A scintillator is a transparent material that absorbs X-rays and convert the energy into visible light. It’s usually more efficient than film, but nowhere near 100%.

Anyway I found this PDF file that compares different dental X-ray detectors. It says the “mean minimum entrance exposure achieved under these conditions was 128 mGy”, while the exposure range for film was 427-644 mGy. If I understood the paper correctly, it implies that digital sensors can work with 1/3 as much radiation. However, I notice that the maximum radiation level they can work with is over 10 times higher than film. To me, this suggests that dentists may not actually use a lower dosage than they did for film.

mapcase, you are maybe a bit naive. I have worked in dentistry for 24 years and most of my bosses have forgotten long ago anything they ever learned about x-rays. They haven’t got a clue, they are only interested in the readable quality of the x-ray they are diagnosing from, and a few of them have cheap equipment and don’t even care about that. Do you know we have only just begun to use the thyroid collar in dentistry? And that is because the media has started talking about it. We always used to shove that thing out of the way before! We in Dentistry believe the radiation is less with digital, but I am searching for that information right now for some self study (which is how I came across this thread) and I’m not finding it fast…wish me luck. Poster Francis Vaughan sounds convincing…

There, the inefficiency is largely due to the tricks that they use to get color. If you’re willing to settle for a monochrome image (as with an X-ray), you can still get much higher.

And I don’t know about dental equipment, but most astronomical X-ray instruments do in fact use CCDs. There’s no reason that transparency of flesh and silicon would be the same. If anything, the argument “it’d just go right through” would be much more relevant for film, which is both much thinner than any CCD, and of a composition more like flesh.

Run like hell.

You’re thinking of soft X-ray instruments like Chandra, which operate in the range of 0.1-10 keV or so. My understanding is that medical generators are usually in the 10-60 keV range, well into the “hard X-ray” range. If you look at the QE curves for the AXAF/Chandra ACIS detectors here, for example, you’ll see that the sensitivity drops down fast around 10 keV and beyond. Astronomical instruments designed for hard X-ray generally use scintillators or semiconductors with high atomic number (germanium, CdTe, CdZnTe, etc).

The mass attenuation coefficient goes up quickly at higher atomic number. The photo-sensitive material in film is silver halide, and silver has an atomic weight of 108.

Actually, I was mostly thinking of solar X-ray instruments, not Chandra, but on doing the unit conversions (solar folks usually talk in terms of kelvins, not eV), it looks like they only get up to around 1 keV or so, so your point remains.