Digital motion X-ray (DMX) is an X-ray video: many hundreds or even thousands of X-ray images strung together.1 This technology seems amazing, and maybe it offers some diagnostic hope to people with serious, mysterious chronic pain, especially in the neck and back. For instance, these two videos (part 1, part 2) show several cervical spine injuries that somehow (!) escaped previous diagnosis. Some DMX videos are really eyebrow raising, like this cringe-inducer:
I asked my friend Dr. Rob if what he knew about DMX. (This is Dr. Rob of One-Minute Medical School and two medical specialty degrees, including nuclear medicine — the man knows a lot about imaging and rays.) His initial answer: “Not a thing, and that right there should tell you something. I’m not aware of this in any radiology practice.”
Why not? The technology is fascinating — but rather morbidly so. Despite it’s capabilities, this is not a common or mainstream medical technology. It is used almost exclusively by chiropractors, and has a dark side: radiation exposure. Getting any X-ray involves some risk, and DMX requires a lot of X-rays.Dr. Rob:
You need a potent fluoro beam to shoot through the neck and make the bones light up that nicely, and the beam just keeps going and going. I can see why Health Canada pulled the license.2
With great power comes great responsibility. Radiation is dangerous! When you quickly soak up one Sievert — a measure of radiation — your lifetime risk of a cancer goes up by about 8%. That’s a lot of radiation, and a normal X-ray is a lot less. A series of five conventional cervical spine X-rays doses a patient with about .27mSv (thousandths of a Seivert),3 which is pretty small. Nevertheless, good doctors take it seriously and always avoid unnecessary X-rays. Radiologists and technicians carefully tune X-ray equipment to minimize exposure to both patients and medical staff.
If a regular series of five well-calibrated X-rays involves a little risk from radiation exposure, how much for hundreds of pictures at least? Video X-ray requires a series of X-rays, enough of them for animation, so by definition it involves more radiation exposure. How much more? Unknown — and that’s the problem. There are many variables, but even the best case scenario is a concern. Dr. Rob:
If the best case scenario — if the technology is comparable to flouroscopy, if it’s properly calibrated, if the dosimetry is known and measured — the exposure could be roughly 40 times a normal series of five cervical spine X-rays [10mSv].4 Even that is significant. But the worst case, with poorly operated or calibrated equipment, could easily be much worse, even an order of magnitude [100 mSv]. By linear regression, which is the currently accepted way of estimating risk, that worst case scenario would involve an 0.8% increased lifetime risk of cancer. Which is a lot, when you’re talking about cancer.
Bear in mind that Health Canada banned this technology because of the unknowns: unknown energy output, and unknown calibration status particularly.
One final important note: it’s hard to connect radiation damage to its cause, because cancers can take 5 to 20 years to manifest after exposure. Food for thought.
So, how badly do you need that high-tech diagnosis? Is it worth an increased risk of cancer? Possibly even a greatly increased risk? To diagnose conditions that, mostly, can and should be diagnosed any other way?
Yes, it is true that scary problems can be missed by doctors — although medical mistakes are generally exaggerated and misunderstood.5 But that doesn’t mean it’s a good idea to soak yourself in X-rays to chase them down. Any radiologist who actually missed something as serious as a complete fracture in the upper neck would probably get sued. It is possible that an X-ray movie could occasionally identify something difficult to diagnose by other means — but you could say that about exploratory surgery and autopsy, too. Not all diagnostic procedures are worth the risks, and radiation exposure is one of the worst down-sides in all of medical technology.