full article 1300 words
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 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 its 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? (It’s not really high tech. It’s just an X-ray movie.) 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? Including relatively straightforward dynamic MRI, which just takes a few images in a range of neck positions, visualizing at just as much information (or much more) with well standardized and relatively safe technology.5
Yes, it is true that scary problems can be missed by doctors that might well be spotted with DMX6 — although medical mistakes are generally exaggerated and misunderstood,7 and it 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.
MRI (and all forms of imaging) is notoriously unreliable, almost scandalously so.8 Some might see that as an argument in favour of an alternative like DMX, but it’s probably just the opposite: if the error rate is high in MRI clinics, with much more standardization, more experienced and better-trained technicians, and much better trained radiologists interpreting the results, then what’s it like for something like DMX? The reason MRI is unreliable is simply that this stuff is hard. There’s every reason to be concerned that it won’t be done well (or safely) outside the mainstream.
So, yes, 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.
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.
— Added a couple key points based on references, both comparing DMX to MRI.
People mostly assume that MRI is a reliable technology, but if you send the same patient to get ten different MRIs, interpreted by ten different radiologists from different facilities, apparently you get ten markedly different explanations for her symptoms. A 63-year-old volunteer with sciatica allowed herself to be scanned again and again and again for science. The radiologists — who did not know they were being tested — cooked up forty-nine distinct “findings.” Sixteen were unique; not one was found in all ten reports, and only one was found in nine of the ten. On average, each radiologist made about a dozen errors, seeing one or two things that weren’t there about missing about ten things that were. That’s a lot of errors, and not a lot of reliability. The authors clearly believe that some MRI providers are better than others, and that’s probably true, but we also need to ask the question: is any MRI reliable?
(See also my more informal description of this study, which includes an amazing personal example of an imaging error.)BACK TO TEXT