Digital Motion X-Ray
What’s the risk from the radiation exposure? Is the diagnostic potential worth it?
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:
In this video, the patient’s head is almost literally falling off. The 1st cervical vertebra is not fully attached to the 2nd!
I asked my friend Dr. Rob what he knew about DMX. He has two medical specialty degrees, including nuclear medicine — this 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
X-Rays are dangerous
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 fluoroscopy, 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.
Is it worth it?
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.
About Paul Ingraham
I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of ScienceBasedMedicine.org for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:
What’s new in this article?
2017 — Added a couple key points based on references, both comparing DMX to MRI.
2013 — Publication.
- More specifically, it could be either be video of fluoroscopy or a series of X-rays. Fluoroscopy is a continuous beam of radiation at a lower intensity. An X-ray is a very short burst, often at higher intensity. You could either film the results of a fluoro beam passing through someone for a few seconds, or you could take a lot of X-rays and string them together in an animation (which would involve quite a bit more radiation).
- “License suspension of the Digital Motion X-Ray System,” a letter from Health Canada to health care professionals, March 14, 2012.
- “Doses from Medical X-Ray Procedure.” Health Physics Society.
- A couple technical points: Dr. Tarzwell emphasizes that “10 mSv is an estimate based on standard fluoroscopy dosimetry,” and he’s “not just arbitrarily multiplying a c-spine series by 40, I’m inferring it separately from comparable fluoroscopy.”
- Zhang L, Zeitoun D, Rangel A, et al. Preoperative evaluation of the cervical spondylotic myelopathy with flexion-extension magnetic resonance imaging: about a prospective study of fifty patients. Spine (Phila Pa 1976). 2011 Aug;36(17):E1134–9. PubMed 21785299 ❐
- The most obvious possibility is slight, erratic pinching of the spinal cord that occurs only in certain positions (positional cervical cord compression). It’s well known that “static” MRI can miss this, but “dynamic” MRI (multiple images taken in a rang eof positions) can show it. The minor, intermittent irritation may cause chronic widespread pain and other odd problems. For a full discussion of that, see A Rational Guide to Fibromyalgia.
- Medical error rates are certainly alarming, but please keep them in perspective: the stakes are high in medicine, and the scale of everything is huge. It’s impossible for everything to go well while helping huge numbers of very sick, hurt people. For more information, see Medical Errors in Perspective: Medical error rates have been exaggerated by a popular myth and should not be used to spread fear, uncertainty and doubt.
- Herzog R, Elgort DR, Flanders AE, Moley PJ. Variability in diagnostic error rates of 10 MRI centers performing lumbar spine MRI examinations on the same patient within a 3-week period. Spine J. 2016 Nov. PubMed 27867079 ❐
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 and 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.)