Impedance Tomography Is The New X-Ray Machine

Seeing what’s going on inside a human body is pretty difficult. Unless you’re Superman and you have X-ray vision, you’ll need a large, expensive piece of medical equipment. And even then, X-rays are harmful part of the electromagnetic spectrum. Rather than using a large machine or questionable Kryptonian ionizing radiation vision, there’s another option now: electrical impedance tomography.

[Chris Harrison] and the rest of a research team at Carnegie Mellon University have come up with a way to use electrical excitation to view internal impedance cross-sections of an arm. While this doesn’t have the resolution of an X-ray or CT, there’s still a large amount of information that can be gathered from using this method. Different structures in the body, like bone, will have a different impedance than muscle or other tissues. Even flexed muscle changes its impedance from its resting state, and the team have used their sensor as proof-of-concept for hand gesture recognition.

This device is small, low power, and low-cost, and we could easily see it being the “next thing” in smart watch features. Gesture recognition at this level would open up a whole world of possibilities, especially if you don’t have to rely on any non-wearable hardware like ultrasound or LIDAR.

43 thoughts on “Impedance Tomography Is The New X-Ray Machine

    1. And don’t mind burns, thyroid cancer or leukaemia.

      Seriously, this is the kind of idiocy that kills bystanders through outright statistics. Low numerical risk with dire consequences where exposure can be minimised?

      ALARA all the way (As Low As Reasonably Achievable)

        1. See a doctor who will evaluate your signs and symptoms, weigh up the risks and benefits of radiation exposure, including the need to exclude important differentials (such as fractured that require surgical therapy) and possibly treat (reduce the fracture ie straighten it out) prior to imaging to ensure adequate alignment.

          Don’t get me wrong; I may not have experience with anal fluorescence extraction but there was one case where we couldn’t remove beads-on-a-string from a urethra; the x-Ray showed a knot and proved the need for surgery.

      1. “Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.”

        – American Association of Physicists in Medicine position statement.

        While I don’t know of any groups who aren’t of the position that radiation exposure should be minimized as much as possible, the fact of the matter is that the risk caused by most common medical procedures is overblown in nearly every case.

        The trouble is that even radiologists and physicians in charge of disseminating this information to the public don’t always convey the information appropriately. Below single doses of 100 mSv.

        For the record, a single chest x-ray has a typical effective dose of 0.02 mSv.

        1. Oops, part of my comment was cut off. Should say, “Below single doses of 100 mSv, nearly all of the models are *extrapolated* from doses of radiation above 100 mSv, because the risk becomes so low that the true incidence of cancers and other such nasty things due to the radiation is obscured by the natural rate of these adverse events.”

          1. The extrapolation is called the LNT model, which has been debunked lately.

            Studies done on cell DNA repair mechanisms suggest that they can take a whole bunch of radiation without much disruption – and this makes sense because the naturally occurring background radiation varies over three orders of magnitude depending on where and how you live, and what you eat etc.

            Simple granite and beach sand contains radionuclides because there’s uranium and thorium in the rocks, and they’re constantly breaking down to other more radioactive isotopes, so if you live in a stone or concrete house you’re getting a fair dose already.

        2. Radiation can be good for you if it is at just the right level to induce more apoptosis in defective cells than it damages good cells, because the over all number of cells likely to lead to cancer actually drops. I don’t recall the term for it but it first showed up as an anomaly in the statistics on radiation exposure effects.

          1. It’s called radiotherapy and again it is a risk/benefit thing. If it causes enough oxidative stress and DNA damage that cancer is significantly affected without killing you, destroying your lungs, giving you cerebral palsy of constrictive pericarditis or interstitial lung disease or anti-neoplastic induced cancer…

          2. Nope, I’m not talking about that. It is related to the phenomena noticed at a place in Iran, with one of the worlds highest natural background radiation levels, where the population actually has below average cancer rates.

        3. The “may be nonexistant” part worries me…. Although the “too low to be detectable” means that the sample size was not large enough to provide a statistical difference, that does not automatically imply that it is safe. It “MIGHT” be safe or pose no risk. But from a theoretical point of view, I would prefer to extrapolate say: at 1000mSv there is a 1% chance of complications, then at 50mSv there is a 0.05% chance of complications.

          1. The problem is that 100 mSv is an HUGE dose of radiation, and already the effects are so low that the noise is greater than the signal.

            The evacuated zone around the Fukushima accident for example gives you 20 mSv per year. It’s evacuated only because back when the radiation limits for public safety were decided, people basically went “100 mSv is the smallest dose for which we have any proof of effect whatsoever – let’s say a fifth of that just to be on the safe side” – based on no reason whatsoever.

            And as a result of this extrapolation, thousands of people at Fukushima are now homeless, jobless, and treated like lepers because people have no idea how little effect the radiation has. All they see is that some abstract number is over 20 and that means it’s bad.

    2. Eh….X-rays are ionizing radiation meaning that they can damage and destroy DNA. If you do that and your body doesn’t catch the errors in your genes, it can lead to cancers and mutations. You can be the most healthy person in the world who eats twelve whole chickens and runs 50 miles a day and it won’t stop the effects of ionizing radiation on your DNA.

        1. Beneficial traits can result. But the vast majority of mutations are either benign or detrimental to the organism. Generally the mutations that are beneficial and will be passed on are a result of the process of sexual reproduction, the combining of two or more sets of genetic information, rather than the altering of a few cells in a larger creature.

        2. LOL no, evolution has no direction it just adapts to the change in environment, so if turning into a mindless jellyfish will help you procreate better then that is where you are headed.

      1. Yes, you’re body is designed to fix damaged DNA. In fact, radiotherapy for cancer works because in most cancer cells the processes responsible for that repair mechanism are disabled. The current theory is the ‘2 hit theory’, meaning that if the dosage is low, and you only damage the DNA of a cell in one spot, the normal processes will work. To cause cancer, the DNA must be damaged (in certain ways and areas, because only a small amount of mutations result in viable cells, most others simply would fail to function and die), and a second hit must damage the error checking process, such that the mutation is allowed to continue. That’s why the risk is so low for XRays.
        Interestingly, recent research into Elephants has shown that they have very low cancer rates, supposedly because they have more copies of the error checking genes than other animals.

  1. It is quite impressive that they have managed real-time measurement and field projection.

    I last read around this in 2010 in the context of respiratory function (respiratory impedence tomography) and monitoring ventilated patients. At that stage everything required post-processing, and the individual calibration required was not insignificant. Still only a research tool from what I understand.

    1. This project looks at the impedance between two points and uses that to create a “heat map” using the impedances of the cross connections. Its not measuring any fields and it doesn’t require any calibration according to the dude’s research paper.

  2. Hm, from the look of the diagram on the right of the screen, looks like more sensors might increase the resolution. Seems like it’s measuring impedance between each sensor and each other sensor, then plotting that along lines between them to give the image. Wonder what different frequencies tells you, etc?

    1. The AD5933 chip returns a complex impedance, being “real” + “imaginary”. If you know both of those, you can use them to compute the phase of the impedance and therefore what the resistance and capacitance/inductance. Using that information, you don’t need to use any more frequencies.

      As far as the number of electrodes, you are going to be limited to just how finite you can make things as folks have different sized body parts and you don’t know what part of the body this would be used for. Skimming through the paper, the idea behind this is to make a really inexpensive (sub $40) sensor system that is universal. If you actually DID add electrodes, you are not going to get a much better resolution than they have anyways due to how the mapping works and the limitations of AC signals as sensing signals (AC spreads outwards and doesn’t travel in a thin line….really high voltage powerlines are hollow for this reason).

      1. ” (AC spreads outwards and doesn’t travel in a thin line….really high voltage powerlines are hollow for this reason).”

        That’s a very shitty description of the skin effect. It depends on the magnetic permeability of the material the current is travelling through. Salt water for example has a skin-depth of about a foot at 1 megahertz. Human flesh being similiar to salt water, and usually thinner than a foot, would not exhibit significant “spreading” as you put it for AC up to very high frequencies.

        And the reason why really high voltage lines are hollow also has to do with the fact that a thin solid wire would cause a corona discharge because the charge gets concentrated to the point that air around it breaks down.

        1. It also depends on resistivity. High resistance materials have less difference between their AC and DC resistance because the skin effect is caused by eddy currents in the material, and these currents can’t flow if the material is resistive.

          A hunk of carbon would be pretty much indifferent to whether you put AC or DC through it, because it’s both resistive and non-magnetic.

  3. If they can get a Doppler value for each pixel in their image they can compute the direction and velocity of movement in the tendons and that correlates directly to the kinematics of the fingers. (CC BY 4.0)

  4. An hour ago I was idly trying to think of a way to image my hand (it’s injured atm). I love articles like this because not only do they an interesting device, they also give me (and a bunch of other engineers/nerds) a new term to google – ‘electrical impedance tomography’ which will hopefully lead to some awesome projects.

  5. Maybe they could tweak this into sort of a TDR (time domain reflectometry) circuit. Any discontinuity in the tissue impedance should give some form of reflection back. I guess the main problem with this idea is that you would have to somehow form a space constrained electromagnetic impulse. I could imagine that you can do something similar to an old cathode ray tube where the impulse gets it’s direction controlled by passing thru a static electric/electromagnetic field? Should be possible to explore this on a larger scale, i’m just not shure if you could miniaturize that into a neat little wristband with todays technology.

  6. Am I the only one wondering if technology like this can be used for an assistive tech for helping to potty train the kids or figure out if someone with bladder control or bowel control issues should be brought to the bathroom?

    If the tech is cheap and portable…

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