Tomography Through An Infinite Grid Of Resistors

One of the vast untapped potentials of medicine is the access to imaging equipment. A billion people have difficulty getting access to an x-ray, and that says nothing about access to MRIs or CAT scans. Over the past few years, [Jean Rintoul] has been working on a low-cost way to image the inside of a human body using nothing more than a few electrodes. It can be done cheaply and easily, and it’s one of the most innovative ways of bringing medical imaging to the masses. Now, this is a crowdfunding project, aiming to provide safe, accessible medical imaging to everyone.

It’s called Spectra, and uses electrical impedance tomography to image the inside of a chest cavity, the dielectric spectrum of a bone, or the interior of a strawberry. Spectra does this by wrapping an electrode around a part of the body and sending out small AC currents. These small currents are reconstructed using tomographic techniques, imaging a cross-section of a body.

[Jean] gave a talk about Spectra at last year’s Hackaday Superconference, and if you want to look at the forefront of affordable medical technology, you needn’t look any further. Simply by sending an AC wave of around 10kHz through a body, software can reconstruct the internals. Everything from lung volume to muscle and fat mass to cancers can be detected with this equipment. You still need a tech or MD to interpret the data, but this is a great way to bring medical imaging technology to the people who need it.

Right now, the Spectra is up on Crowd Supply, with a board that can be configured to use 32 electrodes. Measurements are taken at 160,000 samples/sec, and these samples have 16-bit resolution. This is just the acquisition hardware, though, but the software to do tomographic reconstruction is open source and also readily available.

In terms of bringing medical imaging to the masses, this is a very impressive piece of work, and is probably the project from last year’s Hackaday Prize that has the best chance of changing the world.

Towards Open Biomedical Imaging

We live in a world where anyone can build a CT machine. Yes, anyone. It’s made of laser-cut plywood and it looks like a Stargate. Anyone can build an MRI machine. Of course, these machines aren’t really good enough for medical diagnosis, or good enough to image anything that’s alive for that matter. This project for the Hackaday Prize is something else, though. It’s biomedical imaging put into a package that is just good enough to image your lungs while they’re still in your body.

The idea behind Spectra is to attach two electrodes to the body (a chest cavity, your gut, or a simulator that’s basically a towel wrapped around the inside of a beaker). One of these electrodes emits an AC signal, and the second electrode measures the impedance and phase. Next, move the electrodes and measure again. Do this a few times, and you’ll be able to perform a tomographic reconstruction of the inside of a chest cavity (or beaker simulator).

Hardware-wise, Spectra uses more than two electrodes, thirty-two on the biggest version built so far. All of these electrodes are hooked up to a PCB that’s just under 2″ square, and everything is measured with 16-bit resolution at a 160 kSPS sample rate. To image something, each electrode sends out an AC current. Different tissues have different resistances, and the path taken through the body will have different outputs. After doing this through many electrodes, you can use the usual tomographic techniques to ‘see’ inside the body.

This is a remarkably inexpensive way to image the interior of the human body. No, it doesn’t have the same resolution as an MRI, but then again you don’t need superconducting electromagnets either. We’re really excited to see where this project will go, and we’re looking forward to the inevitable project updates.