Tech aficionados are wont to argue about which Steve really built Apple. Anyone who read iWoz knows that the real creator of Apple was Jerry Wozniak, the father who zipped and bulk downloaded the technical heritage of the transistorized zeitgeist into little Steve’s brain and soldering hands. The Woz of the DIY medical world just dumped plans for an open source CT machine onto the archives of Github.

Canadian Peter Jansen was inspired to build his CT machine after a recent (and apparently less than ideal) contact with the US health care system. He figured he could build a reasonably good X-ray scanner for a fraction of the cost of commercial machines. And why not, considering his earlier successes building tricorders and other fun instruments. CT stands for “computed tomography,” which in its usual configuration involves rotation a source of radiation, and a detector, around a patient. After each point in the region of interest is scanned, a 3D image is reconstructed with a computer.

The main hurdle in building an economical DIY CT instrument is matching your radiation source to your detector. The trick here is to use the weakest (and therefore safest), source possible that still gives you enough resolution to see what you want to see, in the time that you are willing to spend in actual imaging.

Janson chose a silicon photodiode from Radiation Watch which comes calibrated to detect high energy (>80 kev) cesium particles. After a lot of experimentation he settled on 10uCi (microCurie) Barium-133 as a source, which in radiation-speak, has a primary emission around 33 kev.

Among the many essential details that need to be successfully juggled, particularly at these low energy levels, are the effects of background radiation. Jansen notes that at a scan distance of around 15cm, an intensity of around 550 counts per minute should be enough to separate a clear image from noise in a few hours scan time. His early results show he is clearly well on his way to achieving this. The larger parts for the project are laser cut components, primary those for the drive mechanisms. Arduino boards control the stepper motors and scan acquisition.

While not a project for the faint of heart, we might expect mutual improvements by different builders to feed off one another and converge on a few near optimal designs. Like our beloved Woz, Jansen readily points to his father who not only got him going in all things technical, but made its pursuit irresistible.