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Comment by gaze | Hacker News Reader

MRI may work... I think there's a skeletal MRI. That will be extremely expensive. CT scan probably would work, but I don't think they'll let you dose yourself with that many X-Rays for fun. Most of these scanners give you voxel data, which you can then threshold some way and generate a water-tight surface which can be turned into an STL and 3D printed

The best 3D printer probably uses a stereolithography process. They give the highest detail at the expense of some mechanical properties. An objet might work well, too.

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> I don't think they'll let you dose yourself with that many X-Rays for fun.

There are companies that will let you get a "baseline" CT scan so that you can compare it with a future scan to see if something has changed. I don't think many doctors recommend this for the general public (because of the high radiation dose), but it does seem to be an available service and not prohibited by the FDA or something.

A CT scan comes with a strikingly high radiation dose, much greater than most people are likely to receive in any other circumstance. https://xkcd.com/radiation/

The FDA barely prevents people injecting themselves with snakeoil stem cell treatments...

"Baseline" CT smells like an expensive solution looking for a problem to sell to hypochondriacs. A hefty dose of ionizing radiation for no clear medical benefit gets a thumb down from me.

MRIs are nearly perfectly safe though.

Yeah, I have the same feeling about the baseline CT service and I'm sorry I wasn't more forthright about it above.

> I don't think many doctors recommend this for the general public

> A CT scan comes with a strikingly high radiation dose

Another challenge is that they probably wouldn't give you a baseline scan from the bottom of your toes to the tip of your head. Abdomen/thorax and/or head/neck, probably. So you can't get the whole skeleton. A planar "scout" scan of two dimensions is normal examination procedure prior to the diagnostic scan. Those can often run a long portion of the body. You might be able to project something from that.

Aside: The Sievert (SI unit referenced in the XKCD comic) is a really interesting (IMO) unit. Instead of measuring the radiation in normal "amount of radiation" style, it measures the "equivalent dose" intended to help understand the ultimate biological impact of the radiation. The radiation emitted might be measured in Joules and the radiation absorbed might be measured in Gray (Joules/kg), but Sievert can be weighted by the tissue that absorbed the radiation. Your gonads or your head would have a greater weight than your ankle (or so I figure). This, I would guess, gives radiologists a much better way to consider the net impact of a diagnostic procedure in order to weigh against the overall diagnosis & prognosis.

Also, another aside: dose has become a more competitive feature for CT manufacturers in the last decade or so and several offer features to measurably reduce the dose.

It's worth pointing out that CT is extremely sensitive for calcium and hence bone, so that bones could be scanned at a lower Xray dose than soft tissue. 30 seconds of Googling showed a study where a whole body CT bone survey was carried out using 4.1 mSv, or about 200 chest xrays. If you're not looking for fine detail in the bones, an even lower dose might suffice.

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