0. https://www.midjourney.com/medical/blogpost

Scanning the Body with Sound

https://www.caltech.edu/about/news/scanning-the-body-with-so...

The hard part is that there can be over hundreds of piezo elements each needing to receive on their own channel. That means lots of expensive ADCs. Not to mention either having many pulser circuits or muxing a pulser to many elements.

A ring of devices at 60cm (70cm for Midjourney) diameter means much longer distances than even the deepest tissue imaging ultrasound is typically used for. Geometric 1/r^2 attenuation through water and exponential attenuation through tissue. Sensitivity is always the key question for any sensor. This is why they use 1MHz ultrasound (lower frequencies attenuate less) rather than say 5-10Mhz, but that also means lower resolution. Sound wavelength in water/tissue at 1MHz is roughly 1.5mm. So in pursuit of sensitivity, good resolution becomes a challenge.

What sensors could we line up around the tank? This work has gone to great lengths to build custom transducers for receiving the ultrasound signal, but I couldn't easily find a direct characterization of sensitivity (pardon me if I missed it; I'd love to know more) but I don't think they are claiming a breakthrough in sensitivity -- only a new (tank) system architecture. AFAIK, all available technology, be it Butterfly/Olympus/whatever have a fundamental tradeoff in cost and sensitivity, because they all pick different operating points on the Pareto curve set by the underlying technology. Butterfly is not as sensitive as the top-grade devices, but the top-grade hospital ultrasound machines are way more expensive and bulky (roughly 150k USD & 150Kg). It would be a real challenge to fit dozens of them around the tank! Let alone pay for them, if one wants to deploy at scale.

If cost and bulk were not a constraint, we could definitely use many hospital-grade sensors and get high-fidelity images. The problem is what happens if the sensitivity is not quite enough. Look at the online discourse from doctors about how low-sensitive full-body scans are asking for trouble from over-diagnosis (incidentalomas) and iatrogenic side-effects. Low sensitivity full-body scan is basically the diagnostic version of p-hacking. Just like the US air force found that there is no "fully average" pilot, every body scanned will always have some anomaly or the other. And most of them never need to be clinically intervened on. That's not quite the fault of the device, but that's still a massive gap in the deployment strategy and it will require retraining doctors and restructuring large parts of the existing healthcare system.

It's easier to just invent technology and build higher-fidelity sensors. This device is mostly just an assemblage of available sensors, we need innovation that produces sensors which are smaller + inexpensive + less power hungry. It's not just a question of assembling it into different form factors or scaling production, or nudging people into using these by frequenting spas. AFAICT that's barely getting any discussion in the chatter around the Midjourney launch.

Lastly, it's really important that this doesn't require a trained sonographer. That's a real scaling bottleneck if we want to enable exponentially more usage of scanning. (Not taking a dig at the paper authors, but only at the online discourse) If we really wanted to scale this to population level use... the tank form-factor is good, but guess what's easier: having smaller devices one could just drop into a bathtub at home :-)

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PS: I also wrote more broadly about the Midjourney scanner, looking at both the tech and the road to deployment: https://woventhought.substack.com/p/visions-and-blindspots-t...

Presumably that's just a matter of better system modelling to fix?