Name a technology that is more useful, more educational, more interesting, and more overpriced than a ultrasound machine. You can look inside of living things without the need for a powerful magnets or radioactivity and it is basically made from a speaker and microphone outputting to a screen.
Why doesn't every high school biology class room have an ultrasound to show how muscles work, and hearts beat? Why don't doctors have them immediately handy like a stethoscope or thermometer? Why can I not get one just because I am interested in how my injuries are healing? Probably because "a £20,000 [$30,000USD] scanner is generally classed as low cost."
After I spent $200 on a doctors visit because of an injured foot, where they used a cabinet sizes ultrasound machine that looked like a 1950’s TV, I wondered how much it would cost to purchase an ultrasound for myself. After a finding that a "cheap" ultrasound is still $8000, I just couldn’t reconcile the cost with the technology and the simplicity and usefulness of such a tool. So I decided to do a little research.
A transducer is a ceramic with two pieces of metal on either side, if you squeeze the transducer it creates a current, if you put a current into the metal it moves the transducer. An ultrasound machine requires a dozen or more MHz frequency transducers formed into an array to get the required resolution. The preferred ceramic for a MHz transducer seems to be Lead zirconate titanate or PZT.
When a current is applied in to the transducer it will expand, reversing the current will make it contract, doing this repeatedly will create a wave with a wavelength of about twice its thickness. Given the speed of sound in ceramics is about 3200m/s, to produce a 5MHz wave, the wavelength will be 0.64mm so the thickness of the PZT will need to be to be around 0.32mm. That is pretty thin.
This precise manufacturing of the transducer array is the probable reason for the cost of ultrasound machines as each transducer has such precise requirements and an ultrasound requires many of them. Individually these transducers cost quite a bit, and if you need 20 of them for an ultrasound then the cost increases quickly.
The cheapest MHz PZT transducers I have found are $12 each for 10Mz PZT discs. This would make a 20 transducer ultrasound still cost north of $200, and to make something more interesting like this 40x40 PZT array for 3D imaging would cost about $19,200 for just the transducer array.
A way to reduce the price could be to make my own transducers. So can I manufacture my own transducer array? Maybe, and here is some resources which could be used to make home made transducers:
- here is a cool video of a person making their own transducer out of Barium Titanate,
- here is a group of people trying to bring printing of integrated circuits to the home.
- here is a Ph.D. thesis on creating thin PZT films
- here is a way to make a “low cost, high density PZT phased array"
- here is a description of how to make a flexible PZT array
- here is a 64x 35MHz array used for imaging in high resolution
One way to manufacture a PZT array is to use the dice-and-fill method described here, which creates a pixel array of transducers. Or I could build individual transducers by putting PZT into a medium like ethanol and then spray it onto some metal (probably silver) so that when the ethanol evaporates it leaves a thin film of PZT on the silver. Either way, these require specialist equipment and it is probably easier to contact a lab or manufacturer with the expertise to build the array, but where is the fun in that?
Hardware and Software
A computer that can run a MHz frequency transducer is easy and cheap these days, e.g. a raspberry pi’s GPIO pins can run that frequency. Screens can be very cheap, or just output directly to a phone or another screen. So I don’t think that the ultrasounds computations and display hardware will be very expensive.
The software may be very expensive, but this is probably because ultrasound machines are each running closed source custom software. If there were a standard hardware platform to make ultrasound software for, with standards and API’s I am sure this would reduce the cost for each machine significantly. There are efforts like this open architecture for ultrasound control, but I am unsure of how much adoption they have.
Where most of the cost comes for the ultrasound machines hardware and software is probably in their medical certification. Quoting from the Hacker News user jes:
Some specifications that must be met include ISO 13485, ISO 14971, IEC 60601 3rd Edition, IEC 62304, and probably ten more that I have forgotten about, such as RoHS, WEE, radiated emissions, etc. [...] If you're measuring the length of a fetal femur and translating the measured length to an estimated gestational age, you don't wish to be wrong
Creating any device for medical purposes can be incredibly expensive, but this ignores all the other uses that ultrasounds can have in education, imaging, sports training and just for fun. The catch 22 is that ultrasounds will never be used for these activities if they are difficult to use and expensive, and they will never become cheaper unless the ultrasound market becomes larger than just health.
Who is doing something about expensive ultrasound machines
Butterfly Network Inc is currently trying to create a medical imaging device, which is basically ultrasound on a single chip, as cheap as a stethoscope. They have raised over $100 million dollars and hopefully it will create some amazing technology so that everyone can purchase an affordable ultrasound machine.
echOpen and its fork Murgen are open source projects to make an ultrasound machine and dev kit. These kinds of projects could really help bring down the price of ultrasounds by making the technology available to developers and engineers, go check them out.