
Show HN: Hacking an ultrasound probe with a Raspberry Pi and low-cost hardware - kelu124
https://kelu124.gitbooks.io/echomods/content/RPI.html
======
WestCoastJustin
Very cool. There was something on HN about a year ago about why ultrasound
machines are so expensive. This might provide some background on why something
low cost makes sense.

[https://news.ycombinator.com/item?id=13230741](https://news.ycombinator.com/item?id=13230741)

~~~
kelu124
Before trolling a bit, I remember the main costs don't come from hardware
(though it definitely costs something) - rather for r&d, patents, and most of
all proper certification, since, in the end, it's a matter of life and death.
That being said, this experiment is mostly a dev kit to help curious tinkerers
explore the topic :)

~~~
agumonkey
Am I allowed to built an ultrasonic probe the way I want if I don't use it on
anybody else but me ?

~~~
bluGill
Yes. Just come up with a non-medical/safety use for it and you are good. Check
your car's engine to see if it will last through the next race - a very useful
thing to do and nobody will think twice. Check a boiler to be sure it won't
explode - you better get this right or people will die so don't talk about
potential uses here.

~~~
agumonkey
Yes, more and more (since I started reusing old devices), I wished I could
inspect things non invasively. To find locking or friction points.

------
gadgetoid
Really enjoying this little bubble of Raspberry Pi content; it's close to my
heart. Keep it up HN!

------
blensor
I have no idea how hackernews always reads my mind about this kind of things
but I started thinking about this topic due to a personal interest a few days
ago.

And my question is. Can the ultrasound probe be made of off-the shelf parts. I
think I understand why it's not possible with electromagnetic parts alone
(kind of a speaker) they just can't vibrate fast enough to reach the Mhz
frequency range.

But would it be possible to use a regular crystal oscillator they should be
cheap, can easily be found for Mhz frequencies and are basically the same
technology as the PZTs used in ultrasound probes. Just remove the casing and
excite them, would that work?

~~~
wiml
I'd been thinking about this technology recently as well, but hadn't gotten
any further than perusing data sheets a little.

My impression is that quartz crystals as found in oscillators are so brittle
that it's hard to use them for things like this; I guess PZT (lead zirconium
titanate) is more robust somehow? There are also polymer-based piezo
materials, like PVDF.

~~~
awelkie
Another potential issue is that ultrasound machines send out an impulse
instead of a single frequency. So maybe the quartz crystal oscillators aren't
good at producing a short high-bandwidth signal?

That being said, there's a type of radar system called "stepped frequency
continuous wave" radar that uses a bunch of single frequency transmissions
instead of an impulse transmission. The basic idea is that instead of using a
high-bandwidth transceiver to send and receive the impulse, you can use a low-
bandwidth transceiver to send and receive tones, and then hop this transceiver
over the large bandwidth to get a high-resolution image (the tradeoff being
that it takes longer to acquire an image). Since ultrasound is basically
radar, I'd imagine this technique could be used for ultrasound too.

~~~
blensor
But wouldn't a lower frequency be at the cost of spatial resolution due to the
longer wavelength?

~~~
awelkie
The spatial resolution depends on the bandwidth of your transmission. An
infinite-bandwidth signal is a delta in time, and gives infinite precision.
Any finite bandwidth impulse will be a sinc in time, with temporal width
proportional to the inverse of the bandwidth. So a higher bandwidth impulse
will be shorter in time, which would give better temporal resolution.

Typical radar works by sending and receiving a high-bandwidth impulse, which
requires high-bandwidth transceivers. Let's say that transmission occupies
frequencies between f0 and f1. SFCW radar works by sending a bunch of
individual low-bandwidth transmissions between f0 and f1. So each transmission
is small, but together they occupy the same f0 to f1 bandwidth. Assuming the
environment didn't change in the time it took to send all of those low-
bandwidth transmissions, you've effectively simulated a high-bandwidth impulse
using a bunch of low-bandwidth impulses. So the spatial resolution will be the
same.

------
anotheryou
Could one use this as a sense-prothesis (without a motor)?

How small can the probe head get? Can I tape it to my ringfinger? Any health
hazzards?

My first try would be taping it to my finger and listening to the signals
enveloped mapped to my audible range.

~~~
kelu124
Could be indeed! Augmented sensing, there's definitely something one can do. A
ping (radar-like) every 5s, and in time you listen to echoes. The more
intense, the higher the frequency. Ping me through the contact in the doc if
you're keen on discussing about this!

~~~
anotheryou
Actually I fear 5s is far too slow to develop a sense-like feel for it :/

But thank you for the offer to discuss more :)

------
anfractuosity
Wow that's really awesome, I'm just skimming the site at the moment, are you
planning on selling the pulser boards etc. out of interest, if so roughly how
much do they cost?

~~~
kelu124
Hey! Theres a link for tindie in the doc. It's quote expensive, high voltage
being the main reason, but I'm planning on reducing the costs and have a
cheaper on-board extension for the pi once this hardware stabilizes

------
dchichkov
It's tough to get right with discrete components.

As a side note, does anyone reading this have MAX2082EVKIT# lying around in a
trash pile somewhere? I'm looking for one.

~~~
kelu124
Let me know if you can spare one too ;)

------
ultrasdr
could rtl-sdrs and rpitx be used at all?

~~~
kelu124
It's been a question I'd love to be able to answer to!

