
New laser ultrasound technique can remotely image the inside of a person - happy-go-lucky
https://news.mit.edu/2019/first-laser-ultrasound-images-humans-1219
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_Microft
Even after minutes my mind is still blown by the idea that there _exists_ a
_proof of concept_ device for a _remote sound generation - laser microphone -
ultrasound imaging technique_. Maybe we will actually live to see something
like Star Trek tricorders.

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jbob2000
The lasers aren't generating the sound waves per se, your body is. The laser
heats up your body, causing things to expand, then the laser is turned off,
causing things to contract. It's the expanding and contracting of your body
that is creating the sound waves. These sound waves are then detected by
something stuck to your body that converts the wave into an electrical signal.

This is different than ultrasound, which generates its own sound waves that
are then reflected by the body back to the device.

It's novel, but it doesn't solve the problem of being "non-invasive"; you
still need a sensor stuck to the body to pick up the sound waves.

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_Microft
It's using a laser to read the reflections contact-free.

>The researchers tested this idea with a laser setup, using one pulsed laser
set at 1,550 nanometers to generate sound waves, and a second continuous
laser, tuned to the same wavelength, to remotely detect reflected sound waves.

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srtjstjsj
How does it help to have the sensing laser at the same wave length as the
pulsing laser, if the pulsing laser is triggering sound waves which have a
different wavelength?

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jcims
If they had two lasers of similar frequencies they would get interference
beats/aliases in the data. If they use the exact same frequency (eg by
splitting the source) it shouldn’t show up. Should allow for less
stable/expensive laser sources too.

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hwillis
> If they had two lasers of similar frequencies they would get interference
> beats/aliases in the data.

1\. They _did_ use different frequencies- 1540 nm and 1550 nm.

2\. The measuring was done with doppler interferometry, so beats would not
impact measurements. The sensor is only responding to the difference between
two signals, not the intensity.

3\. 10 nm wavelength shift is a much larger difference than anything they'd be
measuring, so the only thing that would actually even "show up" (as noise)
would be light at the same wavelength as the measuring laser. Any constant
noise at the same wavelength as the measuring laser will be filtered out. Only
slight frequency deviations would come through- like the kind from vibrations
shaking the laser.

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gojomo
Mary Lou Jepson's 'OpenWater' work is a similar project where light +
computation is rapidly advancing the options for deep, real-time medical
imaging:

[https://www.youtube.com/watch?v=k879MFfB_3Q](https://www.youtube.com/watch?v=k879MFfB_3Q)

~~~
deepnotderp
The two are very different. Openwater, as per their patent filings, uses
ultrasound to change the refractive index of tissue and/or phase shift and use
an inverse distortion matrix to undo scattering. I've yet to see a real result
on dynamically changing tissue. By contrast, this uses light to generate
ultrasound waves, basically photoacoustic tomography.

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tjohns
This sounds a lot like optical coherence tomography (OCT), which is
essentially laser-based “ultrasound” used to image the inside of retinal
tissue. (It’s not actually ultrasound, it’s entirely optical but uses similar
principles.)

[https://en.m.wikipedia.org/wiki/Optical_coherence_tomography](https://en.m.wikipedia.org/wiki/Optical_coherence_tomography)

It’s already a common diagnostic tool used for patients who are at risk for
glaucoma. By creating a 3D cross section of the eye’s retinal structures, it
lets physicians detect early damage from the disorder, hopefully before any
vision loss.

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Tharkun
Thanks for linking to that. I had this done a while back but didn't know what
it was called or how it worked. If only all imaging techniques were as fast
and pleasant this one. It was over in seconds. Although I suppose the small
size of retinas likely play a part in that as well.

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epmaybe
How is this different from photoacoustic tomography?

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rubyfan
I’m sure this is a serious question but I lol’d when I read it. I’m going to
use that line at a party or a meeting some time to sound smart.

~~~
KenanSulayman
Or you could assume he’s more experienced than you in that field and not be
offensive?

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chance_state
You could also notice that it was clearly a light-hearted joke and not be so
quick to take offense.

~~~
rubyfan
Definitely no offense meant. It just sounded so smart that you could say it in
context or out of context and most people wouldn’t know what you’re talking
about but would probably assume you are experienced in whatever field.

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_Microft
Paper (Open Access):
[https://www.nature.com/articles/s41377-019-0229-8](https://www.nature.com/articles/s41377-019-0229-8)

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MrBuddyCasino
Conventional ultrasound transducer arrays aren’t cheap. Could this solve the
cost issue, e.g. for developing countries?

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deepnotderp
I believe so. I'm a bit surprised that microring resonator based optical
ultrasound detector arrays haven't already been used.

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dghughes
> one laser remotely generates sound waves that bounce through the body...

This is oddly related to what I was just watching. It was a SciShow episode
that discussed how phonons which can be generated (come from??) sound waves.
The phonons may be affected by gravity in the reverse way than all other
matter and may even repel matter.

Phonons it seems are not just sound. The MIT website explains "phonon is just
a fancy word for a particle of heat."

Anyway it seemed somewhat related especially "The resulting mechanical
vibrations generate sound waves that travel back up". But I guess the
researchers in the article may not have meant the sound waves literally go up.

[http://news.mit.edu/2010/explained-
phonons-0706](http://news.mit.edu/2010/explained-phonons-0706)

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nacnud
Would this work over larger distances - e.g. remote sensing from space?

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Enginerrrd
I doubt it just because there would be so much noise.

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waste_monk
I saw a thing about the Voyager 1 probe, and how they communicate with it
using two satelite dishes - one pointed at Voyager, and one pointed in the
direction of but very slightly off of Voyager. Since both have the same
background noise but only one dish has the transmissions from Voyager in it,
you essentially subtract the non-Voyager dish's input from the other one and
are left with the clean (or at least a lot cleaner) signal from Voyager.

Perhaps something similar could be done to reduce noise, using an empty patch
of ground nearby the target.

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kupiv
Cool! Sounds really impressive!

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14
I truly wish Gene Roddenberry could be alive today to see how far we have
come.

~~~
The_rationalist
But what's the use case?

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ComputerGuru
Is there a single true technological innovation (not some weekend or IoT
gadget) that doesn’t end up with a use case, sooner or later?

~~~
tal8d
Technology is the application of scientific knowledge, so you've got a
tautology there. That said: Capacitance Electronic Disc.

