[HN Gopher] Photon transport through the entire adult human head
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Photon transport through the entire adult human head
Author : gnabgib
Score : 63 points
Date : 2025-06-13 23:15 UTC (3 days ago)
(HTM) web link (www.spiedigitallibrary.org)
(TXT) w3m dump (www.spiedigitallibrary.org)
| ggm wrote:
| Is this likely to be less risk than xray or nmr mri for
| comparable imaging quality?
| jocaal wrote:
| This will probably never get the image quality of either of
| those. The image quality you get is proportional to the density
| of the detecting elements. These types of infrared methods
| usually have to touch the skin, so you would need a flexible
| array of detectors and your not going to get the same quality
| with that.
| ars wrote:
| You could solve that by scanning across the skin, and
| immersing the side of the head and the detector in some kind
| of fluid that helps light transmission (avoids reflections on
| the skin), so you don't actually have to touch the skin.
| metalman wrote:
| inserting a medical light bulb in the pattients mouth will
| decrease the distance the light has to travel, and
| presumably it could be a high intensity "flash" tuned to
| conditions with very precisely known timing
| mpreda wrote:
| In the nose as well.
| saltcured wrote:
| Suddenly, the idea of aliens sticking probes into various
| orifices takes on a new light...
| ars wrote:
| Yes, less risk, but the image quality is non-existent - at
| least as of right now.
| freehorse wrote:
| Yes. They use 800nm wavelength which is near infrared.
|
| I don't think this can give a structural image, but not sure
| what this can be used whatsover. It is probably more comparable
| to fmri because the technique, applied on short source-detector
| paths, is usually showing fluctuations in oxygenation levels in
| the cortex, as proxy of brain activity, but in contrast to fmri
| it could not go deeper into subcortical structures of the
| brain.
| aetherspawn wrote:
| Clicked it because I thought they teleported a photon through a
| head.
| ars wrote:
| This only works on white patients, so if it actually becomes
| clinically useful it will be pretty controversial.
| JumpCrisscross wrote:
| Can we temporarily and locally induce vitiligo?
| andsoitis wrote:
| > This only works on white patients
|
| Where did you read that in the article? I couldn't find it.
| eminence32 wrote:
| First paragraph of the "4. Discussion and Conclusion" section
|
| > We speculate that the participant's fair skin and lack of
| hair were significant factors that reduced the attenuation of
| light to feasibly detect a signal. In addition to the
| participant wherein a signal was observed, the experiment
| also included trials on seven other subjects. The details of
| the subject pool are as follows: two females and six males;
| 25 to 35 years old; 14.5 to 15.5 cm head diameter;
| Fitzpatrick skin types: 3 type I, 4 type II, and 1 type V;
| hair types: 1 bald, 4 short and light-colored, and three
| dense and dark-colored. We did not observe any significant
| time-correlated signals above background noise for the seven
| other subjects.
| rkagerer wrote:
| In case anyone is wondering why (from the paper):
|
| _Photons measured in this regime explore regions of the brain
| currently inaccessible with noninvasive optical brain imaging._
| ars wrote:
| I can't figure out how they would collect depth information from
| the resulting photon pattern.
|
| I believe reflected photons are much more useful, by measuring
| how long in between signal and response you can get flight time
| which tells you depth. Of course I have no idea if infrared light
| reflects on anything in the brain.
| dabiged wrote:
| I suspect they do a radon transform of the paths to determine
| the infrared transmissibility value. Similar to how CT scans
| are constructed from 1000's of micro x-rays.
| freehorse wrote:
| This uses near-infrared light, building on current techniques of
| using near-infrared light in shorter source/detector paths to
| measure fluctuations of oxygenated/deoxygenated haemoglobin on
| the cortex of the brain as a proxy of brain activity. The
| standard technique is called functional near-infrared
| spectroscopy, and is similar to fMRI but can only look into
| superficial brain tissue and not subcortical brain structures
| like fMRI, with the advantage that it is cheaper, easier, and
| essentially portable.
|
| In standard fNIRS, a light source and a detector forming a
| channel have to be ~2-3cm apart. The light leaves the source,
| goes into the scalp in a banana shape due to refraction, and
| reaches the detector. The idea is that due to differential
| absorption of different wavelengths by oxygenated and
| deoxygenated haemoglobin, you can send 2 wavelengths and solving
| a 2x2 system gives you the fluctuations in oxygenated and
| deoxygenated haemoglobin in the tissue the light transversed.
| This is a proxy of brain activation in that area. If the neurons
| fire a lot, they consume more oxygen and the brain then sends
| more oxygen there, this is called Brain-oxygenation level
| depedent (BOLD) response. If the path length is too short, the
| light cannot get refracted deep enough to reach the cortex, so
| you do not measure brain. If it is longer, too much light is
| absorbed on the way and less signal reaches the detector. The
| researchers here try to detect light with source/detector
| diametrically opposite on the scalp, and they show they can.
| However, it is not clear what kind of application this can have.
| It was done under very restrictive conditions (subjects very
| light-skinned, no hair, 30 minutes recording). Moreover, an
| advantage of standard fNIRS is the high spatial specificity, and
| it is not clear how to actually translate the light intensity
| data in their case to brain activation (and probably it is going
| to be very noisy) as the light transverses all the head.
|
| In any case, they are experimenting with a novel technique, more
| like a PoC that they can at least detect photons but nothing more
| than that, and we are probably far away from any potential
| applications, if any is even come out of this. But it could also
| lead to applications we cannot actually imagine right now. As for
| applying this to measure brain activity in the way current fNIRS
| and fMRI do, I am skeptical.
| leereeves wrote:
| > Moreover, an advantage of standard fNIRS is the high spatial
| specificity, and it is not clear how to actually translate the
| light intensity data in their case to brain activation (and
| probably it is going to be very noisy) as the light transverses
| all the head.
|
| The X-rays in CT scans also transverse all the head. Would it
| be possible to use the same algorithms as CT to construct a 3D
| image with this tech?
| dgfl wrote:
| IIRC the highly diffractive nature of the medium limits
| resolution to something like 1 cm^3. I'm not an expert but I
| talked with some people working in the field a few years ago
| and this is what I remember. The computational problem is
| almost intractable.
|
| No short term brain computer interface with optical
| techniques just yet.
| layer8 wrote:
| No thought screening in airports and public spaces either.
| ;)
| antiquark wrote:
| Wow, weak signal... "The measured experimental attenuation was
| found to be of the order 10^18, corresponding to a detection of
| around one photon per second for a 1.2 W source."
| Someone wrote:
| So, around a factor of 10 per cm. I would have expected way
| worse.
| xnx wrote:
| Is this technique useful or already used for other tissues? I'm
| always surprised how much of my body I can see through with a
| bright (visible wavelength) light.
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