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Comment by lars_thomas | Hacker News Reader

Photon counting sensors have been available for quite a while. This is unfortunately not new. It’s not ’color’ it’s multi channel imaging. X-ray tubes produce wide spectrum of x-rays, these type of sensors are able to put different bands to different buckets.

Coloring is arbitrary and conveniently chosen in the example to look like visible wavelength response as if the patient was dissected. It does not work for more complicated anatomy and even in this case needs very likely post processing.

I wish we could have a peek inside the patient as if we had opened it up but this is not yet that.

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It seems like this is more akin to 'false color'.[1]

[1] https://en.wikipedia.org/wiki/False_color

Which similar to images we see of space where they have altered detectors' responses from different wavelengths of light to be images in the visible spectrum. So we produce beautiful images, but they aren't accurate to what space would look like to the naked eye.

Probably more useful than the naked eye in many cases. The colors our eyes can see mostly evolved to detect ripe fruit, not diseased tissue.

On the contrary, finding edible food is certainly important, but avoiding poisonous/diseased food is even more important.

If we can detect ripe, surely we can infer not ripe.

There's probably an app for that.

Why did fruit evolve to change colors when ripe?

In many cases so animals would eat them, digest the seeds, and poop them out somewhere else.

Why did animals evolve an attraction to ripe-colored fruit?

That's what I understood at first, but what seems to be the case is that light from deep space undergoes "red shift", and by the time it reaches us, visible spectrum has been shifted into x-ray spectrum. The "false color" is just a correction back to almost the original visible spectrum. The degree of red shift is how we determine distance.

Red shift only comes into play for distant galaxies. Nothing in our galaxy, or nearby galaxies, is going to be red shifted in any significant way.

> visible spectrum has been shifted into x-ray spectrum.

No, x-rays are way more energetic than visible light (MUCH shorter wavelenths..). Red shift, as the name implies, refers to shifting of wavelengths to the red/infrared side of the spectrum, not towards the blue/ultraviolet/x-ray/gamma ray side. The most distant, oldest thing we can see is in the microwave wavelengths, and that's the remnants of the big bang.

The real issue is with dust, and the inverse square law (that the intensity of radiation follows).

Some objects are obscured by dust, and so the only way to see them is by looking at wavelengths that are able to penetrate the dust.

The further an object is, the less intense the radiation is reaching us, so we have to stare at it for a very long time in order to collect enough photons to form good images. This is why views of Andromeda through a telescope with your eyeballs do not look like this visible light image of Andromeda: https://apod.nasa.gov/apod/ap991114.html

Instead it looks more like this under the absolute best viewing conditions on Earth with a quality telescope (nominal is a blurred version of this): http://www.deepskywatch.com/images/articles/see-in-telescope...

hey thanks for clearing that up.

Yep. All those fantastic color pictures of the Orion nebula are just that. (Personally I think there should be a requirement to post, alongside them, true color photos.)

Why? Many times the true colour images aren't even available. How would you represent an infrared or x-ray picture properly, in your view?

False colour images aren't meant to mislead. They're meant to be more useful to understand what you're looking at. "True colour" has no meaning, really.

I'd say because without a modicum of knowledge you'd take it for granted. Compare to "images" of dinosaurs where you'll often read "this is what it should look like" vs "we know squat about the color of their skin". And for space pictures, which are 99% touted as "pictures" and not reproductive works, it's even worse. Hell, as I'm writing this I'm tempted to double check what I know about color-correctness of any space photo, and my point was already that I'm in the second stage of not knowing - that there could be something I don't know [0]

[0] https://en.wikipedia.org/wiki/Four_stages_of_competence

Why aren't space photos real? For deep space photos, where we have to wait for individual photons, maybe they're false color, but many photos are taken by putting colored filters in front of the lens and then combining the exposures, so they are actually true color.

I'm not saying they're fake - I am just saying people believe what they see. So a specific or general disclaimer of "the colors might not be accurate" would be cool, if it's the case for a specific photo.

Tell that to the color-blind.

Exactly. Researchers have been doing tomography with energy-dispersive detectors for decades, especially at synchrotrons. They often represent that data in 3D with false color indicating material properties. If there is something particularly novel about this work, it's not clear from the article, which reads like a rehash of a University PR piece.

TV cameras originally produced color by taking black-and-white video through 3 different filters, transmitting these as a bundle, and outputting these to the electron scanner. The colors didn't get mixed until after they hit the TV screen, as the photons were traveling to our eyes.

That's still how most imaging sensors work. Few, if any, actually parse the photon energy from within the imaging pixel itself.

>> I wish we could have a peek inside the patient as if we had opened it up but this is not yet that.

Surgery rarely looks like that. We are messy creatures. Our parts all overlap and fold among each other. It never looks as open as in the scan, short of dissecting the patient well beyond what is ever needed for any actual procedure.

The example image certainly looks cool, but it is too 2d. It doesn't have the 3d structure visible in traditional x-rays. An expert can look at an old photographic x-ray and see the layers of tissue and bone atop each other. It is a rather good 2d visualization of a complex 3d shape. Giving tissues more solid color take away from the translucence and, imho as a non-doctor, removes much of the information.

I agree, PCD's have been available for some time, but this is the first time a 3D reconstruction of a living human has been produced. The image colors do actually represent the energy spectrum of the transmitted photons. However, if we wish to see this information then we must map the X-ray color to the visible spectrum or there would nothing to visualize. In this case using a tissue color scheme that we understand is just convenient.

This tech also does work quite nicely on complex anatomy.

>Coloring is arbitrary

By my understanding, it's not possible to determine an objections interaction characteristics with a wavelength of X with a wavelength of Y. (Unless you were able to create some sort of beat frequency tuned to mimic X by sending in Y+delta? Just thinking off the top of my head). It seems fraudulent for the company to say that it's capturing color.

>these type of sensors are able to put different bands to different buckets.

Would the best summarization be, photon counting sensors allow for the capture of x-ray imagine with higher dimensionality?

Pretty much. Normal x-ray sensors are like camera sensors and produce an estimate of total energy of the photons / pixel. Photon counting sensors are able to estimate how many photons of certain energy range hit the sensor. So instead of value ’1023’ you might get ’63’ of < 20kv, ’500’ of 20-50kv and ’50’ of > 50kv. So poor mans spectroscopy. Naive way to produce ’color images’ would be to put those buckets to red green and blue channel and now different materials along the beam path might yield equal values with normal x-ray sensors but slightly different colors with photon counting sensors. edit: clarified last sentence

The way "color images" are produced is to map the Hounsfield scale to the visible colour spectrum: i.e. blood red, bone white, steel gray etc.

https://en.wikipedia.org/wiki/Hounsfield_units#Value_in_part...

CT machines have this calibrated as standard, DICOM images have the corresponding fields for the values. Any DICOM viewer will do this (i.e. 3D Slicer, ParaView, OsiriX etc.)

As you say, there is nothing new in this, just PR. Medipix also has been around for a while, it's basically a solid state detector with an integrated USB readout on the silicon. Neither has been invented at CERN, its COTS.

In this case it’s more than HU value LUT though. Photon counting allows per energy bin attenuation to capture more information. It’s cool and promising but costly and not new per se.

Agreed. Photon counting has been around in (medical) imaging for ages.

To be more precise, CERN took part in Medipix3's development.

https://medipix.web.cern.ch/medipix3-collaboration-members

Yes, this is a PR release for tech using the Medipix3. If I understand correctly (which I very probably don't since this HN thread is the first time I've heard of this technology), this is analogous to faster/more accurate AI software being developed with some chip company's latest massively parallel processor - representative of real, but nowhere near groundbreaking, technological advancement.

> I wish we could have a peek inside the patient as if we had opened it up but this is not yet that.

What's stopping us? Are you saying that there's no way to tell different kinds of tissues apart (e.g. not even with an MRI)? I imagine if we did, we could also add "color" (via post-processing) and enable a "dissection". Or are you saying it has something to do specifically with color?

I think the point was that the x-ray 'colors' do not have 1:1 mapping with the colors that our eyes see. So the color is useful to discern different tissues and bones and stuff, but the colors won't look like the colors of those things in real life.

We see in a range of wavelengths 0.4--0.7 um. X-rays have no intersection with our visible range. Therefore the best you can do is define some function that maps x-rays into our color range, but things look very different in x-ray land than they do in color land. For starters, most things would be transparent if you could see x-rays (hence x-ray imaging!).

http://www.columbia.edu/~vjd1/electromag_spectrum.htm

Maybe a good way of explaining it would be like this: if someone magically had a blue spine, this technique would still show their spine as being white (unless the doctor already knew their spine was blue and adjusted the parameters accordingly)?

My point is, showing spine as white on X-ray (well, that's probably easy, but generalizing this to other tissues and their "normal"/"expected" color probably isn't) would be tremendously helpful in diagnosis... "peeking inside patients without cutting them up" - and I'm wondering, what's stopping us from doing just that?

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