Visible Light 'X-Ray' Sees Through Solid Objects 122
disco_tracy writes "Some day we may not need X-rays to see inside people, thanks to a new way to decipher light that passes through opaque surfaces. Normally visible light becomes too scattered to detect after passing through opaque surfaces. But scientists in France have developed a way to reconstruct images from light passing through such surfaces by deciphering just how the material makes the light scatter. In the short term the research will help improve the strength of telecommunications signals and fiber optics cables, but years from now the technology could supplement or even replace traditional ultrasounds for baby imaging and X-rays for weapons detection at airports."
We don't use X-rays to see in utero fetii (Score:2, Informative)
This is a pretty cool idea, but it will probably not take the place of x-rays. X-ray is cheap, easy, accurate, and relatively harmless (in small doses).
This sounds expensive, requires a large amount of processing capability, isn't very portable, and relies on light actually passing through the object. For some applications this may be useful, but for the vast majority of imaging tasks that require visualizing the internals of an object, x-rays will be the better solution.
Now, an x-ray scanner that didn't require film plates. That would be good!
Re:Visible? Opaque? (Score:3, Informative)
How does visible light make its way through an opaque object?
I know you aren't supposed to read TFA, but ""It's like putting a flashlight behind your hand," said Sylvain Gigan... "You cannot see an image, but you can still see a faint glow.""
Re:Peeping toms will love this... (Score:5, Informative)
Not likely (in the US at least). Kyllo V United States [go.com] established that using IR to peer into a home requires a warrant, and that's a pretty strong precedent. A key issue of the case was that using IR didn't even need to penetrate the house (it just "recorded" what was being emitted) and yet was STILL not allowed without a warrant. Anything that "peers in" will be just as illegal.
A better explanation (Score:2, Informative)
Amazing! A friend of mine has done his Ph.D. in exactly this field. He was shining a beam of light right THROUGH an opaque sheet of material (paper, I think) already a few years ago, and published about it in 2008. I think it's pretty much the same idea, from what I understand of it (but keep in mind, I chose the evil path of Business instead of Science, so I have no brain).
Anyway; on his page [ivovellekoop.nl] there's a much better explanation, with cute pictures and all that, of the same idea.
Re:Visible? Opaque? (Score:2, Informative)
Re:Visible? Opaque? (Score:3, Informative)
Thanks to quantum tunneling nothing is ever completely opaque. A particle's path from A to B doesn't necessarily have to pass through all the points in between. Some tiny fraction of the photons will always act as though the object isn't even there.
Re:Visible? Opaque? (Score:5, Informative)
The idea is that you send light against an opaque medium, the photons getting blocked or scattered is a statistical process. Some of them, simply as a matter of probability, "sneak through" in a straight line.
To get around the low probability, you use a strong light source, modulate it (if you modulate the light, you can pick it out with a tuning circuit, so that you can screen out background light), and then average over a long period of time.
Eventually, you get enough ballistic photons through that you can map out an image.
Re:Correction of trivial relevance (Score:3, Informative)
Ultrasound is for listening to sounds inside the body, such as the faint heartbeat of an unborn human.
No it isn't. Ultrasound is ultrasonic, by definition. (Higher frequency than normal sound.) Ultrasound is often used for imaging; the resulting images are called sonograms. Ultrasound can detect heartbeats through movement (Doppler shifting the ultrasound waves). It's not for listening to normal sound waves originating from inside the body. That's just a stethoscope (or fancier variant thereof).
Re:Correction of trivial relevance (Score:4, Informative)
A sonogram is the image produced by an ultrasound machine. Ultrasound imaging is called "ultrasonography."
Listening to sounds within the body is called auscultation.
Re:Visible? Opaque? (Score:4, Informative)
Eventually, you get enough ballistic photons through that you can map out an image.
Physicists don't actually use terms like "opaque" very often. We are more likely to talk about material that is "highly absorbing" or "highly scattering". The human body contains lots of both.
One area where people have tried to apply this is in optical mamography: women's breasts are primarily fatty tissue that is highly scattering but very weakly absorbing, so you get a surprisingly large fraction of transmitted light. You have to do a huge amount of processing to deconvolve the scattering kernel, but when I worked in the area in the late '90's it was getting close to useful.
For people reading this who are female or who have wives or girlfreinds willing to go along, go into a dark room and hold a flashlight under your (partner's) breast. You'll be amazed by the amount of veinous structure and whatnot you can see. Squeeze the breast flat to get more detail. Insert joke here about how now you're in a dark room with a woman who has at least one breast exposed so you know what comes next...
Very athletic women with smaller breasts may not see much: the chest muscles are highly absorbing and any any photon that scatters into them is lost.
High-speed computation is making visible light a more useful medium of detection all the time, and the work described in TFA is an interesting step along the way.