Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: scientizscht on 20/07/2019 19:32:05
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With HIFU we can heat a point with precision without affecting the surrounding points. Can we do that with cooling?
Thanks!
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No.
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With HIFU we can heat a point with precision
Be careful what you mean by "a point".
HIFU = High-Intensity_Focused_Ultrasound
Like all waves, it is extremely difficult to focus ultrasound energy to within 1 wavelength.
This region is small compared to human organs (so might be used for scalpel-free surgery), but still much larger than human cells.
And the heat quickly leaks away into surrounding tissues, so it does affect surrounding areas too.
See: https://en.wikipedia.org/wiki/High-intensity_focused_ultrasound
When it comes to cooling objects, that involves extracting diffuse thermal energy from the system, and putting it into an external system.
- This is much harder than taking concentrated energy from an external system and delivering it somewhere.
- To cool something, you have to take the random thermal motions of the atoms, and slow them down.
- In a human body at 37C, the thermal radiation of some cells inside the body is totally swamped by the thermal radiation of the surrounding tissue, so you can't absorb the thermal radiation.
- Anything you did cool (eg with a cryogenic probe) would soon heat up again from surrounding tissues.
- In theory, you could try to read the precise thermal motions of the atoms, and apply an opposing force. But even the effort of reading the motion of the atoms requires the injection of energy, as analysis of "Maxwell's demon" showed.
See: https://en.wikipedia.org/wiki/Maxwell%27s_demon#Criticism_and_development
There are some applications where you can cool a gas (in a near-vacuum) by using lasers.
- In this case, the atoms/molecules themselves select whether they are eligible to be cooled.
See: https://en.wikipedia.org/wiki/Laser_cooling
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Heat moves from hot areas to cold areas without any encouragement (this is Thermodynamics).
- This makes it easy to heat things.
But if you have an area at 37C surrounded by other areas at 37C, it won't change in temperature all by itself.
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But if you have an area at 37C surrounded by other areas at 37C, it won't change in temperature all by itself.
In fairness to the OP, that's also true of heating.
Nobody said anything about "all by itself". The whole point was whether you can do it by some intervention.
You could- sort of- do it by putting a small peltier cooler there.
But I'm pretty sure that's not what the OP had in mind.
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Utrasound combined "search and destroy" has been a research objective for many years. It is beset by several problems associated with sound transmission in biological tissue
absorption en route
inhomogeneous tissue en route
differential speed of transmission
inhomogeneous surface coupling to the transducer....
all of which get more significant at higher frequencies. But you need high frequency (short wavelength) to obtain a small focal spot. The equations are in principle solvable in real time but in practice the "point" is very fuzzy and damage to the surrounding tissue is difficult to avoid.
It turns out in practice that healthy biological tissue repairs itself quite well from a needle insertion, so a neater way of destroying a target is to insert a thermode through a cannula (using x-ray or ultrasound guidance) and heat or cool the tip with a Peltier junction, laser, or cold helium. You can also inject a variety of therapeutic or cytotoxic agents such as ozone or acetic acid to stimulate or kill the target.