Is it possible to develop an imaging technique based on ... gravity?

[The Angriest Bird]

---

Members don't see this ad.

I had this idea, more like a day-dream in some sense, about developing the new generation of imaging technique. I got so excited that I just have to share with you guys.

If you surf through the history of body imaging, it invariably follows the understanding of one thing - a "force" that is able to penetrate the body. The story began with X-ray, which is perfectly capable of penetrating flesh and bones. The physics behind CT is nearly identical to that of X-ray. SPECT uses gamma ray instead of X-ray due to gamma ray's short wavelength. MRI is based on the photons emitted by hydrogen nuclei when they drift into a lower-energy state. PET scan is even more bizarre - it detects the two photons emitted by the matter-anti-matter anhilation between an electron and a positron.

I made a bold generalization that for every physical entity that is able to penetrate the body, we ought to be able to develop an imaging technique.

Now, how about the the oldest such entity that was discovered by scientists - gravity?

Here's my design of a "Gravitational Scan." According to Einstein's laws of generalized relativity, gravitational field distorts the spacetime fabric around it. It even bends light because light travels along the spacetime fabric. Imagine I could build a detector made of a "mesh" of fine laser beams. If I put this detector near your knee, the gravity generated by your knee will distort the mesh. Let's now imagine there's an abscess in your knee. Because there is more matter in your knee joint, there is greater gravitational field. The mesh would be further distorted in a specific way. I could train a computer to analyze the laser mesh and relay the information to a readable image on the computer screen.

The advantage of such imaging technique would be unimagable:

1. No radiation whatsoever
2. Much lower cost than MRI, which requires generation of enormous magnetic field based on superconductor immersed in liquid nitrogen
3. It detects density of matter, which is hugely superb to X-ray which detects barreir to radiation and MRI which detects water density.
4. This procedure literally has no risk. It's even safer than ultrasound
5. If you could shrink the device enough, it would be a handle held device at bedside, giving physicians the "superman's eyes"

Any comments?

 

[TarHeelEMT]

Interesting, but...

1) Imaging with gravity hasn't succeeded on any scale to my knowledge, although it has been proposed as an astronomical tool.
2a) Gravity is an exceptionally weak force. If we could image with it, it would have to be with very large objects (think galaxies).
2b) The gravity produced by organs would be absolutely overwhelmed by the background gravity of everything else (earth in particular).

There are other reasons, but rest assured, it won't work, primarily because of the absurd insignificance of the force of gravity from a human being.


To image the gravitational force between two objects with 100g of mass (too large for useful medical imaging), your detector would have to be able to detect a force equal to about 6.6700e-11 Newtons. Nothing you can practically use in a hospital will come within 8 or 9 orders of magnitude of that degree of sensitivity.

 

[The Angriest Bird]

Interesting, but...

1) Imaging with gravity hasn't succeeded on any scale to my knowledge, although it has been proposed as an astronomical tool.
2a) Gravity is an exceptionally weak force. If we could image with it, it would have to be with very large objects (think galaxies).
2b) The gravity produced by organs would be absolutely overwhelmed by the background gravity of everything else (earth in particular).

There are other reasons, but rest assured, it won't work, primarily because of the absurd insignificance of the force of gravity from a human being.

I most definitely agree with you points. However, let me introduce a historical experiment. You may have heard of it before. It's called the Cavenish Experiment. Feel free to wikipedia it. In a nutshell, Henry Cavendish measured the gravity between two metal balls in the lab and calculate the gravitational constant.

My point is that, 300 years ago, scientists were able to elaborate gravitational interactions on the room-scale. Yes, the gravity generated by the body would be tiny, however techniques do exist to amplify the signal.

 

[Flopotomist]

Can I please make sure that neither of you are ever invited to one of my dinner parties? My head just exploded.

 

[MassTransport]

I think the best you could do is find the mass of the leg.

 

[Hayden2102]

I just had this strange image of dropping patients from a reasonable height and measuring the impact they make on the floor...

 

[MassTransport]

Then the debate's going to be what's a reasonable height. 😀

I think it's an interesting idea. Looks like you're measuring how a target affects photons based on its gravitational pull, kinda like how OCT measures how a target affects photons based on its optical properties, right?

 

[pseudoknot]

The biggest theoretical problem with this that I can see is that the resolution of any imaging technique is limited by the wavelength of the radiation it uses (due to the Nyquist sampling limit). You would need to generate gravity waves with a frequency of at least 10^11 Hz to get millimeter resolution, and I don't think that would be very feasible. Of course, there is also no technology that would even come close to being able to detect these.

Who knows though, maybe in a hundred years we'll see some progress on this.

 

[coldweatherblue]

interesting idea.

The main problem I see is that the tissues trying to be imaged have such a negligible effect on gravity that they would be almost impossible to detect and therefore differentiate on film. The difference between the gravitational effect and densities of the humerus versus the muscle and vessels surrounding it is so small that it would make imaging extremely difficult. Also one can't really just increase the gravitational effect 100X in order to magnify differences in density because it would lead to the death of the patient, etc. 😀

 

[strv04]

i hope they don't find the higgs boson where they should

that will be much more exciting

 

[ZonaRidicularis]

z

 

[Ashers]

I just had this strange image of dropping patients from a reasonable height and measuring the impact they make on the floor...

That's basically what I thought too.

 

[Habeed]

Good Yeast : ultimately, even if it could be done, you would need some incredibly exotic (meaning expensive) sensors. An MRI machine is not made of solid gold : with more mass production the cost could be brought down a huge amount. Further, much of the cost of an MRI image does not come from the cost of the machine or the energy to run it.

 

[gro2001]

for every physical entity that is able to penetrate the body, we ought to be able to develop an imaging technique

And I will be working on an imaging technique based on swords!

 

[coffeebythelake]

And I will be working on an imaging technique based on swords!

or bullets!

 

[inkare]

I had this idea, more like a day-dream in some sense, about developing the new generation of imaging technique. I got so excited that I just have to share with you guys.

If you surf through the history of body imaging, it invariably follows the understanding of one thing - a "force" that is able to penetrate the body. The story began with X-ray, which is perfectly capable of penetrating flesh and bones. The physics behind CT is nearly identical to that of X-ray. SPECT uses gamma ray instead of X-ray due to gamma ray's short wavelength. MRI is based on the photons emitted by hydrogen nuclei when they drift into a lower-energy state. PET scan is even more bizarre - it detects the two photons emitted by the matter-anti-matter anhilation between an electron and a positron.

I made a bold generalization that for every physical entity that is able to penetrate the body, we ought to be able to develop an imaging technique.

Now, how about the the oldest such entity that was discovered by scientists - gravity?

Here's my design of a "Gravitational Scan." According to Einstein's laws of generalized relativity, gravitational field distorts the spacetime fabric around it. It even bends light because light travels along the spacetime fabric. Imagine I could build a detector made of a "mesh" of fine laser beams. If I put this detector near your knee, the gravity generated by your knee will distort the mesh. Let's now imagine there's an abscess in your knee. Because there is more matter in your knee joint, there is greater gravitational field. The mesh would be further distorted in a specific way. I could train a computer to analyze the laser mesh and relay the information to a readable image on the computer screen.

The advantage of such imaging technique would be unimagable:

1. No radiation whatsoever
2. Much lower cost than MRI, which requires generation of enormous magnetic field based on superconductor immersed in liquid nitrogen
3. It detects density of matter, which is hugely superb to X-ray which detects barreir to radiation and MRI which detects water density.
4. This procedure literally has no risk. It's even safer than ultrasound
5. If you could shrink the device enough, it would be a handle held device at bedside, giving physicians the "superman's eyes"

Any comments?

Interesting idea !!! but there are issues ...

First off, it's not a force able to penetrate a body (x-rays aren't forces). It's particles able to penetrate the body and measuring their attenuation (except for MRI, which is based on relaxation times of proton magnetization). As far as I know, gravitational fields are not attenuated when passing through the body. I don't even know if it's correct to say that they pass through the body, since an object bends the spacetime fabric as you said.

Second, tomography is acquiring projections of an object at different angles (x-ray is not tomography whereas CT, which uses x-rays of the object at different projections, is). You can then use these projections to reconstruct the object (using the Fourier slice theorem or the backprojection algorithm). How would you acquire different projections of the "attenuated gravitational force" through the body ? The entire object is attracted to your "gravitational source", so different projections won't suffice. In MRI, you spatially localize the signal by using a magnetic gradient field gradient. If this is what you had in mind, you would need a gravitational gradient. Also you can't produce uniform gravitational fields you can for magnetic fields (hmmm, unless you have to huge plates, like a capacitor .... would that make the gravitation between them uniform ?)

Anyways, there are other fields or waves that have been a hot research area such as electric fields or radio waves. Neither gets attenuated by tissue, meaning that you can't use absorption as your contrast agent. However, if you find other contrast agents, exogenous ones, you can have your own imaging modality.

 

[OwnageMobile]

Interesting idea !!! but there are issues ...

Second, tomography is acquiring projections of an object at different angles (x-ray is not tomography whereas CT, which uses x-rays of the object at different projections, is). You can then use these projections to reconstruct the object (using the Fourier slice theorem or the backprojection algorithm). How would you acquire different projections of the "attenuated gravitational force" through the body ? The entire object is attracted to your "gravitational source", so different projections won't suffice. In MRI, you spatially localize the signal by using a magnetic gradient field gradient.

I think this is an important issue. While I don't see it as that he's trying to send gravity waves--he's trying to simply measure how the knee's gravity affects a beam of light--you still must collect more data. I think that having an array of high tolerance laser beams shooting just over the skin, being bent, then hitting a receiving plate/microscope to analyze its change in trajectory will really not suffice in terms of data dimensions. The knee image, I'd glibly think, would look radial at best. I.e. different intensity rays coming from the axis of revolution, but nothing more.

And I'd think that the tolerance/precision you'd need to make such fine measurements would be $$$$$$. I like the idea, though.


EDIT: I can't find that experiment on wiki.

 

[MassTransport]

I think you'd need to chart the path of each beam in 3D space to be able to calculate the size and position of the objects affecting them. Otherwise I see it being sort of a less clear xray.