[link] The World's Most Powerful MRI Takes Shape
post by moreati · 2013-10-23T20:42:55.334Z · LW · GW · Legacy · 11 commentsContents
11 comments
http://spectrum.ieee.org/biomedical/imaging/the-worlds-most-powerful-mri-takes-shape
Standard hospital scanners have a spatial resolution of about 1 millimeter, covering about 10 000 neurons, and a time resolution of about a second. The INUMAC will be able to image an area of about 0.1 mm, or 1000 neurons, and see changes occurring as fast as one-tenth of a second, according to Pierre Védrine, director of the project at the French Alternative Energies and Atomic Energy Commission, in Paris
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comment by [deleted] · 2013-10-23T22:57:16.245Z · LW(p) · GW(p)
Disclaimer: I'm a graduate student in medical imaging -- but not on the hardware side of things, so my remarks in these areas are likely to be incorrect.
I'm sure some are reading this hoping for applications to uploading (as the comparison to neurons is compelling), but IMHO (emphasis on humble) I don't expect MRI to be the path to nondestructive human brain imaging.
Problems:
Increasing the strength of the magnetic field is an easy way to increase resolution, but there are hard limits as to how much magnetic field a human brain can take. Already at 2 Tesla an MRI can heat and sometimes burn patients; the risk at 11.75 Tesla (as in the article) is proportionally greater.
Not all brain-related information that may be necessary for reconstruction is visible to an MRI, e.g., some kinds of neurotransmitters.
MRI resolution can be high, but contrast can be low -- particularly for those applications to sodium and potassium nuclear resonance the article briefly mentions. You can improve contrast by injecting contrast agents, but this also comes with safety risks, and the blood-brain barrier makes it difficult to chose good contrast agents.
Increased resolution implies increased acquisition time, and increases in acquisition time imply increased artifacts from motion blurring. In the early days of MRI they used to sedate or briefly kill patients to obtain decent imagery, so this problem is not insurmountable.
For a while, at least, destructive imaging is going to be my best bet for uploading.
EDIT: Removed some confused remarks in 4.
Replies from: gwern, passive_fist, Blade2187↑ comment by passive_fist · 2013-10-23T23:38:27.140Z · LW(p) · GW(p)
A stationary magnetic field cannot heat and burn patients. What you are referring to is radio frequency heating, caused not by the magnetic field but by the radio waves used to do the actual probing. You do not need to increase the RF power to make use of the increased resolution offered by higher magnetic fields.
Replies from: None↑ comment by [deleted] · 2013-10-24T00:07:22.337Z · LW(p) · GW(p)
A stationary magnetic field cannot heat and burn patients.
Yes, this is true -- but only if the patient is also stationary. Which they aren't, usually; see 4. It's true that the vast majority of MRI burns are not of this type, but I'm aware of some examples.
What you are referring to is radio frequency heating, caused not by the magnetic field but by the radio waves used to do the actual probing. You do not need to increase the RF power to make use of the increased resolution offered by higher magnetic fields.
Right, my phrasing in 4 is a bit bad. However, I'm not referring to RF in 1.
Replies from: passive_fist↑ comment by passive_fist · 2013-10-24T00:39:07.324Z · LW(p) · GW(p)
The magnetic field itself (at least in current machines) is not capable of burning the patient. TVMF (Time-varying magnetic field) MRI can cause eddy currents, but these are very small, and the primary danger from these is shocks and siezures, not burns. If the patient has electrically-conductive items in their body (implants, etc.) the magnetic field can also cause harm in that way, but this is usually not a problem since patients are screened for these types of implants beforehand.
Replies from: None↑ comment by Blade2187 · 2013-10-28T20:54:28.901Z · LW(p) · GW(p)
As passive_fist already covered, the strength of the magnetic field is mostly irrelevant in terms of safety. The human brain doesn't suddenly stop functioning at 11 Tesla, nor does it get heated by the static magnetic field. Radiofrequency heating safety at high field is still an ongoing topic of discussion, but it should (presumably) not be insurmountable problem, and there are technologies in development that may reduce the required RF power substantially.
The bigger question, assuming you were being serious with your reference to uploading, is what MRI can actually measure. You touched upon this in mentioning contrast limitations. Keep in mind that MRI only produces a spatially and temporally varying signal intensity map. This signal arises from the average signal across all molecules in the nominal target voxel, and the nature of the signal depends on the design of the RF pulse sequence used and any contrast agents administered. For example, there is the Blood Oxygenation Level Dependent (BOLD) signal used for functional magnetic resonance imaging (fMRI) studies, which is designed to highlight the differences between areas of the brain with high blood oxygenation vs. low. That's just a single, very specific type of contrast. Think about how many different sorts of contrast maps you might need to measure to be able to generate an accurate enough simulation of your brain to result in an accurate simulation of your personality and consciousness, and on what scale of spatial and temporal resolution, and look at how crude even the proposed new MRI system is in comparison. The level of MRI-like technology you would need to pull off such a feat would make tomorrow's MRI systems look like slings and stones in the face of modern weapons technology.
Replies from: None↑ comment by [deleted] · 2013-10-29T15:08:25.451Z · LW(p) · GW(p)
The human brain doesn't suddenly stop functioning at 11 Tesla
I don't recall saying anything of the sort, and the safety risks were hashed out in the cousin thread. There's still an occupational safety risk around strong, static magnetic fields.
assuming you were being serious with your reference to uploading
This is still LessWrong, right? I didn't accidentally post this comment to RationalWiki?
The level of MRI-like technology you would need to pull off such a feat would make tomorrow's MRI systems look like slings and stones in the face of modern weapons technology.
I have no idea what this sentence is supposed to mean. The paragraph preceding it seems to be arguing against the feasibility of neuron-level imaging, but then this analogy makes it seem possible.
Replies from: Blade2187↑ comment by Blade2187 · 2013-10-30T08:03:36.123Z · LW(p) · GW(p)
I don't recall saying anything of the sort
Well, I'm not sure what else to make of the "hard limits" regarding the magnetic field that a human brain can "take" that you were referring to. What exactly did you mean?
There's still an occupational safety risk around strong, static magnetic fields.
Such as? What occupational risks are so elevated at high field that they would pose a "problem" to human brain imaging?
but then this analogy makes it seem possible
Maybe it is, maybe it isn't. I wouldn't hold my breath if I were you, but I also can't comment on what is and isn't possible for technology hundreds or thousands of years into the future.
comment by Gurkenglas · 2013-10-23T22:33:04.486Z · LW(p) · GW(p)
If adding stronger magnets increases the resolution, why did this only get 200 million dollars?
Replies from: None