X-Message-Number: 5134 From: (David L Evens) Newsgroups: sci.cryonics Subject: Re: Beyond 2000 and Mind Uploading Date: 5 Nov 1995 21:40:37 GMT Message-ID: <47jb0l$> References: <> <> Anders Sandberg () wrote: : David L Evens wrote: : >The reason why MRIs are of limited resolution is we can only extract : >limited ammounts of data from the signal (since there is substantial : >noise and computing power is finite). I expect that by the time we can : >build a computer powerful enough to upload to that would be cheap enough : >for individuals to actually afford, we will probably be able to build an : >NMRI system capable of extracting the neccessary data. : But isn't the resolution also limited by the field gradients? To get : higher resolution you need stronger gradients, and this can become : downright troublesome above a certain level (didn't lab rats levitate : in fields of a few tesla?), especially since when the fields are changed : the resulting heat could fry the brain. Hmm, that might be less of a : problem in finding the structure of a cryonically preserved brain in : liquid nitrogen (if we ignore the risk of additional cracks). My understanding is that field strength changes are performed by the use of radio waves. (I have used a NM spectrometer that used a powerful permanent magnet for producing the field, and the principle difference between MNS and MRI is the method of data extraction and processing.) The effectiveness of the instrument is measured both in terms of magnetic field strength, which is intended to be highly uniformly produced by the magnetic coils, and the intensity and precision of the radio wave pulse used to activate the nuclei that are to be sampled. My impression at the time was that the higher an RF frequency was used, the cleaner the data would be, but the stronger the field required was. There might be some problems with the energy input to the brain while the field is established or the brain inserted, but it should be possible to image with a relatively low flux of energy available for absorbtion by the brain, if enough time is taken in the imaging process. Certainly, a frozen brain is going to be arround for as long as you care to take, so extremely low flux rates can be used to get the data without damaging the brain. -- ---------------------------+-------------------------------------------------- Ring around the neutron, | "OK, so he's not terribly fearsome. A pocket full of positrons,| But he certainly took us by surprise!" A fission, a fusion, +-------------------------------------------------- We all fall down! | "Was anybody in the Maqui working for me?" ---------------------------+-------------------------------------------------- "I'd cut down ever Law in England to get at the Devil!" "And what man could stand up in the wind that would blow once you'd cut down all the laws?" ------------------------------------------------------------------------------ e-mail will be posted as I see fit. ------------------------------------------------------------------------------ Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5134