X-Message-Number: 5135 From: (Brian Wowk) Newsgroups: sci.cryonics Subject: Re: Beyond 2000 and Mind Uploading Date: 6 Nov 95 17:53:08 GMT Message-ID: <> References: <> <47jb0l$> In <47jb0l$> (David L Evens) writes: >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 field strength changes needed for MRI are produced by low-frequency current pulses in gradient coils. The nuclei to be observed are excited by a separate rf coil that produces radio-freqency magnetic oscillations. Radio waves are not used in MRI or MRS. >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. Substitute "radio wave pulse" with "rf pulse", and this paragraph is essentially correct. >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. The rate at which you can extract data with MR is inherently limited by the T1 relaxation time of the sample, which actually increases with field strength. It is also extremely difficult (i.e. tedious) to do MR on solids like ice because the signal persists for only microseconds after each excitation (extremely short T2). What really kills you, though, is the infamous 6th power relation between scan time and resolution (at constant SNR) that exists in MRI. If you could scan an entire brain with 1mm resolution in 1 second, it would take you 10^28 years to scan that brain with 1 nanometer resolution. Even I don't believe that patients can be kept frozen for that long (or that they would WANT to be frozen that long!:) X-ray CT scanning can be ruled out for similar reasons. The bottom line is that it is not possible within the bounds of known physical law to non-invasively obtain the detailed neural information needed for uploading. In-situ nanotechnology is essential. (None of this precludes the possibility that someday people will redesign their brains so that rapid data readout is possible, but that again requires advanced NT.) ---Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5135