X-Message-Number: 27639 From: Date: Tue, 21 Feb 2006 02:14:42 EST Subject: Uploading technology (1.ii.3) Brain reader steps 2. Uploading technology (1.ii.3) Brain reader steps 2. The main magnetic field in an MRI scanner is continuous. It is very difficult to get a high field producing a strong polarization and at the same time a good homogeneity. I think it would be interesting to produce a pulsed main field, may be up to 5 Teslas or even more without too much smoothness and then shut it down and let a weaker field with very good homogeneity. The first brain reader would be only a "cracks reader", a system looking at microcracks in the body. It could be derived directly of the gas demonstrator and use liquid neon 21, the common isotope of neon. It would work at minus 240 C, a step colder than liquid nitrogen. The cold temperature would bring a factor of ten in magnetisation and so in received power. One atom out of 20 000 would be polarized at 5 Teslas. The antennas would be put in the neon bath and could be build from high purity aluminum or berylium. The Q coefficient (a mesure of the resonator quality) may be in the million range with them at these temperatures. One possibility is to boost Q with an operational amplifier using the high mobility electron transistors technology. That system is used for satellite reception for example. One problem is the 1/f noise or "brown noise", it dominate the electronics and thermal noise under 150 MHz. Unfortunately, MRI above that frequency implies a very strong field. It could be interesting to look at harmonics of the main signal, one drawback, beyond the reduced signal power, is the aliasing noise produced at high frequency. The strong coupling of atoms in a solid reduce both, the T1 (spin-network relaxation time) and T2 (spin-spin exchange). T1 is above one second in most liquids and gas, it is under the millisecond here. This is seen as a strong drawback in the traditional view. Here, it is a good thing. A short T1 will radiate all the energy in a short time, giving more power. Power, not energy, is what count in the signal/noise ratio. Getting a better S/N is very important for microscopic MRI where voxels (volume elements) are tiny. The most interesting signals would come from phosphorous and sodium, both are tracer of the membranes and neural receptors. Water (hydrogen) gives a strong signal, but most molecules are not interesting. Carbon 13 may be more useful,. the most common form of carbon, carbon 12, has no nuclear spin. Both, C13 and P31 are "classical" spin 1/2 systems, Na23 has a spin 3/2 structure. If chemical analysis can be included, by detection of the molecular shift, then hydrogen would be more interesting, may be deuterium could be the target, reducing the interaction between nearby atoms. The D spin is 1 and the Larmor frequency is : 654.5 Hz/Gauss. It is common practice in two dimensional MRI to code along X in frequency and along Y in phase. The process is then inversed and a picture is taken with frequency coding along Y and phase along X. Without phase coding, a set of frequency coding in a number of tilted directions can build back a picture. Using simultaneously the two process, that is, taking a large number of tilted frequency-phase 2-d pictures could recover the chemical shift "dimension". The third space dimension would be coded in echo time by a time shift in the pi/2 radio pulse. Spin recovery sequence is not a possibility here if the magnetization field is pulsed. This situation is similar to the hyperpolarized gas case. Not all these elements would be implemented at start, so this summarize a number of steps, may be ten years of R&D. Yvan Bozzonetti. Content-Type: text/html; charset="ISO-8859-1" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=27639