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Biotech / Medical : Caprius(CAPR), Breast MRI(former ANMR/MAMO) -- Ignore unavailable to you. Want to Upgrade?

To: luis a. garcia who wrote (2135)	11/12/1997 1:36:00 AM
From: Zeev Hed	Read Replies (1) \| Respond to of 2615

Luis, I am afraid that under the hood you will find what they call "chemical shift". A hydrogen nucleous might have a larmor frequency at 1/5 Tesla of about 42 or so MHz. The hydrogen "sees" around another hydrogen and an oxygen, in fat the hydrogen "sees" around it mostly carbon, oxygen and other hydrogen and in protein the poor hydrogen is burdened with "seeing" nitrogen as well (and sometimes in some strange spatial situations). As a result, the "chemical field" around hydrogen nuclei (or protons) differ a little between these different chemical fields, and you get a small shift in the Larmor frequency, but large enough to differentiate between hydrogen in one or other environment. In essense, it used to be that the systems usually tune and measures the water protons and reject the non water (so fat may look lighter, less spin density) and water containing tissue darker (more spins density), of course dark and white is just an artificial selection and now they may tune to each separately and obtain two images as you stated. The important thing is that the "chemical" field between proton in diferent chemical bond environment result in absorption ( and then decay and reemission) of the RF pulse at slightly different frequencies for proton in different compounds. Unfortunately it gets much more complex as you get your head more under the hood (VBG). Zeev