PHYS1008 Study Guide - Final Guide: University Of Manchester, Voxel, White Matter

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Two voxels in x-y plane of a slice through the brain: voxel a = region of grey matter, voxel b = region of white matter. Aim = distinguish these two voxels on the basis of signals received following t1 and t2 relaxation. T1 is significantly longer than t2 and within a magnetic field strength of 1. 5t: a grey matter: t1 = 900msec, t2 = 100 msec, b white matter: t1 = 780msec t2 = 90msec. Grey matter is longer for both t1 and t2. Figure shows effect of a 90 degree rf pulse on t1 relaxation. As grey matter has a longer t1 of 900msec than white matter 780msec, it will take longer for its signal to re-grow to its maximum value. I. e. grey matter takes longer to recover, grey matter loses energy slower in t1 relaxation and takes longer for its longitudinal magnetism to grow to 63% of mo.