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Hi Finn, The dummy scans are collected to get to a (longitudinal) steady state. Therefore, the relevant parameter is not the number of dummies, but their duration: it should be about 2 or 3 times T1 (for a 90 deg. flip angle). Then, for a shorter TR you would need more dummies than for a long TR (when your TR is of about 5 or 6 seconds, you probably don't need any dummies, since you will get full T1 recovery between acquisitions; but you can test this empirically...). -Pablo On Thu, 23 Apr 2009 09:27:00 +0200, Finn Lennartsson <[log in to unmask]> wrote: >Hi, > >Taking up an old thread. > >Have acquired 6 b0 in the start of the scan and can also see differences in >signal intensity from 1 b0 and the subseqent b0:s. So I guess that this >means I should throw away the first b0 considering I am interested in MD:s >and eigenvalues as well as FA? > >If you go for a short TR, do you need more than 1 dummy then? > >So would it be advisable to go for dummies always in a diffusion scans since >there will always be this preparation difference between the first and the >following scans, even if this is only one b0 and then several diffusion >directions? Thinking of the situation with few directions, e.g. 2 b0 + 15 >directions or 1 b0 + 6 directions. > >Cheers, >Finn