Thanks for your answers! Following your comments, I have thought to select only first two sequences, as they are the more frequent in our database and only differ on the TE parameter. We will also create balanced groups.
cheers Daniel 2012/8/18 Andre van der Kouwe <an...@nmr.mgh.harvard.edu> > Hi Daniel, > > I agree, those flip angle differences are quite big and would make a > difference to contrast. I suspect gray/white contrast is better for the > higher TI and lower flip angles in those scans (and they could benefit from > longer TR). So if you have a balanced study/control group it's ok but I > wouldn't compare subjects with systematically different protocols like > those below. > > Cheers, > > Andre. > > > Bruce Fischl wrote: > >> Hi Daniel >> >> those are pretty big differences in flip angle. I'll cc Andre van der >> Kouwe on this so he can comment, but I would be hesitant. The increased TE >> will have a big effect on dura (darkening it), but will also reduce >> gray/white contrast. >> >> cheers >> Bruce >> >> >> On Fri, 17 Aug 2012, Daniel Ferreira wrote: >> >> Dear all, >>> We are designing a study based on clinical data. We want to work with a >>> MPRAGE sequence but subjects have been given 4 different sets of >>> parameters: >>> >>> - TR: 1900; TE: 4,38; TI: 1100; flip angle: 15 >>> - TR: 1900; TE: 3,55; TI: 1100; flip angle: 15 >>> - TR: 1900; TE: 3,39; TI: 900; flip angle: 9 >>> - TR: 1900; TE: 3,39; TI: 900; flip angle: 15 >>> >>> I wonder how these differences could affect the images and thus the >>> results. >>> Can I combine all of them or at least some of them? Are they so different >>> that I should just study them by separate? >>> >>> thank you very much on advance >>> >>> Daniel Ferreira >>> >>> >>> > > The information in this e-mail is intended only for the person to whom it > is > addressed. If you believe this e-mail was sent to you in error and the > e-mail > contains patient information, please contact the Partners Compliance > HelpLine at > http://www.partners.org/**complianceline<http://www.partners.org/complianceline>. > If the e-mail was sent to you in error > but does not contain patient information, please contact the sender and > properly > dispose of the e-mail. > >
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