Hi Bruce, Thanks for your response.
On Thu, Apr 25, 2013 at 1:45 PM, Bruce Fischl <fis...@nmr.mgh.harvard.edu>wrote: > Hi Dan > > how do you do the B1 correction? using -afi with a custom B1 map. > And why would we need to know the field strength? The T1 is certainly a > function of the field strength, but we will just find the T1 for whatever > strength field the input data was acquired with. > > And yes, we search in 5ms increments. You could certainly change that if > you want (it's a constant in the code), but I don't think we have the > sensitivity to distinguish 5ms differences in T1 from typical input data. > > The bigger problem is getting stable estimates of T2* from a max echo time > of <15ms. The maps we have generated are *really* noisy. Note that by > default we don't remove the T2* component from the PD unless you specify > -correct on the command line, in which case we will write out a > PDcorrected.mgz as well that is divided by the T2* decay term. > > I haven't used this option. What criteria should be used to decide if it is necessary. > I guess in the end I'm not clear what problem you are trying to solve. If > the discretization only has a small effect on the estimates, do you need to > fix anything? > I am using the resultant PD.mgz from two different measurements to calculate equilibrium magnetization dependent temperature changes. I am just trying to learn more and make sure that I am not violating any of the assumptions in mri_ms_fitparms. Thanks Dan > Bruce > > > On Thu, 25 Apr 2013, dgw wrote: > > I have run mri_ms_fitparms (version 5.1.0) on phantom data from two >> multiecho flash volumes (5 and 20 degrees with 8 echos: 1.67ms - 14.83ms >> in >> 1.88ms steps) at 7T utilizing a b1 map for correction. >> >> How does mri_ms_fitparms know the field strength (I can't figure out where >> the information is when I read the mgz files using MRIread.m)? >> >> I notice that the T1 volume seems to have graded steps of 5ms. Is this due >> to the table of 1ms stepped T1 values in the table described in Fischl et >> al. 2004 (and the data in this case being collected at 7T)? >> >> Is there any way to increase the sensitivity? >> >> Interestingly, this effect seems to only have a small effect on the values >> of the PD.mgz; however, from the 2004 Fischl paper, I would have expected >> it >> to have a large effect. >> >> What concerns should I have about using the PD.mgz to represent the >> Equilibrium Magnetization in terms of accuracy of the values? >> >> Thank You, >> Dan >> >> >> >> >> > > 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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