Jason--
Yes, you are correct. The 'bcrvs1.dat' file accounts for the hardware
(which is assumed to be stable over time). The 'ref.dat' file is a
function of shimming, and, therefore, unique to each scanning session.
Best,
Wil
.............................................................................
William Irwin Laboratory for Affective Neuroscience
Department of Psychology lab: 608-262-4443
University of Wisconsin fax: 608-265-2875
1202 West Johnson Street http: psyphz.psych.wisc.edu
Madison, Wisconsin 53706 [log in to unmask]
.............................................................................
On Tue, 29 Aug 2000, Jason Steffener wrote:
> Thank you for such a quick response.
> I will check with your reference. I just thought of another question on
> this topic.
> The ref.dat file is one file that gets created for all the sessions in one
> experiment. (One trip to the magnet) And the bcrvs1.dat file is one file
> that gets used over and over without update. Is this correct or does the
> bcrvs1.dat file need to be updated after every shimming?
> thank you,
> Jason.
>
>
> On Tue, 29 Aug 2000, Wil Irwin wrote:
>
> > Jason--
> >
> > 'epirecon' was developed here at Wisconsin, so I'll take a stab at
> > commenting on your questions.
> >
> > The bandpass asymmetry correction adjusts for bias in the A-to-D sampling
> > (basically). You will notice reduced ghosting with this applied, and, to
> > the extent that any ghosting is not half-field-of-view, this would affect
> > signal distribution in the region of interest (i.e., brain proper).
> >
> > The adjustment for phase correction isn't going to yield differences that
> > are necessarily visible. I would refer you to the work of Jezzard and
> > colleagues for a full treatment of this rather complicated topic.
> >
> > As you note, there are subtle differences between data processed with and
> > without these corrections. However, in my opinion, there is no reason not
> > to apply them; the increase in processing time is trivial.
> >
> > Best,
> > Wil
> > .............................................................................
> > William Irwin Laboratory for Affective Neuroscience
> > Department of Psychology lab: 608-262-4443
> > University of Wisconsin fax: 608-265-2875
> > 1202 West Johnson Street http: psyphz.psych.wisc.edu
> > Madison, Wisconsin 53706 [log in to unmask]
> > .............................................................................
> >
> > On Tue, 29 Aug 2000, Jason Steffener wrote:
> >
> > > Hello all,
> > > I know this is not the most appropriate place to ask this
> > > question, but I dont know where else to ask.
> > > I am using epirecon to reconstruct GE format Pfiles.
> > > The options for 'epirecon' use are to use the bcrvs1.dat file for Bandpass
> > > Assymetry Correction and to use the
> > > ref.dat file
> > > for phase correction. My question is what is the result (differences) of
> > > using or not using these files in the reconstruction? I have done the
> > > reconstruction and SPM preprocessing and analysis on images
> > > using and NOT using these "dat" files. I see some differences in the
> > > final statistics. (Not great differences) I would just like to know the
> > > source of the differences.
> > > Thank you for any insight or better direction,
> > > Jason.
> > >
> > >
> > > Jason R. Steffener, RTSV
> > > Department of Psychiatry, University Hospital, UMDNJ
> > > Office: (973) 972-1604
> > > http://www.umdnj.edu/~steffejr/jason.html
> > >
> > >
> > >
> >
>
> Jason R. Steffener, RTSV
> Department of Psychiatry, University Hospital, UMDNJ
> Office: (973) 972-1604
> http://www.umdnj.edu/~steffejr/jason.html
>
>
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