Dear Juha,
We really need more information than this.
What values have you put into your slice profile and
what object voxel sizes are you using in the simulator?
The size of the object voxels (that is, the voxels used to
represent the object - not the voxels that appear in the
output image) is critical in determining how the RF field
is applied, as each object voxel sees a single value of
the RF field. Therefore if your slice is very narrow but
your object voxels are not then the simulation will not
work correctly.
Please give us some more information and we will try
to help.
All the best,
Mark
On 8 Nov 2010, at 11:55, Juha Pajula wrote:
> Hi!
> Could You help me once again with the slcprofile of POSSUM simulator?
>
> I got instructions from you how to define our own slice profile for POSSUM simulator.
>
> I created one according to the instructions and verified it by our fMRI technician. I have tested it with our own data as well as the default data from POSSUM. It won't work. The same simulation with the possum defaults works, but when I change the slcprofile to our own the output is a mess.
>
> Earlier instructions were following:
>
> "The slice profile is simply truncated at a convenient point where
> the amplitude is less than 0.3% of the maximum - since it needs
> to be truncated at some arbitrary point. The frequency
> difference is normalised as a percentage of the Larmor frequency. "
>
> Should the profile have some defined length? Our profile has really narrow band. Can that cause the problem?
>
> Results are looking like this (all data is possum default, except the slcprofile):
> http://www.cs.tut.fi/~pajula2/possum.png
>
>
> Waiting your answer,
> --
> Juha Pajula,
> Research Assistant,
> Methods and Models for Biological Signals and Images group of Signal
> Processing department in Tampere University of Technology,
> Finland
>
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