Hi,
I'm not sure why the intensity range is different in your nifti
image, but use that range. It is more likely that the reconstruction
software tries to use the range 0 to (2^n - 1) for the intensity
range. Hence you should map the range 2048 to 2*pi. You
could also argue that 2047 is better - but the difference, which
is less than 0.05% won't affect anything significantly, given
the typical SNR in MR images.
All the best,
Mark
On 11 May 2009, at 21:39, Siew-Min Gan wrote:
> Hi, on the fsl practical page, there is a step on preparing phase
> difference map to a fieldmap in rad/sec with the following command
> "fslmaths phasemap -sub 2048 -div 2048 -mul 3.14159 phase_rad -odt
> float".
>
> When I look at the histogram of the intensity of the phasedif map, the
> dicom file has a range of intensity from -4096 to 4092. In nifti
> format,
> it's intensity range is 0 to 4094. May I ask if it is more accurate
> to
> keep to 2048 or to substitute 2048 to 2047 in the above calculation?
>
> Thanks
>
> Siewmin
>
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