This is helpful. So this means that your scanner will always result in
intensity of 4096 when phase is its max of 2pi, but if you did not have
any noise voxels with phase=2pi, with your modification phase will still
I am using Philips 3T Achieva. Wondering if anyone knows how it scales
its B0 maps?
-Ajna Borogovac, Columbia University
Jim Lee wrote:
> I also use Chloe's great code, but modified that particular line
> to be more absolute in its assignment of phase, based on the knowledge
> that the phase difference maps on a Siemens Trio range in value from
> -4095 to 4096, and represent -pi to +pi.
> % JNL. More accurate statement
> svol = vol * pi / 4096;
> Jim Lee
> University of Utah
> Dear SPMers,
> I am wondering if anyone knows what is the significance of scaling the
> phase difference image to +pi to -pi range...
> The matlab code provided by Chloe Hutton among the updates finds the
> entire image max and min and uses this to scale the phase difference
> to this range. First problem I have with this code is that it does not
> discriminate between brain and non-brain voxels in the image to create
> the scale, and so the scaling ends up being based on noise outside the
> brain and therefore in a way arbitrary...
> Second, I have conceptually hard time understanding why the image would
> be scaled to have the max and min set to +pi and -pi, rather than
> be somewhere within this range. I.e. if max phase difference was for
> example lower than pi radians, why are we setting this voxel to pi?
> All input would be greatly appreciated!
> -Ajna Borogovac, Columbia University