[Mristudio-users] update of gradient table in DtiStudio

[HUA KEGANG]

Hi, Luca
 
The MI algorithm optimizes the normalized mutual information.
 
Thanks! 

KEGANG(LUKE) HUA
Department of Radiology
Johns Hopkins University School of Medicine
720 Rutland Ave Traylor217
Baltimore, MD, 21205



 
> Date: Mon, 27 Dec 2010 09:38:00 +0100
> From: luca.binotto at unipd.it
> Subject: [Mristudio-users] update of gradient table in DtiStudio
> To: mristudio-users at mristudio.org
> 
> Hello Susumu,
> 
> I would like to know something about the way DtiStudio performs the update
> of the gradient table after the realignment of the dti dataset with
> respect to the mean_b0 volume.
> 
> The registration algorithm implemented in DtiStudio using mutual
> information (MI):
> 1) does it uses normalized mutual information or which other formulation ?
> 2) how is the gradient table updated ? (rough simple theory)
> After realignment of the DWI volumes, b-matrix (the gradient table) must
> be updated.
> 
> Patient motion and eddy currents can cause errors in the calculation of
> parameters that describe diffusion in each voxel of a DWI dataset.
> In normal conditions eddy currents contribution should be
> very small (< 1% ?).
> But the b-matrix (gradient table) is calculated with respect to a fixed
> coordinate system (at the acquisition time) so the b-matrix must be
> rotated accordingly to the transformation applied for image registration
> otherwise we should get poor fiber statistics and some fibers possibly
> deviate.
> 
> So the gradient table is affected by rotations. Translations don't
> change it.
> But what does it happen with resampling (applying a scaling factor: es.
> affine transformation) to a dwi dataset?
> According to you is normally its effect small (as for eddy currents
> effect) or can be more important?
> For example a scaling factor such that a volume with a voxel size of
> 2x2x2 mm3 is resliced to a 1x1x1 mm3 voxel size can be important its
> effect or "only" a lower image quality (eg. I read somewhere of a
> "red background" superimposed to the correct color map)?
> 
> 
> thanks in advance,
> best regards,
> 
> Luca
> 
> 
> 
> 
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