dki-questions > Direction Scheme
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Mar 17, 2016  07:03 AM | Eric Miller
Direction Scheme
Is it possible for DKE to process uneven sampling scheme such (i.e. b=500, 1000, and 3000 and directions=20, 40, and 64, respectively) or do the gradient directions have to be the same for each b value? Thanks in advance!
Mar 19, 2016  06:03 AM | Russell Glenn - Medical University of South Carolina
RE: Direction Scheme
Hi Eric,

Yes, it is possible. Currently what you have to do is create a separate gradient table for each b-value and then you can set the following variables in the parameters file used to run DKE:

ndir = [20,40,64];
fn_gradients = {'path_to_table_1','path_to_table_2','path_to_table_3'};
idx_gradients = {1:20,1:40,1:64};

Hope that helps,

Russell

Documentation

ndir is the number of gradient directions; if a scalar value is specified, the number of gradient directions for all b values is set to the scalar; otherwise, a 1-by-(nbval-1) vector should be specified, with each element of the vector corresponding to the number of gradient directions for a nonzero b-value

fn_gradients is the path to a text file containing the gradient vectors; each row corresponds to a gradient vector; if a different gradient set was used for each b-value, a 1-by-(nbval-1) cell array of file names should be specified, with each cell specifying the gradient file name for the corresponding nonzero b-value

idx_gradients is a cell containing indices of gradient directions to be used for DKI map estimation; unacceptable diffusion-weighted images (e.g., those affected by motion- or patient table vibration-induced diffusion signal loss) can be excluded here; there must be as many cells as there are nonzero b-values, with each cell corresponding to a nonzero b-value