Hello,

I'm using HARDI data (>100 directions, b-value=4000). In the "hardi_mat" command there is an option to select the maximum order of spherical harmonics (-order) that will be used in the reconstruction of the orientational distribution functions (odf_recon). However, using different values for this parameter (for example, "-order 4" or "-order 6" or "-order 8" ) I obtained the same results (the same hardi_odf image in each case, and as a result, the same tracks). Although the tractography results are fine (pretty pictures), I am interested in exploring different levels of spherical harmonic expansions.

Any suggestion?

Thanks in advance,

Regards,

Erick

Hi Ruopeng,

My ODFs are completely identical, even ranging the -order parameter from 2 to 8.

Apparently the hardi-matrix is created using the default value of 4. There is something wrong with this sentence?

hardi_mat "/HARDI_b4000/bvecs_for_trackvis.txt" "/HARDI_b4000/temp_mat.dat" -ref "/HARDI_b4000/data_b4000.nii" -order 6 

Another different point, what rules do you follow to extract the ODF maximum?
all the local maxima are considered, or all local maxima above a certain threshold and/or all local maxima within an angular neighbourhood?

Many Thanks

Best Regards

Erick