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Hi - DTIFIT uses least squares on the log-transforned signal by default (indeed using pinv). The weighted least squares option (—wls) uses the approach suggested in http://onlinelibrary.wiley.com/wol1/doi/10.1002/hbm.20076/full No need for the user to specify “weights”. However the user can also optionally specify a confounds file. This has been used, e.g., to diminish the effect of a once infamous artefact http://www.ncbi.nlm.nih.gov/pubmed/19603408 Cheers, Saad On 22 Sep 2016, at 16:21, Michael Knight <[log in to unmask]<mailto:[log in to unmask]>> wrote: That unless you give dtifit a set of weights, I think it goes ahead with ordinary least squares. type dtifit -h to get the help, or see the wiki page Here's a tutorial page (one of many) on an easy approach to diffusion tensor fitting, easy to follow and implement in Matlab/Python etc. At the final step, I'm pretty certain dtifit uses the Moore-Penrose psuedo-inverse of the design matrix, not simply the inverse (inverting a design matrix is not 100% sensible). http://www.diffusion-imaging.com/2014/04/from-diffusion-weighted-images-to.html On 22 September 2016 at 15:52, Ana Maria Escorza <[log in to unmask]<mailto:[log in to unmask]>> wrote: what you mean with "But the weights are user-supplied if WLLS, default OLLS"? thanks cheers, Ana. 2016-09-22 16:44 GMT+02:00 Michael Knight <[log in to unmask]<mailto:[log in to unmask]>>: OLLS or WLLS (by moore-penore psuedo-inverse I think). But the weights are user-supplied if WLLS, default OLLS On 22 September 2016 at 15:41, Ana E. <[log in to unmask]<mailto:[log in to unmask]>> wrote: What diffusion tensor estimation does "dtifit" use? OLLS,WLLS,NLLS??? -- Michael John Knight, PhD Elizabeth Blackwell Institute Early Career Fellow School of Experimental Psychology and School of Clinical Sciences University of Bristol Tel 07920 113060 -- Michael John Knight, PhD Elizabeth Blackwell Institute Early Career Fellow School of Experimental Psychology and School of Clinical Sciences University of Bristol Tel 07920 113060