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Ged, Thanks for your reply. So I take it that setting -ds to a lower number will result in more control points for a given image (and thus more degrees of freedom?). I wonder does anyone know what the optimum control spacing for registering high-resolution structural scans to a template, or has tried to do this before? Thanks, Matt. -----Original Message----- From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of DRC SPM Sent: Friday, November 09, 2007 11:35 AM To: [log in to unmask] Subject: Re: [FSL] RE : [FSL] RE : Re: [FSL] nreg - Registering structural data to DTI data Hi Bhargav, Matt, everyone, Roughly... (you'd have to ask Daniel Rueckert or Julia Schnabel if you want 100%precise answers) -ds 20 sets the B-spline control-point spacing to 20mm; the degrees of freedom for the registration is three for each control-point, where the number of control points relates to the sizes in mm of the image along each of the x, y, z-dimensions. The dx dy and dz options let you specify anisotropic control-point spacings, though I've never seen this used. I can't give you an exact formula for the total degrees of freedom in terms of the image size because I'm not sure about the implementation details in terms of boundary effects. E.g. do they put one or more control-points beyond the edges of the original image? As these could influence voxels inside the image, since the "support" of a cubic b-spline extends over +/- twice the control-point spacing, I think... I can't see a "-tp" option... If you mean -Tp (I'm fairly sure the options are case sensitive) then hopefully this will be clear: http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0709&L=FSL&P=R36244 Best, Ged On 05/11/2007, Bhargav Kumar Errangi <[log in to unmask]> wrote: > Hello steve, > Thank you very much for making me clear about the cost functions. I am not > sure about some of the other parameter settings like -ds (Initial control > point spacing paramter) and -tp (padding function). Can you please explain > to me what are these settings?. Also these settings were set to -ds 20 -tp 0 > in tbss_reg. Do these parameters change when i regsiter structural data to > diffusion data. Also is there any thing to do so that i can control/change > the number of degrees of freedom in non-linear registration. Also is there > any thing documented about these settings? > Thank you very much. > Bhargav. >