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Dear SPMers,

I am having some difficulties with the FieldMap toolbox in SPM2, and would 
would be most grateful for some advice.

I have been trying to generate fieldmap data from two sets of non-EPI phase 
and magnitude images, at a short and a long TE. However, after loading the 
images via the FieldMap GUI, setting the correct TEs, and pressing the 
Calculate button, I get the following error message:

??? Error using ==> sparse
Index exceeds matrix dimensions.

Error in ==> c:\spm\spm2\toolbox\FieldMap\pm_angvar.m
On line 32  ==> MH = sparse(round((hs-1)*((imag(cmap(:))-mini)/(maxi-mini))
+1),...

Error in ==> c:\spm\spm2\toolbox\FieldMap\pm_unwrap.m
On line 162  ==> angvar = pm_angvar(ci);

Error in ==> c:\spm\spm2\toolbox\FieldMap\pm_make_fieldmap.m
On line 156  ==> [fm.upm,angvar,fm.mask,fm.opm] = pm_unwrap
(cmap,pxs,flags.method);

Error in ==> c:\spm\spm2\toolbox\FieldMap\FieldMap.m
On line 1257  ==>          IP.fm = pm_make_fieldmap([IP.P{1} IP.P{2} IP.P
{3} IP.P{4}],IP.uflags);

Error in ==> c:\spm\spm2\toolbox\FieldMap\FieldMap.m
On line 557  ==>       status=FieldMap('CreateFieldMap',IP);


I am using Matlab 6.5.1 on a PC, with the latest version of FieldMap 
installed. The phase images have been scaled to +/-pi using Chloe Hutton's 
script, posted previously on the mailing list. The second set of phase and 
magnitude images was coregistered to the first set, and then both sets of 
images were coregistered to the first EPI image in the time series. The 
phase and magnitude images were then resliced into the same space as the 
EPI image, as the FieldMap algorithms require all images to have the same 
dimensions and voxel size. I have successfully generated fieldmap and vdm 
data using real and imaginary images that have undergone the same series of 
coregistration and reslicing steps. However there are some scaling issues 
with our real and imaginary images, and I would like to be able to use the 
phase and magnitude images instead.

I have tried several permutations (one set of phase and magnitude images 
only, both sets, omitting coregistration to the EPI) without success. Can 
anyone suggest where I'm going wrong?

Many thanks in advance,

Jane Warren


Dr. Jane Warren
Language/Stroke Recovery Group
Cyclotron Unit
Hammersmith Hospital
Du Cane Road
London W12 0NN