I have a question regarding resampling of high resolution PET images. We
have a Seimens EXACT HR+ scanner. The images are reconstructed with voxel
sizes of 1.88 mm (X) x 1.88 (Y) x 2.42 mm (Z). There are 63 planes with
128 x 128 matrix in each plane yielding a FOV of 24 cm X 24 cm in plane and
15.2 cm in the z-axis.
As a result the images include the entire brain with room to spare on all
sides. I have noticed that the top and bottom (brainstem) of the brain
appears smeared after spatial normalization. I am using the PET.img
template with the MNI bounding box. Spatial normalization parameters are 4
x 5 x 4 basis functions, 8 non-linear iterations, sinc interpolation and
2.0 x 2.0 x 2.0 mm voxel size.
I have tried changing the normalization parameters, but there is very
little difference to my eye. I have even changed the normalization fudge
factor in the spm_defaults.m, but the 0.02 default value seems to be best.
My questions are:
1) Given that the images have slightly greater resolution in the x and y
voxel dimensions than the default normalized voxel sizes, would it be
better to resample at 1.5 x 1.5 x 1.5 mm voxel size ?
2) Given the high resolution of the images, would it be preferable to
reduce the extent of the sinc interpolation, and if so, how does one change
the parameters for sinc interpolation. Alternatively, would the other
interpolation methods be better ?
3) What parameters for normalization are other people using for Seimens
EXACT HR+ images ?
Thanks.
sg
Steven Grant, Ph.D.
Etiology and Clinical Neurobiology Branch
Div. Clinical and Services Res
National Institute on Drug Abuse
Room 10A-46
5600 Fishers Lane
Rockville, MD 20857
Voice (301) 443-4877
Fax (301) 443-6814
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