| I have spatially normalized SPECT data encoded on 2 bytes on SPM SPECT
| Template, and I have noticed that there are some negative values in the
| resulting normalized data, especially in the borders of the image. Has
| anyone already noticed that ? Is it possible or may I have made a mistake
Unless the values have been truncated at zero (not recommended as it introduces
bias), your original filtered back-projected images should contain some negative
values in the background. If these images are all positive, then spatial
normalisation may introduce small negative values if you use sinc interpolation.
If you have very large negative values, check that the image format you have
is fully compatible with SPM.
Best regards,
-John
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