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H-preserve ¨ once it has been determined that the output voxel will be part of the ROI, preserve the original ROI value of that voxel (and not some fraction of that value).  For example, if our ROI mask has values of Ò4Ó:
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¥3dresample does this conversion as well:
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å3dresample -master func+orig
å -inset ROI_high_res+orig
å -rmode NN
å -prefix ROI_low_res
å
H-master func+orig: the destination grid we want our ROI mask resampled to
H-inset ROI_high_res+orig: The ROI mask dataset that is being resampled from high to low resolution
H-prefix ROI_low_res: The output from 3dresample -- a low res ROI mask that corresponds with the voxel resolution of our functional dataset
H-rmode NN: If a voxelÕs ÒneighborÓ is included in the ROI mask, include the voxel in question as well
This voxel is 80% filled with the ROI value -- keep it.
Without the -preserve option, this voxel would be given a value of Ò3.2Ó (i.e., 80% of Ò4Ó). 
With -preserve, it is labeled as Ò4Ó