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# NIfTI-1 Statistical parametrical data

NIfTI-1 Statistical distributions

Statistics in NIfTI-1 chart

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#### STATISTICAL PARAMETRIC DATASETS (i.e., SPMs):

Values of intent_code from NIFTI_FIRST_STATCODE to NIFTI_LAST_STATCODE (inclusive) indicate that the numbers in the dataset should be interpreted

as being drawn from a given distribution. Most such distributions have auxiliary parameters (e.g., NIFTI_INTENT_TTEST has 1 DOF parameter).

If the dataset DOES NOT have a 5th dimension, then the auxiliary parameters are the same for each voxel, and are given in header fields intent_p1, intent_p2, and intent_p3.

If the dataset DOES have a 5th dimension, then the auxiliary parameters are different for each voxel. For example, the header values

- dim[0] = 5

- dim[1] = 128

- dim[2] = 128

- dim[3] = 1 (indicates a single slice)

- dim[4] = 1 (indicates no time axis)

- dim[5] = 2

- datatype = DT_FLOAT

- intent_code = NIFTI_INTENT_TTEST

mean that this is a 2D dataset (128x128) of t-statistics, with the t-statistic being in the first "plane" of data and the degrees-of-freedom parameter being in the second "plane" of data.

If the dataset 5th dimension is used to store the voxel-wise statistical parameters, then dim[5] must be 1 plus the number of parameters required by that distribution (e.g., intent_code=NIFTI_INTENT_TTEST implies dim[5] must be 2, as in the example just above).

Note: intent_code values 2..10 are compatible with AFNI 1.5x (which is why there is no code with value=1, which is obsolescent in AFNI).

Information from nifti1.h by RW Cox, NIH