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intent_code


nifti1.h header documentation

/---------------------------------------------------------------------------/ /* INTERPRETATION OF VOXEL DATA: ---------------------------- The intent_code field can be used to indicate that the voxel data has some particular meaning. In particular, a large number of codes is given to indicate that the the voxel data should be interpreted as being drawn from a given probability distribution.

VECTOR-VALUED DATASETS: ---------------------- The 5th dimension of the dataset, if present (i.e., dim[0]=5 and dim[5] > 1), contains multiple values (e.g., a vector) to be stored at each spatiotemporal location. For example, the header values - dim[0] = 5 - dim[1] = 64 - dim[2] = 64 - dim[3] = 20 - dim[4] = 1 (indicates no time axis) - dim[5] = 3 - datatype = DT_FLOAT - intent_code = NIFTI_INTENT_VECTOR mean that this dataset should be interpreted as a 3D volume (64x64x20), with a 3-vector of floats defined at each point in the 3D grid.

A program reading a dataset with a 5th dimension may want to reformat the image data to store each voxels' set of values together in a struct or array. This programming detail, however, is beyond the scope of the NIFTI-1 file specification! Uses of dimensions 6 and 7 are also not specified here.

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).

OTHER INTENTIONS: ---------------- The purpose of the intent_* fields is to help interpret the values stored in the dataset. Some non-statistical values for intent_code and conventions are provided for storing other complex data types.

The intent_name field provides space for a 15 character (plus 0 byte) name string for the type of data stored. Examples: - intent_code = NIFTI_INTENT_ESTIMATE; intent_name = "T1"; could be used to signify that the voxel values are estimates of the NMR parameter T1. - intent_code = NIFTI_INTENT_TTEST; intent_name = "House"; could be used to signify that the voxel values are t-statistics for the significance of activation response to a House stimulus. - intent_code = NIFTI_INTENT_DISPVECT; intent_name = "ToMNI152"; could be used to signify that the voxel values are a displacement vector that transforms each voxel (x,y,z) location to the corresponding location in the MNI152 standard brain. - intent_code = NIFTI_INTENT_SYMMATRIX; intent_name = "DTI"; could be used to signify that the voxel values comprise a diffusion tensor image.

If no data name is implied or needed, intent_name[0] should be set to 0.

DEFINED CODES

nifti1 intent codes

Created by Alex Clark
Last modified 2005-04-14 18:42
 

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