The following are the names of dimensions and their corresponding
dimension variables. Only `MIvector_dimension` does not have a
corresponding dimension variable.

`MIxspace`- Dimension and coordinate variable for x axis.
`MIyspace`- Dimension and coordinate variable for y axis.
`MIzspace`- Dimension and coordinate variable for z axis.
`MItime`- Dimension and coordinate for variable time axis.
`MItfrequency`- Dimension and coordinate variable for temporal frequency.
`MIxfrequency`- Dimension and coordinate variable for spatial frequency along the x axis.
`MIyfrequency`- Dimension and coordinate variable for spatial frequency along the y axis.
`MIzfrequency`- Dimension and coordinate variable for spatial frequency along the z axis.
`MIvector_dimension`- Dimension only for components of a vector field.

In addition to dimension variables, we can have dimension width variables that specify the FWHM width of the sample at each point.

`MIxspace_width`- Width of samples along x axis.
`MIyspace_width`- Width of samples along y axis.
`MIzspace_width`- Width of samples along z axis.
`MItime_width`- Width of samples along time axis.
`MItfrequency_width`- Width of samples along temporal frequency axis.
`MIxfrequency_width`- Width of samples along x spatial frequency axis.
`MIyfrequency_width`- Width of samples along y spatial frequency axis.
`MIzfrequency_width`- Width of samples along z spatial frequency axis.

The attributes associated with dimension and dimension width variables are given below:

`MIspacing`- A string with value
`MI_REGULAR`(for a regularly spaced grid) or`MI_IRREGULAR`(for irregular spacing of samples). If the value is`MI_REGULAR`, then the variable is permitted to be a scalar instead of a vector varying with the dimension of the same name. Can be used for both dimension and dimension width variables. `MIstep`- A number indicating the step between samples
for regular spacing. This value may be negative to indicate
orientation (to specify that
`MIxspace`runs from patient right to left, for example). If the spacing is irregular, then the value can be an average step size. Applies only to dimension variables. `MIstart`- The coordinate of the index 0 of the dimension. Applies only to dimension variables.
`MIspacetype`- A string identifying the type of
coordinate space. Currently one of
`MI_NATIVE`(the coordinate system of the scanner),`MI_TALAIRACH`(a standardized coordinate system), or`MI_CALLOSAL`(another standardized coordinate system). Applies only to dimension variables. `MIalignment`- A string indicating the position of the
coordinates relative to each sample (remembering that each sample
has a width). Can be one of
`MI_START`,`MI_CENTRE`or`MI_END`. Applies only to dimension variables. `MIdirection_cosines`- A vector with
`MI_NUM_SPACE_DIMS`(=3) elements giving the direction cosines of the axes. Although axes are labelled x, y and z, they may in fact have a signficantly different direction -- this attribute allows the direction relative to the true axes to be specified exactly. Applies only to dimension variables. Note that the dot product of the direction cosine with the corresponding axis (, or ) should be positive so that the sign of the attribute`MIstep`contains the orientation information. `MIwidth`- For regularly dimension widths, this numeric attribute gives the FWHM width of all samples. It can be used for irregular widths to specify the average width. Applies only to dimension width variables.
`MIfiltertype`- A string specifying the shape of the
convolving filter. Currently, can be one of
`MI_SQUARE`,`MI_GAUSSIAN`or`MI_TRIANGULAR`. Applies only to dimension width variables.