fmri_spheremask
===============

.. currentmodule:: fmri_toolbox

Description
-----------
FMRI_SPHEREMASK  Spherical ROI mask centred on a given voxel.
Creates a vectorized binary brain mask (228453 x 1) where all voxels
within a sphere of the specified radius around the centre voxel are set
to 1. Useful for creating seed regions for connectivity analyses.

Usage
-----
.. code-block:: matlab

    s = fmri_spheremask(center, radius)

Inputs
------
- **CENTER**: Centre of the sphere as voxel subscripts [x y z] (1 x 3), or as a linear brain index (scalar). For MNI coordinates, first convert: center = fmri_mni2sub([x y z]).
- **RADIUS**: Sphere radius in voxels (1 voxel = 2mm). Default: 2 (= 4mm).

Outputs
-------
- **S**: Binary brain mask (228453 x 1). 1 = inside sphere.

Examples
--------
.. code-block:: matlab

    % 10mm sphere at MNI [20 -58 18]
    mask = fmri_spheremask(fmri_mni2sub([20 -58 18]), 5);
    % Seed time series for FC
    seed_ts = mean(data(logical(mask), :), 1);
    r = fmri_corregressor(seed_ts', data);

See Also
--------
- fmri_regionmask
- fmri_mni2sub
- fmri_corregressor