fmri_snri
=========

.. currentmodule:: fmri_toolbox

Description
-----------
FMRI_SNRI  Image-domain signal-to-noise ratio (SNR-i) for each fMRI scan.
Computes the image SNR for each time point as the ratio of the mean signal
across all brain voxels to its standard deviation:
SNR-i = mean(S_t) / std(S_t)
A high SNR-i indicates that signal variation across voxels within a
scan is small relative to the mean, suggesting low inter-voxel noise.

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

    SNR = fmri_snri(v)

Inputs
------
- **V**: fMRI data, vectorized (228453 x T) or volume (91 x 109 x 91 x T).

Outputs
-------
- **SNR**: Image SNR per time point (T x 1).

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

    snr = fmri_snri(data);
    plot(snr); xlabel('Scan'); ylabel('SNR-i')

See Also
--------
- fmri_snrt
- fmri_cnr