Smooth (SPM)
============

**Purpose.** Spatially smooth selected perfusion files using SPM Smooth.

Inputs
------

For each subject, the module collects:

- ``perf/r{M0}.nii`` (if M0 present)
- ``perf/rmean{asl}.nii`` and ``perf/rr{asl}.nii`` for each ``{asl}``

Outputs
-------

- Smoothed versions written in place per SPM defaults.

Configuration
-------------

=================  ==================  ======================================
Key                Type / Default       Meaning
=================  ==================  ======================================
``fwhm``           list / ``[6,6,6]``   Gaussian kernel FWHM (mm) per axis
=================  ==================  ======================================

YAML example
------------

.. code-block:: yaml

    modules:
      - name: Smooth
        config:
          fwhm: [6, 6, 6]