MRICloudCalculateM0
===================

**Purpose.** Create an **M0 map** and two brain masks (display/calculation) following MRICloud logic.

What it does
------------

- If M0 is **provided** (separate scan or included volumes), averages to form M0,
  optionally coregisters to the control image.
- If ``M0Type == "Estimate"``, estimates M0 from control images with optional
  background suppression timing.
- Generates:
  - ``M0map.nii`` — final M0 in perf space
  - ``brnmsk_dspl.nii`` — display mask
  - ``brnmsk_clcu.nii`` — calculation mask

Inputs
------

- ``derivatives/<sub>/perf/r{asl}_ctrl.nii`` (from :doc:`mricloud_calculate_diffmap`)
- Optional M0 inputs from ``data_descrip`` or ``ASLContext``
- TPM file: ``pyasl/tpm/TPM.nii`` (internal helper)

Outputs
-------

- Saved under ``derivatives/<sub>/perf/``:
  - ``M0map.nii``
  - ``brnmsk_dspl.nii`` (int16)
  - ``brnmsk_clcu.nii`` (int16)

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

=================  ===================  ==========================================
Key                Type / Default       Meaning
=================  ===================  ==========================================
``t1_tissue``      int / ``1165``       Tissue T1 (ms) used in BGS factor estimation
``bgs_eff``        float / ``0.93``     Background suppression efficiency
=================  ===================  ==========================================

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

.. code-block:: yaml

    modules:
      - name: MRICloudCalculateM0
        params:
          t1_tissue: 1165
          bgs_eff: 0.93