Source code for AFQ.models.QBallTP

import numpy as np
from dipy.reconst.shm import anisotropic_power

__all__ = ["anisotropic_index", "anisotropic_power"]




def anisotropic_index(shm):
    """
    Calculates anisotropic index based on spherical harmonics coefficients.

    Code from Dmipy
    ---------------
    The MIT License (MIT)

    Copyright (c) 2017 Rutger Fick & Demian Wassermann

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.

    https://github.com/AthenaEPI/dmipy

    References
    ----------
    .. [1] Jespersen, Sune N., et al. "Modeling dendrite density from
        magnetic resonance diffusion measurements." Neuroimage 34.4 (2007):
        1473-1486.
    """
    sh_0 = shm[..., 0] ** 2
    sh_sum_squared = np.sum(shm**2, axis=-1)
    AI = np.zeros_like(sh_0)
    AI = np.sqrt(1 - sh_0 / sh_sum_squared)
    return AI