# -*- coding: utf-8 -*-
##########################################################################
# pySAP - Copyright (C) CEA, 2017 - 2018
# Distributed under the terms of the CeCILL-B license, as published by
# the CEA-CNRS-INRIA. Refer to the LICENSE file or to
# http://www.cecill.info/licences/Licence_CeCILL-B_V1-en.html
# for details.
##########################################################################
"""Single channel reconstruction."""
from ..operators import GradAnalysis, GradSynthesis, WaveletN
from .base import ReconstructorBase
from ..operators.fourier.utils import check_if_fourier_op_uses_sense
[docs]class SingleChannelReconstructor(ReconstructorBase):
"""Single channel MR image Reconstruction.
Notes
-----
For the Analysis case, finds the solution for x of:
..math:: (1/2) * sum(||F x - y||^2_2, 1) + mu * H (W x)
For the Synthesis case, finds the solution of:
..math:: (1/2) * sum(||F Wt alpha - y||^2_2, 1) + mu * H (alpha)
with ..math:: alpha = W x and x = Wt alpha
Parameters
----------
fourier_op: Instance of OperatorBase.
Defines the fourier operator F in the above equation.
linear_op: OperatorBase, default None
Defines the linear sparsifying operator denoted :math:`W` in the equation above.
This must operate on x and have 2 functions, op(x) and adj_op(coeff)
which implements the operator and adjoint operator. For wavelets, this
can be object of class WaveletN or WaveletUD2 from `mri.operators.linear`
If None, sym8 wavelet with nb_scale=3 is chosen.
regularizer_op: operator, (optional default None)
Defines the regularization operator for the regularization function denoted :math:`H` in the equation above.
If None, the regularization chosen is Identity and the optimization
turns to gradient descent.
gradient_formulation: str between 'analysis' or 'synthesis',
default 'synthesis'
defines the formulation of the image model which defines the gradient.
verbose: int, optional default 0
Verbosity levels
1 => Print basic debug information
5 => Print all initialization information
20 => Calculate cost at the end of each iteration.
30 => Print the debug information of operators if defined by class
NOTE - High verbosity (>20) levels are computationally intensive.
**kwargs : Extra keyword arguments
for gradient initialization:
Please refer to mri.operators.gradient.base for information
regularizer_op: operator, (optional default None)
Defines the regularization operator for the regularization
function H. If None, the regularization chosen is Identity and
the optimization turns to gradient descent.
See Also
--------
ReconstructorBase : parent class
"""
def __init__(self, fourier_op, linear_op=None,
gradient_formulation="synthesis", verbose=0, **kwargs):
# Ensure that we are not in multichannel config
if linear_op is None:
# TODO change nb_scales to max_nb_scale - 1
linear_op = WaveletN(
wavelet_name="sym8",
dim=len(fourier_op.shape),
nb_scale=3,
verbose=bool(verbose >= 30),
)
if fourier_op.n_coils != 1 and not check_if_fourier_op_uses_sense(fourier_op) or linear_op.n_coils != 1:
raise ValueError("The value of n_coils cannot be greater than 1 "
"for single channel reconstruction")
if gradient_formulation == 'analysis':
grad_class = GradAnalysis
elif gradient_formulation == 'synthesis':
grad_class = GradSynthesis
super().__init__(
fourier_op=fourier_op,
linear_op=linear_op,
gradient_formulation=gradient_formulation,
grad_class=grad_class,
verbose=verbose,
**kwargs,
)
