Simple example of NiftiMasker use#

Here is a simple example of automatic mask computation using the nifti masker. The mask is computed and visualized.

Note

If you are using Nilearn with a version older than 0.9.0, then you should either upgrade your version or import maskers from the input_data module instead of the maskers module.

That is, you should manually replace in the following example all occurrences of:

from nilearn.maskers import NiftiMasker

with:

from nilearn.input_data import NiftiMasker

Retrieve the brain development functional dataset

from nilearn import datasets
dataset = datasets.fetch_development_fmri(n_subjects=1)
func_filename = dataset.func[0]

# print basic information on the dataset
print('First functional nifti image (4D) is at: %s' % func_filename)
First functional nifti image (4D) is at: /home/runner/work/nilearn/nilearn/nilearn_data/development_fmri/development_fmri/sub-pixar123_task-pixar_space-MNI152NLin2009cAsym_desc-preproc_bold.nii.gz

Compute the mask

from nilearn.maskers import NiftiMasker

# As this is raw movie watching based EPI, the background is noisy and we
# cannot rely on the 'background' masking strategy. We need to use the 'epi'
# one
nifti_masker = NiftiMasker(standardize=True, mask_strategy='epi',
                           memory="nilearn_cache", memory_level=2,
                           smoothing_fwhm=8)
nifti_masker.fit(func_filename)
mask_img = nifti_masker.mask_img_

Visualize the mask using the plot_roi method

from nilearn.plotting import plot_roi
from nilearn.image.image import mean_img

# calculate mean image for the background
mean_func_img = mean_img(func_filename)

plot_roi(mask_img, mean_func_img, display_mode='y', cut_coords=4, title="Mask")
plot nifti simple
<nilearn.plotting.displays._slicers.YSlicer object at 0x7f6a567f04f0>

Visualize the mask using the ‘generate_report’ method This report can be displayed in a Jupyter Notebook, opened in-browser using the .open_in_browser() method, or saved to a file using the .save_as_html(output_filepath) method.

NiftiMasker Applying a mask to extract time-series from Niimg-like objects. NiftiMasker is useful when preprocessing (detrending, standardization, resampling, etc.) of in-mask :term:`voxels<voxel>` is necessary. Use case: working with time series of resting-state or task maps.

image

This report shows the input Nifti image overlaid with the outlines of the mask (in green). We recommend to inspect the report for the overlap between the mask and its input image.

Parameters
Parameter Value
detrend False
dtype None
high_pass None
high_variance_confounds False
low_pass None
mask_args None
mask_img None
mask_strategy epi
memory Memory(location=nilearn_cache/joblib)
memory_level 2
reports True
runs None
smoothing_fwhm 8
standardize True
standardize_confounds True
t_r None
target_affine None
target_shape None
verbose 0


Preprocess data with the NiftiMasker

nifti_masker.fit(func_filename)
fmri_masked = nifti_masker.transform(func_filename)
# fmri_masked is now a 2D matrix, (n_voxels x n_time_points)
/usr/share/miniconda3/envs/testenv/lib/python3.8/site-packages/nilearn/maskers/base_masker.py:112: UserWarning:

Persisting input arguments took 0.81s to run.
If this happens often in your code, it can cause performance problems
(results will be correct in all cases).
The reason for this is probably some large input arguments for a wrapped
 function (e.g. large strings).
THIS IS A JOBLIB ISSUE. If you can, kindly provide the joblib's team with an
 example so that they can fix the problem.

Run an algorithm

from sklearn.decomposition import FastICA
n_components = 10
ica = FastICA(n_components=n_components, random_state=42)
components_masked = ica.fit_transform(fmri_masked.T).T
/usr/share/miniconda3/envs/testenv/lib/python3.8/site-packages/sklearn/decomposition/_fastica.py:494: FutureWarning:

Starting in v1.3, whiten='unit-variance' will be used by default.

/usr/share/miniconda3/envs/testenv/lib/python3.8/site-packages/sklearn/decomposition/_fastica.py:120: ConvergenceWarning:

FastICA did not converge. Consider increasing tolerance or the maximum number of iterations.

Reverse masking, and display the corresponding map

components = nifti_masker.inverse_transform(components_masked)

# Visualize results
from nilearn.plotting import plot_stat_map, show
from nilearn.image import index_img
from nilearn.image.image import mean_img

# calculate mean image for the background
mean_func_img = mean_img(func_filename)

plot_stat_map(index_img(components, 0), mean_func_img,
              display_mode='y', cut_coords=4, title="Component 0")

show()
plot nifti simple

Total running time of the script: ( 0 minutes 17.768 seconds)

Estimated memory usage: 777 MB

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