This example shows how to use nilearn.regions.RegionExtractor to extract spatially constrained brain regions from whole brain maps decomposed using dictionary learning and use them to build a functional connectome.
This example can also be inspired to apply the same steps to even regions extraction using ICA maps. In that case, idea would be to replace dictionary learning to canonical ICA decomposition using nilearn.decomposition.CanICA
Please see the related documentation of nilearn.regions.RegionExtractor for more details.
Fetching ADHD resting state functional datasets by loading from datasets utilities
from nilearn import datasets adhd_dataset = datasets.fetch_adhd(n_subjects=20) func_filenames = adhd_dataset.func confounds = adhd_dataset.confounds
Extracting resting-state networks with DictionaryLearning
# Import dictionary learning algorithm from decomposition module and call the # object and fit the model to the functional datasets from nilearn.decomposition import DictLearning # Initialize DictLearning object dict_learn = DictLearning(n_components=5, smoothing_fwhm=6., memory="nilearn_cache", memory_level=2, random_state=0) # Fit to the data dict_learn.fit(func_filenames) # Resting state networks/maps components_img = dict_learn.masker_.inverse_transform(dict_learn.components_) # Visualization of resting state networks # Show networks using plotting utilities from nilearn import plotting plotting.plot_prob_atlas(components_img, view_type='filled_contours', title='Dictionary Learning maps')
Extracting regions from networks
# Import Region Extractor algorithm from regions module # threshold=0.5 indicates that we keep nominal of amount nonzero voxels across all # maps, less the threshold means that more intense non-voxels will be survived. from nilearn.regions import RegionExtractor extractor = RegionExtractor(components_img, threshold=0.5, thresholding_strategy='ratio_n_voxels', extractor='local_regions', standardize=True, min_region_size=1350) # Just call fit() to process for regions extraction extractor.fit() # Extracted regions are stored in regions_img_ regions_extracted_img = extractor.regions_img_ # Each region index is stored in index_ regions_index = extractor.index_ # Total number of regions extracted n_regions_extracted = regions_extracted_img.shape[-1] # Visualization of region extraction results title = ('%d regions are extracted from %d components.' '\nEach separate color of region indicates extracted region' % (n_regions_extracted, 5)) plotting.plot_prob_atlas(regions_extracted_img, view_type='filled_contours', title=title)
Computing correlation coefficients and plotting a connectome
# First we need to do subjects timeseries signals extraction and then estimating # correlation matrices on those signals. # To extract timeseries signals, we call transform() from RegionExtractor object # onto each subject functional data stored in func_filenames. # To estimate correlation matrices we import connectome utilities from nilearn from nilearn.connectome import ConnectivityMeasure correlations =  # Initializing ConnectivityMeasure object with kind='correlation' connectome_measure = ConnectivityMeasure(kind='correlation') for filename, confound in zip(func_filenames, confounds): # call transform from RegionExtractor object to extract timeseries signals timeseries_each_subject = extractor.transform(filename, confounds=confound) # call fit_transform from ConnectivityMeasure object correlation = connectome_measure.fit_transform([timeseries_each_subject]) # saving each subject correlation to correlations correlations.append(correlation) # Mean of all correlations import numpy as np mean_correlations = np.mean(correlations, axis=0).reshape(n_regions_extracted, n_regions_extracted) # Visualization # Plotting connectome results import matplotlib.pyplot as plt from nilearn import image regions_imgs = image.iter_img(regions_extracted_img) coords_connectome = [plotting.find_xyz_cut_coords(img) for img in regions_imgs] title = 'Correlation interactions between %d regions' % n_regions_extracted plt.figure() plt.imshow(mean_correlations, interpolation="nearest", vmax=1, vmin=-1, cmap=plt.cm.bwr) plt.colorbar() plt.title(title) plotting.plot_connectome(mean_correlations, coords_connectome, edge_threshold='90%', title=title)
Plotting regions extracted for only one specific network
# First, we plot a network of index=4 without region extraction (left plot) img = image.index_img(components_img, 4) coords = plotting.find_xyz_cut_coords(img) display = plotting.plot_stat_map(img, cut_coords=coords, colorbar=False, title='Showing one specific network') # Now, we plot (right side) same network after region extraction to show that # connected regions are nicely seperated. # Each brain extracted region is identified as separate color. # For this, we take the indices of the all regions extracted related to original # network given as 4. regions_indices_of_map3 = np.where(np.array(regions_index) == 4) display = plotting.plot_anat(cut_coords=coords, title='Extracted regions in one specific network') # Now add as an overlay by looping over all the regions of index 4 # color list is random (you can choose your own color) color_list = [[0., 1., 0.29, 1.], [0., 1., 0.54, 1.], [0., 1., 0.78, 1.], [0., 0.96, 1., 1.], [0., 0.73, 1., 1.], [0., 0.47, 1., 1.], [0., 0.22, 1., 1.], [0.01, 0., 1., 1.], [0.26, 0., 1., 1.]] for each_index_of_map3, color in zip(regions_indices_of_map3, color_list): display.add_overlay(image.index_img(regions_extracted_img, each_index_of_map3), cmap=plotting.cm.alpha_cmap(color)) plotting.show()
Total running time of the script: ( 5 minutes 7.498 seconds)