Tvtk segmentation example — mayavi 4.7.1 documentation

# Tvtk segmentation example

Using VTK to assemble a pipeline for segmenting MRI images. This example shows how to insert well-controled custom VTK filters in Mayavi.

This example downloads an MRI scan, turns it into a 3D numpy array, applies a segmentation procedure made of VTK filters to extract the gray-matter/white-matter boundary.

The segmentation algorithm used here is very naive and should, of course, not be used as an example of segmentation.

Python source code: `tvtk_segmentation.py`

    ### Download the data, if not already on disk ##################################
    import os
    if not os.path.exists('MRbrain.tar.gz'):
        # Download the data
        try:
            from urllib import urlopen
        except ImportError:
            from urllib.request import urlopen
        print("Downloading data, Please Wait (7.8MB)")
        opener = urlopen(
                    'http://graphics.stanford.edu/data/voldata/MRbrain.tar.gz')
        open('MRbrain.tar.gz', 'wb').write(opener.read())

    # Extract the data
    import tarfile
    tar_file = tarfile.open('MRbrain.tar.gz')
    try:
        os.mkdir('mri_data')
    except:
        pass
    tar_file.extractall('mri_data')
    tar_file.close()

    ### Read the data in a numpy 3D array ##########################################
    import numpy as np
    data = np.array([np.fromfile(os.path.join('mri_data', 'MRbrain.%i' % i),
                                            dtype='>u2') for i in range(1, 110)])
    data.shape = (109, 256, 256)
    data = data.T

    ################################################################################
    # Heuristic for finding the threshold for the brain

    # Exctract the percentile 20 and 80 (without using
    # scipy.stats.scoreatpercentile)
    sorted_data = np.sort(data.ravel())
    l = len(sorted_data)
    lower_thr = sorted_data[0.2*l]
    upper_thr = sorted_data[0.8*l]

    # The white matter boundary: find the densest part of the upper half
    # of histogram, and take a value 10% higher, to cut _in_ the white matter
    hist, bins = np.histogram(data[data > np.mean(data)], bins=50)
    brain_thr_idx = np.argmax(hist)
    brain_thr =  bins[brain_thr_idx + 4]

    del hist, bins, brain_thr_idx

    # Display the data #############################################################
    from mayavi import mlab
    from tvtk.api import tvtk

    fig = mlab.figure(bgcolor=(0, 0, 0), size=(400, 500))
    # to speed things up
    fig.scene.disable_render = True

    src = mlab.pipeline.scalar_field(data)
    # Our data is not equally spaced in all directions:
    src.spacing = [1, 1, 1.5]
    src.update_image_data = True

    #----------------------------------------------------------------------
    # Brain extraction pipeline

    # In the following, we create a Mayavi pipeline that strongly
    # relies on VTK filters. For this, we make heavy use of the
    # mlab.pipeline.user_defined function, to include VTK filters in
    # the Mayavi pipeline.

    # Apply image-based filters to clean up noise
    thresh_filter = tvtk.ImageThreshold()
    thresh_filter.threshold_between(lower_thr, upper_thr)
    thresh = mlab.pipeline.user_defined(src, filter=thresh_filter)

    median_filter = tvtk.ImageMedian3D()
    median_filter.set_kernel_size(3, 3, 3)
    median = mlab.pipeline.user_defined(thresh, filter=median_filter)

    diffuse_filter = tvtk.ImageAnisotropicDiffusion3D(
                                        diffusion_factor=1.0,
                                        diffusion_threshold=100.0,
                                        number_of_iterations=5, )

    diffuse = mlab.pipeline.user_defined(median, filter=diffuse_filter)

    # Extract brain surface
    contour = mlab.pipeline.contour(diffuse, )
    contour.filter.contours = [brain_thr, ]

    # Apply mesh filter to clean up the mesh (decimation and smoothing)
    dec = mlab.pipeline.decimate_pro(contour)
    dec.filter.feature_angle = 60.
    dec.filter.target_reduction = 0.7

    smooth_ = tvtk.SmoothPolyDataFilter(
                        number_of_iterations=10,
                        relaxation_factor=0.1,
                        feature_angle=60,
                        feature_edge_smoothing=False,
                        boundary_smoothing=False,
                        convergence=0.,
                    )
    smooth = mlab.pipeline.user_defined(dec, filter=smooth_)

    # Get the largest connected region
    connect_ = tvtk.PolyDataConnectivityFilter(extraction_mode=4)
    connect = mlab.pipeline.user_defined(smooth, filter=connect_)

    # Compute normals for shading the surface
    compute_normals = mlab.pipeline.poly_data_normals(connect)
    compute_normals.filter.feature_angle = 80

    surf = mlab.pipeline.surface(compute_normals,
                                            color=(0.9, 0.72, 0.62))

    #----------------------------------------------------------------------
    # Display a cut plane of the raw data
    ipw = mlab.pipeline.image_plane_widget(src, colormap='bone',
                    plane_orientation='z_axes',
                    slice_index=55)

    mlab.view(-165, 32, 350, [143, 133, 73])
    mlab.roll(180)

    fig.scene.disable_render = False

    #----------------------------------------------------------------------
    # To make the link between the Mayavi pipeline and the much more
    # complex VTK pipeline, we display both:
    mlab.show_pipeline(rich_view=False)
    from tvtk.pipeline.browser import PipelineBrowser
    browser = PipelineBrowser(fig.scene)
    browser.show()

    mlab.show()