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3D-Medical-Imaging-Preprocessing-All-you-need

This Repo contains the Preprocessing Code for 3D Medical Imaging

From the last year of my undergrad studies I was very queries about Biomedical Imaging. But until the starting my master I don't have the chance to go deep into medical imaging. Like most people at the beginning, I also suffered and was a bit confused about a few things. In this notebook, I will try to easily explain/show commonly used Preprocessing in Medical Imaging especially with 3D Nifti.

In this tutorial we will be using Public Abdomen Dataset From: Multi-Atlas Labeling Beyond the Cranial Vault - Workshop and Challenge Link: https://www.synapse.org/#!Synapse:syn3193805/wiki/217789

Reference: https://github.com/DLTK/DLTK

In this Notebook we will cover

  1. Reading Nifti Data and ploting
  2. Different Intensity Normalization Approaches
  3. Resampling 3D CT data
  4. Cropping and Padding CT data
  5. Histogram equalization
  6. Maximum Intensity Projection (MIP)

if You want know about MRI Histogram Matching, Histogram Equalization and Registration, You could have a look to my repo

To Learn about Segmentation

Libraries need

* SimpleITK
* numpy
* scipy
* skimage
* cv2

Reading Nifti Data and ploting

ct_path='D:/Science/Github/3D-Medical-Imaging-Preprocessing-All-you-need/Data/img0001.nii.gz'
ct_label_path='D:/Science/Github/3D-Medical-Imaging-Preprocessing-All-you-need/Data/label0001.nii.gz'

# CT
img_sitk  = sitk.ReadImage(ct_path, sitk.sitkFloat32) # Reading CT
image     = sitk.GetArrayFromImage(img_sitk) #Converting sitk_metadata to image Array
# Mask
mask_sitk = sitk.ReadImage(ct_label_path,sitk.sitkInt32) # Reading CT
mask      = sitk.GetArrayFromImage(mask_sitk)#Converting sitk_metadata to image Array

ct_mask

Intensity Normalization

def normalise(image):
    # normalise and clip images -1000 to 800
    np_img = image
    np_img = np.clip(np_img, -1000., 800.).astype(np.float32)
    return np_img


def whitening(image):
    """Whitening. Normalises image to zero mean and unit variance."""

    image = image.astype(np.float32)

    mean = np.mean(image)
    std = np.std(image)

    if std > 0:
        ret = (image - mean) / std
    else:
        ret = image * 0.
    return ret


def normalise_zero_one(image):
    """Image normalisation. Normalises image to fit [0, 1] range."""

    image = image.astype(np.float32)

    minimum = np.min(image)
    maximum = np.max(image)

    if maximum > minimum:
        ret = (image - minimum) / (maximum - minimum)
    else:
        ret = image * 0.
    return ret


def normalise_one_one(image):
    """Image normalisation. Normalises image to fit [-1, 1] range."""

    ret = normalise_zero_one(image)
    ret *= 2.
    ret -= 1.
    return ret

Normalization

Resampling

def resample_img(itk_image, out_spacing=[2.0, 2.0, 2.0], is_label=False):
    # resample images to 2mm spacing with simple itk

    original_spacing = itk_image.GetSpacing()
    original_size = itk_image.GetSize()

    out_size = [
        int(np.round(original_size[0] * (original_spacing[0] / out_spacing[0]))),
        int(np.round(original_size[1] * (original_spacing[1] / out_spacing[1]))),
        int(np.round(original_size[2] * (original_spacing[2] / out_spacing[2])))]

    resample = sitk.ResampleImageFilter()
    resample.SetOutputSpacing(out_spacing)
    resample.SetSize(out_size)
    resample.SetOutputDirection(itk_image.GetDirection())
    resample.SetOutputOrigin(itk_image.GetOrigin())
    resample.SetTransform(sitk.Transform())
    resample.SetDefaultPixelValue(itk_image.GetPixelIDValue())

    if is_label:
        resample.SetInterpolator(sitk.sitkNearestNeighbor)
    else:
        resample.SetInterpolator(sitk.sitkBSpline)

    return resample.Execute(itk_image)

Resampling

Crop or Padding

def resize_image_with_crop_or_pad(image, img_size=(64, 64, 64), **kwargs):
    """Image resizing. Resizes image by cropping or padding dimension
     to fit specified size.
    Args:
        image (np.ndarray): image to be resized
        img_size (list or tuple): new image size
        kwargs (): additional arguments to be passed to np.pad
    Returns:
        np.ndarray: resized image
    """

    assert isinstance(image, (np.ndarray, np.generic))
    assert (image.ndim - 1 == len(img_size) or image.ndim == len(img_size)), \
        'Example size doesnt fit image size'

    # Get the image dimensionality
    rank = len(img_size)

    # Create placeholders for the new shape
    from_indices = [[0, image.shape[dim]] for dim in range(rank)]
    to_padding = [[0, 0] for dim in range(rank)]

    slicer = [slice(None)] * rank

    # For each dimensions find whether it is supposed to be cropped or padded
    for i in range(rank):
        if image.shape[i] < img_size[i]:
            to_padding[i][0] = (img_size[i] - image.shape[i]) // 2
            to_padding[i][1] = img_size[i] - image.shape[i] - to_padding[i][0]
        else:
            from_indices[i][0] = int(np.floor((image.shape[i] - img_size[i]) / 2.))
            from_indices[i][1] = from_indices[i][0] + img_size[i]

        # Create slicer object to crop or leave each dimension
        slicer[i] = slice(from_indices[i][0], from_indices[i][1])

    # Pad the cropped image to extend the missing dimension
    return np.pad(image[slicer], to_padding, **kwargs)

Cropandpad