ITK Elastix deformation field Issue

Hello,

I am trying to use itk elastix to estimate the deformation happened between two images (Suppose to be ultrasound images, but I am using some known deformation data to verify the results first). I am obtaining the deformation field by using:

deformation_field = itk.transformix_deformation_field(moving_image, result_transform_parameters)

Then I store the data to csv files using:

def_array_x = np.array(deformation_field[:,:,1])
def_array_x = pd.DataFrame(def_array_x)
def_array_x.to_csv("x_deformation_field.csv")
def_array_y = np.array(deformation_field[:,:,0])
def_array_y = pd.DataFrame(def_array_y)
def_array_y.to_csv("y_deformation_field.csv")

After that, I compute the pixel size in x and y direction of the input images and convert the pixel deformation field to actual displacement. However, my result does not come close to the actual at all, but I have no idea what I have done wrong, or I am not supposed to use the deformation_field that way.

Please help me with this issue and if needed, I can upload the code I have, right now, the deformation field code is in python, but the converting to displacement code is in MATLAB.