text: #%% Demo 4: Simple Image reconstruction
  #
  #
  # This demo will show how a simple image reconstruction can be performed,
  # by using OS-SART and FDK
  #
  # --------------------------------------------------------------------------
  # --------------------------------------------------------------------------
  # This file is part of the TIGRE Toolbox
  #
  # Copyright (c) 2015, University of Bath and
  #                     CERN-European Organization for Nuclear Research
  #                     All rights reserved.
  #
  # License:            Open Source under BSD.
  #                     See the full license at
  #                     https://github.com/CERN/TIGRE/blob/master/LICENSE
  #
  # Contact:            tigre.toolbox@gmail.com
  # Codes:              https://github.com/CERN/TIGRE/
  # Coded by:           Ander Biguri
  # --------------------------------------------------------------------------
  #%%Initialize
  import tigre
  import numpy as np
  from tigre.utilities import sample_loader
  from tigre.utilities import CTnoise
  import tigre.algorithms as algs
  
  #%% Geometry
  geo = tigre.geometry_default(high_resolution=False)
  
  #%% Load data and generate projections
  # define angles
  angles = np.linspace(0, 2 * np.pi, 100)
  # Load thorax phatom data
  head = sample_loader.load_head_phantom(geo.nVoxel)
  # generate projections
  projections = tigre.Ax(head, geo, angles)
  # add noise
  noise_projections = CTnoise.add(projections, Poisson=1e5, Gaussian=np.array([0, 10]))
  
  #%% Reconstruct image using OS-SART and FDK
  
  # FDK
  imgFDK = algs.fdk(noise_projections, geo, angles)
  # OS-SART
  
  niter = 50
  imgOSSART = algs.ossart(noise_projections, geo, angles, niter)
  
  #%% Show the results
  tigre.plotimg(np.concatenate([imgFDK, imgOSSART], axis=1), dim="z")
  