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+%------------------------------------------------------------------------
+% This file is part of the
+% All Scale Tomographic Reconstruction Antwerp Toolbox ("ASTRA-Toolbox")
+%
+% Copyright: iMinds-Vision Lab, University of Antwerp
+% License: Open Source under GPLv3
+% Contact: mailto:astra@ua.ac.be
+% Website: http://astra.ua.ac.be
+%------------------------------------------------------------------------
+
+
+% In this example we will create a reconstruction in a circular region,
+% instead of the usual rectangle.
+
+% This is done by placing a circular mask on the square reconstruction volume:
+
+c = -127.5:127.5;
+[x y] = meshgrid(-127.5:127.5,-127.5:127.5);
+mask = (x.^2 + y.^2 < 127.5^2);
+
+figure(1); imshow(mask, []);
+
+
+vol_geom = astra_create_vol_geom(256, 256);
+proj_geom = astra_create_proj_geom('parallel', 1.0, 384, linspace2(0,pi,50));
+
+% As before, create a sinogram from a phantom
+P = phantom(256);
+[sinogram_id, sinogram] = astra_create_sino_gpu(P, proj_geom, vol_geom);
+figure(2); imshow(P, []);
+figure(3); imshow(sinogram, []);
+
+% Create a data object for the reconstruction
+rec_id = astra_mex_data2d('create', '-vol', vol_geom);
+
+% Create a data object for the mask
+mask_id = astra_mex_data2d('create', '-vol', vol_geom, mask);
+
+% Set up the parameters for a reconstruction algorithm using the GPU
+cfg = astra_struct('SIRT_CUDA');
+cfg.ReconstructionDataId = rec_id;
+cfg.ProjectionDataId = sinogram_id;
+cfg.option.ReconstructionMaskId = mask_id;
+
+% Create the algorithm object from the configuration structure
+alg_id = astra_mex_algorithm('create', cfg);
+
+% Run 150 iterations of the algorithm
+astra_mex_algorithm('iterate', alg_id, 150);
+
+% Get the result
+rec = astra_mex_data2d('get', rec_id);
+figure(4); imshow(rec, []);
+
+% Clean up. Note that GPU memory is tied up in the algorithm object,
+% and main RAM in the data objects.
+astra_mex_algorithm('delete', alg_id);
+astra_mex_data2d('delete', mask_id);
+astra_mex_data2d('delete', rec_id);
+astra_mex_data2d('delete', sinogram_id);