Attenuation correction

Dear CASToR users

I reconstructed a GATE simulated phantom with PET and used the Mu Map actor to create Mu Map for attenuation correction. But my image was not corrected as well especially the center of the image. What is the reason for this issue? The voxel size of the Mu Map actor was similar to the image reconstruction command and the matrix size of the Mu Map was smaller than it. My reconstructed image is attached.
Thank you.