imageCT Reconstruction

Hi,
I’m a PFD student who is doing an assignment of CT simulation with Gate. I’ve done every step introduced in the Gate users’ guide except the final step of data processing because I have got some problems on it. My goal of processing data is to obtain an image of the cross section of the phantom. I have tried 3 types of output: ASCII, ROOT and ImageCT .

I need some help on output types.