Finding the anterior comissure to set origin in a SPECT image using SPM/ISAS
You can use the Whole Brain Atlas by Harvard to look at the normal brain anatomy in 3-D with MRI/PET.

Check the Anterior Commissure (AC) on the MRI and sync it with the PET or SPECT. It helps.

More specifically, select "Anterior Commissure" and T1/FDG and click sync to show all the orientations in the same modalities and anatomical structure. It helps to find the anterior commissure in a normal brain using nuclear medicine image.