We describe the evaluation of the registration of Positron Emission Tomography (PET) scans with X-ray Computed Tomography (CT) scans of the human brain. A CT scan and a PET scan of the same person were obtained with fiducial markers placed on the person's head. The CT scan and the PET scan were then registered, first by using the fiducial markers, and next by applying the registration method currently under question, completely ignoring fiducial markers. In both cases, the positions of fiducial markers in PET scan and the positions of corresponding fiducial markers in CT scan were compared. The results based on aligning only one patient scans are encouraging, and in the future we hope to obtain more PET and CT scan pairs to validate the registration method.