The invention relates generally to biopsy needle guidance which employs an x-ray/gamma image spatial co-registration methodology. A gamma camera is configured to mount on a biopsy needle gun platform to obtain a gamma image. More particular, the spatially co-registered x-ray and physiological images may be employed for needle guidance during biopsy. Moreover, functional images may be obtained from a gamma camera at various angles relative to a target site. Further, the invention also generally relates to a breast lesion localization method using opposed gamma camera images or dual opposed images. This dual head methodology may be used to compare the lesion signal in two opposed detector images and to calculate the Z coordinate (distance from one or both of the detectors) of the lesion.