In respect to CT, nuclear techniques are much more sensitive, but they yield less resolved images and lack of anatomic information. For this reason, the two modalities are often associated using a device which combines in a single system both a PET(SPECT) and a CT scanner. In (micro)-PET(SPECT)-CT images, images are acquired from both devices sequentially, in the same session, and combined into a single superimposed (co-registered) image. Thus, functional imaging obtained by PET(SPECT), which depicts the spatial distribution of metabolites or biochemical activity in the body, can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. Two- and three-dimensional image reconstruction may then be rendered.