X-Ray, CT, Ultrasound and Magnetic Resonance (MR) produce "anatomical images" while PET produces "functional images". Anatomical images are vital for a wide range of conditions, however, changes in Metabolism and blood flow often precede and may overshadow important changes in the anatomical appearance of a tissue or organ. Only PET allows for the measurement of function and metabolism in normal and diseased tissue.

... from other Nuclear Medicine Imaging Procedures such as SPECT

PET has much better resolution. Unlike single photon emitters, the unique decay mode of the PET Radionuclide allows for coincidence detection.