The Fourth Edition includes new or expanded sections and information for: * PET/MR, including the attenuation correction method and its quality control tests; * accreditation of nuclear medicine and PET facilities; * solid state digital cameras; * time of flight and scatter correction techniques; * CT scanners and attenuation correction in SPECT/CT; * partial volume effects; * quality control of CT scanners; * ion chamber survey meters, proportional counters, and G-M counters.