To distinguish from the medical imaging modalities that measure the attenuation of radiation originating from an external source, called transmission imaging (e. g., con­ventional X-ray radiography and CT), the imaging of radiation emitted by radio­pharmaceuticals inside a patient’s body is generally referred to as emission imaging.

• Static scintigraphy: images from one or several views are acquired after the distribution of the radiopharmaceutical reaches equilibrium.

Static imaging was possible even before the gamma camera was invented, using a radiation detector that scanned the target organ, having a print head yoked to it.

• For dynamic imaging, a series of images from the same view is taken, following the pro­cess of accumulation, secretion, or excretion of the radiopharmaceutical. Besides obtain­ing the distribution at different points in time, we can investigate how the radioactivity concentration of any region changes with time.

• Whole-body imaging means linking several static images by the computer to show an area bigger than the field of view. A large-field-of-view gamma camera generally covers the width of a patient’s body, and we need three to five steps to scan its length. See details of this process later in this chapter.

• The last and most powerful way of imaging is tomography, when the distribution of the radiopharmaceutical in various sections of the body is calculated from measurements of many projections. Consecutive slices together represent a three-dimensional distribution:

• SPECT (single photon emission computed tomography) applies gamma emitters, while

• PET utilizes positron emitters (see Section 12.6).