ABSTRACT

Nuclear imaging portrays distribution of radionuclides inside the patient’s body by external measurement of

g

-rays emanating from the body; this gave the modality its alternative generic name of

g

-imaging

or

gammagraphy

(the latter is usually used only for planar imaging). Radioactive substances of short half-lives in the range of minutes to weeks are administered to patients intravenously, orally, or inhaled. The radiopharmaceuticals then circulate in the organism and concentrate gradually in diagnosed regions, from where they are consequently excreted depending on the activities of the observed regions. The information to be obtained by an external measurement consists of generally time-dependent spatial distribution of the radioactive substance. This way, not only the shape of organs or lesions can be estimated, but also the local activity-dependent time-course of radioactivity density.