Positron emission tomography (PET) is a method by which the in vivo distribution of a radiopharmaceutical can be measured with high resolution and sensitivity. Conventional nuclear medicine imaging with a γ camera requires the use of an absorptive collimator that limits the percentage of internally emitted photons that are detected with the γ camera to about 0.01%. PET, on the other hand, uses annihilation coincidence detection rather than absorptive collimation to localize the event leading to an increase in sensitivity of several orders of magnitude for the same spatial resolution. This improved sensitivity is typically manifest as either an enhancement in image quality or an improvement in quantitative accuracy.

The radioactive nuclides that are associated with the elements that are considered biologically interesting, such as carbon, nitrogen, and oxygen, tend to be positron emitters (e.g., ¹¹C, ¹³N, and ¹⁵O). In addition, an ¹⁸F atom can often be used to substitute for an H or an OH. In this manner, positron-emitting radiopharmaceuticals can be developed from naturally occurring materials (e.g., ¹⁵O water, ¹¹C carbon monoxide, or ¹³N ammonia). Also, radioactive analogues of other biologic substances can be developed, such as ¹⁸F fluoro-2-deoxy-2-glucose (FDG) or ¹⁸F labeled fluorodopa.<sup>7 Phelps M.E., Huang S.C., Hoffman E.J. , e al. Tomographic measurement of local cerebral glucose metabolic rate in humans with18F 2-fluoro-2-deoxy-D-glucose: Validation of method Ann Neurol 1979 ;  6 : 371-388  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> A variety of other positron-emitting agents have also been developed that, for example, can image the neuroreceptor system<sup>9 Wagner H.N., Burns D.H., Dannals R.F. , e al. Assessment of dopamine receptor densities in the human brain with carbon-11-labelled-N-methylspierone Ann Neurol 1984 ;  15 : s79-s84  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> or the proliferation rate of tumor cells. The improved physical capacity of PET scanning and the development of exciting positron-based radiopharmaceuticals has led to the development of PET instrumentation over the past 40 years.<sup>1 Brownell G.L., Sweet W.H. Localization of brain tumors with positron emitters Nucleonics 1953 ;  11 : 40-45

Cliccare qui per andare alla sezione Riferimenti, 2 Burnham C.A., Brownell G.L. A multi-crystal positron camera IEEE Trans Nucl Sci 1972 ;  19 : 201-205  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 8 Ter-Pogossian M.M., Phelps M.E., Hoffman E.J. , e al. A positron emission transaxial tomograph for nuclear medicine imaging (PETT) Radiology 1975 ;  114 : 89-98

Cliccare qui per andare alla sezione Riferimenti, 10 Wrenn F.R., Good M.L., Handler P. The use of positron emitting radioisotopes for localization of brain tumors Science 1951 ;  113 : 525-527

Cliccare qui per andare alla sezione Riferimenti</sup>