Compact cyclotrons for the production of tracers and radiopharmaceuticals

The idea of in vivo measurement of biological and/or biochemical processes was already envisaged in the 1930’s when the first artificially produced radionuclides of the biologically important elements carbon, nitrogen and oxygen were discovered with help of the then recently developed cyclotron. These radionuclides decay by pure positron emission and the annihilation of positron and electron results in two 511 keV γ-quanta under a relative angle of about 180, which are measured in coincidence. This idea of PET could only be realized when the inorganic scintillation detectors for the detection of γ-radiation, electronics for the coincidence measurements and the computer capacity for data acquisition and image reconstruction became available. For this reason the technical development of Positron Emission Tomography [6] as a functional in vivo imaging discipline began just over 30 years ago. PET employs mainly short-lived positron emitting radiopharmaceuticals. The most widely used radionuclides are: C (t1/2 = 20.38 min), N (t1/2 = 9.96 min), O (t1/2 = 2.03 min) and F (t1/2 = 109.7 min). Carbon, oxygen, nitrogen and hydrogen are the elements of life and the building blocks of nearly every molecule of biological importance. However, hydrogen has no radioactive isotope decaying with the emission of radiation which can be detected outside the human body. For this reason, the Compact cyclotrons for the production of tracers and radiopharmaceuticals Anne M. J. Paans