Positron emission tomography (PET) is one of the most powerful non-invasive diagnostic tools for tracing organ functioning.
Quality control of the short-lived radiopharmaceuticals is challenging, not least because of the tough time limits, the radiation
issue and the near nanomole radiotracer quantities.
This article presents a likewise rugged and versatile multichannel radio IC system that controls the production of the radionuclide
F]fluoride (precursor) and the two radiotracers synthesized from it, [
F]fluorodeoxyglucose and [
F]fluorocholine, in accordance with pharmacopoeial regulations.
Principles of Positron Emission Tomography (PET)
Radiopharmaceuticals are radioactive substances used in nuclear medicine to diagnose, treat or prevent disease. They contain
a radioactive isotope, a so-called radionuclide, attached to a biologically inert or active molecule.
Radionuclides are unstable isotopes that have an excess of either neutrons or protons and, therefore, radioactively decay,
resulting in the emission of gamma rays or subatomic particles. In proton-rich nuclides, a proton changes to a neutron, whereby
a positron (antiparticle of the electron or an electron with a positive charge, also called B+ particle) is emitted together with a neutrino (ν) according to proton (p) → neutron (n) + positron (B+) + neutrino (ν).
While travelling in the surrounding media, the released positron loses its kinetic energy and then combines with an electron.
The encounter annihilates both positron and electron and results in two photons (gamma rays) each with an energy of 0.511
MeV that are emitted in opposite directions (Figure 1).
Figure 1: Principle of positron emission tomography.
+ + me
– → 2γ
Sophisticated scanners (detector) can detect such pairs of photons by coincidence detection. From the data collected, three-dimensional
images of tissue structures are then calculated. The most commonly used short-lived, cyclotron-produced radionuclides in radiopharmacy
are 11C, 13N, 15O and 18F. Their respective half-lives are 20.38, 9.96, 2.03 and 109.7 min.