Clinical Radiopharmacy
Other type of generators:
1. - 68Ge/68Ga where the "mother" decays with a half-life of 280 days into 68Ga.
The latter decays with a period of 68 minutes, into 68Zn and emission of
positrons. The system has EDTA 0,005 M solution as eluant and alumina as
inert carrier. Currently
68Ga labeling dotatate is used for detecting neuroendocrine tumors with a
PET-CT camera.
2. - 82Sr/82Rb where the "mother" decays with a half-life of 25.5 days to 82Rb
and it decays with a half life period of 6.3 hours and also 1.27 min into 82Kr.
The system has as eluant 0.9% NaCl solution while the inert support is tin
oxide.
3. - 188W/188Re where the "mother" decays with a decay period of 69 days to
188Re that in turn decays with a half period of 16.9 hours into 188Os. The
system has as eluant 0.9% NaCl solution while the inert support is alumina.
This radionuclide is eluted as sodium perrhenate (188Re) with low concentration
of activity, however the system has an anion cation exchange column thus
obtaining solutions of high specific activity.
Note following practical tips regarding generators: 1) Expensive device, except
if the number of exams done daily is high enough. 2) Use fresh eluate to get rid
of 99Tc, which may affect image quality and labeling of molecules such as EC or
ECD. 3) Carry out elutions at least 3-4 h apart each other to get a good yield
of 99mTc. 4) Keep the generator to use for the second week.
A
radiopharmaceutical or radiotracer consists of two components:
• A radionuclide that determines the physical properties and
• A drug, which determines the biological behavior of the radiopharmaceutical or
radiotracer.
The nuclides or elements are atoms that have a defined number of protons and
neutrons in the nucleus. Radionuclides are those unstable nuclides that decay
spontaneously to a more stable atom.
The drug is the chemical fraction of
organic or inorganic part of the radiopharmaceutical or radiotracer and
determines its biodistribution, ie the transporter of the radionuclide to the
site of interest within the body. The drug is chosen, according to the following
characteristics:
1. Its location in the body and participation in physiological processes.
2. Excretion pathways. Once its task within the body is over the
radiopharmaceutical or radiotracer should be eliminated. This determines the
biological half-life of the radiomolecule.
3. The possibility of being branded without altering the biological properties
of the molecule. When working with radionuclides of short half-life, the
radiochemical synthesis must be rapid and easily reproducible.
4. It should not be toxic at the concentration used.
Radiopharmaceutical or Radiotracer purity.
It is determined through different characteristics:
1. Radionuclidic, given by the radionuclide, defined as the fraction of activity
of the radioisotope of interest in the total radioactivity.
2. Chemical purity which assesses the degree of purity of the chemical structure
in which is included the radionuclide, and can be of organic or inorganic
nature.
3. Radiochemical purity is the fraction of the total radioactivity found in the
desired chemical form.
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