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This method is widely used to produce certain short-lived radioisotopes in a hospital or clinic. It involves obtaining a relatively long-lived radioisotope which decays into the short-lived isotope of interest.
A good example is 99mTc which as we have noted before is the most widely used radioisotope in nuclear medicine today. This isotope has a half-life of six hours which is rather short if we wish to have it delivered directly from a nuclear facility. Instead the nuclear facility supplies the isotope 99Mo which decays into 99mTc with a half life of about 2.75 days. The 99Mo is called the parent isotope and 99mTc is called the daughter isotope.
So the nuclear facility produces the parent isotope which decays relatively slowly into the daughter isotope and the daughter is separated chemically from the parent at the hospital/clinic. The chemical separation device is called, in this example, a 99mTc Generator:
It consists of a ceramic column with 99Mo adsorbed onto its top surface. A solution called an eluent is passed through the column, reacts chemically with any 99mTc and emerges in a chemical form which is suitable for combining with a pharmaceutical to produce a radiopharmaceutical. The arrangement shown in the figure above is called a Positive Pressure system where the eluent is forced through the ceramic column by a pressure, slightly above atmospheric pressure, in the eluent vial.
The ceramic column and collection vials need to be surrounded by lead shielding for radiation protection purposes. In addition all components are produced and need to be maintained in a sterile condition since the collected solution will be administered to patients.
Finally an Isotope Calibrator is needed when a 99mTc Generator is used to determine the radioactivity for preparation of patient doses and to check whether any 99Mo is present in the collected solution.
A number of photographs taken in nuclear medicine hot labs are shown below:
| File:TcGens.jpg Five 99m-Tc generators. |
Pb shielding surrounding the laminar flow cabinet, where radiopharmaceuticals are prepared.
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Another view of the Pb shielding surrounding a laminar flow cabinet.
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