Clinical Radiopharmacy

        Within the human body it is of great interest to monitor  function, metabolism and blood flow  by injecting a suitable compound.  This agent that can be followed up in a given system is  called a tracer. If it is used for diagnosis and tagged with a radionuclide, we will call it a radiotracer . If employed for therapy, it is called a radiopharmaceutical.

        The advantage of a radiotracer, among other features described elsewhere in this document, is that it makes it possible to study and keep track of body function, using special equipment to detect radiation emitted  from inside of the body.

        Gamma emitting radionuclides and positron emitters more recently, have been used in clinical diagnosis through images.  Nuclear Medicine generally uses radionuclides that decay by isomeric transition (IT) or electron capture (EC) for diagnostic imaging because in this type of decay, gamma photons are produced. Emitters of alpha and beta particles travel only a few mm, so they cannot be detected from outside of the body, but are adquate to be used for selective irradiation and therapy.

            Radionuclides can be found in nature, but those more commonly employed in nuclear medicine are artificially produced. There are different ways to get these radionuclides, so for example those with short half lives are obtained from generators or in cyclotrons while those ones with long half lives are frequently made in nuclear reactors. As a representative example,  it is of great interest to know more about the generator.

            Figure 1 shows the outline of a molybdenum-99 and Tc-99m generator. This device, approximate size 30 x 30 x 20 cm, has inside and under lead shielding an alumina column with molybdenum-99. It contains a pyrex glass cylinder with glass filter to retain the alumina, the "mother" (99 Mo) and sodium pertechnetate (99mTc), the "daughter." By passing a saline solution (Eluant) through this column Tc-99m is removed, for use in the various clinical applications. When properly eluted, the amount of molybdenum or Tc99, in the eluate are small and do not interphere in the quality of scans.

            It has also  at the input end a filter pore size 0.22 m  which allows sterile air to get in. At the output and connected to the lower column end, there is a filter pore size of 0.22 m that allows a sterile Eluate to go into the collecting flask.

Figure 1

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