Hi My name is Paulien, I’m a Belgian nuclear medicine resident and this video is about the production of technetium. This is not an easy topic, but I’ll try to explain it as simple as I can. First, I will tell you why we need a generator to produce technetium, then I will tell you what a generator is and finally, I’ll go through the different steps of the production process.
Technetium is a radioisotope that has a half-life of 6 hours. This means that half of the radioisotope has decayed after 6 hours. After another 6 hours, the activity of technetium is 25% of the original activity or half of the value after the first 6 hours.
After approximately 40 hours (or 7 half-lives), there is very little activity remaining compared with the initial activity. Technetium is often the agent of choice in nuclear medicine. Its short half-life, ease of incorporation into a variety of carrier molecules, low energy gamma emission, and rapid excretion make it ideal for obtaining images of the major internal organs and skeleton of the human body.
However, the time available for processing, transportation, storage and dispensing is very limited because of their fast decay. The use of a generator solves the problem associated with the transportation of short-lived radioisotopes. Generators are devices that produce a useful short-lived radioisotope (also known as ‘the daughter’) from the radioactive transformation of a long-lived radioisotope (also known as ‘the parent’).
Molybdenum, the parent, has a half-life of 66 hours and can easily be transported over long distances without serious loss of activity. Its short half-life decay product, technetium, also called ‘the daughter’, can be extracted and used at a remote facility. In other words, By having a supply of the parent at a facility, the daughter can be continually generated on-site.
The generator is often referred to as a cow. The word cow alludes to the fact that the device “milks” technetium from molybdenum, then waits for a day and milks it again, just like a cow. The decay of Molybdenum is shown by the upper curve.
The generator enables the separation of the daughter radioisotope from the parent. This separation process is called an elution (also referred to as a "milking"). Once separation occurs, the generator starts generating more daughter that can be again separated in sufficient quantity at a later time.
Because the half-life of Mo-99 is 66 hours or slightly less than 3 days, the supply of parent product will deplete to insufficient levels in roughly one week and must be replaced with a fresh system. The generator system is a simple apparatus composed of a column of alumina (Al2O3) on which the molybdenum (MoO42-) is absorbed due to its very high affinity for alumina. Molybdenum decays to form pertechnetate (TcO4-), which is less tightly bound to the column because of its single charge.
Next, a normal saline solution is passed through the column of the immobilized molybdenum and pertechnetate is eluted,. This radioisotope is ready for injection or for the preparation of other radiopharmaceuticals. After flushing, the concentration of Tc-99m is largely depleted from the column but immediately starts to increase again.
This increase of daughter activity continues but ultimately begins to slow. Eventually, the daughter activity is produced at a rate that nearly equals that at which it decays, the system is said to be in equilibrium. It takes about 4 daughter half-lives (or 24 hours) to reach equilibrium with the parent.
Once equilibrium has been achieved between the parent and daughter, the time is ripe to remove technetium from the column. The peak activity of technetium decreases as molybdenum decays, this is why the generator has to be replaced every week. Please remember that: The Use of a generator avoids the challenge of distributing short-lived radioisotopes from the original production site (typically a nuclear reactor) to individual users; the loss of activity due to decay in transit can result in too little being supplied or the need for much larger initial quantities to be sent out.
The most common radioisotope generator is the 99Mo-99mTc generator in which a stored quantity of 99Mo decays with a half-life of 66 hours into the 6-hour half-life product 99mTc. These generators are produced and delivered weekly and provide all of the 99mTc used daily.
