6.2 Producing the radioactive substance (elution)

In the radiopharmacy Tc-99m is produced in a generator.

Mo-99, a product of the fission of uranium, is isolated from a nuclear reactor and absorbed on to an alumina column in the generator. When a saline solution is passed over the column, ion exchange results in the production of sodium pertechnetate. This can then be chemically manipulated to form a variety of compounds. The removal of the technetium by the passage of saline is known as elution.

Conveniently, the optimum interval between elutions is 24 hours. As the half-life of Mo-99 is 66 hours the generator itself can be used for approximately one week. It is then returned to the supplier and replaced with a new one.

Activity 12

Click on the video clip to watch the elution process. Why do you think protective clothing needs to be worn?

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Transcript: Radionuclide Introduction

Clean Room

The first step in radionuclide imaging is the preparation of the radiopharmaceutical. This must be carried out under stringent conditions of sterility. There are also strict guidelines to protect staff members from ionizing radiation.

The radionuclide used for most imaging techniques is Technetium-99m. This is extracted from a generator on a daily basis by passing saline solution through the generator – a process known as elution. Inside the generator an ion exchange process results in the production of a solution of sodium pertechnetate.

Having drawn off the sodium pertechnetate it is important to measure and record the activity of the eluate.

In order to image a particular organ, the technetium must be combined with a substance that targets that organ. To do this the sodium pertechnetate must be chemically reacted with an appropriate compound.

Here the technetium needs to be combined with macro-aggregated albumen in order to target the lungs. To do this the appropriate quantity of pertechnetate is diluted with saline and then added to the Pulmocis powder and shaken. This radiopharmaceutical will be ready for injection into the patient after fifteen minutes.

Injection Room

The patient’s identity must be checked by two members of staff before the injection is given. They must also check the radiopharmaceutical is the correct one for the procedure being carried out.

A lead covered syringe offers protection to the personnel performing the injection.

The time between injection of the radiopharmaceutical and imaging depends on the specific procedure. In some cases imaging is carried out immediately, in others there can be a delay of several hours.

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Radionuclide Introduction

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Answer

The pharmaceutical will be injected directly into the patient, so it must be produced in completely sterile conditions. The suit and mask are worn to prevent germs from the person reaching the eluate.