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Elution of the ⁹⁹Mo → ^99mTc generator

Introduction

The steps involved in the elution of the generator are described below and illustrated in the video.The procedures for elution are designed to provide a sterile, pyrogen free product suitable for human injection or for elaboration into other radiopharmaceutical preparations. Commercial generators will be prepared from sterilized and medically suitable components and with proper care can be maintained in this state through their working life. Because the design of individual commercial generators varies, the precise methods used for their elution will also vary, however, the same general principles apply to all designs.

How Supplied

Generators are supplied in a variety of ⁹⁹Mo activities. For example those supplied by Amersham are listed as 30.7GBq up to 614.2 GBq (0.83 to 16 Ci) at the time of calibration. Those provided by Nordion are advertised as 6.5 to 70 GBq (0.17 to 1.89 Ci). In addition to the generator itself a variety of supplies and accessories will be required during the elution. These include:
1. Sterile isotonic saline solution (0.9% Sodium Chloride) used as the eluent
2. Sterile evacuated vials of various sizes
3. Sterile needles
4. Sterile wipes
4. Elution vial shield
5. Finished eluent labels and packing inserts

Aseptic technique must be observed during the use of the generator to maintain a sterile and pyrogen-free system. Gloves should be worn during all elution procedures. The sealed column and fluid path MUST NOT be removed from the shielding system.

1.	The generator will be removed from its shipping container and placed in an appropriate area in the laboratory. In some cases an auxiliary shield will be used to reduce operator radiation dose during the dispensing procedures.
2.	A sterile isotonic saline solution must be provided for the elution step. In most designs the eluent will be obtained from a standard septum vial by attaching the vial to the generator using the inlet spike provided for this purpose. In this latter design there will be a set procedure to maintain sterility of the system, which will involve wiping the elution vial with an alcohol swab and allowing it to dry, then uncovering the inlet spike on the generator and attaching the vial by piercing the spike into the vial. In some generator designs the saline is provided in the form of an internal reservoir with sufficient volume to provide all the elutions that will be performed during the lifetime of the generator.
3.	A sterile elution vial of sufficient volume to hold the eluate to be drawn through the generator is prepared. These vials have been evacuated and this vacuum will serve to draw the saline through the generator. The eluate vial is placed in a suitable shield to absorb the radiation from the 99mTc activity that will be removed from the generator. The septum is wiped with an alcohol swab and allowed to dry. Removing a protective cap exposes the elution port and generally a fresh sterile needle is placed on the elution port for this and each subsequent elution. The elution vial in its shield is then pushed down onto the elution needle fully piercing the septum. The vacuum in the elution vial causes the saline to be drawn through the generator column thereby eluting the 99mTc activity. This step may take a few minutes as the saline moves through the bed of alumina and is pulled through the internal plumbing of the generator. The volume of eluted radioactivity is controlled by the size of the evacuated vial used and/or by the supply of isotonic saline solution provided in the vial attached to the inlet spike. Various generator designs provide supports and mechanical devices to aid in the alignment and spiking of the inlet and elution vials.
4.	The elution vial in its shield is removed from the generator and the elution needle can be capped or protected or replaced with a fresh sterile needle. If the generator uses an eluent vial this will be left on the inlet needle until the next elution. The elution vial shields are usually equipped with a shielded cover that protects against radiation passing through the exposed septum end of the vial. The vial is taken for activity assay and quality control tests of the eluted 99mTc before being released for dispensing or use in the preparation of various 99mTc radiopharmaceuticals (see Product issues with eluted 99mTc). Various methods are used for appropriate labelling and inventory control of this product. Adequate radiation shielding must be maintained at all times.

Subsequent elutions

Subsequent elutions follow the same general set of steps as outlined above. Depending on the generator design it may be necessary to replace the used eluent vial from the previous elution with a new supply of sterile isotonic saline in a fresh vial. The elution port should be exposed and provided with a fresh sterile needle if this was not done as part of the previous elution protocol. All remaining steps in the elution will remain the same as with the first elution.