Recently the issue of thyroid uptake following the Ventilation part of a V/P S.P.E.C.T. nuclear medicine study has been raised. Specifically, the involvement of the carbon crucible in the process.

The reason for thyroid uptake is always the generation of pertechnetate which can cross the alveolus and enter the blood stream and find its way to the thyroid where images of the thyroid will be obtained. If the field of view is wide this can confuse the lung image. The radio-aerosol, Technegas, is trapped in the alveolus and remains there providing an image of the lung structure: it does not readily cross the alveolus.

At the outset, while not wishing to disagree with learned colleagues, thirty five years of experience servicing, maintaining and teaching nuclear medicine technologists all around the world has taught me that there are several reasons for this phenomenon occurring.

Before proceeding further; when in doubt read the User Manual!

It is available on-line by Googling “User Manual for the Technegas Generator” and following the links. There are many reasons, described in the User Manual, for visualizing thyroid uptake and some are very simple to resolve. This should be your first attempt at problem resolution

The Argon gas should be high purity Argon. Mixtures for welding purposes may have impurities which could generate unwanted impurities which the patient should not breathe.

In addition, some Argon gas comes with 3% oxygen content. Even this small amount can lead to the production of pertechnetate and poor image quality.

The contacts must be changed when the generator prompts you to do so. As a routine, this should be done when a new box of consumables is opened. The old contacts should be removed and discarded, the new contacts inserted and tightened so that they are NOT loose.

As the contacts age throughout their life-cycle, they become pitted and uneven leading to poor contact, low yield and potential problems in the burn cycle.

The carbon crucibles should only be used ONCE!!. The crucibles lose their optimal functionality if repeatedly used and optimal Technegas generation is compromised with repeated use. 

The crucibles should be located between the carbon contacts and twisted a few times until a squeaking sound is heard. This ensures that the crucible is properly "seated" and ready for Technegas generation.

An appropriate current is thereby produced during the burn which raises the temperature of the crucible to 2,750 C and produces Technegas.    

Prior to administering the radio-aerosol, the patient MUST be trained on the proper way to breathe the gas. This should simulate the actual test but without the radio-aerosol being administered. The patient should be resting on the bed, connected to the generator, and asked to take several breathes. They should ensure that they breathe through the plastic tubing provided and all measures to prevent gas escaping into the atmosphere complied with.

Alcohol is required to prevent bubble formation during the burn phase. The alcohol lines the inside of the crucible and stops the Technetium from erupting out of the crucible and into the chamber.

If the crucible is dry by the time that you are administering the Technetium, remoisten and top with Technetium while still wet.

IT’ S NOT TO STERILIZE THE CRUCIBLE!!     

The level of isotope injected into the crucible should be concave when the needle is withdrawn from the crucible. If it is convex, there is the potential for Argon to blow the excess Technetium out of the crucible, contaminate the chamber and reduce yield.

Regular servicing prevents easily rectifiable problems from becoming serious issues. Ideally, the generator should be serviced annually or after 500 burns.

Issues such as simmer temperature, burn temperature and cleanliness can be addressed by the service engineer and problems such as low yield, excess salt in the chamber, excess soot in the chamber, etc. mitigated by such preventative measures.

Excess salt in the ash tray may be an indication that the simmer temperature may not be quite right. If this is a problem try cancelling out of the simmer after 6 minutes and re-simmering. The crucible should be dry before the burn is attempted.

In some instances the hose regulators may be faulty. In this case air may be sucked into the system (venturi effect) during generation of the radio-aerosol. If this occurs pertechnegas will be generated and thyroid uptake will occur.

This is the value of a general service once per annum. Your service engineer can check all of these issues and repairs can be effected immediately.

Any of these issues may lead to the production of pertechnetate in the generator.

The cause of the generation of pertechnetate is the availability of oxygen at the time of the burn NOT the presence of carbon.

So, if you are experiencing thyroid uptake;

1. Read the User Manual
2. Ensure steps 1 to 8 above are being followed
3. Call the Berentt Medical Technology service engineer.

This much overlooked useful tool, available to ALL Technegas users should be kept handy for ready reference. It can be accessed on-line BUT it is usually provided to purchasers of Technegas generators in either hard-copy or on CD.

A comprehensive list of Error Messages is detailed in the User Manual. By referencing the Error Message in the User Manual, it is possible to identify and rectify many of the common problems preventing optimal functioning of the Technegas generators.

YOU SHOULD NOT START PUSHING buttons in the hope that a problem can be rectified. Pushing buttons may program the generator to perform a non-desired function. As a matter of course, you should always wait, read the message on the screen and perform the function indicated. Don’t pre-empt the machine; this can lead to problems with Technegas production.

Batteries for the electronic version of the generators should be changed every three years and for manual version every two years. That is if the advised protocol is adhered to. So, it is worth repeating the recommended procedure:

1. Turn the generator ON at the start of the day
2. Leave on all day which charges the battery
3. Turn OFF at the end of the day
4. This optimises the life of the battery
5. Refer to Item 6.6, page 17 of the TechnegasPlus User Manual (version dated 12/08/2022

While the Technegas generators are robust and require little attention if looked after, IT IS RECOMMENDED that the generator is serviced at least once per annum or after 500 burns. This attention ensures that the generator is appropriately calibrated and any functioning optimally.

We have trained technicians on the ground in Victoria and N.S.W. to attend to emergency call-outs and offer phone assistance to resolve simple matters.

The annual Service Contract is a cost-effective way to ensure that your generator operates always at full functional efficiency.