Medical Device Link.

Originally Published EMDM October 2003

ENGINEERING INSIGHT

The Drytec technetium generator aids in the early diagnosis of diseases.

The European Union has made an effort to harmonize standards in nuclear medicine, but not fast enough for some. Wrestling with country-specific design issues, Amersham Health (Little Chalfont, Bucks, UK) decided to revamp its Drygen and Amertec 2 technetium generators. Adapting the square generators to a rounded shape to satisfy client demand was a crucial part of the two-year process. 

That’s what Kinneir Dufort (KD; Bristol, UK), an industrial design agency, was up against when Amersham Health selected the firm to consolidate its technology in a new-generation design. The Drytec technetium generator, designed for use in hospitals, produces precise amounts of radiation. Technetium is used as an additive for diagnostic imaging agents and aids in the early diagnosis of diseases.

The generator contains a radioactive core loaded with an isotope called molybdenum 99, which decays to a daughter isotope, technetium 99m. This radioactive fluid is collected and diluted with sodium chloride, mixed with a range of diagnostic agents, and injected into patients. The radioactive substance collects in certain parts of the body and can be viewed by a gamma camera. The parent molybdenum 99 has a 2.75-day half-life, while the daughter isotope has a half-life of only 6 hours, minimizing its time in the body. The generator must be returned to the company after 2 to 3 weeks, when the isotope has expired. 

In the early design stage, KD made 200 prototype generators to start the 2-year testing and evaluation process. First, engineers experimented with putting together the generator upside down in order to shorten assembly time. “We experimented with an inverted assembly concept to reduce assembly times and limit disturbances to the tubing set,” says Philip Walsh, senior product designer at Kinneir Dufort. The generator has a lot of sterile tubing parts that transport fluid. It became clear that this was not a solution, but KD’s rapid prototyping capabilities enabled the design team to cross off a number of ideas on their list. 

Failure mode and effects analysis protocol, a standard preventative engineering quality method, was used to analyze the prototype product. 

Next, mechanical trials, ergonomics studies, and handling tests were in order. The generator can weigh between 10 and 17 kg, and must be safe and easy to transport. “We conducted drop trials,” says Walsh. “We wet the box for 30 minutes and dropped a steel spike on it to make sure the radiation will not leak.” Because of technetium’s short half-life, some of Amersham Health’s international clients in the Middle East, Asia, and Mexico need their generators air-shipped to them. Handling tests were conducted to ensure that hospital technicians knew how to quickly put the generator into an environmental cabinet, or isolator. 

Each generator is equipped with a collection shield, which is not part of the environmental cabinet. “The collection shield is made of a tungsten-filled polymer, a substance with interesting properties,” says Walsh. “It has the same density and shielding properties as lead, but can be injection moulded. And unlike lead, it is safe to handle.” People can walk around the generator safely because of its internal shield, but hospitals house the product behind additional shields in order to ensure patient and technician safety.

The additional shielding, or isolator, proved to be an even greater challenge to both KD and Amersham Health. Although the EU is working on harmonizing radiation-shielding standards, regulations vary from country to country, according to Walsh. “In Germany, the generators are placed on an open bench with a second shield. This shield is a product in its own right, providing an additional 50 mm of lead around the generator,” he says. In Italy, shielding bricks made out of lead form a wall behind which the technician stands. Walsh and Amersham engineers checked out facilities in Italy, Germany, and the United Kingdom in order to understand the operating environment, as well as how the unit would be used. 

Taking into account measurements, market indicators, usage, and client feedback, the design team worked on creating a round generator, even though the predecessor Amertec 2 is square. “Most of the generators on the market are round, and we want to sell into all markets,” says Walsh.

With its next-generation product, Amersham Health hopes to expand its market share. Indeed, the company has announced that a new manufacturing facility is in the works.

Laura Angela Bagnetto

Copyright ©2003 European Medical Device Manufacturer