Replacing Lead in CT Scanners
First published in print in Medical Plastics News in July 2011.
A leading multinational manufacturer of computed tomography (CT) scanners for healthcare decided to find a replacement for lead, which was used to make radiation-shielding components. Although European regulations currently allow an exemption for lead in medical devices, the OEM wanted to make the switch proactively. As a result, its engineers and designers began a search for a sustainable replacement material that would shield radiation effectively while offering additional manufacturing benefits.
To ensure safety, CT scanners must be shielded effectively to minimize radiation exposure to the patient and care giver. Central to the CT device is a collimator that traditionally uses lead-lined steel components to filter X-rays. At first, the OEM engineers tried replacing the lead and steel blades in the collimator with the metal compound molybdenum, which is easier to machine but has a higher raw material cost.
Tests of this solution found a one-eighth-inch-diameter “hot spot” of potential radiation leakage that needed to be addressed. The designers then turned to supplier USA-based Thogus Products. Thogus designed and moulded a “patch” for the hotspot using PolyOne’s trademarked Trilliant Healthcare Radiation Shielding compound. Trilliant is a highly filled polymer that incorporates PolyOne’s exclusive trademarked Gravi-Tech metal replacement technology, and is specifically formulated for the healthcare industry.
The PolyOne Difference
Tests at this manufacturer and others showed that the Trilliant material blocks radiation at levels that meet or exceed those of pure lead. Furthermore, the impact-modified grade of Trilliant worked so well for the “patch” that designers began replacing other parts with the highly filled polymer.
The collimator blades, for example, were being machined from molybdenum at a cost of over €100 each just for the raw material. The decision to use Trilliant reduced the material cost to €25. In addition, production time fell significantly. Once the tooling was built, it was only a matter of days before blades were ready to be assembled into the collimator.
Each CT scanner is fully tested and inspected before it is shipped. In more than four years of production, the machines equipped with Trilliant blades have continued to meet or exceed high standards for performance and quality.
Throughout this period, Thogus has continued to work with PolyOne to ensure repeatability in resin production. This lot-to-lot consistency is crucial to the success of these applications.
Benefits of Trilliant
Trilliant Healthcare Radiation Shielding Compounds, according to PolyOne, provide the following benefits compared with traditional lead-based compounds:
- Reduce overall material costs by as much as 30 to 50 percent
- Improve environmental footprint thanks to significantly better handling, manufacturing, disposal and safety aspects
- Reduce costs in terms of system design, machining and regulation.
- Improve radiation-shielding performance, as proven by tests performed by the CT manufacturer.
- Parts consolidation. Trilliant offers designers the opportunity to consolidate parts and thereby save time and money. For example, designers replaced a multi-part housing that had been assembled at a cost of €1,400. Working with PolyOne and moulder Thogus, the manufacturer switched to a single Trilliant part for a saving of more than 50 percent.
- More robust finished parts. Moulded Trilliant parts are less prone to damage than softer leaded equivalents, and there are fewer service and field replacements.
- Design freedom. Trilliant enables the CT device manufacturer to shield portions of the X-ray tube that were previously impractical to shield. For example, engineers were able to freely design a moulded part so that an opening for signal and power cables could be completely shielded to prevent radiation leaks.