Philips Medical Systems has evolved a new computer tomograph with lower radiation exposure of the patient and improved imaging of the human body. Highest demands on the material properties were not only made by the high-voltage supply and centrifugal forces of the fast rotating X-ray sources but also by their strong heat emission. Together with Hedrich, Philips developed an innovative procedure to pour a cast resin filled with micro-hollow balls for producing the carrier components of the X-ray sources of the apparatus with little weight.

When it comes to health, neither any compromise must be made in medical engineering. The more examination methods become precise, the more technical requirements to the systems and materials employed increase. Despite all progress: Highest priority is always given to the wellfare of the patient, this means least possible stressing during the examinations. Medical science technology meets this requirement by a high rate of innovation and continuous research and development. This also applies to the range of image-guided examination methods like the computer tomography. This method allows to generate three-dimensional images of objects on the basis of X-rays which are very close to reality.

Philips Medical Systems, a leading supplier in the range of computer tomography, has been researching a new method that considerably reduces the stress to the patient by the X rays and, at the same time, provides better images. The essential innovation is the X ray sources of the Philips computer tomograph that rotate around the couch very fast, considerably diminishing both time of examination and radiation stress to the patient. Together with Hedrich, innovative procedures were developed for the high-voltage generators to process carrier components made of cast resin. With least weight, they provide good insulation properties at high material sturdiness and very good mechanical performance.

Not only in aerospace or the automotive industry, but also in medical engineering, materials that combine apparently contradictory material properties are much sought-after. For the development of a new computer tomograph, Philips Medical Systems was searching for an insulation carrier for high-voltage generators with least possible weight, highest possible sturdiness, excellent dielectric properties and appropriately sufficient heat conductivity. The very fast rotating X-ray sources integrated into the apparatus had to be supplied with 140 kV high voltage and, at peak power, convert up to 120 kW into X-rays for examination purposes. Conventional, filled cast resins (e.g. with quartz powder) do have good insulation properties, but were sorted out due to the demands on the weight for this application. Together with Hedrich, Philips therefore looked for a completely new resin mixture.

One of the greatest challenges in developing a material was the very high rotation speed of the so-called gantries that incorporate the power electronics, high-voltage generator and the X-ray tubes. During the examination, they rotate around the horizontal couch up to four times a second. This fast rotating speed creates a centrifugal force that is forty times higher than gravitation, increasing the (self-)weight of materials used by factor 40. In addition, the X ray sources release strong heat during operation. Owing to physical properties, only a little part of the power achieved is converted into X radiation. This heat needs to be fed away from the ambient material fast and efficiently in order to minimize stress due to the heat. The fact of centrifugal force encountering heat demands a great deal to the quality of the materials used which, even being subject to this stress, must not form any cracks.

Together with Hedrich, Philips started to develop a completely new procedure to process cast resin with a hybrid technology. Hollow, gas-filled glass balls of only a few micrometer's size were mixed with a cast resin of low viscosity until some kind of hard foam was built that was afterwards cast into a mould and cured fast. In the epoxy resin foam, conduits and cavaties were introduced during casting. The conduits, in later application, were meant to transport cooling liquids; the cavaties carried technical components of the rotating high-voltage generator.

With the hybrid resin, a new material was evolved that combines least weight and highest sturdiness with excellent insulation values. At the same time, the new material and the design of the casting mould for the carrier components allowed integration of more electronic components, thus reducing the assembly time of the high-voltage generator by 50 %. The Hedrich production line for the continuous manufacture of the carrier components comprises four main process stages - from material storage to material preparation up to material casting. The process handling time for one carrier is less than 30 minutes. After demoulding from the clamping machine, the part can directly be finished.

In order to treat the new material as careful as possible during preparation and casting as well as to maintain the weight specification of the carrier components to be manufactured, Hedrich designed an especially adapted process technology. Common proceedings involved the risk of destroying the micro-hollow balls, resulting in the density increasing during processing. So, Hedrich adapted the employed pumping, dosing and mixing technique accordingly. Also for manufacturing the casting parts, the special properties of the casting material demanded extremely careful treatment. After many series of tests, the Automatic Pressure Gelation (APG) turned out to be the optimum casting process. This sophisticated project was realized for Philips Medical Systems by linking the entire know-how of the Hedrich Group. Besides the Ultra-Fast-Compound heater (UFC) developed by Hedrich Vacuum Systems, clamping machines and moulds of the Vogel Moulds and Machines AG were used.

Medical experts are enthusiastic about the new computer tomograph (CT) that is marketed by Philips by the name of Brilliance iCT. Being able to make images of the human body as fast as lightning and in to that date unknown precision, it scans the heart within only two beats. A overall-body scan would not even last for a minute. Due to the high examination speed, the patient is exposed to a lower radiation dose (80% lower than preceding CT apparatuses). While the entire gantry surrounds the patient four times a second, it takes pictures of the body from all perspectives. These pictures are then put together by the computer to a three-dimensional image of the body or individual organs. This technology provides detailed and clear 3D images of a whole organ including the heart and the brain, and also shows long-term deviations. The Philips CT offers clinical insight for wide-spread applications in the range of radiology and cardiology, with the improved visualization being of great value for doctors in diagnosing and treating heart problems. The doctor can see the examined organ from various views and from different perspectives and make more precise diagnoses.

We thank Philips Medical Systems for the confidence in our competency and the smooth cooperation. We in fact feel a bit proud of having contributed to a successful realization of this new development in medical engineering by our innovative process technologies.

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