por John W. Mitchell
, Senior Correspondent | August 26, 2019
From the August 2019 issue of HealthCare Business News magazine
As cutting edge imaging modalities come and go, the primary components that make them function have remained essentially the same: a vacuum tube with a cathode to emit electrons and an anode to collect them, establish a flow of electrical current to generate an X-ray image.
Although the physics remain relatively unchanged, these tubes continue to become more sophisticated to meet the needs of healthcare providers. Today, CT tubes are lasting longer and seeing greater utilization than they did in years gone by. Meanwhile, the market forces that impact tube production and availability have undergone transitions of their own.
The CT tube market has historically been difficult to break into, due to the cost of technology development and access to R&D, and experienced manufacturing engineering expertise. While major imaging OEMs like GE, Philips, Siemens and Canon (Toshiba) manufacturer their own tubes, there are also independent tube manufacturers like Varex, the Dunlee brand of Philips, Chronos, and Richardson Healthcare.
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“Anyone can build the mechanical structure of an X-ray device,” said Jerald Olsen, vice president of sales and business development at Richardson Healthcare. “But the out-gassing, processing, and pumping down the vacuum on the inside of the device is difficult to do perfectly, and that’s why there are so few manufacturers of X-ray tubes in the world.”
As an electron strikes the anode an X-ray is created in the tube port at a specific size, focal spot, and even distribution for imaging. “In a CT system, an X-ray tube and the detector need to be completely aligned and calibrated to each other,” said Olsen, who has almost a decade of experience working with R&D engineers who design tubes. “That’s why when you do a tube change it’s vital to get an X-ray tube lined up with the detector properly so all the X-ray beam radiation is centered on the detector array.”
If that sounds simple enough, think again. In the encapsulation of the tube, all the compounds of normal atmosphere, especially hydrogen, (which is highly conductive and will interfere with the high voltage stability inside of an X-ray tube, distorting an image from the tube) have to be meticulously removed.
“You have to heat up an X-ray tube insert and pump down the vacuum inside the insert to create a pure vacuum tight environment,” he explained. “When a tube becomes unstable it can be caused by outside atmosphere that has leaked back into the tube and eventually it’ll start arcing and fail.”
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