The research and development behind HDCT
My name is Jim Vartuli and I am currently the manager of the Advanced Ceramics Laboratory at GE Global Research in Niskayuna, NY. Back in 2000 I was part of a team working on the development of a suite of state-of-the-art technologies that include a new Gemstone scintillator material, HALO data acquisition system (DAS), and HD detector calibration and reconstruction algorithms. These developments have since been implemented by GE Healthcare (GEHC) and this week one product that came out of that research, the Discovery CT750HD is being highlighted at a GEHC event at Rockefellar Plaza in New York City. Developed to meet the demand of GE Healthcare’s Computed Tomography customers who desired to see more details with less x-ray dosage, the Discovery CT750HD, is an Ultra-premium High-Definition Computed Tomography (HDCT) system that delivers faster and clearer images with significant reduction in x-ray dose.
In a CT system, the scintillator converts x-rays to light, which is translated into electrical signals by a photodiode. In the 30+ year history of CT imaging, only 2 scintillator materials have been used – neither of which satisfied the stringent stability, efficiency, uniformity, and speed requirements we thought would be possible with a new HDCT system. The new scintillator we were working to develop had to have at least 50X faster speed, and meet or exceed the other primary factors of light output, transparency, afterglow, radiation damage, density, stopping power, spectral match to the photodiode, and environmental and temperature stability.
The research on this new scintillator material, that later came to be called Gemstone, began in October 2000 with the simple vision of delivering a CT detector that would provide a step-change improvement in image quality over on the competitors in the market. By the end of 2001, we examined over 150,000 possible material compositions, processed hundreds of unique compositions to converge on the origins of Gemstone. It took a full 3 years to obtain a composition close to today’s Gemstone performance. In late 2004, GE Healthcare started a pilot facility in Milwaukee. The pilot facility was later expanded to a state-of-the art clean room and full-scale manufacturing facility.
The primary goal for this new scintillator was to have very fast speed while meeting other performance requirements. After evaluating hundreds of thousands of materials as potential candidates, we finally selected a rare earth based garnet material as the new scintillator. This material has a cubic garnet structure that can enable high transparency without having to grow a single crystal. Cerium was selected as the activator to leverage its fast transition and its emission spectra, which is well-matched to the silicon photodiode’s sensitivity curve. Heavy rare earths are selected to increase stopping power of the scintillator to achieve higher quantum detection efficiency. Extensive research was conducted to optimize the composition in order to achieve the best performance for CT applications. The final composition of this material not only delivered performance, it also enabled a robust manufacturing process.
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Very intteresting. What does the linearity curve look like for the photo diodes. Also, is the spectral flatness relatively tight? I think this is a great breakthrough on technology and would welcome further information for me to look over.