Program Information
Waveform Measurements On a Fast-KV Switching CT System
J Nute1*, S Shepard2 , M Jacobsen1 , D Cody2 , (1) UT MD Anderson Cancer Center, Department of Imaging Physics, Houston, TX; UT Graduate School of Biomedical Sciences at Houston, (2) UT MD Anderson Cancer Center, Department of Imaging Physics, Houston, TX
Presentations
TU-EF-204-6 (Tuesday, July 14, 2015) 1:45 PM - 3:45 PM Room: 204
Purpose: To evaluate the timing and shape of the kilovoltage (kV) waveform for a fast-kV switching dual-energy CT system using a non-invasive method.
Methods: A kV divider with mobile filter pack was connected to a digital oscilloscope and scanned using a fast-kV switching dual-energy CT system in service mode. The tube was stationary, so exposure time was equivalent to rotation time. In this system, the generator switches quickly between two nominal voltages of 80kV and 140kV. The predicted waveform period was calculated given 1968 projections per exposure/rotation. Two Gemstone Spectral Imaging (GSI) service settings, GSI-2 and GSI-3, with exposure times of 0.8sec and 0.5sec, respectively, were analyzed. The data were binned into high (>110kV) and low (<110kV) projection regions. Waveform periods were calculated using the intersections of the waveform with 110kV. The waveform was analyzed for period accuracy, minimum and maximum kV, and average kV of the high and low kV projection regions. The effective spectral separation was the difference between the average kVs of the low and high projection regions.
Results: The shape of the waveform was neither square nor sinusoidal. The minimum and maximum kVs were 81.6kV and 139.6kV for GSI-2 (0.8sec) and 84.8kV and 131.6kV for GSI-3 (0.5sec), which were within 6% of the nominal kVs. GSI-2 and GSI-3 had average waveform periods of 0.8134msec and 0.5064msec, respectively, within 0.5% of the calculated periods. The average kV for the high and low projections yielded effective spectral separations of 38.3kV (89.2kV to 127.5kV) for GSI-2 (0.8sec) and 27.2kV (93.7kV to 121.4kV) for GSI-3 (0.5sec).
Conclusion: A method for analyzing the kV waveform of a fast-kV switching x-ray tube was demonstrated. The pseudo-sinusoidal shape of the kV waveform lowers spectral separation compared to that of an ideal square wave, which may impact the quality of dual-energy CT material decomposition.
Funding Support, Disclosures, and Conflict of Interest: This research was conducted at the MD Anderson Center for Advanced Biomedical Imaging in-part with equipment support from General Electric Healthcare
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