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Raw-Data Effective Atomic Number and Electron Density Assessment Accuracy: A Phantom Study

C Schaeffer*, S Leon, C Olguin, M Arreola, University of Florida, Gainesville, FL

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: This study assesses the accuracy and consistency of Zeff and electron density measurements on Canon Dual-Energy CT (DECT) scanners.


Methods: Measurements were made on a Canon Genesis sequential DECT system using Gammex Multi-Energy CT head and body phantoms with rods simulating 34 different materials. Electron densities for each rod were provided by the manufacturer; Zeff values were calculated from the chemical composition of the rods provided by the manufacturer using the Mayneord equation, which depends on a parameter n that is fitted empirically. The most common published value for n is 2.94; however, we performed a least-squares fit on n to minimize the error. The head and body phantoms were scanned in volumetric mode with vendor-recommended protocols. Results are reported for both n=2.94 and the best-fit n. To test the potential impact of positioning errors, we repeated the test with the phantom shifted off-center (up, down, left, and right) by 1cm increments up to 3 cm.


Results: For n=2.94, percent errors from Zeff measurements in the body phantom averaged 6.4% (range -9.9% to -3.3%) and for the head phantom averaged 3.2% (range: 0.3% to 6.5%) The least-squares fit gave values of n=2.67 and n=3.04 for the body and head phantoms, respectively. Best-fit errors for the body phantom averaged 3.4% (range -7.2% to 5.6%); for the head phantom, they averaged 2.0% (range -3.1% to 5.6%). Electron density measurements gave average absolute percent errors of 4.7% and 0.9% for the body and head phantoms, respectively. Positioning tests found the variance in measurements made off-center to be more than the variance between scans and showed a noticeable trend.


Conclusion: With no error greater than 10%, the Canon Zeff and electron density measuring software provides an accurate and consistent way of measuring Zeff and electron density.

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Funding Support, Disclosures, and Conflict of Interest: Funded by Canon Medical Systems

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