Daisuke Kawahara1,2, Shuichi Ozawa3,4, Kazushi Yokomachi1, Sodai Tanaka5, Toru Higaki6, Chikako Fujioka1, Tatsuhiko Suzuki2, Masato Tsuneda2, Takeo Nakashima1, Yoshimi Ohno1, Yasushi Nagata3,4. 1. 1 Division of Clinical Support, Radiation Therapy Section, Hiroshima University Hospital , Radiation Therapy Section, Hiroshima University Hospital , Hiroshima , Japan. 2. 2 Medical and Dental Sciences Course, Graduate School of Biomedical & Health Sciences, Hiroshima University , Hiroshima , Japan. 3. 3 Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University , Institute of Biomedical & Health Sciences, Hiroshima University , Hiroshima , Japan. 4. 4 Hiroshima High-Precision Radiotherapy Cancer Center , Hiroshima , Japan. 5. 5 Department of Nuclear Engineering and Management, School of Engineering, University of Tokyo , School of Engineering, University of Tokyo , Tokyo , Japan. 6. 6 Departments of Diagnostic Radiology and Radiology, Hiroshima University , Hiroshima University , Hiroshima , Japan.
Abstract
OBJECTIVE: To evaluate the accuracy of raw-data-based effective atomic number (Zeff) values and monochromatic CT numbers for contrast material of varying iodine concentrations, obtained using dual-energy CT. METHODS: We used a tissue characterization phantom and varying concentrations of iodinated contrast medium. A comparison between the theoretical values of Zeff and that provided by the manufacturer was performed. The measured and theoretical monochromatic CT numbers at 40-130 keV were compared. RESULTS: The average difference between the Zeff values of lung (inhale) inserts in the tissue characterization phantom was 81.3% and the average Zeff difference was within 8.4%. The average difference between the Zeff values of the varying concentrations of iodinated contrast medium was within 11.2%. For the varying concentrations of iodinated contrast medium, the differences between the measured and theoretical monochromatic CT values increased with decreasing monochromatic energy. The Zeff and monochromatic CT numbers in the tissue characterization phantom were reasonably accurate. CONCLUSION: The accuracy of the raw-data-based Zeff values was higher than that of image-based Zeff values in the tissue-equivalent phantom. The accuracy of Zeff values in the contrast medium was in good agreement within the maximum SD found in the iodine concentration range of clinical dynamic CT imaging. Moreover, the optimum monochromatic energy for human tissue and iodinated contrast medium was found to be 70 keV. Advances in knowledge: The accuracy of the Zeff values and monochromatic CT numbers of the contrast medium created by raw-data-based, dual-energy CT could be sufficient in clinical conditions.
OBJECTIVE: To evaluate the accuracy of raw-data-based effective atomic number (Zeff) values and monochromatic CT numbers for contrast material of varying iodine concentrations, obtained using dual-energy CT. METHODS: We used a tissue characterization phantom and varying concentrations of iodinated contrast medium. A comparison between the theoretical values of Zeff and that provided by the manufacturer was performed. The measured and theoretical monochromatic CT numbers at 40-130 keV were compared. RESULTS: The average difference between the Zeff values of lung (inhale) inserts in the tissue characterization phantom was 81.3% and the average Zeff difference was within 8.4%. The average difference between the Zeff values of the varying concentrations of iodinated contrast medium was within 11.2%. For the varying concentrations of iodinated contrast medium, the differences between the measured and theoretical monochromatic CT values increased with decreasing monochromatic energy. The Zeff and monochromatic CT numbers in the tissue characterization phantom were reasonably accurate. CONCLUSION: The accuracy of the raw-data-based Zeff values was higher than that of image-based Zeff values in the tissue-equivalent phantom. The accuracy of Zeff values in the contrast medium was in good agreement within the maximum SD found in the iodine concentration range of clinical dynamic CT imaging. Moreover, the optimum monochromatic energy for human tissue and iodinated contrast medium was found to be 70 keV. Advances in knowledge: The accuracy of the Zeff values and monochromatic CT numbers of the contrast medium created by raw-data-based, dual-energy CT could be sufficient in clinical conditions.
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