[A comparison of several convenient methods of estimating effective energy in X-ray computed tomography]

The measurement of half-value layers (HVLs) and effective energy in X-ray computed tomography (CT) using conventional nonrotating methods is regarded as a highly challenging task, as it necessitates the use of a nonrotating X-ray tube and the assistance of service engineers. Several convenient methods have been proposed to circumvent this limitation; however, to the best of our knowledge, there are no reports that provide a comparative study on the accuracy of each method. This prompted us to compare the accuracy and practicality of each method. Effective energy was calculated using four methods: lead shielding, copper pipe, localization, and inner-metal center-air ratio (IMCAR). The accuracy of each method for the measurement of effective energy in X-ray CT was evaluated and compared with the conventional nonrotating method. The differences in the effective energy were 0.0 to 0.6 keV (0.0% to 1.1%) for lead shielding, -2.2 to -0.6 keV (1.4% to 4.3%) for copper pipe, 4.7 to 16.7 keV (9.9% to 31.4%) for localization, and -7.4 to -0.3 keV (0.6% to 17.5%) for the IMCAR method. The results indicate that the lead shielding method is the most accurate and practical method of estimating effective energy in X-ray CT.