Feasibility of the new copper pipe method for evaluating half‐value layer in computed tomography: A measurement and Monte Carlo simulation study

This study aimed to verify the accuracy of half‐value layer (HVL) measured using the new copper pipe method with the CT ionization chamber while the X‐ray tube is rotating and to compare it with the conventional nonrotating method and Monte Carlo simulation method based on the actual measurement and geometry of the new copper pipe method. HVL was measured while the X‐ray tube was rotating using a CT ionization chamber surrounded by copper pipe absorbers and located at the isocenter of the CT gantry. The exposure as the copper pipe thickness approached 0 mm was extrapolated from the attenuation curve to take the influence of scatter radiation into consideration. The results of the new copper pipe method were compared with those of the other two methods. Data were acquired using two different CT scanners on a single axial scan. The two one‐sided test (TOST) equivalent test yielded equivalence between HVLs derived from the new copper pipe and the nonrotating methods (P < 0.05) and those derived from the new copper pipe and the simulation methods (P < 0.05) at the equivalence margins of ± 0.03 mmCu. The mean absolute difference in HVL between the new copper pipe and conventional nonrotating methods was 0.01 ± 0.02 mmCu, which corresponded to an error of effective energy of (0.86 ± 1.66)%. The new copper pipe method can ensure that HVL of CT scanner can easily be evaluated using solely the CT ionization chamber and copper pipe absorbers without requiring service engineering mode.