1Department of Radiology, Shimane University Hospital, Izumo, Japan
2Biological Systems Sciences Program, Graduate School of Comprehensive Scientific Research, Prefectural University
of Hiroshima, Hiroshima, Japan
Objective: In this study, we aimed to validate the accuracy of computed tomography-based attenuation correction (CTAC) using the bilinear scaling method. Methods: The measured attenuation coefficient (μm) was compared to a theoretical attenuation coefficient (μt ) using four different CT scanners and an RMI 467 phantom. The effective energy of the CT beam X-rays was calculated, using the aluminum half-value layer method, and was used in conjunction with an attenuation map to convert the CT numbers to μm values for the photon energy of 140 keV. We measured the CT number of the RMI 467 phantom for each of four scanners, and compared the μm and μt values for the effective energies of the CT beam X-rays, effective atomic numbers, and physical densities. Results: The μm values for CT beam X-rays with low effective energies decreased in high construction elements, compared with CT beam X-rays of high effective energies . As the physical density increased, the μm values elevated linearly. Compared with other scanners, the μm values obtained from the scanner with CT beam X-rays of the maximal effective energy increased once the effective atomic number exceeded 10.00. The μm value of soft tissue was equivalent to the μt value. However, the ratios of the maximal differences between the μm value and the μt value were 25.4% (lung) and 21.5% (bone) respectively. Additionally, the maximal differences in the μm values were 6.0% in the bone tissue for each scanner. Conclusion: The bilinear scaling method could accurately convert CT numbers to μ values within the soft tissues.
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