Validation of computed tomography-based attenuation correction of deviation between theoretical and actual values for four computed tomography scanners

Document Type : Original Article

Authors

1 Department of Radiology, Shimane University Hospital, Izumo, Japan

2 Biological Systems Sciences Program, Graduate School of Comprehensive Scientific Research, Prefectural University of Hiroshima, Hiroshima, Japan

Abstract

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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Main Subjects


1. Ishii K, Hanaoka K, Okada M, Kumano S, Komeya Y, Tsuchiya N, et al. Impact of CT attenuation correc­tion by SPECT/CT in brain perfusion images. Ann Nucl Med. 2012;26(3):241-7.
2. Apostolopoulos DJ, Spyridonidis T, Skouras T, Gi­annakenas C, Savvopoulos C, Vassilakos PJ. Com­parison between 180 degrees and 360 degrees acquisition arcs with and without correction by CT-based attenuation maps in normal hearts at rest. Nucl Med Commun. 2008;29(2):110-9.
3. Patton JA, Turkington TG. SPECT/CT physical prin­ciples and attenuation correction. J Nucl Med Tech­nol. 2008;36(1):1-10.
4. Ay MR, Shirmohammad M, Sarkar S, Rahmim A, Zaidi H. Comparative assessment of energy-map­ping approaches in CT-based attenuation correc­tion for PET. Mol Imaging Biol. 2011;13(1):187-98.
5. Iida H, Noto K, Mitsui W, Takata T, Yamamoto T, Matsubara K. A new method of measuring ef­fective energy using copper-pipe absorbers in X-ray CT. Nihon Hoshasen Gijutsu Gakkai Zasshi. 2011,67(9):1183-91.
6. Kan WC, Wiley AL Jr, Wirtanen GW, Lange TA, Mo­ran PR, Paliwal BR, et al. High Z elements in human sarcomata: assessment by multienergy CT and neutron activation analysis. AJR Am J Roentgenol. 1980;135(1):123-9.
7. Yang M. Dual energy computed tomography for proton therapy treatment planning. [Dissertations Theses]. Texas: The University of Texas Health Sci­ence Center at Houston Graduate School of Bio­medical Sciences; 2011. P. 127.
8. Berger MJ, Hubbell JH, Seltzer SM, Chang J, Coursey JS, Sukumar R, et al. XCOM: Photon Cross Sections Database. Physical Measurement Laboratory. Avail­able at: URL: http://www.nist.gov/pml/data/ xcom/; 2009.
9. Koyama S, Shoji T, Ochiai K. Actual dose measure­ment in X-ray CT. In: Japanese society of radiologi­cal technology the radiation measurement section. Textbook of medical dosimetry: patient exposures and dosimetry for X-ray procedures, Koyama S, ed­itors. 2nd ed. Kyoto: Japanese Society of Radiologi­cal Technology; 2006. p. 53.
10. Singh VP, Badiger NM. Effective atomic numbers of some tissue substitutes by different methods: a comparative study. J Med Phys. 2014;39(1):24-31.
11. LaCroix KJ, Tsui BM, Hasegawa BH, Brown JK. In­vestigation of the use of X-ray CT images for attenu­ation compensation in SPECT. IEEE Trans Nucl Sci. 1994;41(6):2793-9.
12. Blankespoor SC, Xu X, Kaiki K, Brown JK, Tang HR, Cann CE, et al. Attenuation correction of SPECT us­ing X-ray CT on an emission transmission CT sys­tem: myocardial perfusion assessment. IEEE Trans Nucl Sci. 1996;43(4):2263-74.
13. Kinahan PE, Hasegawa BH, Beyer T. X ray-based attenuation correction for positron emission to­mography/computed tomography scanners. Semin Nucl Med. 2003;33(3):166-79.