Abstract
Background: X-ray CT numbers are in Hounsfield Units (HU) and represent body tissues’ attenuations. Hounsfield numbers are calculated using water’s attenuation coefficient as their reference. Accurate calculations of CT numbers are critical for clinical diagnosis as a small difference in HU may differentiate cancer from normal tissues. In practice, various artefacts such as beam hardening need to be corrected and CT systems calibrated before CT numbers are presented. Despite all these efforts, the CT numbers still vary depending on locations within the body and patient body sizes. These variations of CT numbers need to be corrected in order to achieve a true quantitative CT.
Purposes: The purposes of this work are to establish a scheme and system for correcting location and body size effects on CT numbers and present correction results for various CT systems.
Methods: The attenuation coefficient of water was found to be dependent on the depth from body’s entrance surface. Energy dependent geometric and body size correction factors for water attenuation coefficient have been established for correcting the HU numbers. CT number variations from various CT systems were used to test the newly established scheme for the HU corrections.
Results: For a GE 4 slice vintage CT scanner, a perfect match has been achieved for positon shifts as well as a combination of size increase and position shifts. For a Philips Allura Xper-FD20 C-arm CT system, the position shift contributed about 5% error in additional to measurement error. For a GE Discovery HD 750 CT system, the size effect on the CT numbers are in excellent agreement with correction factors.
Conclusions: The newly established geometric and body size correction factors should be implemented in clinical X-ray CT imaging systems to improve CT accuracy.
Keywords: X-ray CT imaging; Hounsfield Unit correction, water attenuation coefficient, size effect, location dependent.
Purposes: The purposes of this work are to establish a scheme and system for correcting location and body size effects on CT numbers and present correction results for various CT systems.
Methods: The attenuation coefficient of water was found to be dependent on the depth from body’s entrance surface. Energy dependent geometric and body size correction factors for water attenuation coefficient have been established for correcting the HU numbers. CT number variations from various CT systems were used to test the newly established scheme for the HU corrections.
Results: For a GE 4 slice vintage CT scanner, a perfect match has been achieved for positon shifts as well as a combination of size increase and position shifts. For a Philips Allura Xper-FD20 C-arm CT system, the position shift contributed about 5% error in additional to measurement error. For a GE Discovery HD 750 CT system, the size effect on the CT numbers are in excellent agreement with correction factors.
Conclusions: The newly established geometric and body size correction factors should be implemented in clinical X-ray CT imaging systems to improve CT accuracy.
Keywords: X-ray CT imaging; Hounsfield Unit correction, water attenuation coefficient, size effect, location dependent.
| Original language | English |
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| Publication status | Published - 2018 |
| Event | World Congress on Medical Physics and Biomedical Engineering 2018 - Prague Congress Centre , Prague, Czech Republic Duration: 03 Jun 2018 → 08 Jun 2018 http://www.iupesm2018.org/ (conference website) |
Conference
| Conference | World Congress on Medical Physics and Biomedical Engineering 2018 |
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| Abbreviated title | Make progress, face challenges, get solutions |
| Country/Territory | Czech Republic |
| City | Prague |
| Period | 03/06/18 → 08/06/18 |
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