Hip Implant Metal Artifact Reduction in Pelvic CT Scans
Sossin, Artur (2013)
2013
Master's Degree Programme in Biomedical Engineering
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2013-06-05
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201306141232
https://urn.fi/URN:NBN:fi:tty-201306141232
Tiivistelmä
Radiotherapy utilizes Computed Tomography (CT) data to perform structure contouring and dose calculations in the treatment planning process. Considerations are drawn to patients with high atomic number (high-Z) materials present in their bodies: dental fillings, hip prostheses, surgical rods, spinal cord fixation devices, et cetera. The high-Z materials introduce beam hardening artifact to CT datasets which, in combination with scatter and edge effects, produces the so called metal artifact. As a result, the dose computation accuracy is compromised and structure delineation may become cumbersome.
In order to improve the metal artifact corrupted pelvic CT images used in radiotherapy treatment planning, a novel metal artifact reduction (MAR) method was designed. The algorithm incorporated several components to deal with various distortions caused by metal present in patient anatomy. The method was tested on two CT datasets containing a single and double metallic hip prosthesis, respectively. Visual assessment of corrected CT images was carried out. Additionally, mean and standard deviation were measured in homogeneous soft and fat tissue regions in the distorted image area.
Qualitative analysis of the processed images indicated a significant improvement in anatomical tissue Hounsfield Unit (HU) accuracy, especially in the double hip implant case. This was further confirmed through the quantitative measurements which showed mean values much closer to the theoretical tissue HU value ranges. Furthermore, an up to 95% decrease in standard deviations of homogeneous tissue regions indicated a substantially lower level of artifact induced discontinuities. Finally, visual assessment of the images corrected by the proposed MAR method reflected a partial or complete restoration of bladder, bone and muscle tissue, patient body and metal object contours.
Although the MAR approach proposed in this work provided an incomplete restoration of the metal artifact corrupted CT images, the improvements made after processing are still substantial. However, it remains a matter of future work to quantitatively assess the impact on dose calculation accuracy in radiotherapy.
In order to improve the metal artifact corrupted pelvic CT images used in radiotherapy treatment planning, a novel metal artifact reduction (MAR) method was designed. The algorithm incorporated several components to deal with various distortions caused by metal present in patient anatomy. The method was tested on two CT datasets containing a single and double metallic hip prosthesis, respectively. Visual assessment of corrected CT images was carried out. Additionally, mean and standard deviation were measured in homogeneous soft and fat tissue regions in the distorted image area.
Qualitative analysis of the processed images indicated a significant improvement in anatomical tissue Hounsfield Unit (HU) accuracy, especially in the double hip implant case. This was further confirmed through the quantitative measurements which showed mean values much closer to the theoretical tissue HU value ranges. Furthermore, an up to 95% decrease in standard deviations of homogeneous tissue regions indicated a substantially lower level of artifact induced discontinuities. Finally, visual assessment of the images corrected by the proposed MAR method reflected a partial or complete restoration of bladder, bone and muscle tissue, patient body and metal object contours.
Although the MAR approach proposed in this work provided an incomplete restoration of the metal artifact corrupted CT images, the improvements made after processing are still substantial. However, it remains a matter of future work to quantitatively assess the impact on dose calculation accuracy in radiotherapy.