University of Twente Student Theses


Quantification and optimization of metal artefact reduction in hip prostheses imaging using novel CT-techniques

Wellenberg, R.H.H. (2015) Quantification and optimization of metal artefact reduction in hip prostheses imaging using novel CT-techniques.

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Abstract:Purpose: To quantify the value of three novel CT--‐techniques: iterative model--‐based reconstruction (IMR), orthopaedic metal artefact reduction algorithm (O--‐MAR) and virtual monochromatic Spectral CT--‐imaging in the CT--‐imaging of metal hip prostheses. Methods and Materials: A water--‐filled phantom was used made of PMMA containing different prostheses surrounded by 18 hydroxyapatite pellets representing bone. Scans were acquired on the 256--‐slice iCT scanner and the 128--‐slice Spectral IQ on CT--‐scanner at various dose--‐levels and kVp--‐settings. Images were reconstructed with filtered back projection (FBP), iterative reconstruction (IR, iDose4) and model--‐based iterative reconstruction (IMR). Polychromatic images were reconstructed with and without the use of O--‐ MAR. Spectral virtual monochromatic images were analysed and high keV (max 200 keV) monochromatic images were compared to monochromatic images of 70 and 74 keV, which are the effective energies of polychromatic images acquired at 120 and 140--‐kVp. In order to determine the degree of metal artefacts and metal artefact reduction (MAR) image quality parameters: mean Hounsfield Unit (HU), noise [HU] and contrast--‐to--‐noise--‐ratio (CNR) of all pellets with and without the insertion of different prostheses were calculated and analysed using a standardized measurement template. Results: At all dose--‐levels and kVp settings, mean CNRs are statistically higher (p<0.001) and noise levels [HU] are statistically lower (p<0.001) for IMR relative to FBP and iDose4 reconstructions. A categorization into four degrees in metal artefacts is made: no, mild, moderate and severe artefacts. O--‐MAR is capable of substantially reducing metal artefacts. O--‐MAR is most effective at 140--‐kVp, for severe artefacts and when combined with IMR (p<0.005) resulting in the greatest HU, noise and CNR corrections towards baseline values of unaffected pellets. Virtual monochromatic imaging reduces metal artefacts by reducing beam--‐ hardening effects and streak artefacts and is most effective for moderate artefacts. High--‐keV monochromatic imaging decreases deviations in mean HUs, noise and CNRs of by metal artefact affected pellets but results in a reduced overall image contrast. With the use of IMR and O--‐MAR, acceptable CNR and noise levels are maintained with a reduction in radiation dose of 80% relative to current clinical practice. Conclusions: Image quality with IMR is superior compared to FBP and iDose4 at all dose levels and kVp settings. IMR combined with O-­‐MAR significantly improves CNR and reduces noise and metal artefacts in the CT-­‐imaging of metal hip prostheses. O-­‐MAR is more effective in MAR compared to high-­‐keV monochromatic imaging and it is most effective at 140-­‐kVp and when combined with IMR. Virtual monochromatic imaging reduces beam-­‐hardening effects and streak artefacts but is incapable of reducing metal artefacts caused by photon-­‐starvation, unlike O-­‐MAR. IMR combined with O-­‐MAR allows for significant radiation dose reduction of 80% while maintaining sufficient image quality. This research fuels the necessity of combining O-­‐MAR, IMR and Spectral CT in prosthetic imaging. Further clinical validation is needed to give more insights in the additional value of these techniques in clinical practice.
Item Type:Essay (Master)
Isala Klinieken, Zwolle
Philips Medical, Best
Philips Medical, Brussel
Philips Medical, Haifa
Faculty:TNW: Science and Technology
Subject:01 general works, 33 physics, 44 medicine, 50 technical science in general
Programme:Technical Medicine MSc (60033)
Awards:Best oral presentation, European Congress of Radiology 2015
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