Christen, Patrik
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Patrik
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Patrik Christen
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- PublikationSystem Metamodelling of Open-Ended Evolution Implemented with Self-Modifying Code(Complex Systems Publications, inc., 2023) Christen, Patrik [in: Complex Systems]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationAutomatic programming as an open-ended evolutionary system(Machine Intelligence Research Labs, 2022) Fix, Sebastian; Probst, Thomas; Ruggli, Oliver; Hanne, Thomas; Christen, Patrik [in: International Journal of Computer Information Systems and Industrial Management Applications]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationFormation dominates resorption with increasing mineralized density and time postfracture in cortical but not trabecular bone: a longitudinal HRpQCT imaging study in the distal radius(Wiley, 2021) Atkins, Penny R.; Stock, Kerstin; Ohs, Nicholas; Collins, Caitlyn J.; Horling, Lukas; Benedikt, Stefan; Degenhart, Gerald; Lippuner, Kurt; Blauth, Michael; Christen, Patrik; Müller, Ralph [in: JBMR Plus]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationAssociation of higher bone turnover with risk of curve progression in adolescent idiopathic scoliosis(Elsevier, 2021) Zhang, Jiajun; Wang, Yujia; Cheng, Ka-lo; Cheuk, Kayee; Lam, Tsz-ping; Hung, Alec L.H.; Cheng, Jack Chun-Yiu; Qiu, Yong; Müller, Ralph; Christen, Patrik; Lee, Yuk-Wai Wayne [in: Bone]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationAutomated segmentation of fractured distal radii by 3D geodesic active contouring of in vivo HR-pQCT images(Elsevier, 2021) Ohs, Nicholas; Collins, Caitlyn J.; Tourolle, Duncan C.; Atkins, Penny R.; Schroeder, Bryant J.; Blauth, Michael; Christen, Patrik; Müller, Ralph [in: Bone]Radius fractures are among the most common fracture types; however, there is limited consensus on the standard of care. A better understanding of the fracture healing process could help to shape future treatment protocols and thus improve functional outcomes of patients. High-resolution peripheral quantitative computed tomography (HR-pQCT) allows monitoring and evaluation of the radius on the micro-structural level, which is crucial to our understanding of fracture healing. However, current radius fracture studies using HR-pQCT are limited by the lack of automated contouring routines, hence only including small number of patients due to the prohibitively time-consuming task of manually contouring HR-pQCT images. In the present study, a new method to automatically contour images of distal radius fractures based on 3D morphological geodesic active contours (3D-GAC) is presented. Contours of 60 HR-pQCT images of fractured and conservatively treated radii spanning the healing process up to one year post-fracture are compared to the current gold standard, hand-drawn 2D contours, to assess the accuracy of the algorithm. Furthermore, robustness was established by applying the algorithm to HR-pQCT images of intact radii of 73 patients and comparing the resulting morphometric indices to the gold standard patient evaluation including a threshold- and dilation-based contouring approach. Reproducibility was evaluated using repeat scans of intact radii of 19 patients. The new 3D-GAC approach offers contours within inter-operator variability for images of fractured distal radii (mean Dice score of 0.992 ± 0.004 versus median operator Dice score of 0.993 ± 0.006). The generated contours for images of intact radii yielded morphometric indices within the in vivo reproducibility limits compared to the current gold standard. Additionally, the 3D-GAC approach shows an improved robustness against failure (n = 4) when dealing with cortical interruptions, fracture fragments, etc. compared with the automatic, default manufacturer pipeline (n = 40). Using the 3D-GAC approach assures consistent results, while reducing the need for time-consuming hand-contouring.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationSimulating metaphyseal fracture healing in the distal radius(MDPI, 2021) Engelhardt, Lucas; Niemeyer, Frank; Christen, Patrik; Müller, Ralph; Stock, Kerstin; Blauth, Michael; Urban, Karsten; Ignatius, Anita; Simon, Ulrich [in: Biomechanics]Simulating diaphyseal fracture healing via numerical models has been investigated for a long time. It is apparent from in vivo studies that metaphyseal fracture healing should follow similar biomechanical rules although the speed and healing pattern might differ. To investigate this hypothesis, a pre-existing, well-established diaphyseal fracture healing model was extended to study metaphyseal bone healing. Clinical data of distal radius fractures were compared to corresponding geometrically patient-specific fracture healing simulations. The numerical model, was able to predict a realistic fracture healing process in a wide variety of radius geometries. Endochondral and mainly intramembranous ossification was predicted in the fractured area without callus formation. The model, therefore, appears appropriate to study metaphyseal bone healing under differing mechanical conditions and metaphyseal fractures in different bones and fracture types. Nevertheless, the outlined model was conducted in a simplified rotational symmetric case. Further studies may extend the model to a three-dimensional representation to investigate complex fracture shapes. This will help to optimize clinical treatments of radial fractures, medical implant design and foster biomechanical research in metaphyseal fracture healing.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationEnhance reflection skills with social video learning(ETH, 2020) Schmidt, Pascal; Lehner, Marion; Christen, Patrik [in: ETH Learning and Teaching Journal]01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationVirtual supersampling as post-processing step preserves the trabecular bone morphometry in human peripheral quantitative computed tomography scans(Public Library of Science, 2019) Schulte, Friederike A.; Christen, Patrik; Badilatti, Sandro D.; Parkinson, Ian; Khosla, Sundeep; Goldhahn, Jörg; Müller, Ralph [in: PLOS ONE]In the clinical field of diagnosis and monitoring of bone diseases, high-resolution peripheral quantitative computed tomography (HR-pQCT) is an important imaging modality. It provides a resolution where quantitative bone morphometry can be extracted in vivo on patients. It is known that HR-pQCT provides slight differences in morphometric indices compared to the current standard approach micro-computed tomography (micro-CT). The most obvious reason for this is the restriction of the radiation dose and with this a lower image resolution. With advances in micro-CT evaluation techniques such as patient-specific remodeling simulations or dynamic bone morphometry, a higher image resolution would potentially also allow the application of such novel evaluation techniques to clinical HR-pQCT measurements. Virtual supersampling as post-processing step was considered to increase the image resolution of HR-pQCT scans. The hypothesis was that this technique preserves the structural bone morphometry. Supersampling from 8201A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationLeast-detectable and age-related local in vivo bone remodelling assessed by time-lapse HR-pQCT(Public Library of Science, 2018) Christen, Patrik; Boutroy, Stephanie; Ellouz, Rafaa; Chapurlat, Roland; Rietbergen, Bert van [in: PLOS ONE]We previously developed an image analysis approach for the determination of local sites of bone remodelling using time-lapse in vivo HR-pQCT. The involved image filtering for removing noise was chosen rather aggressively, and also removed some effects of the bone remodelling. In this paper, we quantify these filtering settings using ex vivo reproducibility HR-pQCT images, and determine the least-detectable bone remodelling using in vivo reproducibility HR-pQCT images, as well as testing whether the approach is capable of capturing age-related bone remodelling by use of in vivo long-term HR-pQCT images. We found that a threshold value of 225 mg HA/cm3 for the filtering led to acceptable results with falsely determined bone remodelling of less than 0.5%, and that the least-detectable bone formation and bone resorption are 2.0 ± 1.0% and 2.2 ± 0.7% respectively. We also found that age-related local bone remodelling can be captured satisfactorily in postmenopausal women. The latter revealed new insights into the effect of ageing on bone remodelling, and showed that bone remodelling seems to take place through a few small formation packets and many large resorption volumes leading to a net bone loss. We conclude that local in vivo bone remodelling can be successfully assessed with time-lapse in vivo HR-pQCT capable of assessing age-related changes in bone remodelling.01A - Beitrag in wissenschaftlicher Zeitschrift
- PublikationMoving beyond the genome with computer modeling(Future Medicine, 2018) Christen, Patrik [in: Personalized Medicine]Once personalized computer simulations can provide the appropriate models and explanations to model biological and mechanical processes, we will be able to move beyond genome-based personalized medicine, enabling better use of the valuable medical data.01A - Beitrag in wissenschaftlicher Zeitschrift