Browsing by Author "Scheffer, C."

Now showing 1 - 4 of 4
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    Development of a computer assisted gantry system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy
    (Sociedade Brasileira de Urologia, 2010) Zarrabi, A. D.; Conradie, J. P.; Heyns, C. F.; Scheffer, C.; Schreve, K.
    Purpose: To design a simple, cost-effective system for gaining rapid and accurate calyceal access during percutaneous nephrolithotomy (PCNL). Materials and Methods: The design consists of a low-cost, light-weight, portable mechanical gantry with a needle guiding device. Using C-arm fluoroscopy, two images of the contrast-filled renal collecting system are obtained: at 0-degrees (perpendicular to the kidney) and 20-degrees. These images are relayed to a laptop computer containing the software and graphic user interface for selecting the targeted calyx. The software provides numerical settings for the 3 axes of the gantry, which are used to position the needle guiding device. The needle is advanced through the guide to the depth calculated by the software, thus puncturing the targeted calyx. Testing of the system was performed on 2 target types: 1) radiolucent plastic tubes the approximate size of a renal calyx (5 or 10 mm in diameter, 30 mm in length); and 2) foam-occluded, contrast-filled porcine kidneys. Results: Tests using target type 1 with 10 mm diameter (n = 14) and 5 mm diameter (n = 7) tubes resulted in a 100% targeting success rate, with a mean procedure duration of 10 minutes. Tests using target type 2 (n = 2) were both successful, with accurate puncturing of the selected renal calyx, and a mean procedure duration of 15 minutes. Conclusions: The mechanical gantry system described in this paper is low-cost, portable, light-weight, and simple to set up and operate. C-arm fluoroscopy is limited to two images, thus reducing radiation exposure significantly. Testing of the system showed an extremely high degree of accuracy in gaining precise access to a targeted renal calyx.
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    Developoment of a magnetic intra-uterine manipulator
    (South African Institution of Mechanical Engineering, 2013) Doll, S.; Scheffer, C.; Du Toit, G.
    This paper introduces the concept of a novel magnetic intra-uterine manipulator, intended to overcome conventional medical devices’ shortcomings, and enabling non-invasive uterine manipulation during surgery. However, analyses have shown that the magnetic manipulator is unable to compete in terms of the range of motion of the existing devices. A limited anterior sagittal rotation range of 60° was observed in a magnetic manipulator compared to a range of 140° for conventional devices. Despite these limitations, use of a magnetic manipulator could eliminate the need for an additional medical assistant during surgery; it is also reusable and thus also more economical. The second goal of the research was to investigate which type of setup would be most successful in effective uterine manipulation. Through concept analysis, a cart-onarch system was deemed most effective. To lift an effective load of 1 N over an air gap of 150 mm, rareearth N38 neodymium (NdFeBr) magnets showed the most promise as magnetic actuators for the manipulator. Finite Element Analysis (FEA) simulations of the magnetic set-up were validated experimentally and produced an acceptable Mean Absolute Error (MAE) of 0.15 N.
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    Recurrence quantification analysis of resting state EEG signals in autism spectrum disorder – a systematic methodological exploration of technical and demographic confounders in the search for biomarkers
    (BioMed Central, 2018-07-02) Heunis, T.; Aldrich, C.; Peters, J. M.; Jeste, S. S.; Sahin, M.; Scheffer, C.; De Vries, P. J.
    Background: Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a worldwide prevalence of 1–2%. In low-resource environments, in particular, early identification and diagnosis is a significant challenge. Therefore, there is a great demand for ‘language-free, culturally fair’ low-cost screening tools for ASD that do not require highly trained professionals. Electroencephalography (EEG) has seen growing interest as an investigational tool for biomarker development in ASD and neurodevelopmental disorders. One of the key challenges is the identification of appropriate multivariate, next-generation analytical methodologies that can characterise the complex, nonlinear dynamics of neural networks in the brain, mindful of technical and demographic confounders that may influence biomarker findings. The aim of this study was to evaluate the robustness of recurrence quantification analysis (RQA) as a potential biomarker for ASD using a systematic methodological exploration of a range of potential technical and demographic confounders. Methods: RQA feature extraction was performed on continuous 5-second segments of resting state EEG (rsEEG) data and linear and nonlinear classifiers were tested. Data analysis progressed from a full sample of 16 ASD and 46 typically developing (TD) individuals (age 0–18 years, 4802 EEG segments), to a subsample of 16 ASD and 19 TD children (age 0–6 years, 1874 segments), to an age-matched sample of 7 ASD and 7 TD children (age 2–6 years, 666 segments) to prevent sample bias and to avoid misinterpretation of the classification results attributable to technical and demographic confounders. A clinical scenario of diagnosing an unseen subject was simulated using a leave-one-subject-out classification approach. Results: In the age-matched sample, leave-one-subject-out classification with a nonlinear support vector machine classifier showed 92.9% accuracy, 100% sensitivity and 85.7% specificity in differentiating ASD from TD. Age, sex, intellectual ability and the number of training and test segments per group were identified as possible demographic and technical confounders. Consistent repeatability, i.e. the correct identification of all segments per subject, was found to be a challenge. Conclusions: RQA of rsEEG was an accurate classifier of ASD in an age-matched sample, suggesting the potential of this approach for global screening in ASD. However, this study also showed experimentally how a range of technical challenges and demographic confounders can skew results, and highlights the importance of probing for these in future studies. We recommend validation of this methodology in a large and well-matched sample of infants and children, preferably in a low- and middle-income setting.
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    A user interface for a seven degree of freedom surgical robot
    (South African Institution of Mechanical Engineering, 2013) Heunis, J. S.; Scheffer, C.; Schreve, K.
    This paper presents the design of a joystick-type user interface for the master-slave control of a seven degree of freedom (DOF) minimally invasive surgical robot. The joystick is a seven DOF all revolute articulated arm. The electronic design implements AS5040 magnetic rotary encoders for the joystick’s position and orientation tracking. The control system required the mathematical modelling of the joystick and robot using the Denavit- Hartenberg convention. Testing demonstrates the intuitiveness of the joystick control.