Browsing by Author "Dreyer, Rita Liezl"

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    Anatomical variation of the carotid bifurcation in a Stellenbosch University cadaver cohort
    (Stellenbosch : Stellenbosch University, 2019-04) Dreyer, Rita Liezl; Page, Benedict; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Anatomy and Histology.
    ENGLISH ABSTRACT: The carotid bifurcation is the point where the common carotid artery bifurcates into the internal and external carotid artery. A precise anatomical knowledge of the carotid bifurcation is required for various medical specialities. The anatomy of the carotid bifurcation influences the risks, location and prognosis of related pathology. Furthermore, the anatomy of the carotid bifurcation affects treatment as it determines which surgical techniques can be used in an area of high risk. The aim of the study was to determine the anatomical variations of the carotid bifurcation in a Stellenbosch cadaver cohort. One hundred and twenty-eight specimens were examined. This research focuses on the height, angle, general structure, and diameters of the carotid bifurcation, as well as the length and diameter of the carotid sinus. The internal anatomical variation of the carotid bifurcation was added as the study progressed. This study used the gonion as the landmark when measuring height. The Stellenbosch cadaver cohort had a high frequency of high bifurcation with the mean distance of 2.12 cm on the right and 2.06 cm on the left. The angle of bifurcation was 18.53° on the right and 20.24° on the left and was smaller than previous reports in the literature, which ranged between 51-67°. Females had a higher bifurcation and larger angle of bifurcation than males. Sex affected the correlation between angle and height of the bifurcation. The general structure correlated with the standard description and was not influenced by other factors pertaining to the carotid bifurcation, sex or age. Kinks were found in the internal and external carotid artery. The diameters of the carotid bifurcation were larger on the left than on the right. The height of the bifurcation did not influence the probability of kinks in this study, contrary to the literature. The diameters of the internal, external and common carotid arteries in addition to the carotid sinus diameter were larger on the left side and in males. The external carotid had the weakest correlation with the other diameters, which was due to the external carotid artery’s embryological origin. The length of the carotid sinus was 1.74 cm on the right and 1.83 cm on the left. The diameters and the length of the carotid sinus was larger in the males. All external variation slightly increased with age over time as the elasticity of arteries decreased. A variation of the flow diverter was observed in 59% of the cadaver cohort. Supplementary flow diverters were a rare abnormality observed in the internal, external and common carotid arteries. The reason for the carotid bifurcation to present with supplementary flow diverters is still up for debate as this has not been observed in living patients; however, a pathological origin was suggested. Folds in the common carotid were observed. Internal anatomical variation was not affected by external variation or age; however, men had a higher probability of presenting with variation. The Stellenbosch cadaver cohort illustrated variations in the carotid bifurcation which was population-specific. Sex influenced various aspects and correlations of the carotid bifurcation, which means discrepancies can occur and should be considered. Further studies on the carotid bifurcation are needed.
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    Investigating the effect organic tissue has on the electromagnetic waves when targeting the visual cortex
    (Stellenbosch : Stellenbosch University, 2023-03) Dreyer, Rita Liezl; Van der Merwe, J.; Van den Heever, Dawie; Stellenbosch University. Faculty of Engineering. Institute of Biomedical Engineering.
    ENGLISH SUMMARY: The concept of using electromagnets to stimulate the visual cortex to elicit a phosphene response in the visual field is not novel. Instead, it is the basis of one of the prefered non-invasive neurostimulation methods to address vision loss. The problem, however, lies in the lack of effectiveness and specificity of electromagnetic-based prostheses. The current trend is to improve the design of micro-scale magnetic coils. The effect of the organic tissue, explicitly human organic layers over the visual cortex, on electromagnetic waves has not been explored yet. This study aimed to investigate how organic tissues (skin, facia, skull and meninges) affect electromagnetic waves targeting the visual cortex. This effect should be considered when calibrating electromagnetic-based neurostimulation devices. This study focused explicitly on the maximum field strength, RMS (root-mean-square) value of an alternating current (AC) waveform and the difference between the input and output frequencies. The study tested individual layers of organic tissue and the amalgamation of the layers, including a section of the visual cortex, at 5, 10, 15, 20, and 25 Hz. A bloodless pig's head proved to be a reliable test material since it is physiologically and anatomically similar to human tissue. A fluxgate was used as a sensor to detect changes in all three axes, as the visual cortex is a three-dimensional area. To minimise external interference, the experiment was conducted in a wooden box on the premises of the South African National Space Agency (SANSA), as it has buildings that have minimal electromagnetic interference. The frequency and sinusoidal wave format were controlled by a signal generator, while a DC power supply controlled the current and power. A single pig's head was dissected, with each layer placed in a plastic ziplock bag. The individual layers were tested by placing them between the electromagnet and the fluxgate on a wooden frame held up by a wooden jig. Each test was conducted three times while keeping the distance constant. Temperature control was considered; however, due to electromagnetic interference, the set-up was removed. The experiment was conducted instead at a room temperature of 30 °C. The results showed, unexpectedly, that organic tissue generally increased rather than decreased the magnetic field (maximum field strength, RMS). This trend was observed in the z-, y- and x-axes, where the z-axis had the highest magnetic strength, and the x-axis had the lowest. The effect of the organic tissue was dependent on the input frequency and the type of organic tissue used. The results observed in each axis were independent of the other axes. Only organic tissues of the skin, skull, and brain had an impact on the frequency. One could hypothesize that variations in the output frequencies for these particular organic tissues were caused by the resonance frequencies of these tissues. The findings of this thesis can help to calibrate electromagnetic-based visual prostheses in order to increase the effectiveness and specificity of the devices. However, further studies on a human model should be conducted for more precise calibration.