Browsing by Author "Mutsvangwa, Tinashe E M"

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    3D approximation of scapula bone shape from 2D X-ray images using landmark-constrained statistical shape model fitting
    (2016) Wasswa, William; Mutsvangwa, Tinashe E M; Douglas, Tania S
    Two-dimensional X-ray imaging is the dominant imaging modality in low-resource countries despite the existence of three-dimensional (3D) imaging modalities. This is because fewer hospitals in low-resource countries can afford the 3D imaging systems as their acquisition and operation costs are higher. However, 3D images are desirable in a range of clinical applications, for example surgical planning. The aim of this research was to develop a tool for 3D approximation of scapula bone from 2D X-ray images using landmark-constrained statistical shape model fitting. First, X-ray stereophotogrammetry was used to reconstruct the 3D coordinates of points located on 2D X-ray images of the scapula, acquired from two perspectives. A suitable calibration frame was used to map the image coordinates to their corresponding 3D realworld coordinates. The 3D point localization yielded average errors of (0.14, 0.07, 0.04) mm in the X, Y and Z coordinates respectively, and an absolute reconstruction error of 0.19 mm. The second phase assessed the reproducibility of the scapula landmarks reported by Ohl et al. (2010) and Borotikar et al. (2015). Only three (the inferior angle, acromion and the coracoid process) of the eight reproducible landmarks considered were selected as these were identifiable from the two different perspectives required for X-ray stereophotogrammetry in this project. For the last phase, an approximation of a scapula was produced with the aid of a statistical shape model (SSM) built from a training dataset of 84 CT scapulae. This involved constraining an SSM to the 3D reconstructed coordinates of the selected reproducible landmarks from 2D X-ray images. Comparison of the approximate model with a CT-derived ground truth 3D segmented volume resulted in surface-to-surface average distances of 4.28 mm and 3.20 mm, using three and sixteen landmarks respectively. Hence, increasing the number of landmarks produces a posterior model that makes better predictions of patientspecific reconstructions. An average Euclidean distance of 1.35 mm was obtained between the three selected landmarks on the approximation and the corresponding landmarks on the CT image. Conversely, a Euclidean distance of 5.99 mm was obtained between the three selected landmarks on the original SSM and corresponding landmarks on the CT image. The Euclidean distances confirm that a posterior model moves closer to the CT image, hence it reduces the search space for a more exact patient-specific 3D reconstruction by other fitting algorithms.
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    Characterization of the facial phenotype associated with fetal alcohol syndrome using stereo-photogrammetry and geometric morphometrics
    (2009) Mutsvangwa, Tinashe E M; Douglas, Tania S; Meintjes, Ernesta
    Fetal Alcohol Syndrome (FAS) is a clinical condition caused by excessive pre-natal alcohol exposure and is regarded as a leading identifiable and preventable cause of mental retardation in the Western world. The highest prevalence of FAS was reported in the wine-growing regions of South Africa but data for the rest of the country is not available. Required, therefore, are large-scale screening and surveillance programmes to be conducted in South Africa in order for the epidemiology of the disease to be understood. Efforts to this end have been stymied by the cost and labour-intensive nature of collecting the facial anthropometric data useful in FAS diagnosis. Stereo-photogrammetry provides a low cost, easy to use and non-invasive alternative to traditional facial anthropometry. The design and implementation of a landmark-based stereo-photogrammetry system to obtain 3D facial information for fetal alcohol syndrome diagnosis (FAS) is described. The system consists of three high resolution digital cameras resting on a purpose-built stand and a control frame which surrounds the subject's head during imaging. Reliability and assessments of accuracy for the stereo-photogrammetric tool are presented using 275 inter-landmark distance comparisons between the system and direct anthropometry using a doll. These showed the system to be highly reliable and precise.
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    Mobile phone-based evaluation of talent tuberculosis infection
    (2018) Naraghi, Safa Kagiso; Mutsvangwa, Tinashe E M; Douglas, Tania S
    The tuberculin skin test (TST) is the most widely used method for detecting latent tuberculosis (TB) infection (LTBI) in adults and active TB disease in children. This work presents the development of a screening tool to detect LTBI's, which works in conjunction with the TST and serves as an alternative for measuring the TST induration. The screening tool makes use of a mobile application developed on the Android platform to capture images of an induration, and photogrammetric reconstruction using Agisoft PhotoScan to reconstruct the induration in 3D, followed by 3D measurement of the induration with the aid of Python functions. The screening accuracy of the developed process was tested using a 3D printed induration and an HTC One smartphone to capture images. In this accuracy test, the developed screening tool was found to measure indurations more accurately than current measurement methods, as indicated by the lower standard deviation produced. An experiment to simulate real-world conditions was conducted by using the developed screening tool on a set of mock skin indurations, created by a make-up artist, and evaluating its performance. It was found that the height of the skin induration and definition of its margins are the most significant factors that influence the accuracy of the screening tool under simulated real-world conditions. Future work should explore possible improvements to the developed image capture protocol and the bimodal segmentation methods employed in this project.
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    Statistical analysis of facial landmark data for optimisation of Fetal Alcohol Syndrome diagnosis
    (2006) Mutsvangwa, Tinashe E M; Douglas, Tania S
    This project involved the statistical analysis of facial landmark used in Fetal Alcohol Syndrome (FAS) diagnosis. FAS is a clinical condition caused by excessive maternal consumption of alcohol during pregnancy. Diagnosis of FAS depends on evidence of growth retardation, CNS neurodevelopment abnormalities, and a characteristic pattern of facial anomalies, specifically a short palpebral fissure length, smooth philtrum, flat upper lip and flat midface. The unique facial appearance associated with FAS is emphasized in diagnosis that relies, in part, on the comparison of linear measurements of facial features to population norms.