Masters Degrees (Medical Physics)

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Browsing Masters Degrees (Medical Physics) by Author "Groenewald, Annemari"

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    Radiation dose reduction in diagnostic neonatal x-ray imaging
    (Stellenbosch : Stellenbosch University, 2013-03) Groenewald, Annemari; Groenewald, Willem Adolf; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medical Imaging and Clinical Oncology. Medical Physics.
    ENGLISH ABSTRACT: Introduction - X-ray imaging is used to diagnose and follow up various conditions in neonates (i.e. pre-term babies and babies up to the age of 28 days). Chest anterior-posterior (AP) radiographs are used to check the condition of the lungs and heart. Acceptable images requiring lower doses of radiation can be produced digitally by using a computed radiography (CR) system. Radiation can induce cancer in the young child. Lower doses are therefore important since neonates are more sensitive to radiation and have a relatively longer life expectancy. To minimise the risk of inducing cancer in neonates, x-ray exposures must adhere to the principle of ALARA (i.e. as low as reasonably achievable). Reducing radiation doses during a radiographic examination of a neonatal chest often results in reduced image quality. Dose reduction while maintaining optimum image quality and the risk of inducing cancer must therefore be considered in conjunction with one another. Aim - The aim of this study is to develop an anatomical and radiological simulation phantom of a real neonatal chest and, using the phantom, to derive methods of decreasing the radiation dose while maintaining acceptable quality of the clinical image at a reduced cancer induction risk. Materials and methods - Following guidelines in literature on the subject, as well as principles of medical physics, a phantom simulating a real neonatal chest anatomically and radiologically was developed. Anatomical equivalence was based on a computed tomography (CT) scan of a neonatal cadaver. Radiological equivalence was obtained by matching density, elemental composition, attenuation, scatter and absorption characteristics of real neonatal tissues to possible substitute materials. The phantom was used to derive x-ray imaging protocols to decreased radiation dose, as well as the risk of cancer induction, while maintaining acceptable quality of the image. To achieve this exposure technique factors, such as tube voltage and current, exposure time and filtration, were varied experimentally. Image quality was evaluated quantitatively in a physics image quality assessment phantom, by calculating signal-to-noise ratios and modulation transfer functions. Images were ranked according to measured doses, visual and quantitative image quality and cancer induction risks. Results - The simulation phantom acceptably matched a real neonatal chest anatomical and radiologically. The radiation dose and image quality of various exposures were compared with the standard exposure for neonatal chest AP x-ray imaging. In eight different exposures the dose was decreased to below the standard. The largest dose reduction was approximately 63%. Seven of these images had an improved visual image quality compared with the standard. The greatest improvement being about 21%. In two of the eight options a cancer induction risk analysis showed that, despite reduced doses, the risk could be greater than the standard exposure risk. Discussion and conclusion - In six different exposure options a decrease in the dose was achieved while maintaining, and even improving, image quality and lowering the cancer inducing risk. These exposure protocols were recommended to be used in the Diagnostic Radiology Division of Tygerberg Academic Hospital.