A study of scattered radiation in diagnostic radiology using Monte Carlo simulation

The aim of the work described in this thesis was to investigate ways of optimising radiological imaging procedures. Scattered X-rays, which are generated in the patient during the examination, degrade image quality by reducing contrast. The conventional scatter removal methods are grids and air gaps. In film-screen imaging, the use of grids and air gaps means that patient dose needs to be increased in order to maintain the optical density on the film. Removing the scatter by post-processing the image would avoid this dose increase. Although dose increase is not a problem for digital imaging, it would benefit from the development of a scatter removal method which was more effective than grids and air gaps. Therefore part of this work has been to understand the scatter distributions in both pelvic and chest X-rays and to investigate ways of predicting them. In the case of the pelvic examination a simple model was developed to predict the shape of the X-ray distribution in terms of patient parameters. The chest scatter was more complicated and a simple model was not possible. Therefore the investigation was carried out with a view to identifying the most important organs contributing to the shape of the scatter distribution. This was so that the relevant organs could be put into a voxel model and the scatter could be calculated using Monte Carlo methods. Additionally dynamic range in adult chest examinations was studied. The dynamic range problem is that X-ray transmission varies over the image, with transmission being higher in the lungs than in the mediastinum. This means that not all the exit signal can fit onto the linear part of the film. The effect of scatter removal on the dynamic range was investigated for both grids and air gaps. The technique chosen to study the above problems was Monte Carlo simulation in conjunction with voxel phantoms. (author)Available from British Library Document Supply Centre-DSC:DXN027354 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo