| Abstract [eng] |
There is a number of different diagnostic imaging modalities used for diagnostics and postoperative control of developmental dysplasia of the hip (DDH). One of them is computed tomography (CT). Considering, that in pediatrics there is high demand for low dose protocols, the goal of this thesis was to approve the possibility for a significant reduction of CT examination doses to the pediatric patients, suffering from DDH. This was implemented using a phantom based noise simulation approach. The investigation was performed in Vilnius University Hospital Santaros Klinikos Children’s Hospital, using the CT scanner “Siemens Somatom Sensation 64” and in collaboration with local radiologists. During the study, a noise simulation algorithm was constructed, which uses generated noise samples obtained from CT scans made using the phantom measurements performed at different mAs (tube current and exposure time scanning parameter). These noise samples indicated the amount of noise that was present in the CT image when it was scanned using specific parameters. The noise samples were combined with the original patient images obtained using various scanning parameters and the end-result was an image with a noise level at the selected scan parameter. Using the created noise simulation algorithm, the image sets from 20 patients were simulated for 13, 20 and 50 mAs scans. Simulated image sets were revised and evaluated by the radiologist from Santaros Klinikos Children’s Hospital. There were 6 evaluation criteria selected, with a 3 point scale for quality: 1 - poor visibility of structures, 2 – acceptable visibility, 3 – good visibility. The results were differentiated into two outcome groups: 1 point – negative outcome, 2 or 3 points – positive outcome. After analyzing the results from the evaluations it was found that there were no negative outcomes for the 50 mAs and 20 mAs simulations. For 13 mAs simulations there were only 3 negative outcomes that were not critical for the control of the pathology and they represented 2.51% from overall evaluations. Based on these evaluation results it was concluded, that the images scanned using 13 mAs are of an acceptable quality for successful clinical evaluation and postoperative control of the DDH case. An optimized low dose CT protocol was recommended for examination of pediatric patients having developmental dysplasia of the hip. After analysing the scan data of the original patients, it was found that if these patients were scanned with the suggested low dose CT protocol, their dose, on average, would have been significantly reduced - by a factor of 6.7±3.8. |
