Comparison of two Fluoroscopic Systems used for EVAR Procedures : an Approach to Analyze X-ray Image Quality Limited to Tube Output

Abstract: Image quality in medical x-ray imaging is dependent on the characteristics of the x-ray photons produced  by  the  x-ray  tube,  the  detection  of  the  x-ray  photons  in  the  detector  and  the  image processing. X-ray image guidance during endovascular interventions is usually performed with C-arm fluoroscopy. It is of major importance that the image quality is sufficient for the procedure. The understanding of what affects the image quality could be made easier if the performance of the different parts of the system were to be judged separately, rather than considering the system as a whole.   The term Image QualityTube Output that is used throughout this thesis describes the image quality that only depends on the characteristics of the x-ray beam, such as spectral distribution and fluence, without the consideration of detector characteristics or image processing. The aim of this thesis was to  propose  a  method  to  evaluate  the  Image  QualityTube  Output  and  then  compare  two  different fluoroscopy systems used for endovascular interventions with respect to Image QualityTube  Output, patient dose and personnel exposure, all as a function of patient thickness.   To limit to the x-ray tube output a third x-ray system was used. In that way detector and image processing would be the same and the differences in image quality would only be due to the tube output. The imaging parameters set by the Automatic Dose Rate Control, ADRC, for various patient thicknesses, was found by using Polymethyl-methacrylate, PMMA, as patient. A test object was introduced and exposed together with the PMMA of varying thickness, using the parameters set by the ADRC. The images were evaluated with respect to low contrast sensitivity and contrast to noise ratio, CNR. The effective dose rate to the patient was calculated using Monte Carlo simulation. Finally, the personnel exposure was measured using active dosimeters. The  results  showed  differences  in  the  systems  performance  and  Image  QualityTube  Output.  Also interesting differences in the effective dose rate to the patient was found. Altogether the results indicate that the proposed method is a feasible way to compare the Image QualityTube Output of two fluoroscopic systems.