This work presents the results of investigation of influence of main exposure parameters on the patient dose and image noise on five clinical computed tomography units. Patient dose was determined by means of the quantity CTDIair free on air measured with pencil shaped ionization chamber. The image noise was estimated as a standard deviation of CT numbers in a 500 mm2 central region of interest in a water-equivalent phantom positioned in the centre of rotation. The alteration of tube voltage and tube current show the potential in patient dose reduction up to 40% but may deteriorate image quality and has to be carefully applied in order to optimize the clinical CT protocols taking into account the specific clinical task. This survey is essential for optimization of routine CT protocols especially for CT units without automatic exposure control systems, which are main part of CT units in Bulgaria.
Institute of Physics and Engineering in Medicine. Measurement of the performance characteristics of diagnostic X-ray systems used in medicine, Report 32. Part III: Computed tomography X-ray scanners. 2nd edition, 2003.
Jerrold T. Bushberg, J. Anthony Seibert, Edwin M. Leidholdt, John M. Boone. The Essential of Medical Imaging.
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