ABSTRACT
The degree of contrast to differentiate between tissues with varying attenuation characteristics is called the contrast resolution. Because CT has a much better contrast resolution than conventional radiography, tissues with only very small differences in density can be distinguished. The contrast resolution is affected by a number of fixed factors such as the detector sensitivity and the patient size. Factors that can be influenced include the radiation intensity (the current and voltage of the X-ray tube), the slice thickness, reconstruction filtering and image noise (Figure 1.18). Additionally, the display of the tissue contrast is affected by the window settings. The display size and the distance of the radiographer from the screen influence the perception of contrast resolution. Image noise, which is the fluctuation of the measurement compared to the nominal density, negatively affects the contrast resolution. The amount of noise is related to a number of the above-mentioned factors, including the radiation intensity, the slice thickness and detector size.
