Geometric averaging of X-ray signals in automatic exposure control

Abstract

Improper dose control in X-ray cardio-vascular systems leads to a reduced Signal-to-Noise Ratio (SNR) in regions of interest of the X-ray image. We aim at reducing the influence of direct radiation, entering a measuring field for X-ray dose control in a Flat Detector which gives too bright areas (highlights) in the image. It is our desire to use a norm-like signal size that represents a minimal dose value while maximizing information transfer and thus image quality. In a dose control system, it is common practice to employ a special averaging technique for computing a representative signal level controlling the X-ray. We have found that the geometric averaging outperforms the existing techniques and significantly improves the image quality. Our approach reduces the highlight influence and guarantees an adequate Contrast-to-Noise ratio for decentered objects. We provide convincing experimental results showing a strongly improved image quality with respect to contrast and detail.