Using the Medipix2 detector for energy weighting

Abstract

Simulations in Giersch et al. [Nucl. Instr. and Meth. A 531 (2004) 68–74] have shown that the concept of energy weighting can result in improved image quality or significant dose reduction. In this work, the main aim is to show that energy weighting is possible in measurements. The Medipix2 detector can be operated in energy window mode. This offers the possibility to emulate energy resolving measurements and to apply the energy weighting technique. The Medipix2 detector has a 3-bit threshold equalisation for both thresholds. For energy sensitive measurements it is important to optimise the threshold masks, because thresholds within the incident X-ray spectrum are necessary and small energy bin size is desirable. We compared masks generated by different methods with respect to image quality in energy window mode. Detector effects entail a loss of energy information. For the Medipix2 detector with 300 μ m silicon sensor layer, especially the charge-sharing effect has to be considered. We studied if energy weighting is possible under these circumstances. Measurements were performed with a phantom consisting of water and PMMA. For this example, the improvement of image quality by energy weighting is conspicuous.