Fig. 8.

Calculation of the Medipix2 DQE at 120 keV using the statistics of individual electron events. (a) shows the total number of events $(•)$ recorded per frame and the composition in terms of events recorded in a given number of pixels, as a function of the energy threshold. A total of 2100 electrons were expected per frame. For a threshold of one half the incident energy only single pixel events are seen and at 120 keV no events were seen involving six or more pixels even with a very low threshold. (b) shows the DQE calculated using $\mathrm{DQE}(0)={({\sum }_i{\mathit{iN}}_i)}^2/[({\sum }_i{i}^2{N}_i)({\sum }_i{N}_i)]$, where $N_i$ is the number of events in each frame where a single electron is counted in $i$ adjacent pixels. Also shown is the corresponding DQE at Nyquist calculated using Eq. (6).