The present invention relates to an indirect radiation detector for detecting radiation (X), e.g. for medical imaging systems. The detector has an array of pixels (P1-P6), each pixel (P) being sub-divided into at least a first and a second sub-pixel (PE1, PE2). Each sub-pixel has a cross-sectional area (A1, A2) parallel to a surface plane (60) of the array. The cross-sectional area (A1) of the first sub-pixel (PE1) is different, e.g. smaller, from the cross-sectional area (A2) of the second sub-pixel (PE2) to provide a dynamic range of detectable flux densities. Additionally, the first sub-pixel (PE1) has a photosensitive device (PS1) arranged on a side of the sub-pixel, said side being substantially orthogonal to said surface plane of the array of pixels to provide a good optical coupling. The detector allows high-flux photon counting with a relatively simple detector design.