A semiconductor radiation imaging device includes an array of pixel cells having an array of pixel detectors which directly generate charge in response to incident radiation and a corresponding array of individually-addressable pixel circuits. Each pixel circuit is associated with a respective pixel detector for accumulating charge directly resulting from radiation incident on the pixel detector and includes threshold circuitry and charge accumulation circuitry. The threshold circuitry is configured to discard radiation hits on the pixel detector outside a predetermined threshold range, and the charge accumulation circuit is configured to accumulate charge directly resulting from a plurality of successive radiation hits on the respective pixel detector within the predetermined threshold range.