The present invention may provide a particle or radiation detector or imager which may be used for accurate recording of medical (2-D) X-ray images. The imager includes at least one detector panel. The detector panel includes a microgap detector with an array of pixel electrodes of a novel form. Each pixel electrode is insulated from a planar cathode by means of an insulating layer. Each pixel electrode is connected to an underlying contact by means of a via hole in the insulating layer. The insulating layer is preferably conformal with the electrodes. The underlying contact is connected to an electronic measuring element which preferably lies underneath the electrode and is about the same size as the electrode. The measuring element may be a storage device, a digital counter or similar. A switching transistor is connected to the measuring device. The switching transistor may be a thin film transistor. Alternatively, both measuring element and transistor may be formed in a single crystal semiconductor, e.g. a VLSI, and a complete imager formed from several detector panels in an array. The drift electrode of the microgap detector preferably includes a photocathode. The photocathode may be directly evaporated onto a phosphor.