A radiation detector for a computed tomography scanner includes a plurality of radiation detector modules. Each detector module includes an anti-scatter module, at least one radiation absorbing mask and a detector subassembly module. The anti-scatter module includes radiation absorbing anti-scatter plates. The detector subassembly module includes a substrate and an array of detector elements. The radiation absorbing mask is a photoetched grid, formed of a radiation absorbing material and is positioned between the anti-scatter module and the detector elements of array. The strip of the grid, that is parallel to the anti-scatter plates, is wider than each anti-scatter plate. The detector module is aligned with a spatial focus by inserting the alignment pins into the alignment openings of the radiation absorbing mask and the alignment openings of the detector subassembly module.