A detector system for multi-slice X-ray Computed Tomography (CT) system is disclosed. The detector system comprises a plurality of X-ray detector modules for detecting X-ray photons; wherein each detector module is divided into individual detector elements organized in a matrix fashion with element rows (z-axis for row direction) and element columns (x-axis for column direction) for detecting X-ray photons; wherein the individual detector elements are interspaced by gaps (areas that do not detect radiation), which are also organized in a matrix fashion with gap rows and gap columns; and an anti-scatter collimator comprising a plurality of anti-scatter plates, which is placed above the detector modules and aligned to focus on an X-ray source of the CT system; wherein some or all of the anti-scatter plates are placed above the detector elements; wherein those anti-scatter plates that are placed above the detector elements block a portion of primary X-ray photons from the X-ray source in addition to scattered X-ray photons from reaching the detector elements.