A collimator for an imaging detector assembly of a computed tomography imaging system is provided. The collimator includes a collimator module that includes a primary collimation grid having a first edge and a second edge. The primary collimation grid includes multiple radiation absorbing elements spaced apart from each other and configured to provide primary beam collimation. A first radiation absorbing element is disposed on the first edge and a second radiation absorbing element is disposed on the second edge. The collimator module includes multiple plates located on a side of the primary collimation grid and configured to absorb scattered radiation. A respective plate of the multiple plates is disposed over a respective radiation absorbing element of the multiple radiation absorbing elements of the primary collimation grid except the second radiation absorbing element disposed on the second edge of the primary collimation grid.