An efficient method has been developed to represent the space-time behavior of neutron detector signals in nuclear reactors. The method is based on a simplified solution to the neutron shape function in the framework of a quasi-static approximation to the time-dependent diffusion equation. The shape function is obtained as a sum of a modal expansion, representing the global flux perturbations, and a local function, representing the direct perturbations due to reactor parameter changes. The method was applied to the analysis of both integral and differential rod worth measurements obtained at the critical high-temperature gas-cooled reactor test facility, Kahter. The analysis of the Kahter data indicates the applicability of the proposed method in accounting for space-time effects in detector signals.