The unlicensed spectrum bands becomeovercrowded causing an increased level of interference forcurrent wireless sensor nodes. Cognitive Radio Sensor Networks(CRSNs) overcome this problem by allowing sensor nodes toaccess opportunistically the underutilized licensed spectrumbands. The sink assigns the spectrum holes to the secondaryusers (SUs). Therefore, it must rely on reliable information aboutthe spectrum holes to protect the primary users (PUs). In thispaper the sink uses two ways to determine the available channelsand alerts the SUs if an unexpected activity of PU occurs. Ourobjective is to design an algorithm able to detect the unexpectedpresence of PUs in the multi-hop network while maximizingthe throughput. To achieve our goal, we propose an optimizedversion of our previous scheduling algorithm Opportunisticcentralized TIme slot assignment in COgnitive Radio sensornetworks (OTICOR). We then evaluate its performance in termsof number of slots and throughput.