A new idea as well as CMOS implementation of a pulse-shaping filter useful in nuclear medicine to realize a multi-element detection by means of a multi-channel readout front-end ASIC have been presented. The filter changes the shape of pulses delivered by a charge amplifier in order to increase the detection speed and robustness. By canceling falling edges of the pulses, a significant increase in the pulse counting rate has been reached (between 3 and 10 MSps in a single channel). The filter takes advantage of a RESET function that is controlled by an asynchronous multiplexer. Including only two resistors, two capacitors and four configuration transistors, it is simpler than other solutions reported to overcome this problem. The proposed shaper together with a peak detector, that receives the shaper signals, dissipates a small amount of power (about 80 μW) for 1V supply voltage. When being inactive, i.e. waiting for the next pulse, the circuit consumes only 200 nW of power.