An apparatus for collecting data is provided. According to an example, the apparatus for collection data may include: n number of detector arrays, n number of DAS circuits and a back-end processor. Each of the DAS circuits may include an analog-to-digital converter and a front-end processor coupled with the analog-to-digital converter. Each of front-end processors is coupled with the back-end processor via an independent transmission line. For each of the detector arrays, the detector array may be configured to output analog signals based on detected scanning rays penetrating through a subject. The analog-to-digital converter may be configured to perform an analog-to-digital conversion on the analog signals to generate raw data. The front-end processor may be configured to logarithmically compress the raw data and transmit the logarithmically-compressed raw data to the back-end processor via the transmission line.