A system for generating a digital subtraction image of at least two input images. A vessel wall separates a vessel exterior from a vessel interior and has a wall aperture. A nozzle for discharging coolant can be provided at one end of each channel. The signal output processing unit is coupled to the subcarrier demodulation unit, and used for capturing and outputting real parts of the complex signal. The combination of a heat dissipation module, a wind power generation module, and a reception module effectively saves energy by utilizing or recycling the fluid generated by the first fan, converting the fluid into usable energy, and supplying the energy to the reception module for use or storage.