The present disclosure relates to a system for PET imaging. The system may include a first device and a second device. The first device may include a first scanning channel. The second device may include a second scanning channel connected to the first scanning channel, a heat generating component, and a cooling assembly configured to cool the heat generating component, wherein the cooling assembly may include an inlet chamber and a return chamber, the heat generating component may be closer to a first side of the second device than at least one of the inlet chamber or the return chamber, and the first side of the second device may face the first device.