The present disclosure is related to methods and systems for imaging. The method may include obtaining current information of a target subject. The current information may include information relating to current radiation attenuation of the target object. The method may also include obtaining reference information of the target subject. The reference information may include information relating to historical radiation attenuation of the target object. The method may also include determining at least one current parameter of the target subject based on the current information and the reference information. The method may also include obtaining a target image of the target subject based on the at least one current parameter.