Systems and methods for image reconstruction are provided. The methods may include obtaining a scout image including a target object, determining a first area and a second area based on the scout image, wherein the second area is located in the first area, obtaining positron emission tomography (PET) data of the first area and first computed tomography (CT) data of the second area, and reconstructing a PET image with respect to the first area based on the PET data and the first CT data.