A method for correcting PET data includes acquiring first PET data at a time interval. The method also includes acquiring a first normalization coefficient corresponding to the first PET data. The method also includes determining a scale factor based at least partially on the first normalization coefficient. The method also includes determining second PET data based on the first PET data, the scale factor, and the second normalization coefficient. The method also includes determining a first dead time correction coefficient corresponding to the second PET data. The method also includes determining third PET data based on the second PET data and the first dead time correction coefficient. The method further includes reconstructing a first image based on the third PET data.