1. A method of correcting motion blurring in positron emission tomography-computed tomography (“PET/CT”) imaging, the method comprising: obtaining PET/CT imaging data of a target tissue in a patient; determining a centroid of the target tissue; obtaining an external motion signal of the patient; determining a mean displacement of the external motion signal; correlating the centroid of the target tissue with the mean displacement; and based on the correlation, reconstructing a PET/CT image corrected for motion of the target tissue.