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 via an imaging system positioned proximate to the 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; selecting a reference frame from a plurality of PET reference frames, wherein the selected reference frame is based, at least in part, on one PET reference frame from the plurality of PET frames that best matches Radon consistency conditions and attenuation correction data; and based on the correlation and the selected reference frame, reconstructing a PET/CT image corrected for motion of the target tissue.