Methods and systems for motion detection in positron emission tomography

Methods and systems are provided for medical imaging systems. In one embodiment, a method for a medical imaging system comprises acquiring emission data during a positron emission tomography (PET) scan of a patient, reconstructing a series of live PET images while acquiring the emission data, tracking motion of the patient during the acquiring by determining a per-voxel variation for selected voxels in a current live PET image of the series of live PET images, and outputting an indication of patient motion based on the per-voxel variation for the selected voxels in each live PET image. In this way, patient motion during the scan may be identified and compensated for via scan acquisition and/or data processing adjustments, thereby producing a diagnostic PET image with reduced motion artifacts and increased diagnostic quality.