sentences:  After one year he was invited to a research fellowship at the Massachusetts General Hospital (MGH) in the field of PET (positron emission tomography) imaging.Following his work in PET, he began his involvement in magnetic resonance imaging (MRI).Upon joining the team at the MGH Nuclear Magnetic Resonance (MGH-NMR) Center, Kwong pursued an interest in perfusion (the distribution of blood an nutrients to tissue) and diffusion (the detection of random dispersion of particles, principally water) in living tissues.