Each compound was injected intravenously into CD-1 mice (a, 25 nmol), SD rats (b, 100 nmol), and Yorkshire pigs (c, 5 μmol) 4 h prior to imaging. Scale bars = 1 cm. (d) Signal-to-background ratio (SBR) in kidneys and liver against surrounding muscle was observed up to 4 h post-injection measured in pigs. Abbreviations used are: Bl, bladder; Du, duodenum; GI, gastrointestinal track; He, heart; In, intestine; Ki, kidneys; Li, liver; Lu, lungs; Mu, muscle; Pa, pancreas; Re, rectum; Sp, spleen; St, stomach and Ur, ureter.