PET(SPECT)/optical imaging.(a) Preparation of dual functional PET/NIRF probe DOTA-QD-RGD. DOTA = 1,4,7,10-tetraazacyclododecane-N,N’,N”,N”’-tetraacetic acid; QD = Quantum Dot; RGD = arginine-glycine-aspartic acid; PEG = polyethylene glycol. (b)In vivo PET of mice bearing U87MG tumor with dual functional PET/NIRF probe. Whole-body coronal PET images of mice at 1, 5, 18, and 25 h after injection of 64Cu-labeled DOTA -QD or DOTA -QD -RGD. Arrows indicate tumors. GI = gastrointestinal tract; L = liver. (c)Ex vivo PET (left) and NIRF (right) image of harvested tissues at 5 h after injection of 64Cu-labeled DOTA-QD-RGD. (d) Histologic analysis of DOTA-QD-RGD distribution in U87MG tumors and other tissues. Overlay of bright-field and QD fluorescence images of frozen tissue slices (5 μm thick) (left). Immunofluorescence staining (CD31 and mouse β3) of frozen U87MG tumor slices from mice injected with 64Cu-labeled DOTA-QD-RGD (right). (Adapted with permission from ref. 54. Copyright (2010) The Society of Nuclear Medicine and Molecular Imaging).