In vivo fluorescence imaging of the reticuloendothelial system using quantum dots in combination with bioluminescent tumour monitoring.
OBJECTIVE
We characterised in vivo fluorescence imaging (FLI) of the reticuloendothelial system using quantum dots (QD) and investigated its use in combination with in vivo bioluminescence imaging (BLI).


METHODS
In vivo FLI was performed in five mice repeatedly after the intravenous administration of QD without conjugation to targeting ligands. Ex vivo FLI of the excised organs was performed 24 h after QD injection in three mice. Seven days after intravenous inoculation of luciferase-expressing model cells of a haematological malignancy, mice were injected with the QD or saline (n = 5 each), and combined BLI/FLI was performed repeatedly. Additional five mice inoculated with the tumour cells were examined by in vivo BLI/FLI, and the structures harbouring bioluminescent foci were determined by ex vivo BLI. The utility of combining FLI with bioluminescent tumour monitoring was evaluated.


RESULTS
In vivo FLI after QD injection allowed long-term, repeated observation of the reticuloendothelial system in individual mice, although fluorescence intensity and image contrast gradually decreased over time. Ex vivo FLI verified selective accumulation in reticuloendothelial structures. The administration of QD did not affect whole-body bioluminescent signal intensities during longitudinal tumour monitoring. In vivo BLI/FLI, accompanied by fusion of both images, improved the accuracy and confidence level of the localisation of the bioluminescent foci.


CONCLUSIONS
In vivo FLI using QD provides an overview of the reticuloendothelial system in living mice. In combination with bioluminescent tumour monitoring, fluorescent reticuloendothelial imaging is expected to provide valuable information for lesion localisation.
Inoue
Yusuke
Y
Department of Radiology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo, Japan. inoueys-tky@umin.ac.jp
Izawa
Kiyoko
K
Yoshikawa
Kohki
K
Yamada
Haruyasu
H
Tojo
Arinobu
A
Ohtomo
Kuni
K
D000818:Animals; D005260:Female; D007089:Image Enhancement / Q000379:methods*; D008163:Luminescent Measurements / Q000379:methods*; D008164:Luminescent Proteins / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008856:Microscopy, Fluorescence / Q000379:methods*; D012157:Mononuclear Phagocyte System / Q000166:cytology*; D045663:Quantum Dots; D051598:Whole Body Imaging / Q000379:methods*
D008164:Luminescent Proteins