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International Journal of Biomedical Imaging
Volume 2006, Article ID 37470, 7 pages

Increased Depth of Cellular Imaging in the Intact Lung Using Far-Red and Near-Infrared Fluorescent Probes

1Center for Lung Biology and Department of Pharmacology, College of Medicine, University of South Alabama, 307 N. University Boulevand, MSB 3370, Mobile, AL 36688, USA
2SciGro, Inc., Malvern, PA 19355, USA
3PTI Research, Inc., Exton, PA 19341, USA

Received 19 July 2005; Accepted 18 October 2005

Academic Editor: Yue Wang

Copyright © 2006 Abu-Bakr Al-Mehdi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Scattering of shorter-wavelength visible light limits the fluorescence imaging depth of thick specimens such as whole organs. In this study, we report the use of four newly synthesized near-infrared and far-red fluorescence probes (excitation/emission, in nm: 644/670; 683/707; 786/814; 824/834) to image tumor cells in the subpleural vasculature of the intact rat lungs. Transpelural imaging of tumor cells labeled with long-wavelength probes and expressing green fluorescent protein (GFP; excitation/emission 488/507 nm) was done in the intact rat lung after perfusate administration or intravenous injection. Our results show that the average optimum imaging depth for the long-wavelength probes is higher (27.8±0.7 μm) than for GFP (20±0.5 μm; p=0.008; n=50), corresponding to a 40% increase in the volume of tissue accessible for high-resolution imaging. The maximum depth of cell visualization was significantly improved with the novel dyes (36.4±1 μm from the pleural surface) compared with GFP (30.1±0.5 μm; p=0.01; n=50). Stable binding of the long-wavelength vital dyes to the plasma membrane also permitted in vivo tracking of injected tumor cells in the pulmonary vasculature. These probes offer a significant improvement in the imaging quality of in situ biological processes in the deeper regions of intact lungs.