Quantitative effect of reducing body thickness on visualizing murine deep abdominal lymph nodes by in vivo fluorescence reflectance imaging.

Scattering and absorption in the tissues are major problems for in vivo imaging based on a fluorescence reflectance imaging technique. We evaluated the quantitative relationship between body thickness and fluorescent signals from a deep abdominal source in intact mice. Mice were injected with quantum dots (peak emission, 800 nm) into the right rear footpad, and fluorescent signals from the iliac lymph node located deeply in the abdomen were assessed by fluorescence reflectance imaging. Stepwise compression of the mouse abdomen to reduce the body thickness was attained using a homemade simple device. The iliac node signals were weak and diffuse without compression but became stronger and more localized with decreasing body thickness. Using excitation light of approximately 710 nm wavelength, the lymph node/background contrast increased about 16 times with a 4 mm reduction in body thickness. Contrast enhancement was more evident using shorter wavelength excitation light. Overlying tissues profoundly affect signals from a deep source in fluorescence reflectance imaging. Our simple compression method may contribute to quantitatively assessing deep fluorescent sources.