Imaging and quantitation of a tissue-selective lanthanide chelate using an endoscopic fluorometer

Tissue spectroscopy and endoscopy are combined with a tissue site-selective fluorescent probe molecule to demonstrate in vitro, spatial, remote, quantitative imaging of the rat small intestine. The probe molecule employed, Tb-3,6,9-tris(methylene phosphonic acid n-butyl ester)-3,6,9,15-tetraaza-bicyclo[9.3.1]pentadeca-1(15),11,13-triene (Tb-PCTMB), is shown to bind with the small intestine and provide improved image contrast. High sensitivity is possible due to the absorption-emission Stokes's shift exhibited by the Tb-PTCMB complex. Excitation is centered near 270 nm and multifeatured emission is observed at 490, 550, 590, and 625 nm. Sprague-Dawley rats were dosed with the Tb-PTCMB complex, which shows biodistribution, leading to preferential binding to the inner surface of the small intestine. It is shown that the fluorescent image, taken at 550 nm, can be used to quantify the amount of Tb-PCTMB present in an excised tissue sample. The 3σ detection limits are found to be in the femtomole range. An optical mass balance for Tb-PCTMB-dosed small intestine is performed and along with radiotracer biodistribution, demonstrates that approximately 40% of the marker probe resides in the endothelial tissue of the small intestine inner lumen. This result is of particular interest since most adult colon cancers develop in this region. These results demonstrate the ability to perform spatial, quantitative, in vitro, endoscopic imaging of a complex biological sample using a probe marker. © 1998 Society of Photo-Optical Instrumentation Engineers.