Ratiometric spectral imaging for fast tumor detection and chemotherapy monitoring in vivo

Abstract

We report a novel in vivo spectral imaging approach to cancer detection and chemotherapy assessment. We describe and characterize a ratiometric spectral imaging and analysis method and evaluate its performance for tumor detection and delineation by quantitatively monitoring the specific accumulation of targeted gallium corrole (HerGa) into HER2-positive (HER2 +) breast tumors. HerGa temporal accumulation in nude mice bearing HER2 + breast tumors was monitored comparatively by a. this new ratiometric imaging and analysis method; b. established (reflectance and fluorescence) spectral imaging; c. more commonly used fluorescence intensity imaging. We also tested the feasibility of HerGa imaging in vivo using the ratiometric spectral imaging method for tumor detection and delineation. Our results show that the new method not only provides better quantitative information than typical spectral imaging, but also better specificity than standard fluorescence intensity imaging, thus allowing enhanced in vivo outlining of tumors and dynamic, quantitative monitoring of targeted chemotherapy agent accumulation into them.

Figure 1

Construction of composite spectra with varying ratios of spectra of autofluorescence and HerGa fluorescence: the pure spectral signatures of autofluorescence and HerGa fluorescence were obtained from the image cube before (upper-left) and after i.t. injection (upper-right). The ratiometric spectral imaging program generates the reference spectral signatures shown in the lower images with the pure spectral signatures.

Figure 2

Quantitative examination of HerGa accumulation into a mouse at different time points using ratiometric and standard spectral imaging and analysis: (a) ratiometric spectral classification using five reference spectral signatures (right, top), (b) ratiometric spectral classification using three reference spectral signatures (right middle), (c) standard spectral classification (two reference signatures, right bottom), (d) fluorescence intensity images. Arrows indicate tumor regions.

Figure 3

The spectral classified images and fluorescence intensity image for quantitative examination of HerGa accumulation in tumors ex vivo obtained by using (a) ratiometric spectral classification using five reference spectral signatures, (b) ratiometric spectral classification using three reference spectral signatures, (c) standard spectral classification, (d) fluorescence intensity imaging (classification spectra were the same as in Fig. 2).