Quality analysis of in vivo near-infrared fluorescence and conventional gamma images acquired using a dual-labeled tumor-targeting probe

The cyclic peptide, cyclopentapeptide cyclo(lys-Arg-Gly-Asp-phe) (c(KRGDf)), which is known to target(v)3 integrin, is duallabeled with a radiotracer, ¹¹¹indium, for gamma scintigraphy as well as with a near-infrared dye, IRDye800, for continuous-wave(cw)imaging of(v)3 positive human M21 melanoma in xenografts. Twentyfour hours after administration of the dual-labeled peptide at a dose equivalent to 90μCi of ¹¹¹In and 5 nmol of near-infrared(NIR)dye, whole-body gamma scintigraphy and cw imaging was conducted. Image acquisition time was 15 min for the gamma scintigraphy images and 800 ms for the optical images acquired using an NIR sensitive intensified charge-coupled device. The results show that while the target-to-background ratio(TBR)of nuclear and optical imaging were similar for surface regions of interest and consistent with the origin of gamma and NIR radiation from a common targeted peptide, the signal-to-noise ratio(SNR)was significantly higher for optical than nuclear imaging. Furthermore, an analysis of SNR versus contrast showed greater sensitivity of optical over nuclear imaging for the subcutaneous tumor targets. While tomographic reconstructions are necessary to probe TBR, SNR, and contrast for interior tissues, this work demonstrates for the first time the direct comparison of molecular optical and planar nuclear imaging for surface and subsurface cancers.