Dual-modality imaging in vivo with an NIR and gamma emitter using an intensified CCD camera and a conventional gamma camera

Fluorescence-enhanced optical imaging measurements and conventional gamma camera images on human M21 melanoma xenografts were acquired for a "dual-modality" molecular imaging study. The αvβ3 integrin cell surface receptors were imaged using a cyclic peptide, cyclopentapeptide cyclo(lys-Arg-Gly-Asp-phe) [c(KRGDf)] probe which is known to target the membrane receptor. The probe, dual-labeled with a radiotracer, ¹¹¹Indium, for gamma scintigraphy as well as with a near-infrared dye, IRDye800, was injected into six nude mice at a dose equivalent to 90μCi of ¹¹¹In and 5 nanomoles of near-infrared (NIR) dye. A 15 min gamma scan and 800 millisecond NIR-sensitive ICCD optical photograph were collected 24 hours after injection of the dual-labeled probe. The image quality between the nuclear and optical data was investigated with the results showing similar target-to-background ratios (TBR) based on the origin of fluorescence and gamma emissions at the targeted tumor site. Furthermore, an analysis of SNR versus contrast showed greater sensitivity of optical over nuclear imaging for the subcutaneous tumor targets measured by surface regions of interest.