Fluorescence-lifetime molecular imaging can detect invisible peritoneal ovarian tumors in bloody ascites

Blood contamination, such as bloody ascites or hemorrhages during surgery, is a potential hazard for clinical application of fluorescence imaging. In order to overcome this problem, we investigate if fluorescence‐lifetime imaging helps to overcome this problem. Samples were prepared at concentrations ranging 0.3–2.4 μm and mixed with 0–10% of blood. Fluorescence intensities and lifetimes of samples were measured using a time‐domain fluorescence imager. Ovarian cancer SHIN3 cells overexpressing the D‐galactose receptor were injected into the peritoneal cavity 2.5 weeks before the experiments. Galactosyl serum albumin‐rhodamine green (GSA‐RhodG), which bound to the D‐galactose receptor and was internalized thereafter, was administered intraperitoneally to peritoneal ovarian cancer‐bearing mice with various degrees of bloody ascites. In vitro study showed a linear correlation between fluorescence intensity and probe concentration (r2 > 0.99), whereas the fluorescence lifetime was consistent (range, 3.33 ± 0.15–3.75 ± 0.04 ns). By adding 10% of blood to samples, fluorescence intensities decreased to <1%, while fluorescence lifetimes were consistent. In vivo fluorescence lifetime of GSA‐RhodG stained tumors was longer than the autofluorescence lifetime (threshold, 2.87 ns). Tumor lesions under hemorrhagic peritonitis were not depicted using fluorescence intensity imaging; however, fluorescence‐lifetime imaging clearly detected tumor lesions by prolonged lifetimes. In conclusion, fluorescence‐lifetime imaging with GSA‐RhodG depicted ovarian cancer lesions, which were invisible in intensity images, in hemorrhagic ascites.