Research On The Cerenkov Luminescence Optical Imaging

ObjectivesCerenkov luminescence imaging (CLI), as a novel molecular imaging, cannoninvasively monitor biodistribution of the radiopharmaceuticals in small living animals.We investigated the penetration depth and resolution of Cerenkov luminescence emittedfrom18F-FDG and131I. And we report the design and synthesis of a type of rare-earthnanoparticle (RENP), which can be dually excited by CR to enhance the optical imagingof CR in terms of intensity and penetration.MethodsFirstly, we compared the relationship between the intensity of Cerenkov luminescenceand radioactivity of18F-FDG and131I. Then compared the penetration depths of differentradioactivity of131I using the tissue phantoms. The100uCi/μL of18F-FDG and131I sources at different depths of4type of tissues were acquired for luminescence images using thedual-modality ZKKS-Direct3D molecular imaging system (jointly developed byGuangzhou Zhongke Kaisheng Medical Technology CO., Ltd, Xidian University andInstitute of Automation, CAS) to investigated the resolution of CLI. After finished theexperiments on the penetration and resolution, Yb3+-and Er3+-codoped hexagonal NaYF4hollow tubes were synthesized via a hydrothermal route. The phase, morphology, and dualexcitation effects from the decay of radionuclides (131I and18F) were confirmed for theseRENPs by power X-ray diffraction (XRD), scanning electron microscopy (SEM), andspectrophotometry, respectively. A commercial CCD camera equipped with a series ofoptical filters was employed to quantify the CR imaging signals from radionuclides. Theinfluence of the RENP concentration and the131I and18F radioactivity on the CR imagingintensity was also calculated. The enhancement of penetration was investigated byimaging studies of nylon phantoms and nude mouse models.ResultsThe results showed that the intensity of Cerenkov photons increased linearlywithactivity of18F-FDG (r2=0.97，P=0.0001) and131I (r2=0.96，P=0.0001). There was anexponential correlation between the penetration depth and the mean minimum activity.Besides, the intensity of CLI optical signal decreased with the depth of radioactive sources.Moreover, the penetration property was related with type of tissues, and more photonspenetrated from fat tissues than the other porcine tissues. The resolution experimentshowed that the resolution was related with the kind of tissues, the depth of the sourcesand the activity of18F-FDG.Moreover, CR could dually excite the RENPs at thewavelengths of520and980nm, and the emission peaks overlaid at660nm. This strategyapproximately doubled the overall detectable intensity of CR imaging and extended itsmaximum penetration in nylon phantoms from5to15mm. This enhancement effect waspositively correlated with the concentration of RENPs (R2=0.994) and the radioactivityof radionuclides (R2=0.996). The penetration study in living animals yielded similarresults.Conclusions Our study suggested that18F-FDG has better penetration and resolution than131I, whichwas possibly more appropriate for CLI in preclinical applications, but the penetration ofthe both are still not sufficient for CLI of deep seated source.The fat has relatively lowabsorbed and scattered to Cerenkov luminescence. And we demonstrated that CR candually excite RENPs and that the overlaid emissions in the range of660nm couldsignificantly enhance the penetration and intensity of CR imaging. The proposed enhancedCR imaging strategy may have promising applications in the future.