While passive thermal imaging of temperature difference between tumor and neighboring tissue provides limited contrast, active infrared thermal imaging with external heating or cooling may provide a unique contrast mechanism due to distinct thermal responses of tumor from neighboring tissue. We previously developed an active thermo-modulation imaging method with physiologically relevant parameters including the rate of temperature change and thermal relaxation time for tumor detection. Different from conventional passive thermal imaging, active thermo-modulation provides a contrast factor which is the average rate temperature change between tumor and neighboring tissue. With the tumors, the average rate of temperature change was higher than that of neighboring tissue with heating and cooling modulation. For endoscopic infrared thermal imaging, anti-reflection germanium lenses are tested as they have higher reflected indices and transmittance at mid-infrared spectrum. Combined with thermo-modulation, the newly developed infrared endoscopy can advance label-free non-invasive endoscopic screening.
Cerenkov luminescence (CL) is generated when a charged particle moves faster than the speed of light in dielectric media. Recently CL imaging becomes an emerging technique with the use of radioisotopes. However, due to relatively weak blue light production and massive tissue attenuation, CL has not been applied widely. Therefore, we attempted to shift the CL emission to more near infrared (NIR) spectrum for better tissue penetration by using Cerenkov Radiation Energy Transfer (CRET). Gold nanoclusters were conjugated with NIR dye molecules (AuNc-IR820 and AuNc-ICG) to be activated with ultraviolet light. We found optimal conjugate concentrations of AuNc-NIR conjugates by spectroscopy system to generate maximal photon emission. When exposed by ultraviolet light, the emission of NIR light from the conjugates were verified. In quantitative analysis, AuNc-NIR conjugates emit brighter light signal than pure AuNc. This result implies that NIR fluorescent dyes (both IR820 and ICG) can be excited by the emission from AuNc. Following the above baseline experiment, we mixed F-18 fluorodeoxyglucose (F-18 FDG) radioisotope to the AuNc- NIR conjugates, to confirm NIR emission induced from Cerenkov radiation. Long pass filter was used to block Cerenkov luminescence and to collect the emission from AuNc-NIR conjugates. Instead of one long exposure imaging with CCD, we used multiple frame scheme to eliminate gamma radiation strike in each frame prior to combination. In summary, we obtained NIR emission light from AuNc-NIR conjugated dyes that is induced from CL. We plan to perform in vivo small animal imaging with these conjugates to assess better tissue penetration.