Ultrasound-switchable fluorescence thermometry with dual detection channels using temperature-sensitive liposomes.

Temperature measurements in biological tissues play a crucial role in studying metabolic activities. In this study, we introduce a noninvasive thermometry technique based on two-color ultrasound-switchable fluorescence (USF). This innovative method allows for a local temperature mapping within a microtube filled with temperature-sensitive liposomes as nano imaging agents. By measuring the temperature-dependent fluorescence emission of the liposomes using a spectrometer, we identify four characteristic temperatures. The local background temperature can be estimated by analyzing the corresponding appearance time of these four characteristic temperatures in the dynamic USF signals captured by a camera-based USF system with two detection channels. Simultaneous measurements with an infrared (IR) camera showed a 0.38°C ± 0.27°C difference between USF thermometry and IR thermography in a physiological temperature range of 36.48°C-40.14°C. This shows that the two-color USF thermometry technique is a reliable, noninvasive tool with excellent spatial and thermal resolution.