Poster R5 - A Low Power Bluetooth Microscope for Multicontrast Function Imaging

Introduction: Innovative miniaturized microscopes, or "miniscopes," are crucial for understanding the link between neurovascular changes and behavior in animals. Despite their advanced capabilities, a significant drawback is their reliance on tethers or wires for power, data transfer and control. These tethers restrict natural animal behavior and complicate experiments with multiple animals due to the potential for entanglement. Therefore, developing wireless miniscopes is essential. Creating a wireless miniscope necessitates a small, onboard battery, which poses a challenge because even lightweight batteries can burden a small rodent. One promising direction is utilizing low-power surveillance systems, such as the RSL10 smart shot camera evaluation board. This board integrates a Bluetooth Low Energy (BLE) 5.2 System-on-Chip (SoC) and a low-power CMOS image sensor. By adapting this board with an optical front end, we developed the “BLEscope”. The BLEscope streams images from a rodent’s sensory motor cortex at 1 frame per second (fps) over BLE to a smartphone or laptop. It is capable of multicontrast imaging, consisting of 2 channels by incorporating 2 different LEDs: (a) Intrinsic optical signal (IOS) under green LED illumination at 570 nm for visualizing cerebral blood volume, and (b) Fluorescence imaging (FL) under blue LED illumination at 452 nm for visualizing neural activity. Here we demonstrated BLEscope’s versatility for functional imaging applications via in vivo experiments in anesthetized animals (due to the size of this proof-of-concept system). BLEscope paves the way for the future development of completely miniaturized, wireless microscopes, enhancing the study of natural animal behavior and correlative neurovascular dynamics.

Materials and

Methods: The BLEscope leverages an RSL10 smart shot camera evaluation board integrated with a custom 3D-printed microscope as shown in Fig. 1a. This setup utilizes a long-pass filter with a 510 nm cutoff to block blue excitation light. An aspheric lens with a focal length of 4.6 mm focuses images onto a CMOS sensor (ARX3A0). The entire assembly is powered by a 3.7 V LiPo battery. Control of the BLEscope is possible through a smartphone app, PC or laptop, offering two modes: "streaming" for continuous video and "single image capture." The wireless control process is illustrated in Fig. 1b. Here, a laptop locates the BLEscope, and connects via a MATLAB® script. The BLEscope's operation is managed using specific opcodes. For "single image capture," the laptop sends opcode 0x01, triggering image acquisition. The BLEscope then notifies the laptop of the image size, after which the laptop requests the data using opcode 0x04. For "streaming" mode, opcode 0x02 is sent to start, and the laptop continually sends opcode 0x04 with 1s pauses to ensure complete data transfer. The mode is terminated with opcode 0x03. To test the BLEscope's in-vivo imaging capabilities, a carbogen inhalation experiment was performed on two mice with brain tumors. Animals were anesthetized with 1.5% isoflurane and secured on the imaging platform, images were captured at 1 fps in "streaming" mode. A five-minute baseline was recorded with room air, followed by carbogen gas for another five minutes, and a 15-minute period of room air inhalation.

Results, Conclusions, and Discussions: Using the FL channel of the BLEscope, we successfully monitored GFP-expressing brain tumor cells in vivo, as illustrated in Fig. 1c and 1f. The same field of view (FOV) was captured using the IOS channel, and the mean IOS maps over 25 minutes for each animal are shown in Fig. 1d and 1g. To evaluate hemodynamic changes induced by carbogen in tumor-associated and normal blood vessels, we selected four regions of interest (ROIs) shown in Fig. 1d and 1g. These ROIs included the tumor region, a non-tumor background region, a tumor-associated blood vessel, and a normal blood vessel distant from the tumor. The IOS time-series for these ROIs are plotted in Fig. 1e and 1h, respectively. Our analysis of the time-series data (Fig. 1e and 1h) revealed that the tumor region and the tumor-associated blood vessel exhibited a diminished hemodynamic response to carbogen inhalation compared to the non-tumor background region and the normal blood vessel. This suggests that the presence of the tumor alters the local hemodynamic response, reducing sensitivity to vasodilatory stimuli like carbogen. Despite the BLEscope's limitation of capturing images at 1 fps, we were able to visualize the hemodynamic changes due to fluorescently tagged GL261 tumor cells in a preclinical brain cancer model. Additionally, the BLEscope consumed an average current of ~66 mA in "streaming" mode, allowing for ~1.5 hours of continuous imaging at 1 fps with a 100 mAh battery. Future enhancements, such as incorporating an on-board electrowetting lens for automatic focusing and a LED driver for wireless LED control and synchronization, could greatly enhance the potential of a miniaturized BLEscope for wireless functional imaging. Such advancements could significantly contribute to our understanding of brain function.

Acknowledgements (Optional): This work was supported by NIH grant nos. 2R01CA196701, 5R01CA237597-04, and 5R01DE027957-05.