Large-scale transparent photoacoustic cranial window for long-term whole-brain cortical imaging

Ultrasound-sensing cranial windows can provide dual functions of transparent optical imaging windows and photoacoustic signal detection, which can simplify the photoacoustic microscopic brain imaging system. However, the acoustic impedance matching or field of view of the available cranial window materials cannot meet the requirements for high-sensitivity photoacoustic imaging of the whole cerebral cortex. Transparent ITO-coated PVDF has high optical transparency and good piezoelectric properties and can be designed as a wide-bandwidth and highly-sensitive transparent transducer. In addition, PVDF has excellent biocompatibility and mechanical properties and can match the curved structure of the skull to design a large-scale ultrasound-sensing cranial window. This Letter proposes a photoacoustic cranial window strategy based on a PVDF-ITO transparent transducer to achieve long-term monitoring of hemodynamics in the whole cerebral cortex. Large-scale photoacoustic cranial windows can provide centimeter-scale transparent imaging windows, allowing three-dimensional photoacoustic imaging. In vivo experiments showed that imaging has a good signal-to-noise ratio both when the skull is removed and when the skull is intact. Moreover, the proposed photoacoustic cranial window is also suitable for laser speckle blood flow imaging. In the future, this method, combined with brain modulation technology, is expected to provide a reliable way to obtain and intervene in brain function information.