Hemodynamic imaging using an implantable self-reset image sensor

In this study, we examine hemodynamic imaging by using an implantable CMOS image sensor with self-reset pixels. The self-reset function prevents saturation and allows imaging under a high light intensity condition. Thus, effective signal-to-noise ratio (SNR) over the photon shot noise limit in a normal pixel can be achieved. We designed a prototype using a 0.35-pm process. The self-reset function is implemented using a Schmitt trigger inverter driven by a low voltage. A pixel that is relatively small (15 × 15 pm) and consumes low power is applied to an implantable image sensor. An effective SNR of the sensor is approximately 1.5 dB higher than the photon shot noise limit. We demonstrate hemodynamic imaging of a mouse brain by implanting the proposed sensor with a frame synchronized two-color illumination.