We present the first fully wireless implantable imager for distributed long-term high-resolution imaging in the body. The imager consists of two mm-sized piezoelectric transducers (piezos) for ultrasound (US) wireless power and data communication; a capacitive micromachined ultrasound transducer (CMUT) array; and a 65 nm CMOS IC, which includes power harvesting, a high voltage charge pump, a low-power 16-channel front-end with up to $125\ \text{dB}\Omega$ gain and 13 MHz bandwidth, a memory system to store the digitized data at 8.6 Gbps, and a 120 kbps US transmitter. The on-chip realtime calibration, averaging, and interference mitigation help achieve high sensitivity. The system is characterized through a large 6 cm depth of acoustic tissue phantom and has an average power consumption of 1.5 mW at 1 fps.