CAREER: Wireless Optical Sensors for High Resolution Imaging of Biological Structures

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Near infrared (NIR) spectroscopy is emerging as a promising non-invasive imaging tool for fundamental studies of biological processes and structures, offering greater biochemical specificity, high temporal resolution, potential for concurrent intracellular and intravascular event measurement, and portability. Time-resolved NIR techniques allow explicit separation of optical absorption and scattering parameters related to biological structures, such as tissue, and (in theory) provide functional and metabolic information based on spectral and spatial imaging information. However, the visibility of superficial and deep structures remains fairly poor due to the lack of imaging sensor technology combining high-resolution spatial mapping, fast pixel response time, and broad spectral response. The goal of this CAREER program is to develop a new class of highly integrated wireless imaging sensors, combining photonic devices, broadband analog/RF circuits, and free-space optical communication to improve the spatial resolution of time-resolved NIR images; and establish an interdisciplinary educational environment for engineers. The long-term goal is to further expand the field of biological imaging by developing true mixed-mode integrated systems combining microwave, acoustic, photonic, and nanoscale electronic circuits for concurrent measurement of multiple imaging modalities to increase the visibility of sub-millimeter structures.This CAREER program reaches beyond current state-of-the-art to develop imaging sensors incorporating arrayed pixels for phase-sensitive optical detection at high frequencies. Motivated by the need to detect low level optical signals at high-speed, dielectrically-isolated avalanche photodiode structures implemented in digital CMOS technology and integrated at pixel-level with RF analog signal processing circuits will be explored. New approaches to low-noise front-end amplifier design will be explored to enable detection of RF-modulated optical signals at incident power levels below 1nW using chopper stabilization techniques and resonant circuit topologies. Process-variant tolerant (PVT) circuit topologies will be employed to ensure amplitude and phase accuracy within 0.1%. A two-dimensional sensor readout architecture incorporating pixel/column-level data converters and high-speed serial data readout will be developed. As a result of detailed environmental noise (substrate, power/ground supply) modeling and test structure measurement, a design methodology for arrayed high-frequency imaging sensors will be provided to design engineers. Pixel-level/column-level ADC architectures will be explored for optimal performance in terms of pixel form factor, power, and resolution. For the first time, wireless access based on optical transmission will be explored to enable remote data transfer from a wearable NIR imaging device.This synergistic research and education program will have significant broader impacts on in vivo characterization of macroscopic optical properties of multiply scattering tissues and enable development of new theories relating to biophysical mechanisms and correlations between signals generated by complementary imaging modalities (e.g. MRI). The portability of NIR imaging instrumentation is a key merit of the technology, and therefore, this research develops a wearable imaging system with integrated wireless capabilities enabling signal acquisition during movement. Interactive workshops with scientists and students will be organized to guide sensor development. The education program is tightly coupled to the research activities, including new undergraduate and graduate courses that vertically integrate topics from optical/electronic devices to circuits/systems and applications. A cross-campus undergraduate course on technical writing and communication will be developed in collaboration with Howard University to teach strategies in formulating and communicating technical ideas and engage students from under-represented groups in the CAREER program. The PI is committed to broadening opportunities to all engineers, including under-represented students. Workshops on graduate school admission, funding, and academic career opportunities will be organized during visits to minority serving institutions across the country. A complete wireless sensor module will be made available to researchers for experimental testing. Project outcomes and results, including educational materials, will be available to the public through a website (www.ece.tufts.edu/~vjoyner).