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

近红外（NIR）光谱正在成为一种有前途的非侵入性成像工具，用于生物过程和结构的基础研究，提供更高的生化特异性，高时间分辨率，细胞内和血管内事件同步测量的潜力，以及便携性。时间分辨近红外技术允许明确分离与生物结构（如组织）相关的光吸收和散射参数，并且（理论上）提供基于光谱和空间成像信息的功能和代谢信息。然而，由于缺乏结合高分辨率空间映射、快速像素响应时间和广谱响应的成像传感器技术，浅层和深层结构的可见性仍然相当差。CAREER计划的目标是开发一种新型的高度集成无线成像传感器，结合光子器件、宽带模拟/RF电路和自由空间光通信，以提高时间分辨近红外图像的空间分辨率；建立跨学科的工程师教育环境。长期目标是通过开发真正的混合模式集成系统，结合微波、声学、光子和纳米级电子电路，进一步扩展生物成像领域，用于并发测量多种成像模式，以增加亚毫米结构的可见性。这个CAREER项目超越了目前最先进的技术，开发了包含阵列像素的成像传感器，用于高频相敏光学检测。由于需要在高速下检测低电平光信号，将探索采用数字CMOS技术实现的介电隔离雪崩光电二极管结构，并在像素级与RF模拟信号处理电路集成。将探索低噪声前端放大器设计的新方法，利用斩波稳定技术和谐振电路拓扑结构，在低于1nW的入射功率水平下检测rf调制光信号。过程可变容限（PVT）电路拓扑结构将用于确保幅度和相位精度在0.1%以内。结合像素/列级数据转换器和高速串行数据读出的二维传感器读出架构将被开发。作为详细的环境噪声（基片、电源/地电源）建模和测试结构测量的结果，阵列高频成像传感器的设计方法将提供给设计工程师。将探讨像素级/列级ADC架构在像素外形系数、功耗和分辨率方面的最佳性能。将首次探索基于光传输的无线接入，以实现可穿戴近红外成像设备的远程数据传输。这一协同研究和教育计划将对多重散射组织的宏观光学特性的体内表征产生重大而广泛的影响，并使与生物物理机制和互补成像模式（如MRI）产生的信号之间的相关性相关的新理论得以发展。近红外成像仪器的便携性是该技术的一个关键优点，因此，本研究开发了一种具有集成无线功能的可穿戴成像系统，可以在运动过程中采集信号。将组织与科学家和学生的互动研讨会来指导传感器的开发。教育计划与研究活动紧密结合，包括新的本科和研究生课程，垂直整合从光学/电子设备到电路/系统和应用的主题。一门关于技术写作和交流的跨校园本科课程将与霍华德大学合作开发，教授制定和交流技术理念的策略，并吸引来自职业项目中代表性不足群体的学生。PI致力于为所有工程师扩大机会，包括代表性不足的学生。在访问全国少数民族服务机构期间，将组织有关研究生入学、资助和学术就业机会的研讨会。一个完整的无线传感器模块将提供给研究人员进行实验测试。项目成果和成果，包括教育材料，将通过网站（www.ece.tufts.edu/~vjoyner）向公众提供。

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).