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

近红外(NIR)光谱学是一种很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，具有更强的生化特异度、高时间分辨率、同时进行细胞内和血管内事件测量的潜力以及便携性。时间分辨近红外技术允许与生物结构(如组织)相关的光学吸收和散射参数的显式分离，并且(理论上)基于光谱和空间成像信息提供功能和代谢信息。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宽光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。这一职业计划的目标是开发新型高度集成的无线成像传感器，将光子器件、宽带模拟/射频电路和自由空间光通信相结合，以提高时间分辨率近红外图像的空间分辨率；并为工程师建立跨学科的教育环境。我们的长期目标是通过开发结合微波、声学、光子和纳米级电子电路的真正混合模式集成系统来进一步扩展生物成像领域，以同时测量多种成像模式，以提高亚毫米结构的可见度。这一职业计划超越了当前的最先进水平，开发包含阵列像素的成像传感器，用于高频相敏光学检测。出于高速检测低电平光信号的需要，我们将探索以数字CMOS技术实现并与RF模拟信号处理电路在像素级集成的介质隔离雪崩光电二极管结构。将探索低噪声前端放大器设计的新方法，以便能够使用斩波稳定技术和谐振电路拓扑检测入射功率水平低于1nW的RF调制光信号。将采用工艺可变容错(PVT)电路拓扑，以确保幅度和相位精度在0.1%以内。将开发一种结合了像素/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。作为详细的环境噪声(基板、电源/地面电源)建模和测试结构测量的结果，将为设计工程师提供阵列高频成像传感器的设计方法。将探索像素级/列级ADC架构，以在像素形状因数、功率和分辨率方面实现最佳性能。将首次探索基于光传输的无线接入，以实现从可穿戴的近红外成像设备进行远程数据传输。这一协同研究和教育计划将对体内表征多次散射组织的宏观光学性质产生重大而广泛的影响，并使有关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，使其能够在运动时获取信号。将组织与科学家和学生的互动研讨会，以指导传感器的开发。教育计划与研究活动紧密相连，包括新的本科生和研究生课程，这些课程垂直整合从光学/电子设备到电路/系统和应用的主题。将与霍华德大学合作开发一门关于技术写作和交流的跨校园本科课程，教授制定和交流技术想法的策略，并吸引来自代表性不足群体的学生参与职业计划。国际工程师协会致力于扩大所有工程师的机会，包括代表人数不足的学生。在访问全国各地的少数民族服务机构期间，将组织关于研究生入学、资金和学术职业机会的研讨会。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)向公众公布。

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).