OCT for 2D and 3D velocity measurement in micro-fluidic flows

用于微流体流动中 2D 和 3D 速度测量的 OCT

基本信息

批准号：
EP/L014637/1
负责人：
Ralph Tatam
金额：
$ 60.44万
依托单位：
CRANFIELD UNIVERSITY
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FL014637%2F1
关键词：
OCT 2D 3D velocity measurement

项目摘要

This project aims to use optical coherence tomography (OCT) for velocity measurement in sub-millimetre flow channels. A major application for flow-measurement in this regime is in the design and assessment of microfluidic systems, which exemplify an increasing trend for miniaturization pervading many aspects of technology. In fluid-flow engineering, miniaturised instruments offer a reduced laboratory footprint, reduced requirements for energy and expensive or hazardous reagents and the ability to acquire data simultaneously from many systems within a single instrument. Microfluidics is a rapidly-growing field with benefits in healthcare (rapid, lab-on-a-chip, techniques for, e.g. immunoassays and biological phase separation), energy technology (membrane fuel cells) and high-throughput, portable systems for chemical analysis.Currently, the main technique for investigation of micro-fluidic flows is micro particle image velocimetry, which uses high-resolution photography to determine positions of 'seed' particles within a plane illuminated by a thin sheet of laser light. Two images, acquired in rapid succession, allow the distance moved by particles between frames to be calculated, yielding velocity components in the image plane.In very small ducts, a sufficiently thin light sheet cannot be generated. Illumination of a small volume, through a microscope arrangement, is usual, and the measurement plane thickness is defined using optics that exclude light from regions outside the focal plane. For the smallest channels, seed particles must be smaller than the illumination wavelength (approx. 1 micron). This causes difficulties, because light scattering decreases rapidly as particle diameter drops, and can fall so low that the signal-to-noise (SNR) is inadequate for acceptable images. Fluorescent particles and intensified cameras are then required, with filtering to separate the fluorescent signal from the background.OCT is used mainly in medical environments, for detailed biological tissue imaging. However, its high spatial resolution, combined with particle-tracking techniques carried over from PIV, offer the possibility of 2- or 3-component velocity measurement in 2-D or 3-D regions, for flow velocities experienced in micro-fluidic systems. Micro-fluidic flow is not well described by classical flow theory, and experimental techniques are needed to validate models in designing micro-fluidic devices such as mixers, heat exchangers and fuel cells. It is important, for example, to eliminate 'dead zones' in the flow, and to understand the fluid motion in curved or bifurcated micro-channels. With appropriate processing, OCT can acquire images in three perpendicular planes with access from only one direction; a big advantage in micro-fluidics, when access is necessarily limited. High-resolution structural imaging of the channels is possible, alongside velocity measurement, which will help in detecting small variations or defects in wall structure that can have a large effect on flow.OCT offers excellent optical sectioning capability, the image plane thickness being a few micrometres. Strong rejection of scattered light from outside the measurement region eliminates the need for fluorescent particles and eases near-wall measurements. The SNR of OCT is such that signals can be obtained from depths of hundreds of micrometres within turbid biological tissue, which suggests that flow measurements will be possible at higher seeding densities, or greater depths, than for comparable implementations of PIV. Typically, update rates for 2D OCT images are a few tens of Hz. Although micro-fluidic velocities are generally low, the update interval limits measurable velocities to a few mm/s. A shorter interval would be very advantageous in raising this limit. Multiplexing of images acquired from multiple illumination beams is proposed here, to reduce the inter-image interval and allow multiple image planes to be defined simultaneously

该项目旨在利用光学相干断层扫描 (OCT) 测量亚毫米流道中的速度。这种情况下流量测量的一个主要应用是微流体系统的设计和评估，这体现了技术许多方面的小型化日益增长的趋势。在流体流动工程中，小型化仪器可以减少实验室占地面积，减少对能源和昂贵或危险试剂的需求，并且能够在单个仪器内同时从多个系统获取数据。微流体是一个快速发展的领域，在医疗保健（快速、芯片实验室、免疫测定和生物相分离等技术）、能源技术（膜燃料电池）和用于化学分析的高通量便携式系统方面具有优势目前，研究微流体流动的主要技术是微颗粒图像测速技术，它使用高分辨率摄影来确定“种子”颗粒在薄薄的薄膜照射的平面内的位置。激光。快速连续获取的两个图像可以计算帧之间粒子移动的距离，从而产生图像平面中的速度分量。在非常小的管道中，无法生成足够薄的光片。通常通过显微镜布置对小体积进行照明，并且使用排除来自焦平面之外区域的光的光学器件来定义测量平面厚度。对于最小的通道，种子颗粒必须小于照明波长（约 1 微米）。这会带来困难，因为光散射随着颗粒直径的减小而迅速减小，并且可能会降得很低，以致信噪比 (SNR) 不足以获得可接受的图像。然后需要荧光颗粒和增强相机，并通过过滤将荧光信号与背景分离。OCT 主要用于医疗环境中，用于详细的生物组织成像。然而，其高空间分辨率与 PIV 继承的粒子跟踪技术相结合，为微流体系统中经历的流速提供了在 2D 或 3D 区域中进行 2 或 3 分量速度测量的可能性。经典流动理论并不能很好地描述微流体流动，需要实验技术来验证混合器、热交换器和燃料电池等微流体设备设计中的模型。例如，消除流动中的“死区”以及了解弯曲或分叉微通道中的流体运动非常重要。通过适当的处理，OCT 可以仅从一个方向获取三个垂直平面的图像；当访问必然受到限制时，这是微流体的一大优势。可以对通道进行高分辨率结构成像以及速度测量，这将有助于检测对流动产生重大影响的壁结构中的微小变化或缺陷。OCT 提供出色的光学切片能力，图像平面厚度仅为几英寸微米。强烈抑制来自测量区域外部的散射光，无需荧光颗粒，并简化了近壁测量。 OCT 的信噪比使得可以从浑浊生物组织内数百微米的深度获得信号，这表明与 PIV 的类似实施相比，可以在更高的接种密度或更大的深度下进行流量测量。通常，2D OCT 图像的更新率为几十赫兹。尽管微流体速度通常较低，但更新间隔将可测量的速度限制为几毫米/秒。较短的间隔对于提高此限制非常有利。这里提出了从多个照明光束获取的图像的复用，以减少图像间间隔并允许同时定义多个图像平面