Fourier-domain full-field optical coherence tomography using imaging fibre bundles

断层摄影术是一个术语，用来指产生结构的三维地图的成像技术。通常，它指的是产生人体内器官和组织结构图像的医学成像技术，通常目的是定位肿瘤或组织的其他畸形。产生深埋构造地图的层析成像技术包括磁共振成像、正电子发射层析成像、超声波和X射线，但这些技术都无法分辨尺寸小于100微米(大致相当于人类头发的直径)的细节。光学相干层析成像是一种允许以比其他任何可用的方法更高的分辨率来成像地下结构的技术。在最高分辨率的系统中，可以看到直径几微米的单个细胞。OCT使用可见光或红外光，这些光被组织强烈散射，不会穿透到身体太远。信息只能从大约2毫米深的表层获得。虽然这最初看起来是一种劣势，但使用OCT获得的信息非常有用。大多数癌症开始于身体的表面或上皮组织。这些组织包括胃肠道的皮肤和内表面。通过使用柔性光纤内窥镜，OCT探头可以接触到内表面和皮肤，OCT探头可以检测到指示癌前状态的微小组织变化。目前正在开发的大多数OCT探头使用一根光纤将光传输到测量区域。透镜可以将组织中的直径聚焦到几微米。在不同组织类型之间的边界，光被反射回探头，并重新耦合到光纤中，在那里它与参考光束混合在检测器上。如果两束光束行进的路径匹配，并且来自组织的反射很强，探测器就能看到大信号。因此，通过扫描参考光束路径长度，组织内的边界被检测为对应于各种深度的信号脉冲串。如果需要3D信息，则必须在样品表面的许多位置进行测量。这通常是通过用一个移动的小镜子快速扫描光束来实现的。然而，构建用于体内的扫描系统是困难的，因为这些系统必须被微型化以适合内窥镜，并且必须向内窥镜尖端输送电力以驱动扫描仪。我们提出了一种新的技术，它使用一种称为相干纤维束的组件。它可以有几米长，由数千根纤维组成，排列成规则的阵列，直径几毫米。聚焦到一端的光图案原封不动地传输到另一端。这使得每个单独的纤维都可以作为一个单独的OCT系统在样品表面的一系列位置上使用，并使用数码相机来查看图像。因为纤维束非常灵活，所以它可以在内窥镜下使用。现在只需要在身体外部的系统部分进行机械扫描，降低了探测的复杂性。我们打算研究基于光纤束构建OCT系统的技术。光源发出的光将被用来照亮一排光纤或快速连续地照射每一根光纤，并将比较使用这两种技术所获得的性能。存在从全样本深度提取同时信息的处理技术。使用宽谱光源，并使用衍射光栅分离由该宽谱内的许多窄的、离散的波长带产生的干涉条纹频率。或者，通过快速扫描来自激光的窄带光在较宽的光谱范围内，可以在时间上分离来自每个波长的信息。数学处理提取随深度变化的构造数据。

Tomography is a term used to refer to imaging techniques that produce a 3-dimensional map of a structure. Typically, it refers to medical imaging techniques resulting in images of organs and tissue structures within the human body, often with the aim of locating tumours or other malformations of the tissue. Tomographic techniques that produce maps of deeply buried structures include magnetic resonance imaging, positron emission tomography, ultrasound and X-ray, but none of these can resolve detail with dimensions less than about 100 micrometres (roughly the same diameter as a human hair).Optical coherence tomography OCT is a technique that allows sub-surface structure to be imaged with much higher resolution than any of the other available methods. In the highest resolution systems, individual cells, a few micrometres in diameter, can be seen. OCT uses visible or infra-red light, which is strongly scattered by tissue, and does not penetrate far into the body. Information can only be obtained from a surface layer about 2 mm deep. Although this appears initially to be a disadvantage, the information obtained using OCT is extremely useful. A majority of cancers begin in the surface, or epithelial, tissues of the body. These include the skin and internal surfaces of the gastro-intestinal tract. By using flexible optical fibre endoscopes internal surfaces, as well as the skin, are accessible to OCT probes, which can detect minor tissue changes indicative of pre-cancerous conditions.Most OCT probes currently being developed carry light to the measurement region using a single optical fibre. A lens achieves focusing to a diameter of a few micrometres in the tissue. At boundaries between different tissue types, light is reflected back towards the probe, and re-coupled into the optical fibre, from where it mixes on a detector with a reference beam. If the paths travelled by the two beams match, and the reflection from tissue is strong, a large signal is seen by the detector. Thus by scanning the reference beam path length, boundaries within the tissue are detected as signal bursts corresponding to various depths.If 3D information is required, measurements must be made at many positions across the sample surface. This is often achieved by scanning the beam rapidly with a small moving mirror. However, it is difficult to construct scanning systems for use inside the body, as these must be miniaturised to fit inside an endoscope, and electrical power must be delivered to the endoscope tip to drive the scanner. We propose a new technique that uses a component called a coherent fibre bundle. This can be several metres long, comprising many thousand fibres arranged in a regular array a few millimetres in diameter. A pattern of light focused onto one end is transmitted unchanged to the other end. This allows the use of each individual fibre as a separate OCT system at an array of positions across the sample surface, with a digital camera used to view the image. Because the fibre bundle is extremely flexible, it can be used endoscopically. Mechanical scanning is now required only in the part of the system external to the body, reducing the complexity of the probe.We intend to investigate techniques for constructing OCT systems based on optical fibre bundles. Light from the source will be used to illuminate either a row of fibres, or each fibre in rapid succession, and the performance achieved using the two techniques will be compared. Processing techniques exist to extract simultaneous information from the full sample depth. A broad spectrum source is used, and a diffraction grating separates the interference fringe frequencies produced by many narrow, discrete wavelength bands within this broad spectrum. Alternatively, the information from each wavelength can be separated in time, by rapidly sweeping narrowband light from a laser across a broad spectral range. Mathematical processing extracts the depth-dependent structural data.