Needle-probe system for the measurement of tissue refractive index
Needle-based devices, which are in wide clinical use for needle biopsy procedures, may be augmented by suitable optical techniques for the localization and diagnosis of diseased tissue. Tissue refractive index is one optical contrast mechanism with diagnostic potential. In the case of mammary tissue, for example, recent research indicates that refractive index variations between tissue types may be useful for the identification of cancerous tissue. While many coherence-based forward-sensing devices have been developed to detect scattering changes, none have demonstrated refractive index measurement capabilities. We present a novel needle-based device that is capable of simultaneously measuring refractive index and scattering. Coupled to the sample arm of an optical coherence tomography system, the needle device detects the scattering response and optical pathlength through tissue residing in a fixed-width channel. Near-infrared measurements of tissues and materials with known optical properties using a prototype device will be presented. This work demonstrates the feasibility of integrated in vivo measurement of refractive index and scattering in conjunction with existing clinical needle-based devices.
Nature Physics: Interferometric synthetic aperture microscopy
State-of-the-art methods in high-resolution three-dimensional optical microscopy require that the focus be scanned through the entire region of interest. However, an analysis of the physics of the light-sample interaction reveals that the Fourier-space coverage is independent of depth. Here we show that, by solving the inverse scattering problem for interference microscopy, computed reconstruction yields volumes with a resolution in all planes that is equivalent to the resolution achieved only at the focal plane for conventional high-resolution microscopy. In short, the entire illuminated volume has spatially invariant resolution, thus eliminating the compromise between resolution and depth of field. We describe and demonstrate a novel computational image-formation technique called interferometric synthetic aperture microscopy (ISAM). ISAM has the potential to broadly impact real-time three-dimensional microscopy and analysis in the fields of cell and tumour biology, as well as in clinical diagnosis where imaging is preferable to biopsy.
Three-Dimensional Visualization of Lymph Node Morphology Using OCT
We report the first demonstration of OCT for the three-dimensional visualization of lymph node morphology and microarchitecture from human and carcinogen-induced rat mammary tumor specimens.
Optical biopsy of lymph node morphology using optical coherence tomography
Optical diagnostic imaging techniques are increasingly being used in the clinical environment, allowing for improved screening and diagnosis while minimizing the number of invasive procedures. Diffuse optical tomography, for example, is capable of whole-breast imaging and is being developed as an alternative to traditional X-ray mammography. While this may eventually be a very effective screening method, other optical techniques are better suited for imaging on the cellular and molecular scale. Optical Coherence Tomography (OCT), for instance, is capable of high-resolution cross-sectional imaging of tissue morphology. In a manner analogous to ultrasound imaging except using optics, pulses of near-infrared light are sent into the tissue while coherence-gated reflections are measured interferometrically to form a cross-sectional image of tissue. In this paper we apply OCT techniques for the high-resolution three-dimensional visualization of lymph node morphology. We present the first reported OCT images showing detailed morphological structure and corresponding histological features of lymph nodes from a carcinogen-induced rat mammary tumor model, as well as from a human lymph node containing late stage metastatic disease. The results illustrate the potential for OCT to visualize detailed lymph node structures on the scale of micrometastases and the potential for the detection of metastatic nodal disease intraoperatively.