Showing papers by "Xingde Li published in 2000"

Spectroscopic optical coherence tomography.

Abstract: Spectroscopic optical coherence tomography (OCT), an extension of conventional OCT, is demonstrated for performing cross-sectional tomographic and spectroscopic imaging. Information on the spectral content of backscattered light is obtained by detection and processing of the interferometric OCT signal. This method allows the spectrum of backscattered light to be measured over the entire available optical bandwidth simultaneously in a single measurement. Specific spectral features can be extracted by use of digital signal processing without changing the measurement apparatus. An ultrabroadband femtosecond Ti:Al2O3 laser was used to achieve spectroscopic imaging over the wavelength range from 650 to 1000 nm in a simple model as well as in vivo in the Xenopus laevis (African frog) tadpole. Multidimensional spectroscopic data are displayed by use of a novel hue-saturation false-color mapping.

Fiber optic needle probes for optical coherence tomography imaging

Abstract: A fiber optic needle probe for measuring or imaging the internal structure of a specimen includes a needle (5) defining a bore, an optical fiber (11) substantially positioned within the bore, and a beam director (6) in optical communication with the optical fiber (11). At least a portion of the wall of the needle (5) is capable of transmitting light. The beam director (6) directs light from the optical fiber (11) to an internal structure being imaged and receives light from the structure through a transparent portion (7) of the wall. An actuating device (30) causes motion of any, or all of, the needle (5), optical fiber (11), and beam director (6) to scan the internal structure of the specimen. The fiber optic needle probe allows imaging inside a solid tissue or organ without intraluminal insertion. When used in conjunction with an OCT imaging system, the fiber optic needle probe enables tomographic imaging of the microstructure of internal organs and tissues which were previously impossible to image in a living subject.

Imaging needle for optical coherence tomography

Abstract: We describe a miniature optical coherence tomography (OCT) imaging needle that can be inserted into solid tissues and organs to permit interstitial imaging of their internal microstructures with micrometer scale resolution and minimal trauma. A novel rotational coupler with a glass capillary tube is also presented that couples light from a rotating single-mode fiber to a stationary one. A prototype needle with a 27-gauge ∼410‐µm outer diameter has been developed and is demonstrated for in vivo imaging. The OCT needle can be integrated with standard excisional biopsy devices and used for OCT-guided biopsy.

Optical coherence tomography: advanced technology for the endoscopic imaging of Barrett's esophagus.

Abstract: BACKGROUND AND STUDY AIMS Endoscopic optical coherence tomography (OCT) is an emerging medical technology capable of generating high-resolution cross-sectional imaging of tissue microstructure in situ and in real time. We assess the use and feasibility of OCT for real-time screening and diagnosis of Barrett's esophagus, and also review state-of-the-art OCT technology for endoscopic imaging. MATERIALS AND METHODS OCT imaging was performed as an adjunct to endoscopic imaging of the human esophagus. Real-time OCT (13-microm resolution) was used to perform image-guided evaluation of normal esophagus and Barrett's esophagus. Beam delivery was accomplished with a 1-mm diameter OCT catheter-probe that can be introduced into the accessory channel of a standard endoscope. Different catheter-probe imaging designs which performed linear and radial scanning were assessed. Novel ultrahigh-resolution (1.1-microm resolution) and spectroscopic OCT techniques were used to image in vitro specimens of Barrett's esophagus. RESULTS Endoscopic OCT images revealed distinct layers of normal human esophagus extending from the epithelium to the muscularis propria. In contrast, the presence of gland- and crypt-like morphologies and the absence of layered structures were observed in Barrett's esophagus. All OCT images showed strong correlations with architectural morphology in histological findings. Ultrahigh-resolution OCT techniques achieved 1.1-microm image resolution in in vitro specimens and showed enhanced resolution of architectural features. Spectroscopic OCT identified localized regions of wavelength-dependent optical scattering, enhancing the differentiation of Barrett's esophagus. CONCLUSIONS OCT technology with compact fiberoptic imaging probes can be used as an adjunct to endoscopy for real-time image-guided evaluation of Barrett's esophagus. Linear and radial scan patterns have different advantages and limitations depending upon the application. Ultrahigh-resolution and spectroscopic OCT techniques improve structural tissue recognition and suggest future potential for resolution and contrast enhancements in clinical studies. A new balloon catheter-probe delivery device is proposed for systematic imaging and screening of the esophagus.

Three-dimensional diffuse optical mammography with ultrasound localization in a human subject

Abstract: We describe an approach that combines clinical ultrasound and photon migration techniques to enhance the sensitivity and information content of diffuse optical tomography. Measurements were performed on a postmenopausal woman with a single 1.8 x 0.9 cm malignant ductal carcinoma in situ approximately 7.4 mm beneath the skin surface (UCI IRB protocol 95-563). The ultrasound-derived information about tumor geometry enabled us to segment the breast tissue into tumor and background regions. Optical data was obtained with a multifrequency, multiwavelength hand-held frequency-domain photon migration backscattering probe. The optical properties of the tumor and background were then computed using the ultrasound-derived geometrical constraints. An iterative perturbative approach, using parallel processing, provided quantitative information about scattering and absorption simultaneously with the ability to incorporate and resolve complex boundary conditions and geometries. A three to four fold increase in the tumor absorption coefficient and nearly 50% reduction in scattering coefficient relative to background was observed (lambda = 674, 782, 803, and 849 nm). Calculations of the mean physiological parameters reveal fourfold greater tumor total hemoglobin concentration [Hbtot] than normal breast (67 microM vs 16 microM) and tumor hemoglobin oxygen saturation (SOx) values of 63% (vs 73% and 68% in the region surrounding the tumor and the opposite normal tissue, respectively). Comparison of semi-infinite to heterogeneous models shows superior tumor/background contrast for the latter in both absorption and scattering. Sensitivity studies assessing the impact of tumor size and refractive index assumptions, as well as scan direction, demonstrate modest effects on recovered properties.

Near-field diffraction tomography with diffuse photon density waves.

Abstract: An angular spectrum algorithm is presented for fast, near-field diffraction tomographic imaging with diffuse photon density waves in highly scattering media. A general relation in K space is derived that connects the spatial variations of the optical properties of heterogeneities to the spatial spectra of the measured scattered diffuse photon density waves. The theory is verified experimentally for situations when boundary effects can be neglected. We further describe how to reconstruct absorption and scattering properties simultaneously, and how to incorporate boundary conditions into this angular spectrum algorithm for a turbid medium of finite size (e.g., the slab medium). Limitations and potential improvements of the near-field diffraction tomography are also discussed.

Ultrahigh resolution and spectroscopic optical coherence tomography

Abstract: Using state of the art laser technology, in vivo optical coherence tomography imaging with unprecedented axial resolution of 1 um is achieved, approaching the level of conventional histopathology. With an extension of this technique, extraction of spatially resolved spectroscopic information is enabled to improve image contrast and to obtain functional or biochemical properties of the investigated tissue.

Optical biopsy needle for optical coherence tomography

Abstract: Summary form only given.Optical coherence tomography (OCT) is a recently developed imaging technology, which performs cross sectional imaging in materials and biological tissues by measuring the echo delay and magnitude of backscattered light. The advantages of OCT compared with other existing imaging modalities include its high resolution (1-15 /spl mu/m), fast data acquisition speed, small size and portability and can be combined with birefringence, Doppler, and spectroscopic detection.

In vivo cervical imaging with an integrated Optical Coherence Tomography colposcope

Abstract: We report the first demonstration of integrated Optical Coherence Tomography (OCT) colposcopy for in vivo imaging of cervical neoplasia in patients. The cervix is an excellent model system for investigating imaging modalities and cancer. Integrating OCT with colposcopy, or low mimerical aperture microscopy in general, is a powerful technique since it permits simultaneous en face viewing of structural features while allowing precise registration of the OCT scan plane. Image processing techniques can be used for the analysis and interpretation of the OCT images, enabling statistical interpretation and visualization of image data as well as rapid analysis of large volumes of data.

In vivo ultrahigh-resolution, functional optical coherence tomography

Abstract: Summary form only given.Optical coherence tomography (OCT), has been extensively evaluated as a possible diagnostic tool for high-speed, noninvasive, high-resolution in vivo and in situ imaging in a variety of medical fields. Based on low coherence interferometry, the axial resolution of OCT is limited by the bandwidth of the light source, usually a superluminescent diode, to typically 10-15 /spl mu/m. This is approximately one order of magnitude better than any other conventional technique. However many of the early changes associated with diseases are still below its detection limit. Recent developments of femtosecond Kerr-lens mode-locking of Ti:sapphire solid-state lasers have established a generation of powerful low-coherence light sources for OCT.

In Vivo Intravascular Imaging with OCT: Comparison with Ultrasound

Abstract: A true clinical need exists for a high resolution imaging modality to characterize coronary microstructure. In this study, OCT imaging was performed of the in in vivo rabbit aorta examining clot, atherosclerosis, and intravascular stents. The performance of OCT was superior to that of high frequency ultrasound.

Ultrahigh resolution OCT using continuum generation in an air-silica microstructure optical fiber

Abstract: We demonstrate ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure fiber. Using bandwidths near 1.3 µm, longitudinal resolutions of 4.0 µm are achieved. This is the highest resolution imaging performed in this wavelength range and the first demonstration of this new technology for OCT.

Correlation of polarization-sensitive optical coherence tomography with early osteoarthritis and collagen disorganization

Abstract: Summary form only given. Osteoarthritis (OA) is a major cause of disability and morbidity. However, conventional imaging methods lack the resolution or are impractical for assessing early OA. Recently, optical coherence tomography (OCT) has demonstrated a feasibility for assessing articular cartilage. In vitro studies have demonstrated that OCT can determine cartilage width at a resolution of 20 /spl mu/m in addition to the identification of fibrillations, fibrosis, and breakdown of the subcondral plate. It was also noted that the normal cartilage was polarization sensitive. In the study, two theories are tested. The first hypothesis is that the origin of polarization sensitivity in normal cartilage is organized collagen. The second hypothesis is that the loss of polarization sensitivity, and therefore collagen disorganization, is a sign of osteoarthritis that precedes cartilage thinning.