Raman spectroscopy is a rapid nondestructive technique capable of assaying chemicals in human artery tissues and characterizing atherosclerotic plaques in vivo, but clinical applications through optical fiber-based catheters have been hindered by large background signals generated within the fibers. Previous workers realized that this background was reduced significantly in the high wavenumber (HWVN) Raman region (~2400 cm−1 to ~3800 cm−1), and with proper selection of optical fibers, one could collect quality Raman spectra remotely via a single optical fiber with no additional filters or optics. This study compared lipid concentrations in coronary artery tissue that were determined with chemical assay techniques to those estimated from HWVN Raman spectra collected through a single optical fiber. The standard error of predictions between the Raman and chemical assay techniques were small for cholesterol and esterified cholesterols, at 1.2% and 2.7%, respectively.
Despite the growing number of biomedical and micromachining applications enabled by ultra-short pulse lasers in
laboratory environments, realworld applications remain scarce due to the lack of robust, affordable and flexible laser
sources with meaningful energy and average power specifications. In this presentation, we will describe a laser source
developed at the eye-safe wavelength of 1552.5 nm around a software architecture that enables complete autonomous
control of the system, fast warm-up and flexible operation. Our current desktop ultra-short pulse laser system offers
specifications (1-5 microJ at 500 kHz, 800 fs-3 ps pulse width, variable repetition rate from 1 Hz to 500 kHz) that are
meaningful for many applications ranging from medical to micromachining. We will also present an overview of
applications that benefit from the range of parameters provided by our desktop platform. Finally, we will present a novel
scalable approach for fiber delivery of high peak power pulses using a hollow core Bragg fiber recently developed for
the first time by Raydiance and the Massachusetts Institute of Technology for operation around 1550 nm. We will
demonstrate that this fiber supports single mode operation for core sizes up to 100 micron, low dispersion and low
nonlinearities with acceptable losses. This fiber is a good candidate for flexible delivery of ultra-short laser pulses in
applications such as minimally accessible surgery or remote detection.
We placed silica optical fibers into hydrogen environments of up to 30,000 psi (2,041 atm) and characterized their photosensitivity and UV-induced optical loss. We detail the relationship between the hydrogen content in the fiber and the UV-induced index change for a delivered radiation dose. We also observed high UV-induced optical loss (greater than 30 dB/cm) in these fibers and studied the cause of this loss.
In vitro studies have shown that normal and abnormal human coronary artery segments can be differentiated on the basis of their Raman spectra. A compact near infrared Raman spectroscopy system has been constructed for in vivo measurement of the biochemical composition of human coronary artery. A 500 mW air-cooled diode laser generates 830 nm excitation light which is delivered via a fiber optic probe to the arterial wall. Scattered light is collected by the same optical probe and delivered to a f/1.8 imaging spectrograph, which disperses the light onto a liquid-nitrogen-cooled deep-depletion CCD detector. A spectral model has been developed to quantify the protein, lipid and calcium mineral content in coronary artery wall. Raman spectra with sufficiently high S/N for extracting biochemical information can be collected in less than one second. In vivo studies during open heart surgery are currently being conducted which will establish near infrared Raman techniques as a real- time diagnostic tool.
Near infrared (NIR) Raman spectroscopy provides a powerful method for quantitative histochemistry of human tissue and disease diagnosis. The feasibility and potential of this technique for in situ histochemical analysis of human coronary artery has been demonstrated and presented in other reports from our laboratory. In this work, we review recent results obtained with the NIR Raman spectroscopy on a variety of tissue types studied at the MIT Laser Biomedical Research Center. We have collected NIR Raman spectra from colon, bladder, breast, and carotid artery. For colon, bladder and breast, consistent differences between carcinoma and normal tissue spectra were observed. For colon and bladder, the spectral differences appear to be due to an increased content of nucleic acid in carcinomas, while the spectral changes in malignant breast tissue are associated with an increase of protein content. Spectra from carotid artery have similar features as those from aorta and coronary arteries. We also show some preliminary results obtained with a NIR Raman microspectroscopy setup with 20 micron lateral resolution. The biochemical distributions for normal and diseased regions on the same tissue samples are observed. The potential of using this NIR Raman spectroscopy for detection and characterization of carcinoma and atherosclerosis, is discussed.
We have developed a method to analyze quantitatively the biochemical composition of human coronary artery in situ using near infrared Raman spectroscopy. Human coronary arteries were obtained from explanted hearts after heart transplantation. Samples of normal intima/media, adventitia, non-calcified and calcified plaque were illuminated with 830 nm light from a CW Ti:Sapphire laser. The Raman scattered light was collected and coupled into a 1/4 meter spectrometer that dispersed the light onto a liquid nitrogen cooled, deep-depletion CCD detector. Raman spectra with sufficiently high S/N for extracting biochemical information could be collected in under one second. The spectra were analyzed using a recently developed model to quantitate the relative weight fractions of cholesterol, cholesterol esters, triacylglycerol, phospholipids, protein, and calcium salts. After spectral examination, the artery samples were biochemically assayed to determine the total lipid weight and the amount of the major lipid categories as a percentage of the total lipid content. The results of the lipid biochemical assay and the Raman spectral model compare favorably, indicating that relative lipid weights can be accurately determined in situ. Protein and calcium salts assays are underway. This in situ biochemical information may be useful in diagnosing atherosclerosis and studying disease progression.
We are developing a method to quantitatively analyze the biochemical composition of human coronary artery in situ using near-infrared Raman spectroscopy. Samples of normal artery (intima/media and adventitia) and noncalcified and calcified plaque from coronary arteries, obtained from explanted recipient hearts during heart transplantation, were illuminated with 830 nm excitation light from a CW Ti:sapphire laser. Raman spectra were collected in seconds using a spectrograph and a cooled, deep-depletion CCD detector, and calibration and background corrections were made. Artery samples in different stages of atherosclerosis exhibited distinct spectral features, providing clear histochemical indicators for characterizing the type and extent of the lesion. Spectra were analyzed by means of a Raman biochemical assay model to determine the relative weight fractions of cholesterols, triacylglycerol, proteins and calcium minerals. Such information, when obtained clinically, promises to be useful in diagnosing and studying human atherosclerosis, its progression and response to drug therapy.
Raman spectroscopy can provide quantitative molecular information about the biochemical composition of human tissues exhibiting various stages of disease. Fluorescence interference is ubiquitous in Raman spectra of biological samples excited with visible light. However, it can be avoided by using near-infrared (NIR) or ultraviolet (UV) excitation. We are exploring the potential of these methods for detecting precancerous/cancerous changes in human tissues. The NIR studies use 830 nm excitation from a Ti:sapphire laser. Raman signals are collected by an imaging spectrograph/deep-depletion CCD detection system. High quality tissue spectra can be obtained in a few seconds or less. The UV resonance Raman studies employ wavelengths below 300 nm for selective excitation of nucleic acids, proteins and lipids. Excitation is provided by a frequency tripled/quadrupled mode-locked Ti:sapphire laser, and Raman light is collected by a one meter spectrograph/UV-enhanced CCD detector. The two systems can be coupled to appropriate microscopes for extracting morphological and biochemical information at the cellular level, which is important for understanding the origin of the Raman spectra of bulk tissue. The results of the initial studies for cancer detection in various human tissues are reported here.