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Nir spectroscopy lodder- u of kentucky


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Nir spectroscopy lodder- u of kentucky

  1. 1. University of Kentucky Near-Infrared Spectroscopy: Near To or Far From Our Expectations? Steven R. Alford and Robert A. Lodder Advanced Science and Technology Center University of Kentucky Copyright 2002 University of Kentucky
  2. 2. University of Kentucky Near-IR Spectrometry Near-IR spectrometry uses the absorption, emission, or scattering of light in the near-infrared portion of the electromagnetic spectrum (700 - 3000 nm) by atoms or molecules to determine sample composition or characteristics. Editorial slides, VP Watch, February 27, 2002, Volume 2, Issue 8
  3. 3. University of Kentucky Technology is available for spectrometric sensing at very long distances Hyperspectral Imaging and Remote Sensing
  4. 4. University of Kentucky Several techniques are being tested to identify vulnerable plaques before they disrupt. Of these, near-IR and Raman spectrometry seem most relevant to fiber-optic catheters. In 1993 Cassis and Lodder described a near-IR imaging system and parallel vector supercomputer used with a fiber-optic probe to produce chemical maps of the intimal surface of living arteries. Editorial slides, VP Watch, February 27, 2002, Volume 2, Issue 8 Catheter-Based Photonic Technologies for Detection of Vulnerable Plaque
  5. 5. University of Kentucky Romer et al. have demonstrated detection of atherosclerotic plaque using NIR Raman spectroscopy. However, Raman spectroscopy, while offering greater intrinsic spectral resolution, is also more challenging in clinical applications. Naghavi, Soller, and colleagues have used NIR spectroscopy for measuring plaque activity and inflammation parameters such as pH and lactate. Editorial slides, VP Watch, February 27, 2002, Volume 2, Issue 8
  6. 6. University of Kentucky Near-IR predictions of lipid pool, fibrous cap, and macrophage infiltration have been made with good sensitivity and specificity using fiber-optic probes. P. Cherukuri, P. Riggs, I. Darrat, K. Dumstorf, and R. A. Lodder, Near-IR Spectrometry of Structural Components of Susceptible Plaque In Vivo and In Vitro, CPS:analchem/0101001, (Jan) 2001, 1-13. Detection of Lipid Pool, Thin Fibrous Cap, and Inflammatory Cells in Human Aortic Atherosclerotic Plaques by Near-Infrared Spectroscopy; Pedro R. Moreno, Robert A. Lodder, K. Raman Purushothaman, William E. Charash, William N. O’Connor, and James E. Muller ; Circulation 2002 105: 923 - 927; published online before print February 4 2002, 10.1161/hc0802.104291.
  7. 7. University of Kentucky Near-IR Spectrometry Elastic photon scatter Near-IR light penetrates water (and blood) well Decent signal intensities from most organic compounds Sample contact is not really required Better S/N Quantitative calibrations are linear Conventional optics and fibers can be used Lower intrinsic spectral resolution, more band overlap Use collagen I to compare near-IR, IR and Raman spectra
  8. 8. University of Kentucky Peaks are sharp at low energies, and broaden at high energies
  9. 9. University of Kentucky Infrared (IR) Spectrometry elastic photon scatter Good intrinsic spectral resolution Strong signal intensities from most organic compounds Decent S/N IR does not penetrate water (or blood) well Special optics and fibers are required to handle light Attenuated Total Reflectance requires good sample contact Quantitative calibrations are not very linear
  10. 10. University of Kentucky IR peaks of pure compounds are strong and rather well resolved
  11. 11. University of Kentucky Good intrinsic spectral resolution Raman spectrometry can be performed in regions where it penetrates water well Sample contact is not really required NIR and Raman both give more linear calibrations than IR Weak signal intensities from most organic compounds Few photons undergo inelastic scatter, decreasing S/N Technological advances in lasers, holographic notch filters, and detectors make Raman spectroscopy possible. In vitro Raman is a good tool for plaque chemistry Raman Spectrometry Inelastic photon scatter
  12. 12. University of Kentucky Many sharp bands are seen in the Raman spectrum of a pure compound
  13. 13. University of Kentucky Multivariate Calibration Secondary analytical methods like Near-IR, IR, and Raman spectrometry require calibration by primary methods. HPLC, UV-visible spectrometry, capillary electrophoresis and analytical ultracentrifugation are also calibrated by standards (i.e., gravimetry or mass spectrometry serve as the primary analytical methods) Multivariate chemometric methods like PLS, PCA, BEST are required to extract quantitative information from complex samples like atherosclerotic plaques.
  14. 14. University of Kentucky Spectra of pure collagen I and III standards were obtained in vitro through 1 mm of whole blood using a fiber optic probe. Identical integration times were used. Multivariate principal component analysis was used to assess the ability of near-IR, IR, and Raman spectrometry to differentiate between the collagen samples.
  15. 15. University of Kentucky Ten Replicate Spectra of Collagen I = O, Collagen III = + NIR spectra separated well Strong signals scattered back Collagen I and III have distinctive NIR spectra IR spectra did not separate Signals weaker than Near-IR Signals scattered only from blood No light reached the collagens Raman spectra separated somewhat signal level lowest Nd:YAG light reached sample, but noise was high
  16. 16. University of Kentucky NASA JPL MULTIFUNCTIONAL ACTIVE-EXCITATION SPECTRAL ANALYZER (MAESA) The NASA MAESA has a wavelength range from 0.5 to 2.5 micrometers. Selection rules make Near- IR and Raman spectrometry complementary methods. The MAESA includes a laser to illuminate a point or a line on a target. Other optics image the target onto a rectangular focal plane array of InGaAs photodetectors. The light returning from the target is long-wavelength-filtered to remove the laser wavelength component, then focused onto a convex diffraction grating, which spectrally disperses the remaining Raman-scattered light along a row of the array. Removing the grating enables Near-IR spectrometry with a tunable laser. Hyperspectral Imaging can be Accomplished with One Combined NIR and Raman Instrument Diagram: NASA Photonics Tech Briefs Jan. 2002
  17. 17. University of Kentucky New Technologies Remain to be Explored Superconducting transition edge detectors Quantum cascade lasers B. Cabrera, R. M. Clarke, P. Colling, A. J. Miller, S. Nam, and R. W. Romani, Detection of single infrared, optical, and ultraviolet photons using superconducting transition edge sensors, APPLIED PHYSICS LETTERS 1998, 73(6), 735-737. Claire Gmachl, Deborah L. Sivco, Raffaele Colombelli, Federico Capasso & Alfred Y. Cho Ultra-broadband semiconductor laser, Nature 2002, 415, 883-887. Typically, lasers emit light of one pure wavelength. Quantum cascade lasers generate a beam containing wavelengths in a wide region of the electromagnetic spectrum. This new broadband laser can be made to operate in the NIR/IR. The device contains hundreds of extremely thin semiconductor layers, each one affecting the energies of electrons passing through it. A high voltage forces an electric current to penetrate layer after layer in the stack. The physical confinement of many of those stacked layers makes them act as quantum wells. The TE optical detector is so sensitive that it can clock the arrival of a single photon of light and still measure its energy. The detector works in the infrared, optical and ultraviolet portions of the spectrum. An electrical current keeps the detector at its critical transition temperature. The sensor is cooled slightly below the transition temperature and the electrical current raises its temperature to the critical value. When the energy from an individual photon reaches the superconductor, it heats up the electrons in the material. This heating causes an increase in the resistance. The greater resistance causes a decrease in the electrical heating that exactly equals the amount of energy that the photon deposited. This keep the detector at the right temperature and also gives a precise measurement of the photon's energy and arrival time.
  18. 18. University of Kentucky Near To or Far From Our Expectations? Insufficient man-hours and public and private research funding have been directed into spectrometric technologies for detection of vulnerable plaque. Photonic technologies have tremendous untapped potential that will continue to grow as new tools like MAESA, quantum cascade lasers, and superconducting detectors become available. Organizations like AEHA must continue to promote awareness of the problem and the potential solutions so photonics can fulfill our expectations.