Laser Microbeam and Medical Program

Laser Microbeam and Medical Program

Research Emphasis

The program is designed to develop optical instrumentation and biophysical models for understanding mechanisms of light-tissue interaction.

Current Research

Mechanisms of coherent image formation; models for understanding the origin and degradation of coherent light interactions in biological tissues; and combined two-photon excited fluorescence and second harmonic generation imaging in vivo. Applications include monitoring/imaging hemodynamics before, during, and after interventional procedures and imaging cell-extracellular matrix interactions.

Tissue absorption and scattering measurements in complex, heterogeneous, and biological systems; relations between tissue optical properties and physiology/cellular structure; and tissue phantoms, preclinical animal models, and human subjects. Applications include tumor diagnostics in breast, brain, and cervix and the structural origins of tissue optical properties.

Resource Capabilities

Instruments

(1) Microbeam and Microscopy Technologies

Confocal ablation trapping system: Integrates independently controlled, tunable trapping, and ablation beams into a Zeiss laser scanning confocal microscope. Detectors include a cooled color charge-coupled device (CCD) camera and three photomultiplier tubes.

Zeiss LSM 510 META NLO multiphoton microscope: This commercial, user-friendly multiphoton system accommodates studies ranging from low-light-level endogenous signal detection of both fluorescence and second harmonic generation (SHG) in tissues to cellular fluorescence resonance energy transfer-based imaging.

Multiphoton microscopy (MPM): Two-photon fluorescence (TPF) and SHG are detected simultaneously from tissue using two photomultiplier tube channels and a dedicated spectrometer. Intrinsic SHG signals are sensitive to collagen in the extracellular matrix, whereas TPF reports cellular and tissue autofluorescence. Typical scans are 256 times 256 pixels in 1B2 seconds.

Multiphoton microscopy and optical coherence tomography (MPM/OCT): The system simultaneously acquires structural and functional information about cells and extracellular matrix in thick scattering tissues. Our combined MPM/OCT system has three imaging channels that acquire the two-photon excited fluorescence (TPEF) signal from intrinsic sources (e.g., cofactors and proteins) and exogenous fluorophores, the SHG signal from non-centrosymmetric molecules such as collagen, a common structural protein, and the backscattered signal from refractive index discontinuities that occur between tissues of different structure or composition, respectively.

(2) Medical Translational Technologies

Functional optical coherence tomography (OCT): The optical fiber-based OCT systems use superluminescent diodes, photonic crystals, and ultrafast lasers and are capable of multimodal imaging in vivo blood flow and tissue structure simultaneously to depths of 2-4 mm. Fiber probe and microscope platforms are available with video scanning.

Pulsed optoacoustic interferomic spectroscopy (POISe): POISe is a novel optoacoustic technique for imaging and physiological characterization of heterogeneous tissues at depths approaching 1 cm with a spatial resolution <200 µm. Unlike current optoacoustic imaging techniques based on the detection of stress transients, POISe uses an optical interferometric system to measure the surface displacement of a tissue sample at multiple locations in response to pulsed laser irradiation.

Diffuse optical spectroscopy (DOS): These multiwavelength, high-bandwidth (1 GHz) portable frequency-domain photon migration systems are used for quantitative, noninvasive measurements of tissue optical and physiologic properties. Photon density waves (300-KHz to 1-GHz) are produced using up to 10 intensity-modulated diode lasers (674 to 980 nm) combined with a broadband continuous light source. The frequency-dependence of the photon density wave phase and amplitude is used to calculate absorption (µ_a) and reduced scattering (µ_s') spectra with 3-nm resolution. The wavelength-dependence of absorption is used to determine tissue hemoglobin concentration (total, oxy-, and deoxy- forms), tissue oxygen saturation, and lipid and water concentrations.

Modulated imaging (MI): MI is a novel non-contact optical imaging technology that is capable of quantitative imaging, spectroscopy, and tomography of tissues over a large field of view (many cm) and up to a depth of ~1 cm. Although compatible with time-modulation methods, MI alternatively uses spatially modulated illumination for imaging of tissue constituents. Periodic illumination patterns of various spatial frequencies are projected over a large area of tissue, and the remitted diffuse light is detected via a CCD camera. The spatially varying (two dimensional or three dimensional) absorption, scattering, and/or fluorescence characteristics of the sample can then be reconstructed from the measured diffuse reflectance and/or fluorescence, respectively. Estimation of intrinsic tissue chromophores is further enabled by quantifying absorption at many wavelengths. For example, images of tissue hemoglobin concentration (total, oxy-, and deoxy- forms), tissue oxygen saturation, and lipid, water, and melanin concentrations can all be quantified using appropriate red or infrared wavelengths.

Software

Models of Light Transport in Tissue: Monte Carlo/transport, diffusion, and finite element. Virtual Tissue Simulator.

Available Resources

The following support facilities are also available through the LAMMP resource: 1) Medical Clinic (Operating room, and outpatient treatment rooms); 2) Veterinary Treatment Suite (animal operating room); 3) Tissue Culture/Biochemistry and Tissue Engineering Facility; 4) Histology/Electron Microscopy Facility; 5) Image Processing/Computation; and 6) Spectroscopy (absorption/fluorescence, reflectance, and Fourier transform infrared).

Training Opportunites and Workshops

Data processing workshops: Consultations on three-dimensional data restoration, a quantitative approach to SHG/MPF data processing and interpretation, analytical and numerical methods for modeling light transport in tissue, inverse problem solving, and multimodality image coregistration.

Non-linear laser scanning microscopy and imaging: Training focuses on the hands-on manipulation of all essential skills to allow the individual to carry out experiments that involve the use of cultured cells and/or engineered tissues.

Publications

1. Lim, H., Jiang, Y., Wang, Y., Huang, Y. C., Chen, Z., and Wise, F. W., Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 µm. Optics Letters 30:1171-1173, 2005.
2. Shah, N., Gibbs, J., Wolverton, D., Cerussi, A., Hylton, N., and Tromberg, B. J., Combined diffuse optical spectroscopy and contrast-enhanced magnetic resonance imaging for monitoring breast cancer neoadjuvant chemotherapy: A case study. Journal of Biomedical Optics 10:51503, 2005.
3. Tseng, S. H., Hayakawa, C., Tromberg, B. J., Spanier, J., and Durkin, A. J., Quantitative spectroscopy of superficial turbid media. Optics Letters 30:3165-3167, 2005.
4. Wilder-Smith, P., Krasieva, T., Jung, W. G., Zhang, J., Chen, Z., Osann, K., and Tromberg, B. J., Non-invasive imaging of oral premalignancy and malignancy. Journal of Biomedical Optics 10:51601, 2005.