Measurement of optical transport properties of normal and malignant human breast tissue

We report measurement of optical transport parameters of normal and malignant (ductal carcinoma) human breast tissue. A spatially resolved steady-state diffuse reflectance technique was used for measurement of the reduced scattering coefficient (mu(s)?) and the absorption coefficient (mu(a)) of the tissue. The anisotropy parameter of scattering (g) was estimated by goniophotometric measurements of the scattering phase function. The values of mu(s)? and mu(a) for malignant breast tissue were observed to be larger than those for normal breast tissue over the wavelength region investigated (450-650 nm). Further, by using both the diffuse reflectance and the goniophotometric measurements, we estimated the Mie equivalent average radius of tissue scatterers to be larger in malignant tissue than in normal tissue.     

Determination of optical parameters of human breast tissue from spatially resolved fluorescence: a diffusion theory model

We report the measurement of optical transport parameters of pathologically characterized malignant tissues, normal tissues, and different types of benign tumors of the human breast in the visible wavelength region. A spatially resolved steady-state diffuse fluorescence reflectance technique was used to estimate the values for the reduced-scattering coefficient (mu(s)') and the absorption coefficient (mu(a)) of human breast tissues at three wavelengths (530, 550, and 590 nm). Different breast tissues could be well differentiated from one another, and different benign tumors could also be distinguished by their measured transport parameters. A diffusion theory model was developed to describe fluorescence light energy distribution, especially its spatial variation in a turbid and multiply scattering medium such as human tissue. The validity of the model was checked with a Monte Carlo simulation and also with different tissue phantoms prepared with polystyrene microspheres as scatterers, riboflavin as fluorophores, and methylene blue as absorbers.     

Influence of a superficial layer in the quantitative spectroscopic study of strongly scattering media

We have experimentally investigated the meaning of the effective optical absorption [mu(a)((eff))] and the reduced scattering [mu(s)?((eff))] coefficients measured on the surfaces of two-layered turbid media, using the diffusion equation for homogeneous, semi-infinite media. We performed frequency-domain spectroscopy in a reflectance geometry, using source-detector distances in the range 1.5-4.5 cm. We measured 100 samples, each made of one layer (thickness in the range 0.08-1.6 cm) on top of one semi-infinite block. The optical properties of the samples were similar to those of soft tissues in the near infrared. We found that the measured effective optical coefficients are representative of the underlying block if the superficial layer is less than ~0.4 cm thick, whereas they are representative of the superficial layer if it is more than ~1.3 cm thick.     

Quantifying the absorption and reduced scattering coefficients of tissuelike turbid media over a broad spectral range with noncontact Fourier-transform hyperspectral imaging

Absorption (mu(a)) and reduced scattering (mu(s)') spectra of turbid media were quantified with a noncontact imaging approach based on a Fourier-transform interferometric imaging system (FTIIS). The FTIIS was used to collect hyperspectral images of the steady-state diffuse reflectance from turbid media. Spatially resolved reflectance data from Monte Carlo simulations were fitted to the recorded hyperspectral images to quantify mu(a) and mu(s)' spectra in the 550-850-nm region. A simple and effective calibration approach was introduced to account for the instrument response. With reflectance data that were close to and far from the source (0.5-6.5 mm), mu(a) and mu(s)' of homogeneous, semi-infinite turbid phantoms with optical property ranges comparable with those of tissues were determined with an accuracy of +/-7% and +/-3%, respectively. Prediction accuracy for mu(a) and mu(s)' degraded to +/-12% and +/-4%, respectively, when only reflectance data close to the source (0.5-2.5 mm) were used. Results indicate that reflectance data close to and far from the source are necessary for optimal quantification of mu(a) and mu(s)'. The spectral properties of mu(a) and mu(s)' values were used to determine the concentrations of absorbers and scatterers, respectively. Absorber and scatterer concentrations of two-chromophore turbid media were determined with an accuracy of +/-5% and +/-3%, respectively.     

Micro-Raman spectroscopy for optical pathology of oral squamous cell carcinoma

Micro-Raman spectra of formalin-fixed oral squamous normal and carcinoma tissues, stored at room temperature for 2 months, have been recorded. Spectra were recorded both in the epithelial and subepithelial regions of the tissues. No noticeable spectral contamination due to formalin was observed. Very significant differences between spectra of normal epithelial and malignant epithelial samples were found. No such differences in spectra of subepithelial malignant and subepithelial normal samples could be observed. This study shows that spectra from the epithelial region changes drastically because of malignancy-induced biochemical changes in this region. Major differences between normal and malignant spectra seem to arise from the protein composition, conformational/structural changes, and possible increase in protein content in malignant epithelia. The differences between normal epithelial and subepithelial spectra, as expected, arise mainly from the collagen in subepithelial tissue. Principal component analysis of the combined sets of spectra-epithelial and subepithelial, normal and malignant- showed that very good discrimination can be achieved by Raman microspectroscopy. This study thus validates the suitability of formalin-fixed tissues for optical pathology in oral malignancy.     

Characterization of spatial and temporal variations in the optical properties of tissuelike media with diffuse reflectance imaging

We describe a method to characterize spatial or temporal changes in the optical properties of turbid media using diffuse reflectance images acquired under broad-beam illumination conditions. We performed experiments on liquid phantoms whose absorption (mu(a)) and reduced scattering (mu(s)') coefficients were representative of those of biological tissues in the near infrared. We found that the relative diffuse reflectance R depends on mu(a) and mu(s)' only through the ratio mu(a)/mu(s)' and that dependence can be well described with an analytical expression previously reported in the literature [S. L. Jacques, Kluwer Academic Dordrecht (1996)]. We have found that this expression for R deviates from experimental values by no more than 8% for various illumination and detection angles within the range 0 degrees-30 degrees. Therefore, this analytical expression for R holds with good approximation even if the investigated medium presents curved or irregular surfaces. Using this expression, it is possible to translate spatial or temporal changes in the relative diffuse reflectance from a turbid medium into quantitative estimates of the corresponding changes of (mu(a)/mu(s)')(1/2). In the case of media with optical properties similar to those of tissue in the near infrared, we found that the changes mu(a)/mu(s)' should occur over a volume approximately 2 mm deep and 4 mm x 4 mm wide to apply this expression.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part II: Application to breast cancer diagnosis

The Monte Carlo-based inverse model of diffuse reflectance described in part I of this pair of companion papers was applied to the diffuse reflectance spectra of a set of 17 malignant and 24 normal-benign ex vivo human breast tissue samples. This model allows extraction of physically meaningful tissue parameters, which include the concentration of absorbers and the size and density of scatterers present in tissue. It was assumed that intrinsic absorption could be attributed to oxygenated and deoxygenated hemoglobin and beta-carotene, that scattering could be modeled by spheres of a uniform size distribution, and that the refractive indices of the spheres and the surrounding medium are known. The tissue diffuse reflectance spectra were evaluated over a wavelength range of 400-600 nm. The extracted parameters that showed the statistically most significant differences between malignant and nonmalignant breast tissues were hemoglobin saturation and the mean reduced scattering coefficient. Malignant tissues showed decreased hemoglobin saturation and an increased mean reduced scattering coefficient compared with nonmalignant tissues. A support vector machine classification algorithm was then used to classify a sample as malignant or nonmalignant based on these two extracted parameters and produced a cross-validated sensitivity and specificity of 82% and 92%, respectively.     

Dynamic schema for near infrared detection of pressure-induced changes in solid tumors

Differentiation among malignant tumors, benign tumors, and normal tissue is highly important in the diagnosis and treatment of many malignancies. We have proposed a dynamic schema for noninvasive characterization of pressure-induced changes in solid tumors. Our hypothesis has been that the altered neovascularization processes within cancer-bearing tissues may significantly increase vascular resistance and cause a much slower response of hemoglobin concentration during a dynamic compression stimulus. This hypothesis was tested by the evaluation of data generated from human tumor clinical testing and from animal tumor model testing. In the human tumor clinical testing, a unified diagnostic criterion was derived that integrated the relative characteristics of tumor oxygen, hemoglobin, and hemoglobin dynamics. By applying such a unified criterion, we were able to differentiate benign breast lesions and malignant breast tumors with high sensitivity and specificity within a subset of 14 suspicious breast lesions with similar size and depth characteristics. In the animal testing, a stepped compression load was applied to the subcutaneous tumor deposit on an athymic NU/NU nude mouse model with subcutaneous xenograft BxPC-3 cancer. Characteristic differences were observed between the premortem tumor and the postmortem tumor in terms of pressure-induced tumor structural and functional changes.     

Fractal dimension analysis of time-resolved diffusely scattered light from turbid samples

To improve quantification of optical properties in highly scattering and absorbing samples, time-correlated single photon counting measurements were analyzed using quantities related to the correlation dimension. Photon time-of-flight (TOF) distributions were collected in reflection and transmission optical configurations from samples made of cream and water-soluble dye (0 < mu(a) < 0.05 mm(-1); 100 < mu(s) < 250 mm(-1)). It was found that absorption and scattering properties of samples could be accurately quantified from information used to determine the correlation dimension. Scattering coefficients were estimated with less than 4% error for both optical configurations. Absorption estimates were made with CVs of 7.5 and 9.6% for reflection and transmission, respectively. Overall, fractal dimension analysis of TOF distributions provides a simple method of determining the optical properties of a sample.     

Rapid optical method for logging dust concentration versus depth in glacial ice

We describe the design and simulated response of a dust logger consisting of a downward-pointing phototube, ~2 m below side-directed light-emitting diodes (LEDs), attached to a cable that can lower the device down a 3-in. (7.5-cm) borehole filled with butyl acetate. LED photons that enter the ice are scattered or absorbed by dust grains, and those that reach the phototube provide a measure of dust or volcanic ash concentration at a given depth. An increased dust concentration associated with an ancient colder climate will usually result in an increase in collected light, but may decrease collected light if air bubbles are present. Centimeter-thick volcanic ash bands can also be detected. The concept is based on six years of experience with pulsed light sources used to measure optical properties of deep Antarctic ice.     

Quantifying the properties of two-layer turbid media with frequency-domain diffuse reflectance

Noncontact, frequency-domain measurements of diffusely reflected light are used to quantify optical properties of two-layer tissuelike turbid media. The irradiating source is a sinusoidal intensity-modulated plane wave, with modulation frequencies ranging from 10 to 1500 MHz. Frequency-dependent phase and amplitude of diffusely reflected photon density waves are simultaneously fitted to a diffusion-based two-layer model to quantify absorption (mu(a)) and reduced scattering (mu(s)') parameters of each layer as well as the upper-layer thickness (l). Study results indicate that the optical properties of two-layer media can be determined with a percent accuracy of the order of +/-9% and +/-5% for mu(a) and mu(s)', respectively. The accuracy of upper-layer thickness (l) estimation is as good as +/-6% when optical properties of upper and lower layers are known. Optical property and layer thickness prediction accuracy degrade significantly when more than three free parameters are extracted from data fits. Problems with convergence are encountered when all five free parameters (mu(a) and mu(s)' of upper and lower layers and thickness l) must be deduced.     

Analysis of a multielement ultrasound hyperthermia applicator

An unfocused multielement ultrasound applicator was developed for hyperthermia treatment of superficial tumors. The applicator contains sixteen 3.8-cm(2) individually controllable elements on a 15.2-cm(2) piezoelectric ceramic plate. The acoustical power output of each element can be independently applied to facilitate uniform heating throughout the treatment area while minimizing undesired heating in normal tissues. The performance of the applicator was examined by measuring acoustical power output and beam profiles. The results of this analysis indicated that the applicator is capable of producing required therapeutic output levels with excellent localization and control of the power deposition.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part I: Theory and validation on synthetic phantoms

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption (0-20 cm(-1)) and reduced scattering coefficients (7-33 cm(-1)). Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of 350-850 nm. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of 3% or less for phantoms containing hemoglobin and 12% or less for phantoms containing Nigrosin.     

Towards Nonspecific Detection of Malignant Cervical Cells with Fluorescent Silica Beads

To date, the methods for detection of cancer cells are mostly based on traditional techniques used in biology, such as visual identification of malignant changes, cell‐growth analysis, specific ligand–receptor labeling, or genetic tests. Despite being well developed, these methods are either insufficiently accurate or require a lengthy complicated analysis. A search for alternative methods for the detection of cancer cells may be a fruitful approach. Proposed here is a novel method for the detection of cancer cells in vitro, which is based on nonspecific adhesion of silica beads to cells. First, atomic force microscopy is used to study the adhesion of single silica beads to malignant and normal cells cultured from human cervix. It is found that adhesion depends on the time of contact, and can be statistically different for malignant and normal cells. Using these data, an optical method utilizing fluorescent silica beads is developed, which is based on detection of the difference in the number of adherent particles. The method is tested using primary cells cultured from cervical tissues of three healthy individuals and three patients with cervical cancer. The method shows sufficiently high sensitivity for cancer to make it interesting to perform further statistical tests.     

Absorption measurement of nu2 + 2nu3 band of CH4 at 1.33 microm using an InGaAsP light emitting diode

The combination band of nu2 + 2nu3 of CH4 at 1.33 microm (7512 cm(-1)) was observed at 0.3-cm(-1) resolution by a simple experimental arrangement using a near-infrared high-radiant InGaAsP light emitting diode (LED) and a Ge detector. Forty-six line centers were measured with accuracies of 0.03 cm(-1). The assignment of these manifolds was made by inspection of the P, Q, and R branches. The experimental result indicates that the nu2 + 2nu3 band can be used for fully optical remote monitoring of methane using InGaAsP optical sources in conjunction with an ultralow-loss optical fiber network.     

Study of rotational dynamics of receptor-targeted contrast agents in cancerous and normal prostate tissues using time-resolved picosecond emission spectroscopy

We studied the time-resolved polarization-dependent fluorescence spectroscopy of receptor-targeted contrast agents (Cybesin and Cytate) bound with prostate cancer cells in prostate tissue. An analytical model dealing with highly viscous tissue media was developed and used to investigate the rotation times and fluorescence anisotropies of the receptor-targeted contrast agents in prostate tissue. The differences of rotation times and fluorescence anisotropies were observed for Cybesin (Cytate) in cancerous and normal prostate tissues, which reflect changes of the microstructures of cancerous and normal tissues and their different bound affinity with contrast agents. The preferential uptake of Cytate (Cybesin) in cancerous tissue was used to image and distinguish cancerous tissue areas from normal tissue areas. The fluorescence polarization difference imaging technique was used to enhance the image contrast between the cancerous and normal tissue areas. This research may help to introduce a new optical approach and criteria for prostate cancer detection.     

Characteristics of polymeric optical passive single-mode waveguiding devices fabricated by an argon-ion laser

The fabrication of polymeric single-mode Gaussian profile optical waveguides is described. We used poly(methyl methacrylate) and a mixture of two intermiscible monomers for the cladding and the core, respectively, of the waveguides. The cores of the waveguides were fabricated by with an argon-ion laser beam. The waveguides had single-mode Gaussian refractive-index profiles. By using such waveguides, we fabricated directional couplers for power coupling to the adjacent waveguides and also parallel waveguide arrays for preventing power coupling to adjacent waveguides for use in interconnect chips. We analyzed the characteristics of these couplers by using the coupled-mode theory and compared the results with those obtained with the beam propagation method. Experimental results showed good correlation with the theoretical values. We designed optical bus arrays for interconnect chips, considering the variation of normalized frequency V, the power penalty, and the dimensions of the waveguides and the separation between them. The number of waveguides in the bus array increased with increasing V. For a known value of V, a waveguide's density increases with a decrease of its dimensions. The theoretical maximum number of waveguides is ~1490/cm and ~846/cm for 2 mum x 2 mum and 4 mum x 4 mum single-mode waveguides, respectively, to satisfy a 1-dB power penalty criterion at bit-error rate of 10(-9). We fabricated interconnect bus arrays with fifteen 4 mum x 4 mum waveguides for a 3-cm coupling length, and the experimental results were verified to be in good agreement with the theoretical values.     

Estimation of optical properties of turbid media: experimental comparison of spatially and temporally resolved reflectance methods

We compare two methods for the optical characterization of turbid media. The estimates of the absorption and reduced scattering coefficients (mu(a) and mu(')(s)) by a spatially resolved method and a time-resolved method are performed on tissue-like phantoms. Aqueous suspension of microspheres and Intralipid are used as scattering media with the addition of ink as an absorber. mu(')(s) is first measured on weakly absorbing media. The robustness of these measurements is then tested with respect to a variation of mu(a). The spatially resolved method gave more accurate estimates for mu(')(s) whereas the time-resolved method gave better results for mu(a) estimates.     

Earth-to-geosynchronous satellite laser beam transmission

Some experimental results for detection of a ground-based laser beacon by a geosynchronous satellite are reported. A 50-cm diam telescope and silicon intensifier tube camera were used for optical observation of the satellite. The transmitted argon laser beam was detected by the visible channel of a radiometer on board the Japanese Geostationary Meteorological Satellite. Two activities, (1) orbit prediction correction using optical observation and (2) detection of the earth laser beacon by the radiometer, are described.     

Diffuse optical tomography guided quantitative fluorescence molecular tomography

We describe a method that combines fluorescence molecular tomography (FMT) with diffuse optical tomography (DOT), which allows us to study the impact of heterogeneous optical property distribution on FMT, an issue that has not been systemically studied. Both numerical simulations and phantom experiments were performed based on our finite-element reconstruction algorithms. The experiments were conducted using a noncontact optical fiber free, multiangle transmission system. In both the simulations and experiments, a fluorescent target was embedded in an optically heterogeneous background medium. The simulation results clearly suggest the necessity of considering the absorption coefficient (mu(a)) and reduced scattering coefficient (mu'(s)) distributions for quantitatively accurate FMT, especially in terms of the accuracy of reconstructed fluorophore absorption coefficient (mu(a(x-->m))). Subsequent phantom experiments with an indocyanine green (ICG)-containing target confirm the simulation findings. In addition, we performed a series of phantom experiments with low ICG concentration (0.1, 0.2, 0.4, 0.6 and 1.0 microM) in the target to systematically evaluate the quantitative accuracy of our FMT approach. The results indicate that, with the knowledge of optical property distribution, the accuracy of the recovered fluorophore concentration is improved significantly over that without such a priori information. In particular absolute value of mu(a(x-->m) ) from our DOT guided FMT are quantitatively consistent with that obtained using spectroscopic methods.