Biomedical subjects

R R Alfano

Publications and source records attributed to R R Alfano.

At least 37 records · Page 2Linked to original sources

PubMed2004

NIR laser tissue welding of in vitro porcine cornea and sclera tissue.

BACKGROUND AND OBJECTIVE: The objective of this study was to test the hypothesis that an near infrared (NIR) laser system (1,455 nm) in combination with a motorized translational stage to control the position and speed of the laser beam and a shutter to control the laser exposure to the tissue being welded could be used to successfully weld ocular tissues. STUDY DESIGN/MATERIALS AND METHODS: Seventy-five porcine corneas and 23 porcine scleral tissues were welded in vitro in this study. The welded tissues were examined using histopathology and tensile strength analysis. Eight different welding conditions were analyzed for porcine cornea and one for sclera tissues. The tensile strength of the welded groups was compared to a sutured cornea control group. RESULTS: The NIR laser welding system provides strong, full thickness welds and does not require the use of extrinsic dyes, chromophores, or solders. Mean weld strengths of 0.15-0.45 kg/cm(2) were obtained for the cornea and 1.01 kg/cm(2) for sclera welds. The native H(2)O in the ocular tissue serves as an absorber of the 1,455 nm radiation and helps to induce the welds. CONCLUSIONS: We conclude that an NIR laser system using an optimal laser radiation wavelength of 1,455 nm can effectively weld cornea and sclera tissue and that this laser tissue welding (LTW) methodology typically causes minimal disruption of tissue, and thus, avoids opacities and irregularities in the tissue which may result in decreased visual acuity. The optimization of a laser welding system that leads to a strong full thickness tissue bond without tissue destruction, an instant seal that promotes wound healing, and the absence of a continued presence of a foreign substance like a suture, is of considerable importance to the ophthalmology medical community. This need is especially apparent with respect to corneal transplantation and fixing the position of corneal flaps in Laser-Assisted In Situ Keratomileusis (LASIK), a laser procedure used to permanently change the shape of the cornea.

Animals↗

PubMed2004

Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy.

The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.

Coated Materials, Biocompatible↗

PubMed2004

Near infrared spectroscopy and imaging to probe differences in water content in normal and cancer human prostate tissues.

The content of water in cancerous and normal human prostate in vitro tissues was shown to be different using near infrared (NIR) spectroscopy. The water absorption peaks at 1444 nm and 1944 nm are observed in both types of prostate tissues. The measurements show that less water is contained in cancerous tissues than in normal tissues. The OH stretching vibrational overtone mode at 1444 nm and other water overtone modes provide key spectroscopic fingerprints to detect cancer in prostate tissue. Transmission and backscattered spectral imaging were measured in cancer and normal prostate tissues. The degree of polarization for 700 nm, 800 nm, 1200 nm, and 1450 nm is larger for normal than for cancer tissues. The knowledge about water content offers a potential as a diagnostic tool to better determine and image cancer in prostate and in other tissues types such as breast and cervix using the absorption from vibrational overtones of H(2)O molecules in the NIR.

Body Water↗

PubMed2003

Free-space ballistic laser propagation of a pulse coded data stream through fog.

We describe the use of space and polarization gates in a study of free-space optical communication of a coded pulse train as it passes through turbid media. The propagation of coded signals at 10 GHz through adverse environmental conditions is demonstrated. Polarization and space-gating techniques are used to improve the signal-to-noise ratio and to enhance the information fidelity of high-bit-rate transmitted signals, which shows potential improvement for cloud, fog, and smog applications.

Journal Article↗

PubMed2003

Time-resolved polarization to extract coded information from early ballistic and snake signals through turbid media.

Time-resolved polarization is used to extract coded information buried within the multiple scattering profiles from the early ballistic and snake components as they pass through turbid media. By polarization analysis the depolarized diffusive component and the natural-light background are significantly reduced to enhance the signal-to-noise ratio of a coded pulse train. This procedure has the potential to improve optical wireless communication in cloudy environments.

Journal Article↗

PubMed2003

Anomalous diffraction of light with geometrical path statistics of rays and a Gaussian ray approximation.

The anomalous-diffraction theory (ADT) of extinction of light by soft particles is shown to be determined by a statistical distribution of the geometrical paths of individual rays inside the particles. Light extinction depends on the mean and the mean-squared geometrical paths of the rays. Analytical formulas for optical efficiencies from a Gaussian distribution of the geometrical paths of rays are derived. This Gaussian ray approximation reduces to the exact ADT in the intermediate case of light scattering for an arbitrary soft particle and describes well the extinction of light from a system of randomly oriented and (or) polydisperse particles. The implications for probing of the sizes and shapes of particles by light extinction are discussed.

Journal Article↗

PubMed2003

Aorta and skin tissues welded by near-infrared Cr4+:YAG laser.

OBJECTIVE: The aim of our study was to explore the wavelength dependence of welding efficacy. Ex vivo samples of human and porcine aorta and skin tissues were investigated using a tunable Cr(4+):yttrium aluminum garnet (YAG) laser. BACKGROUND DATA: Tissue welding is possible using laser light in the NIR spectral range. Collagen bonding in the tissue induced by thermal, photothermal, and photochemical reactions-or a combination of all of these-is thought to be responsible for tissue welding. Laser tissue welding (LTW) has gained success in the laboratory using animal models. Transition from laboratory to clinical application requires the optimization of welding parameters. MATERIALS AND METHODS: A near-infrared (NIR) Cr(4+):YAG laser was used to weld ex vivo samples of human and porcine aorta and skin at wavelengths from 1430 to 1470 nm. Welding efficacy was monitored by measuring the tensile strength of the welded tissue and the extent of collateral tissue damage. Tensile strengths were measured using a digital force gauge. Changes in tissue morphology were evaluated using optical and scanning electron microscope (SEM). Fluorescence imaging of the welded areas was also used to evaluate molecular changes following tissue welding. RESULTS: Full-thickness tissue bonding was observed with porcine aorta samples. No collateral damage of the aorta samples was observed. Tissue denaturation was observed with human aorta, human skin, and porcine skin samples. The optimum tensile strength for porcine and human aorta was 1.33 +/- 0.15 and 1.13 +/- 0.27 kg/cm2, respectively, at 1460 nm, while that for porcine and human skin was 0.94 +/- 0.15 and 1.05 +/- 0.19 kg/cm2, respectively, achieved at 1455 nm. The weld strength as a function of wavelength demonstrated a correlation with the absorption spectrum of water. Fluorescence imaging of welded aorta and skin demonstrated no significant changes in collagen and elastin emission at the weld site. CONCLUSION: The observation that welding strength as a function of wavelength follows the absorption bands of water suggests that absorption of light by water plays a significant role in laser tissue welding.

Animals↗

PubMed2002

Photon migration in turbid media using a cumulant approximation to radiative transfer.

A photon transport model for light migration in turbid media based on a cumulant approximation to radiative transfer is presented for image reconstruction inside an infinite medium or a bounded medium with a planar geometry. This model treats weak inhomogeneities through a Born approximation of the Boltzmann radiative transfer equation and uses the second-order cumulant solution of photon density to the Boltzmann equation as the Green's function for the uniform background. It provides the correct behavior of photon migration at early times and reduces at long times to the center-moved diffusion approximation. At early times, it agrees much better with the result from the Monte Carlo simulation than the diffusion approximation. Both approximations agree well with the Monte Carlo simulation at later times. The weight function for image reconstruction under this proposed model is shown to have a strong dependence at both early and later times on absorption and/or scattering inhomogeneities located in the propagation direction of and close to the source, or in the field of view of and close to the detector. This effect originates from the initial ballistic motion of incident photons, which is substantially underestimated by the diffusion approximation.

Journal Article↗

PubMed2002

Noninvasive native fluorescence imaging of head and neck tumors.

Fluorescence images were acquired from ex vivo head and neck tumor specimens. The excitation and emission wavelength combinations were selected to image emission from native tissue fluorophores (collagen, tryptophan, elastin and nicotinamide adenine dinucleotide). Two dimensional intensity ratio maps were generated from the fluorescence images and compared to histology images. The ratio maps accurately distinguished the regions of tumor from normal tissue in the specimens. Additional features, such as collagen capsules, blood vessels, mucus glands and muscles were evident in the fluorescence images.

Carcinoma, Papillary↗

PubMed2002

DNA and protein changes caused by disease in human breast tissues probed by the Kubelka-Munk spectral functional.

Malignant, fibroadenoma, normal and adipose breast tissues were studied using diffuse reflectance spectroscopy. The absorption spectra of the breast tissues were extracted from the diffuse reflectance spectra using the Kubelka-Munk function (K-M function). The spectral features of the K-M function were identified and compared with those of the absorption spectra. The spectral features of the K-M function were assigned to DNA, protein, beta-carotene and hemoglobin (oxygenated and deoxygenated) molecules in the breast tissue. The amplitudes of the K-M function averaged from 275 to 285 nm and from 255 to 265 nm and were found to be different for malignant, fibroadenoma and normal tissues. These differences were attributed to changes in proteins and DNA. A set of critical parameters was determined for separating malignant tissues from fibroadenoma and normal tissues. This approach should hold for other tissue types such as cervix, uterus and colon.

Adenocarcinoma, Mucinous↗

PubMed2001

Near-infrared photo-excited emission from tissues treated at different temperature levels.

BACKGROUND AND OBJECTIVE: There is a lack of methods to evaluate the extent of thermal treatment of biological tissue. The intensity of the near-infrared (NIR) emission photo-excitation was investigated from tissue undergoing different levels of heat treatment. STUDY DESIGN/MATERIALS AND METHODS: Chicken muscle was heated in an oven at different temperature levels ranging from 40 degrees C until burn-off. The spectral emission intensity from these heat-treated tissues was measured with a CCD camera and the intensity was calculated. RESULTS: The emission intensity increased proportionally with respect to the extent of treatment temperature until burning. Linear relationships between treatment temperature and the emission intensity from tissue samples were found in three temperature ranges: from 40 to 160 degrees C, from 165 to 220 degrees C, and from 225 to 250 degrees C. CONCLUSIONS: The change in tissue damage after heat treatment could be detected by measuring the NIR emission intensity from the thermally damaged tissues.

Animals↗

PubMed2001

UV reflectance spectroscopy probes DNA and protein changes in human breast tissues.

OBJECTIVE: The absorption spectrum obtained using diffuse reflectance measurements of malignant, fibroadenoma, and normal human breast tissues were studied. The spectral features in the spectrum were assigned to molecular components in the tissues. BACKGROUND DATA: Over the past decade, the methods of fluorescence, excitation, and Raman spectroscopy have been studied as potential noninvasive diagnostic tools. Useful spectroscopic information may be obtained from absorption spectra of tissues as well. However, direct measurement of absorption spectra of tissues by conventional transmission means is complicated by multiple photon scattering in tissues. Diffuse reflectance spectrum offers an indirect way to obtain absorption spectrum. METHODS: Excised malignant, fibroadenoma, and normal breast tissue samples without any treatment were obtained from pathology. Samples were placed in a quartz cuvette. The diffuse reflectance measurements between 250 nm to 650 nm were performed using an automated dual lamp spectrophotometer. The absorption spectra of breast tissues were obtained from the diffuse reflectance measurement. RESULTS: Twenty-one invasive carcinoma, 20 mixed in situ and invasive carcinoma, 14 fibroadenoma, and 39 normal breast tissue samples were studied. The absorption spectra of breast tissues were obtained from diffuse reflectance spectra. Spectral features were assigned to DNA and proteins in human breast tissue. Amplitude of changes averaged over 275 nm to 285 nm and 255 nm to 265 nm and were found to be different for malignant, fibroadenoma, and normal breast tissues. These changes arise from differences in content of protein and DNA. CONCLUSION: The peaks of absorption spectrum derived from diffuse reflectance measurements in the UV region revealed fingerprints from proteins and DNA components. The absorbance in the wavelength ranges of 275-285 nm and 255-265 nm were found to be different for malignant, fibroadenoma, and normal breast tissues. These differences provide a criterion to distinguish malignant from fibroadenoma and normal breast tissues.

Absorption↗

PubMed2001

Time-resolved Fourier optical diffuse tomography.

Time-resolved Fourier optical diffuse tomography is a novel approach for imaging of objects in a highly scattering turbid medium with use of an incident (near) plane wave. The theory of the propagation of spatial Fourier components of the scattered wave field is presented, along with a fast algorithm for three-dimensional reconstruction in a parallel planar geometry. Examples of successful reconstructions of simulated hidden absorptive or scattering objects embedded inside a human-tissue-like semi-infinite turbid medium are provided.

Algorithms↗

PubMed2000

Analytical solution of the polarized photon transport equation in an infinite uniform medium using cumulant expansion.

An analytical solution for time-dependent polarized photon transport equation in an infinite uniform isotropic medium is studied using a circular representation of the polarized light and expansion in the generalized spherical functions. We extend our cumulant approach for solving the scalar (unpolarized) photon transport equation to the vector (polarized) case. As before, an exact angular distribution is obtained and a cumulant expansion is derived for the polarized photon distribution function. By a cutoff at the second cumulant order, a Gaussian analytical approximate expression of the polarized photon spatial distribution is obtained as a function of the direction of light and time, whose average center position and half-width are always exact. The central limit theorem claims that this spatial distribution approaches accuracy in detail when the number of collisions or time becomes large. The analytical expression of cumulants up to an arbitrary high order is also derived, which can be used for calculating a more accurate polarized photon distribution through a numerical Fourier transform. Contrary to what occurs in other approximation techniques, truncation of the cumulant expansion at order n is exact at that order and cumulants up to and including order n remain unchanged when higher orders are added, at least as applied in our photon transport equation.

Journal Article↗

PubMed2000

Intracerebral hemodynamics probed by near infrared spectroscopy in the transition between wakefulness and sleep.

Previous imaging studies have shown that cerebral metabolism is gradually reduced at the beginning of sleep. Few studies have examined the sleep state transition periods from wakefulness to sleep and sleep to wakefulness. The current study used the Near Infrared Spectroscopy (NIRS) technique to describe the intracerebral hemodynamics at the frontal pole in the circumscribed period between wakefulness and sleep. Nine healthy young adults were studied during afternoon naps. Optical probes were placed on the forehead and EEG electrodes on the scalp. At sleep onset oxygenated hemoglobin (oxy-Hb) was reduced (P<0.01) and deoxygenated hemoglobin (deoxy-Hb) showed a near significant reduction (P<0.063). At sleep offset there were increases in oxy-Hb (P<0.005) and deoxy-Hb (P<0.05). In 18 of 26 transitions to sleep there was a coordinated fall in both NIRS parameters, we call the Switch Point, that lasted a mean of 3.6 s. In 32 of 36 transitions to wakefulness there was an analogous Switch Point that lasted a mean of 3.4 s. Before and after the Switch Point, changes were small and the relationship between oxy-Hb and deoxy-Hb was a combination of parallel and reciprocal fluctuations. A synchronized, parallel and short-lived change in oxy-Hb and deoxy-Hb is a discrete event in the transition period between wakefulness and sleep. The concentration of these light absorbing molecules is abruptly set to a new level at sleep-wake transitions and probably reflects the different perfusion demands of these states.

Adult↗

PubMed2000

Laser irradiative tissue probed in situ by collagen 380-nm fluorescence imaging.

BACKGROUND AND OBJECTIVE: There is no ideal method to detect molecular changes in situ of laser-irradiated tissue without removing a section of tissue for histologic examination. A new method is reported to evaluate laser-induced thermal tissue damage in situ by using 380-nm native fluorescence imaging under 340-nm excitation. STUDY DESIGN/MATERIALS AND METHODS: Native fluorescence imaging was performed on laser irradiated bovine tendon tissue and compared with light illuminated photography and histology with picrosirius red F3BA stain. RESULTS AND CONCLUSION: The results indicate that a decrease in collagen fluorescence at 380 nm was observed in laser-induced thermally damaged tissues. The injured region of tissue defined by its fluorescence image coincided with an area defined by photography and histology.

Animals↗

PubMed2000

Brain perfusion monitoring with frequency-domain and continuous-wave near-infrared spectroscopy: a cross-correlation study in newborn piglets.

The newborn piglet brain model was used to correlate continuous-wave (CW) and frequency-domain (FD) near-infrared spectroscopy. Six ventilated and instrumented newborn piglets were subjected to a series of manipulations in blood oxygenation with the effects on brain perfusion known to be associated with brain hypoxia-ischaemia. An excellent agreement between the CW and FD was demonstrated. This agreement improved when the scattering properties (determined by the FD device) were employed to calculate the differential pathlength factor, an important step in CW data processing.

Animals↗

PubMed2000

A comparison of Cunyite and Fosterite NIR tunable laser tissue welding using native collagen fluorescence imaging.

OBJECTIVE: To evaluate the technique of native collagen fluorescence imaging for assessing the extent of welded areas for tissues exposed to different near-infrared (NIR) laser wavelengths. BACKGROUND: Native fluorescence imaging may be used to identify the distribution of collagen and elastin in tissues. Our past work demonstrated that different welding strengths were obtained under the same laser power conditions using different NIR wavelengths. The role of collagen in tissue welding experiments is not well understood. METHODS: Two new NIR tunable lasers were used to weld canine skin. The welded areas on the surface and in cross sections were analyzed by measuring the spatial distribution of native collagen fluorescence at 380 nm excited by 340 nm radiation. RESULTS: The results show that native collagen fluorescence imaging is a useful technique for analyzing the extent of tissue welds produced under a range of laser exposures. Fluorescence imaging reveals the depth of laser interaction with the tissue as well as evaluating collateral damage to the tissue surface. The welded volume obtained in skin using Cunyite laser exposure at 1,430 nm is deeper than that produced with Forsterite laser exposure at 1,250 nm. The post welded tensile strength for the same power density is greater for the Cunyite lasers. Ablated tissue on the surface is more prevalent with Forsterite laser welding at 1,250 nm than with Cunyite at 1,430 nm. CONCLUSION: Native collagen fluorescence can distinguish between tissue welds that have been produced by different NIR wavelengths. Tissue welding using 1,430 nm radiation is more effective than that using 1,250 nm.

Animals↗