M. Alrubaiee

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.

Synthesis and optical spectroscopy of a hybrid cadmium sulfide-dendrimer nanocomposite

Hybrid nanocomposites of cadmium sulfide (CdS) quantum dots and poly(propyleneimine) dendrimer having a 1,4-diaminobutane core have been produced by colloidal synthesis in degassed methanol at room temperature using third-, fourth-, and fifth-generation (G5.0) dendrimers, and their spectroscopic properties have been investigated. The nanoparticles fluoresced from 375 to 650 nm under near-ultraviolet excitation, and their absorption spectra exhibited a strong blueshift of the band edge compared to that of the bulk CdS. The stability of nanocomposites depended significantly, while the size and spectroscopic properties exhibited a weaker dependence, on the dendrimer generation. Most compact and stable nanoparticles were obtained with G5.0 dendrimers. Average diameter was estimated to be 2.2±0.3 nm, assuming nanoparticles of spherical shape within an infinite well potential. The room-temperature luminescence has a fast component with 165±5 ps lifetime and a slow component with a 40±2 ns lifetime. The luminescence is partially polarized with an initial anisotropy of 0.39±0.02.

Three-dimensional localization and optical imaging of objects in turbid media with independent component analysis

A new approach for optical imaging and localization of objects in turbid media that makes use of the independent component analysis (ICA) from information theory is demonstrated. Experimental arrangement realizes a multisource illumination of a turbid medium with embedded objects and a multidetector acquisition of transmitted light on the medium boundary. The resulting spatial diversity and multiple angular observations provide robust data for three-dimensional localization and characterization of absorbing and scattering inhomogeneities embedded in a turbid medium. ICA of the perturbations in the spatial intensity distribution on the medium boundary sorts out the embedded objects, and their locations are obtained from Greens function analysis based on any appropriate light propagation model. Imaging experiments were carried out on two highly scattering samples of thickness approximately 50 times the transport mean-free path of the respective medium. One turbid medium had two embedded absorptive objects, and the other had four scattering objects. An independent component separation of the signal, in conjunction with diffusive photon migration theory, was used to locate the embedded inhomogeneities. In both cases, improved lateral and axial localizations of the objects over the result obtained by use of common photon migration reconstruction algorithms were achieved. The approach is applicable to different medium geometries, can be used with any suitable photon propagation model, and is amenable to near-real-time imaging applications.

Systematic studies of fractal dimension parameters, absorption and scattering coefficients for cancerous and normal prostate tissues

The optical coefficients (μs, μa, μs and g)of human cancerous and normal prostate tissues were investigated and compared in the spectral range of 750nm - 860 nm. The fractal dimensional parameters including fractal dimension (Df), cutoff diameter (dmax) and the most efficient diameter (dm) between the cancerous and normal prostate tissues were determined based on the extinction and diffusion reflection intensity measurements and the determination ofμs, μa, μs and g. The results are in good agreement with prostate cancer evolution defined by Gleason Grades. The difference of fractal dimensional parameters and optic

Spectral and temporal near-infrared imaging of ex vivo cancerous and normal human breast tissues.

Cancerous and normal ex vivo human breast tissues were investigated using spectroscopic and time-sliced two-dimensional (2-D) transillumination imaging methods in order to demonstrate the importance and potential of spectral and temporal measurements in breast cancer detection and diagnosis. The experimental arrangement for time-sliced optical imaging used 120 fs, 1 kHz repetition-rate, 800 nm light pulses from a Ti:sapphire laser system for sample illumination, and a 80 ps resolution ultrafast gated intensified camera system for recording 2-D time-sliced images. The spectroscopic imaging arrangement used 1225–1300 nm tunable output of a Cr: forsterite laser for sample illumination, a Fourier space gate to discriminate against multiple-scattered light, and a near-infrared area camera to record 2-D images. Images recorded with earlier temporal slices of transmitted light highlighted tumors, while those recorded with later slices accentuated normal tissues. When light was tuned closer to the 1203 nm absorption resonance of adipose tissues, a marked enhancement in contrast between the images of adipose and fibrous tissues was observed. A similar wavelength-dependent difference between normal and cancerous tissues was observed. These results correlate well with pathology and nuclear magnetic resonance based analyses of the samples.

Time-resolved and quasi-continuous wave three-dimensional tomographic imaging of objects in tissue-like turbid media

Time-sliced and quasi continuous wave two-dimensional (2-D)transillumination imaging methods were used with independent component analysis (ICA) to generate three-dimensional (3-D)tomographic maps of absorbing and scattering inhomogeneities embedded in tissue-like turbid media. The thickness of the turbid media in both the cases was approximately 50 times the transport mean free path. The experimental arrangement for time-sliced optical imaging used 150-fs, 1 kHz repetition-rate, 800-nm light pulses from a Ti:sapphire laser system for sample illumination, and an ultrafast gated intensified camera system (UGICS) providing a minimal gate duration of 80 ps for recording 2-D images. Quasi continuous wave (CW) imaging used 784-nm CW output of a diode laser as the light source and a cooled charge coupled device (CCD) camera for recording 2-D images. Translation stages were used to scan the samples over an array of points in the x-y plane. The temporal profile of the transmitted pulse was used to extract the average optical properties of the media. An independent component separation of the signal, in conjunction with diffusive photon migration theory was used to locate the embedded inhomogeneities. An improved lateral and axial localization of the inhomogeneity over the result obtained by common photon migration reconstruction algorithm is achieved.

Near-Infrared Center-of-Intensity Time Gated Imaging for Detection of a Target in a Highly Scattering Turbid Medium

A near-infrared optical imaging approach for locating a target embedded in a turbid medium is introduced. The target localization is based on an analysis of the spatial variation of the transmitted-light intensity distribution for illumination at different positions on the sample boundary. The approach is used to detect, locate and generate images of absorbing targets embedded inside model scattering media of thickness approximately 50 times the transport mean free path of the medium, as well as, of ex vivo biological tissue specimens.

Two-dimensional transillumination imaging of tissues using 1250 nm light from a tunable chromium-doped forsterite laser

In this presentation, the authors report on near-infrared (NIR) imaging of objects hidden inside bovine, chicken, and porcine and, more importantly, normal and cancerous human breast tissues of different thicknesses using a Cr/sup 4+/:forsterite laser that operates over the 1150- to 1350-nm spectral range and a Nd:YAG (yttrium aluminum garnet) laser operating at 1064 nm. Fourier space and polarization gates were used to discriminate against the image-blurring scattered light. The experimental arrangement used for NIR imaging is displayed schematically in a figure. The output beam of a Cr/sup 4+/:forsterite laser with an average power of 100 mW was expanded to a 10-mm-diameter beam to illuminate the sample. Light from the Nd:YAG laser with the similar beam diameter and average power was also used to image the object through the same set of tissue samples for comparison. The samples were placed between two movable parallel glass plates that slightly compressed them. A 1.5-mm diameter black metal bar was used as the object. A 4fFourier space gate with a 1.5-mm diameter aperture was used to reduce the off-axis multiple-scattered light. The transmitted image-bearing light was monitored by a 128/spl times/128 pixels InGaAs NIR area camera. A polarization gate was implemented using a linear polarizer before the camera to measure the components of the transmitted light polarized parallel and perpendicular to that of the incident light. No time gate was used.

Optical high resolution cross section imaging of a human breast model using independent component analysis

Optical imaging using independent component analysis (OPTICA) is enhanced to provide a high resolution cross section imaging of objects in a turbid medium by a backprojection technique. The performance is demonstrated by imaging a human breast model made of ex vivo human breast tissues. Cancerous site of 5mm size is detected at the midplane of the 33mm thick breast model. The reconstructed cross section image compares favorably with pathology findings.

Supercontinuum Interference from Fresnel Diffraction Caused by Periodic Filamentation

Periodic filaments produced from diffraction were demonstrated in BK7 glass using femtosecond laser pulses. Stable ring and fringe patterns were observed and contributed to the interference of supercontinuum generation from these kind of periodic structure