Rinat O. Esenaliev

PURIFICATION OF SINGLE-WALL CARBON NANOTUBES BY ULTRASONICALLY ASSISTED FILTRATION

Abstract An efficient method for purification of single-wall carbon nanotubes (SWNT) synthesized by the laser-vaporization process has been developed. Amorphous and crystalline carbon impurities and metal particles are removed from SWNT samples by ultrasonically-assisted microfiltration. Sample sonication during the filtration prevents filter contamination and provides for a fine nanotube–nanoparticle suspension throughout the purification process. The process generates SWNT material with purity of more than 90% and yields of 30–70%, depending on the quality of the starting material. Nanotubes in purified samples are shorter than in pristine samples due to some sonication-induced nanotube cutting. Nanotube bundles in purified samples are also substantially thicker due to spontaneous nanotube alignment.

Sensitivity of laser opto-acoustic imaging in detection of small deeply embedded tumors

Current imaging modalities fail to detect small tumors in the breast. Opto-acoustic tomography is a novel technique for early cancer detection with promising diagnostic capability. The experimental limit of sensitivity and maximal depth of the laser opto-acoustic detection for small model tumors located within bulk phantom tissue were studied. Two phantoms with optical properties similar to that of breast tissue in the near infrared spectral range were used in these studies: turbid gelatin slabs with the thickness of 100 mm and chicken breast muscle slabs with the thickness of up to 80 mm. Gelatin spheres with enhanced absorption coefficient relative to the background absorption and liver tissue were used to simulate small tumors. The experiments demonstrated the capability of laser optoacoustic imaging to detect and localize phantom tumors with the diameter of 2 mm at a depth of up to 60 mm within the gelatin phantoms and 3/spl times/2/spl times/0.6-mm piece of liver tissue within 80-mm chicken breast tissue. Theoretical studies on sensitivity of opto-acoustic detection at various diameters, depths of location, and absorption coefficients of small tumors were performed using the experimental data. Our results suggest that the opto-acoustic imaging may occupy a significant niche in early detection of cancer in the breast and other organs.

Effects of monochromatic low‐intensity light and laser irradiation on adhesion of HeLa cells in vitro

The adhesion of HeLa cells was evaluated after irradiation with monochromatic low‐intensity light or laser irradiation. It is well known that the cell‐cell and cell‐matrix adhesion changes during wound repair. For better understanding of low‐power laser light action on the wound healing process, it would be of interest to study the light action on cellular adhesion in vitro.

Laser-based optoacoustic imaging in biological tissues

A new technique based on time-resolved detection of laser-induced stress transients is proposed to visualize the distribution of absorbed laser fluence in turbid and layered biological tissues.

Laser optoacoustic tomography for medical diagnostics: principles

This paper is to describe principles of laser optoacoustic tomography for medical diagnostics. Two types of imaging modes are presented. The first is the tomography in transmission mode, which utilizes detection of stress transients transmitted from the laser-excited volume toward the depth through thick layers of tissue. The second is the tomography in reflection mode which utilizes detection of stress transients generated in superficial tissue layer and reflected back toward tissue surface. To distinguish the two modes, we have abbreviated them as (1) laser optoacoustic tomography in transmission mode, LOATT, and (2) time-resolved stress detection tomography of light absorption, TRSDTLA, in reflection mode where emphasis is made on high spatial resolution of images. The basis for laser optoacoustic tomography is the time-resolved detection of laser-induced transient stress waves, selectively generated in absorbing tissues of diagnostic interest. Such a technique allows one to visualize absorbed light distribution in turbid biological tissues irradiated by short laser pulses. Laser optoacoustic tomography can be used for detection of tissue pathological changes that result in either increased concentration of various tissue chromophores such as hemoglobin or in development of enhanced microcirculation in diseased tissue. Potential areas of applications are diagnosis of cancer, brain hemorrhages, arterial atherosclerotic plaques, and other diseased tissues. In addition, it can provide feedback information during medical treatments. Both LOATT and TRSDTLA utilize laser excitation of biological tissues and sensitive detection of laser-induced stress waves. Optical selectivity is based upon differences in optical properties of pathologically different tissues. Sensitivity comes from stress generation under irradiation conditions of temporal stress confinement. The use of sensitive wide-band lithium niobate acoustic transducers expands limits of laser optoacoustic tomography. The technology allows us to determine directly temperature distributions in tissues and locate tissues volumes with different absorption. To demonstrate principles of TRSDTLA, experiments were conducted in vivo with mice-model for breast cancer using specially designed front-surface transducers- reflectometers. To present advantages and limitation of LOATT, experiments were performed in phantoms made of gel with polystyrene spheres colored with copper sulfate. Our experimental results and theoretical calculations show that TRSDTLA can be applied for non- invasive histology of layered tissues with in-depth resolution of up to 2 microns. TRSDTLA in acoustic reflection mode is promising for diagnostics of skin and ocular diseases. LOATT in acoustic transmission mode can be applied for detection of small tissue volumes with enhanced absorption located inside organs at the depth of up to 10 cm.

Laser ablation of aqueous solutions with spatially homogeneous and heterogeneous absorption

The ablation efficiency of aqueous solutions with different concentrations and spatially homogeneous (CuCl2 solution) and heterogeneous (ink solution) absorption was studied as a function of the pulse-energy fluence (Nd:YAG laser, λ=1064 nm, τp = 20 ns). The latter was varied over a wide range from 0.15 J/cm2 to 8.00 J/cm2. The ablation threshold of solutions with heterogeneous absorption was found to be much lower (3 to 4 times) than the ablation threshold of solutions with homogeneous absorption and with the same average absorption coefficient. The ablation efficiency of heterogeneous solutions was higher by more than an order of magnitude. It was found that the ablation efficiency increases drastically for both types of solutions as the pulse energy fluence was raised to exceed the ablation threshold by 2 or 3 times. At such energy fluences, along with small droplets, larger droplets (1.5–2 mm cross section) could be ejected. This points to the ablation of solutions being affected by a hydrodynamic shock formed as a result of the pulsed recoil pressure excerted by the ablation products. The differences between the ablation processes for solutions with homogeneous and heterogeneous absorption as well as the hydrodynamic destruction at high energy fluences are discussed.

Lateral and z-axial resolution in laser optoacoustic imaging with ultrasonic transducers

Our studies are directed towards the development of a pulsed laser based optoacoustic technique to visualize absorbed light distribution in irradiated tissues. Optoacoustic technique utilizes the time-resolved detection of laser-induced stress transients to visualize absorbed laser fluence distribution in opaque and heterogeneous tissues. The acoustic signal induced under confined stress conditions of irradiation by an Nd:YAG laser pulse displays Z-axial light distribution and may be used for imaging the tissue layers where a temperature-rise of about 1 degree(s)C is achieved. Scanning of the acoustic transducer along the tissue surface line by line until entire surface of interest is tested, permits reconstruction of a 3D optoacoustic image of the irradiated tissue. Z-axial resolution of optoacoustic imaging is defined as a product of the temporal resolution of piezoelectric transducer and the speed of sound in tissues. Lateral (radial) resolution of optoacoustic images is a funtion of piezoelectric detector diameter, the diameter of laser-induced acoustic wave, and a depth of optoacoustic probing (acoustic diffraction factor). The role of various parameters, such as tissue optical properties, tissue thickness, laser beam diameter, and diameter of piezoelectric element, were evaluated for imaging resolution in lateral direction. The results of our studies demonstrated that a broad- band acoustic transducer may become a useful tool for in vivo diagnostic imaging and feed- back information during clinical laser procedures. First in vivo measurements were performed and found to be in agreement with tissue histology. This study is a very first step in the basic design of optoacoustic tomographic technology for light absorbing tissues.

Laser optoacoustic imaging for breast cancer diagnostics: limit of detection and comparison with x-ray and ultrasound imaging

Laser optoacoustic imaging is a promising diagnostic technique for early breast cancer detection. Capability of laser optoacoustic imaging for visualization of small spherical tumor phantoms located within the bulk collagen gels was studied. The experiments were performed with breast phantoms made of optically turbid collagen gel. Optical properties of the phantom resembled the optical properties of human breast at the wavelength of irradiation, 1064 nm ((mu) a equals 0.11 1/cm, (mu) s equals 2.92 1/cm). Gel spheres with a higher absorption coefficient, (mu) v equals 0.75 1/cm were used to simulate tumors. The experiments demonstrated the capability of laser optoacoustic imaging to detect and localize 2-mm tumors at a depth of up to 60 mm within 100-mm thick breast phantoms. Laser optoacoustic images of the phantom tumors were reconstructed from experimentally measured pressure profiles. The optoacoustic images were compared with images obtained with x-ray mammography and ultrasonography. Comparative study revealed experimental conditions and phantom structure for which the laser optoacoustic imaging outperformed both the x-ray mammography and the ultrasonography. The results suggest that the laser optoacoustic imaging may occupy an important niche in breast cancer diagnostics, particularly, for diagnosis of small tumors in radiologically dense and acoustically homogeneous breast tissues.

Pulsed laser ablation of soft tissues, gels, and aqueous solutions at temperatures below 100°C

It is desirable for laser microsurgical procedures to remove tissue accurately and with minimal thermal and mechanical damage to adjacent non‐irradiated tissues. Pulsed laser ablation can potentially remove biological tissue with microprecision if appropriate irradiation conditions are applied. The major goal of this study was to determine whether laser ablation is possible at temperatures below 100°C. Another aim was to test thermoelastic and recoil stress magnitudes and to estimate their effects on phantom and biological tissue.

Accurate measurement of total attenuation coefficient of thin tissue with optical coherence tomography

Noninvasive accurate measurements of tissue optical properties are needed for many diagnostic and therapeutic applications. Optical coherence tomography (OCT) recently proposed for high-resolution imaging in tissue can potentially be applied for accurate, noninvasive, and high-resolution measurement of tissue total attenuation coefficient. However, confocal function (dependence of OCT sensitivity on the distance of probed site from the focal plane of the objective lens) and multiple scattering substantially limit the accuracy of the measurement with the OCT technique. We studied the influence of the confocal function and multiple scattering on the accuracy of the measurement and proposed methods that provide measurement of the total attenuation coefficient with a significantly reduced systematic error. Experiments were performed in tissue phantoms and porcine and human skin in vitro and in vivo. Our data indicate that the tissue total attenuation coefficient can noninvasively be measured in vivo with the accuracy of 5%-10% in the range from 0.5 to 17 mm/sup -1/ and about 20% in the range up to 40 mm/sup -1/. These results suggest that the proper correction of the OCT-based measurement for the confocal function and multiple scattering provides absolute values of tissue total attenuation coefficient with high accuracy and resolution that may not be achievable by other optical techniques in vivo.