Publications by Year: 2011

I. Barman, Dingari, N. C., Rajaram, N., Tunnell, J. W., Dasari, R. R., and Feld, M. S., “Rapid and accurate determination of tissue optical properties using least-squares support vector machines.,” Biomed Opt Express, vol. 2, no. 3, pp. 592-9, 2011.Abstract
Diffuse reflectance spectroscopy (DRS) has been extensively applied for the characterization of biological tissue, especially for dysplasia and cancer detection, by determination of the tissue optical properties. A major challenge in performing routine clinical diagnosis lies in the extraction of the relevant parameters, especially at high absorption levels typically observed in cancerous tissue. Here, we present a new least-squares support vector machine (LS-SVM) based regression algorithm for rapid and accurate determination of the absorption and scattering properties. Using physical tissue models, we demonstrate that the proposed method can be implemented more than two orders of magnitude faster than the state-of-the-art approaches while providing better prediction accuracy. Our results show that the proposed regression method has great potential for clinical applications including in tissue scanners for cancer margin assessment, where rapid quantification of optical properties is critical to the performance.
L. Lim, Nichols, B., Rajaram, N., and Tunnell, J. W., “Probe pressure effects on human skin diffuse reflectance and fluorescence spectroscopy measurements.,” J Biomed Opt, vol. 16, no. 1, pp. 011012, 2011.Abstract
Diffuse reflectance and fluorescence spectroscopy are popular research techniques for noninvasive disease diagnostics. Most systems include an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. The purpose of this study is to investigate probe pressure effects on human skin spectroscopic measurements. We conduct an in-vivo experiment on human skin tissue to study the short-term (<2 s) and long-term (>30 s) effects of probe pressure on diffuse reflectance and fluorescence measurements. Short-term light probe pressure (P0<9 mN∕mm2) effects are within 0 ± 10% on all physiological properties extracted from diffuse reflectance and fluorescence measurements, and less than 0±5% for diagnostically significant physiological properties. Absorption decreases with site-specific variations due to blood being compressed out of the sampled volume. Reduced scattering coefficient variation is site specific. Intrinsic fluorescence shows a large standard error, although no specific pressure-related trend is observed. Differences in tissue structure and morphology contribute to site-specific probe pressure effects. Therefore, the effects of pressure can be minimized when the pressure is small and applied for a short amount of time; however, long-term and large pressures induce significant distortions in measured spectra.
R. T. Zaman, Rajaram, N., Walsh, A., Oliver, J., Rylander, H. G., Tunnell, J. W., Welch, A. J., and Mahadevan-Jansen, A., “Variation of fluorescence in tissue with temperature.,” Lasers Surg Med, vol. 43, no. 1, pp. 36-42, 2011.Abstract
BACKGROUND AND OBJECTIVE: Previous studies demonstrated a decrease in fluorescence intensity as tissue temperature increased. In vitro samples were increased from room temperature and in vivo canine liver from body temperature. This study investigated variations in fluorescence intensity with temperatures starting at 14°C and compared in vivo and in vitro results for consistency. STUDY DESIGN/MATERIAL AND METHODS: A fiber optic-based noninvasive system was used to characterize the temperature effect on tissue fluorescence in hamster dorsal skin in vivo, and in sclera and cornea of enucleated pig eyes in vitro. As tissue was allowed to progress through the temperature range of 14-42°C, the spectra of auto-fluorescence with respect to temperature was sampled every 1-2 minutes. A pulsed nitrogen laser was used to excite fluorescence through a fiber optic probe with a source-detector aperture separation of 370 µm. RESULTS: Fluorescence intensity decreased as temperature increased from 14 to 42°C in a phantom containing Rhodamine B dye. Results from both in vivo and in vitro tissue followed the same trend of decreasing intensity as tissue temperature increased from 14°C. Spectral intensity lineshape changed around 450 nm due to absorption from tissue. CONCLUSION: Cooling a tissue increased fluorescence intensity of skin in vivo, in all experiments. In vitro results were consistent with in vivo measurements.
S. F. Bish, Rajaram, N., Nichols, B., and Tunnell, J. W., “Development of a noncontact diffuse optical spectroscopy probe for measuring tissue optical properties.,” J Biomed Opt, vol. 16, no. 12, pp. 120505, 2011.Abstract
Optical reflectance probes are often used as tools to obtain optical spectra from superficial tissues and subsequently determine optical and physiological properties associated with early stage cancer. These probes, when placed directly on the tissue, are known to cause significant pressure-dependent changes in local optical properties. To address this, we fit the probe with an optical device that images the illumination and collection fibers onto the tissue surface, eliminating the influence of contact probe pressure on the sampling area. The noncontact probe addition addresses new optical conditions that may affect its performance such as tissue surface contour, and specular reflections by implementing an autofocusing mechanism and cross polarization. Extracted optical properties of tissue simulating phantoms yield errors of 3.46% in reduced scattering and 8.62% in absorbance. Autofocusing has extended the depth of field from 4 mm to throughout the 12 mm range of autofocus travel, while cross polarization has removed the incidence angle dependent specular reflection component from the collected signal.
R. T. Zaman, Rajaram, N., Nichols, B. S., Rylander, H. G., Wang, T., Tunnell, J. W., and Welch, A. J., “Changes in morphology and optical properties of sclera and choroidal layers due to hyperosmotic agent.,” J Biomed Opt, vol. 16, no. 7, pp. 077008, 2011.Abstract
Light scattering in the normally white sclera prevents diagnostic imaging or delivery of a focused laser beam to a target in the underlying choroid layer. In this study, we examine optical clearing of the sclera and changes in blood flow resulting from the application of glycerol to the sclera of rabbits. Recovery dynamics are monitored after the application of saline. The speed of clearing for injection delivery is compared to the direct application of glycerol through an incision in the conjunctiva. Although, the same volume of glycerol was applied, the sclera cleared much faster (5 to 10 s) with the topical application of glycerol compared to the injection method (3 min). In addition, the direct topical application of glycerol spreads over a larger area in the sclera than the latter method. A diffuse optical spectroscopy system provided spectral analysis of the remitted light every two minutes during clearing and rehydration. Comparison of measurements to those obtained from phantoms with various absorption and scattering properties provided estimates of the absorption coefficient and reduced scattering coefficient of rabbit eye tissue.
C. M. Hessel, Pattani, V. P., Rasch, M., Panthani, M. G., Koo, B., Tunnell, J. W., and Korgel, B. A., “Copper selenide nanocrystals for photothermal therapy.,” Nano Lett, vol. 11, no. 6, pp. 2560-6, 2011.Abstract
Ligand-stabilized copper selenide (Cu(2-x)Se) nanocrystals, approximately 16 nm in diameter, were synthesized by a colloidal hot injection method and coated with amphiphilic polymer. The nanocrystals readily disperse in water and exhibit strong near-infrared (NIR) optical absorption with a high molar extinction coefficient of 7.7 × 10(7) cm(-1) M(-1) at 980 nm. When excited with 800 nm light, the Cu(2-x)Se nanocrystals produce significant photothermal heating with a photothermal transduction efficiency of 22%, comparable to nanorods and nanoshells of gold (Au). In vitro photothermal heating of Cu(2-x)Se nanocrystals in the presence of human colorectal cancer cell (HCT-116) led to cell destruction after 5 min of laser irradiation at 33 W/cm(2), demonstrating the viabilitiy of Cu(2-x)Se nanocrystals for photothermal therapy applications.
Biophotonics Series: In vivo clinical imaging and diagnostics. New York: McGraw-Hill, 2011.