Manuel Zevallos

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 700nm, 800nm, 1200nm, and 1450nm 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 H2O molecules in the NIR.

Optical tomographic image reconstruction from ultrafast time-sliced transmission measurements

Optical imaging and localization of objects inside a highly scattering medium, such as a tumor in the breast, is a challenging problem with many practical applications. Conventional imaging methods generally provide only two-dimensional (2-D) images of limited spatial resolution with little diagnostic ability. Here we present an inversion algorithm that uses time-resolved transillumination measurements in the form of a sequence of picosecond-duration intensity patterns of transmitted ultrashort light pulses to reconstruct three-dimensional (3-D) images of an absorbing object located inside a slab of a highly scattering medium. The experimental arrangement used a 3-mm-diameter collimated beam of 800-nm, 150-fs, 1-kHz repetition rate light pulses from a Ti:sapphire laser and amplifier system to illuminate one side of the slab sample. An ultrafast gated intensified camera system that provides a minimum FWHM gate width of 80 ps recorded the 2-D intensity patterns of the light transmitted through the opposite side of the slab. The gate position was varied in steps of 100 ps over a 5-ns range to obtain a sequence of 2-D transmitted light intensity patterns of both less-scattered and multiple-scattered light for image reconstruction. The inversion algorithm is based on the diffusion approximation of the radiative transfer theory for photon transport in a turbid medium. It uses a Green s function perturbative approach under the Rytov approximation and combines a 2-D matrix inversion with a one-dimensional Fourier-transform inversion to achieve speedy 3-D image reconstruction. In addition to the lateral position, the method provides information about the axial position of the object as well, whereas the 2-D reconstruction methods yield only lateral position.

Two-dimensional near-infrared transillumination imaging of biomedical media with a chromium-doped forsterite laser

Transillumination images of objects hidden in normal and cancerous human breast tissues and bovine, porcine, and gallinaceous (chicken) tissues as well as model-random-scattering media were recorded with 1250-nm light from a chromium-doped forsterite laser. A Fourier space gate and a polarization gate were used to sort out image-bearing photons and discriminate against multiply scattered image-blurring photons. Better contrast, higher spatial resolution, and deeper penetration of samples were achieved for imaging with 1250-nm light than those obtained at shorter wavelengths, such as 1064 nm from a neodymium-doped yttrium aluminum garnet (YAG) laser. Better contrast and higher resolution were also obtained when the object was imaged through normal human breast tissue than through cancerous breast tissue. Images with marked distinction between fatty and fibrous human breast tissues were obtained when the Cr:forsterite laser was tuned to 1225 nm, a wavelength that resonates with an optical absorption band of breast fat tissues. Imaging with linearly polarized light revealed that the image quality depends significantly on the orientation of the polarization of the incident light with respect to the fibers in the bovine tissue.

Picosecond electronic time-gated imaging of bones in tissues

Two-dimensional in vivo optical images of metacarpal bones of a human palm and in vitro images of turkey and chicken bones embedded in tissues were obtained in the near-infrared region using femtosecond pulse transillumination and picosecond electronic time-sliced detection technique. A small hole drilled in chicken bone and embedded in chicken breast tissue was imaged using early arriving light. Time-gated fluorescence images of an interior marrow region of a bone injected with a fluorescent dye were recorded. The techniques have potential for monitoring bone fracture, bone diseases such as, osteoporosis and arthritis, and diseases that originate in or affect bone marrow.

Analysis of time-resolved data for tomographical image reconstruction of opaque phantoms and finite absorbers in diffusive media

Experimental time-resolved data was used for direct reconstruction of images of laboratory phantoms in highly scattering media. Using different time zones of the temporal profiles, computed images were calculated by solving a one-step linear perturbation equation derived from transport theory. In nearly all cases tested, high quality reconstructions were obtained even for highly undermined problems.

Computer-controlled optical scanning tile microscope

A new type of computer-controlled optical scanning, high-magnification imaging system with a large field of view is described that overcomes the commonly believed incompatibility of achieving both high magnification and a large field of view. The new system incorporates galvanometer scanners, a CCD camera, and a high-brightness LED source for the fast acquisition of a large number of a high-resolution segmented tile images with a magnification of 800x for each tile. The captured segmented tile images are combined to create an effective enlarged view of a target totaling 1.6 mm x 1.2 mm in area. The speed and sensitivity of the system make it suitable for high-resolution imaging and monitoring of a small segmented area of 320 microm x 240 microm with 4 microm resolution. Each tile segment of the target can be zoomed up without loss of the high resolution. This new microscope imaging system gives both high magnification and a large field of view. This microscope can be utilized in medicine, biology, semiconductor inspection, device analysis, and quality control.

Detection of subsurface defects using a hybrid heating and cooling imaging technique

A middle infrared imaging technique combining sequential heating and cooling of the material is shown to detect internal defects in composite materials. A low power flash lamp is used as the heat source to raise the temperature of the material above the ambient temperature. Alcohol is spread on the front surface of the heated sample to cause rapid cooling and removal of the thermal wall. This technique induces thermal waves in the composite material, reduces the diffusive photons, and enables recording better images of internal defects by a mid-infrared camera. The technique provides substantial improvement over existing methodologies currently in use for nondestructive evaluation of subsurface defects and cracks in materials.

Time-sliced, two-dimensional, near-infrared imaging of normal and malignant human breast tissues

Development of optical modalities for screening of breast cancer is an intensely pursued area of contemporary research. Here, the authors present the initial results of a time-sliced transillumination imaging approach to image and distinguish between normal and cancerous regions of in vitro breast tissue samples. The approach uses optimal picosecond-scale slices of the transmitted light pulse to form images. The experimental arrangement used 800 nm, approximately 130-fs duration, l-kHz repetition-rate pulses with 400-mW average beam power from a Ti:sapphire laser system for transillumination imaging. The beam was expanded by a beam expander, and a 3-cm diameter central part of it was selected out using an aperture to illuminate the sample. Time slicing was accomplished using a gated image intensifier coupled to a charge-coupled device (CCD) camera system that provided an electronic gate pulse whose duration (full width at half maximum) could be adjusted to a minimum of 80 ps and the position could be varied in steps of 25 ps over a 15-ns range. The time-sliced image was recorded by the CCD camera and displayed on a personal computer. The breast tissue sample consisted of a cancerous piece placed between two normal pieces of 5-mm nominal thickness and lateral dimensions between 8-14 mm. The pieces were compressed between two glass plates to provide uniform thickness and good physical contact between the adjacent pieces of tissue. The tissues obtained from National Disease Research Interchange came from the left breast of a 61-yr-old female patient.

Near infrared imaging of human prostate cancerous and normal tissues based on water absorption

Near-infrared imaging measurements were performed on human prostate cancerous and normal tissues. The absorption of water fingerprints in cancerous and normal tissues were studied, and used to distinguish prostate cancerous tissue from surrounding normal tissues.

Wireless spectroscopic Compact Photonic Explorer

A remote, spectroscopic-based Compact Photonics Explorer was designed, assembled, and tested. Spectral images were acquired with the CPE and transmitted to a remote computer.Images will be presented, demonstrating the operational principles for various biomedical applications.