Biomedical subjects

Taner Akkin

Publications and source records attributed to Taner Akkin.

7 recordsLinked to original sources

PubMed2005

Spectral-domain optical coherence phase microscopy for quantitative phase-contrast imaging.

We describe a novel microscopy technique for quantitative phase-contrast imaging of a transparent specimen. The technique is based on depth-resolved phase information provided by common path spectral-domain optical coherence tomography and can measure minute phase variations caused by changes in refractive index and thickness inside the specimen. We demonstrate subnanometer level path-length sensitivity and present images obtained on reflection from a known phase object and human epithelial cheek cells.

Cells, Cultured↗

PubMed2004

Quantitative phase-contrast imaging of cells with phase-sensitive optical coherence microscopy.

We describe a method for en face phase-contrast imaging of cells with a fiber-based differential phase-contrast optical coherence microscopy system. Recorded en face images are quantitative phase-contrast maps of cells due to spatial variation of the refractive index and (or) thickness of various cellular components. Quantitative phase-contrast images of human epithelial cheek cells obtained with the fiber-based differential phase-contrast optical coherence microscopy system are presented.

Cheek↗

PubMed2004

Phase-sensitive optical low-coherence reflectometry for the detection of analyte concentrations.

Optical techniques may potentially be used for noninvasive glucose sensing. We investigated the application of phase-sensitive optical low-coherence reflectometry (PS-OLCR) to the measurement of analyte concentrations. The dependence of the PS-OLCR signal on the concentration of various analytes, including aqueous solutions of glucose, calcium chloride, magnesium chloride, sodium chloride, potassium chloride, potassium bicarbonate, urea, bovine serum albumin, and bovine globulin, were determined in clear and turbid media. Obtained results demonstrated (1) a high degree of sensitivity and accuracy of the phase measurements of analyte concentrations with PS-OLCR; (2) a concentration-dependent change in the phase-shift for glucose that is significantly greater than that of other analytes sampled over the same physiological range; and (3) a high submillimolar sensitivity of PS-OLCR for the measurement of glucose concentration. Further exploration of the application of PS-OLCR to the noninvasive, sensitive, and specific monitoring of glucose concentration seems warranted.

Biosensing Techniques↗

PubMed2004

Differential phase optical coherence probe for depth-resolved detection of photothermal response in tissue.

We describe a differential phase low-coherence interferometric probe for non-invasive, quantitative imaging of photothermal phenomena in biological materials. Our detection method utilizes principles of optical coherence tomography with differential phase measurement of interference fringe signals. A dual-channel optical low-coherence probe is used to analyse laser-induced thermoelastic and thermorefractive effects in tissue with micrometre axial resolution and nanometre sensitivity. We demonstrate an application of the technique using tissue phantoms and ex-vivo tissue specimens of rodent dorsal skin.

Acoustics↗

PubMed2004

Electrokinetic measurement of cartilage using differential phase optical coherence tomography.

When an electric field is applied to cartilage, current-generated stress gradients are produced and stress deformation occurs. Since differential phase optical coherence tomography (DP-OCT) is sensitive to tiny surface displacement, these tiny displacements are induced electrokinetically in cartilage and the electric-current-induced stress gradients were measured with DP-OCT. The electrokinetic surface displacement of cartilage was characterized by applying sinusoidal voltages with two amplitudes (5 and 10 V) and different frequencies (1.0, 0.5 and 0.2 Hz). The results show that by application of DP-OCT the surface displacement increased with increasing applied voltage and decreased with increasing excitation frequency. In the electrokinetic response of cartilage, measured optical phase delay between the surface displacement response and excitation waveform varies inversely with the excitation frequency. Since the streaming potential and other electrokinetic effects in cartilage are directly proportional to proteoglycan density, application of an electric field in cartilage combined with DP-OCT measurements may provide a sensitive indicator of cartilage viability.

Cartilage↗

PubMed2003

Polarization-maintaining fiber-based optical low-coherence reflectometer for characterization and ranging of birefringence.

We describe a polarization-maintaining fiber-based polarization-sensitive optical low-coherence reflectometer for measurement of depth-resolved birefringence. Unlike for other fiber-based polarization-sensitive optical low-coherence reflectometers, here the linear birefringence of a sample can be measured from data recorded in a single A scan. Simultaneous measurement of retardation and orientation of birefringent axes with mica wave plates is demonstrated. The measured retardation is insensitive to sample rotation in the plane perpendicular to ranging.

Birefringence↗

PubMed2003

Imaging tissue response to electrical and photothermal stimulation with nanometer sensitivity.

BACKGROUND AND OBJECTIVES: Tissue response to thermal, electrical, or chemical stimuli are important in the health and survival of tissue. We report experimental results to assess tissue response to various stimuli using a low coherence differential phase interferometer. STUDY DESIGN/MATERIALS AND METHODS: The optical system utilized to measure tissue response is a novel fiber-based phase sensitive optical low coherence reflectometer (PS-OLCR). Inasmuch as the PS-OLCR works with back-reflected light, noninvasive sensing of tissue response to stimuli is possible. In addition to high lateral (approximately 10 microm) and longitudinal (approximately 10 microm) resolution, PS-OLCR can measure sub-wavelength changes in optical path-length (Angstrom/nanometer range) by extracting the phase difference between interference fringes in two channels corresponding to orthogonal polarization modes. RESULTS: When light spatially splits into two polarization states, precise analysis of surface topography or tissue surface response such as swelling or collapse are possible. Time resolved measurements of nanometer-scale path length changes in response to electrical and thermal stimuli are demonstrated using longitudinally delayed polarization channels. CONCLUSIONS: Since PS-OLCR is a useful tool to detect ultra-small path length changes, the system has potential to aid scientists in investigating important phenomena in biomaterials and developing useful diagnostic and therapeutic imaging modalities. Applications include tissue surface profilometry, measurement of tissue, and cell response to various stimuli, high-resolution intensity and phase imaging.

Animals↗