S. G. Demos

Time resolved degree of polarization for human breast tissue

Polarized light propagating through the tissue retains the polarization information. The temporal profiles of the degree of polarization of the output light depends on the wavelength of the light and the type of the tissue that it propagates.

Polarization Filter for Biomedical Tissue Optical Imaging

Abstract— A technique based on the degree that light is depolarized when propagating inside tissues is demonstrated for optical imaging in biomedical systems. The difference in the degree of polarization of the emerging light allows for the discrimination of different types of tissues. The technique was investigated in the transillumination and back‐scattering geometry and in both cases the potential of this method to image and separate out different types of tissues is demonstrated.

Imaging fluorescent objects embedded inside animal tissues using polarization difference technique

Abstract The polarization preservation property of Cardio Green dye and the fluorescence-polarization-difference-imaging (FPDI) technique are introduced to enhance the image quality of an object embedded inside tissues. The spatial FWHM resolution and contrast of the resulted fluorescence polarization difference image were found to be higher than that of the conventional non-polarized optical images by factors of 2.3 and 3.6, respectively.

Imaging objects hidden in scattering media with fluorescence polarization preservation of contrast agents

A method for fluorescence polarization difference imaging is demonstrated for enhancing the image quality of a luminous object embedded in a random medium. The polarization preservation of light propagating in the scattering medium leads to partially polarized light emission by a contrast-agent dye located inside the object. Subtraction of the images of the luminous object detected at two orthogonal polarization directions improves the image resolution compared with a conventional optical imaging approach.

Visibility enhancement of fluorescent objects hidden in animal tissues using spectral fluorescence difference method

Abstract The difference between the fluorescence spectra emitted from Cardio Green dye and chicken breast tissue in the near-infrared (NIR) region was measured and used to select a pair of fingerprint wavelengths for imaging. Using spectral fluorescence difference imaging method, an 1-mm tissue object stained with Cardio Green dye located 3.1 cm underneath the surface of the host chicken tissue was clearly imaged and identified. The spatial resolution and the contrast of the fluorescence difference image were found to be significantly improved over the conventional single wavelength imaging approach.

Far-red and NIR emissions from tissues

Spectral and temporal profiles together with polarization for far-red to NIR emission wing beyond 650 nm were measured form adipose and tissues. The characteristics of the emission arising form adipose and tissues are shown to be different under 532 nm and 632 nm laser excitation indicating a different origin of the emission. The difference in the spectral intensity of the far-red to NIR emission under 632 nm laser excitation was used to image and distinguish adipose from tissue.

Raman spectra of biomedical samples using optical fiber probes

We have investigated various optical fiber probes for remote Raman scattering measurements in tissues. The diameter of the optical fiber probe was kept below 3 mm in order to be able o fit into the working channel of existing endoscopes for in vivo measurements inside the human body. Different designs were tested to examine the best possible arrangement of the required optical. The main problems encountered arising from the Raman scattering and fluorescence emission inside the fiber itself are discussed and possible approaches to overcome the limitations are addressed.

Differential spectral polarization imaging

A new technique is demonstrated for noninvasive optical imaging for biological, medical, and non medical systems based on the polarization characteristics of the backscattered light. Two versions of the technique are demonstrated: one suitable for surface imaging and the other for subsurface imaging.

Temporal polarization preservation in human breast tissue: a method for optical imaging

The degree of polarization of polarized light as it propagates through breast tissues depends on the type of tissue and light wavelength. This feature was used to image cancerous tissue where tumor was clearly distinguished from the normal tissue.

Role of local-phonon mode coupling in the nonradiative relaxation for designing more efficient impurity doped solid state laser crystals

Based on measurements of the dynamics of local and phonon modes in Cr:Mg2SiO4 during the nonradiative relaxation of Cr4+ laser ions, and on the phonon and local spectrum of the analog Cr4+:Ca2GeO4 laser crystal, we propose general criteria to design higher efficiency ion-doped laser crystals