Masroor Ikram

Michelson interferometer for precision angle measurement

An angle-measuring technique based on an optical interferometer is reported. The technique exploits a Michelson interferometric configuration in which a right-angle prism and a glass strip are introduced into a probe beam. Simultaneous rotation of both components along an axis results in an optical path difference between the reference and the probe beams. In a second arrangement two right-angle prisms and glass strips are introduced into two beams of a Michelson interferometer. The prisms and the strips are rotated simultaneously to introduce an optical path difference between the two beams. In our arrangement, optimization of various parameters makes the net optical path difference between the two beams approximately linear for a rotation as great as +/-20 degrees . Results are simulated that show an improvement of 2-3 orders of magnitude in error and nonlinearity compared with a previously reported technique.

Do different turbid media with matched bulk optical properties also exhibit similar polarization properties

We here investigate polarimetric behavior of thick samples of porcine liver, Intralipid, and microsphere-based tissue phantoms whose absorption and scattering properties are matched. Using polarized light we measured reflection mode Mueller matrices and derived linear/circular/total depolarization rates, based on polar decomposition. According to our results, phantoms exhibit greater depolarization rates in the backscattering geometry than the liver sample. The enhanced tissue polarization preservation differs from previous reports of polarimetric transmission studies, with the likely cause of this difference being the angular dependence of the single-scattering phase function. Also, Intralipid approximated polarimetric liver behavior well, whereas the polystyrene phantoms did not.

Study of the efficacy of 5 ALA-mediated photodynamic therapy on human larynx squamous cell carcinoma (Hep2c) cell line

Abstract5-aminolevulanic acid (ALA), a precursor of Protoporphyrin IX, was evaluated as an inducer of photodamage on Hep2c, human larynx squamous cell carcinoma, cell line. Porphyrins are used as active cytotoxic antitumor agents in photodynamic therapy (PDT). The present study evaluates the effects of photodynamic therapy (PDT) with 5-aminolevulinic acid (5-ALA) using human larynx cells as experimental model. Hep2c cell line was irradiated with red light (a diode laser, λ = 635 nm). The influence of different incubation times and concentrations of 5-ALA, different irradiation doses and various combinations of photosensitizer and light doses on the cellular viability of Hep2c cells were studied. The optimal uptake of photosensitizer ALA in Hep-2c cells was investigated by means of spectrometric measurement. Cells viability was determined by means of neutral red assay (NR). It was observed that sensitizer or light doses have no significant effect on cells viability when studied independently. The spectrometric measurements showed that the maximal cellular uptake of 5-ALA occurred after 7 h in vitro incubation. The photocytotoxic assay showed that light dose of 85 J/cm2 gives effective PDT outcome for Hep2c cell line incubated with 55 μg/ml of 5-ALA with a conclusion that Hep2c cell line is sensitive to ALA-mediated PDT.

Ex vivo characterization of normal and adenocarcinoma colon samples by Mueller matrix polarimetry

Abstract. Mueller matrix polarimetry along with polar decomposition algorithm was employed for the characterization of ex vivo normal and adenocarcinoma human colon tissues by polarized light in the visible spectral range (425–725 nm). Six derived polarization metrics [total diattenuation (DT), retardance (RT), depolarization (ΔT), linear diattenuation (DL), retardance (δ), and depolarization (ΔL)] were compared for normal and adenocarcinoma colon tissue samples. The results show that all six polarimetric properties for adenocarcinoma samples were significantly higher as compared to the normal samples for all wavelengths. The Wilcoxon rank sum test illustrated that total retardance is a good candidate for the discrimination of normal and adenocarcinoma colon samples. Support vector machine classification for normal and adenocarcinoma based on the four polarization properties spectra (ΔT, ΔL, RT,and δ) yielded 100% accuracy, sensitivity, and specificity, while both DT and DL   showed 66.6%, 33.3%, and 83.3% accuracy, sensitivity, and specificity, respectively. The combination of polarization analysis and given classification methods provides a framework to distinguish the normal and cancerous tissues.

Optical Properties of Normal and Thermally Coagulated Chicken Liver Tissue Measured ex vivo with Diffuse Reflectance

The purpose of the present study is to determine the optical properties of normal and thermally coagulated chicken liver at 720, 740, 770, 810, 825 and 840 nm wavelengths of laser irradiation. So, we were able to evaluate these optical properties (absorption and scattering coefficients) with ex-vivo study using Kubelka Munk Model (KMM) from the radial dependence of the diffuse reflectance with femtosecond pulsed laser in near IR region. These coefficients were significantly increased with coagulation. The penetration depths of the diffused light have been reported to a maximum value of 8.12 ± 0.36 mm in normal liver and 2.49 ± 0.17 mm in coagulated liver at 840 nm showing increasing behavior towards IR region. The Monte Carlo simulation was used to check the theoretical validation of measured optical properties of the tissue that showed a good match with our experimental results. We believe that these differences in optical properties will be helpful for the understanding arid optimal use of laser applications in medicine and differential diagnosis of tissues by using different optical methods. Especially for the investigation of biological tissue for photodynamic therapy (PDT), the knowledge of the specific optical properties and their thermo-induced changes is important.

The effect of high dose of gamma-irradiation on residual radicals concentration in ultra-high molecular weight polyethylene (UHMWPE) in the presence of vitamin E

Powder samples of UHMWPE (GUR 1020) containing 0.1% by wt. vitamin E (α-tocopherol, α-T) were irradiated at room temperature in air for doses of 30-kGy, 65-kGy or 100-kGy (60Co). After irradiation, they were stored at −78.5°C (dry ice temperature) for one year and then opened to air at room temperature. Following the decay of the primary alkyl and allyl radicals (at room temperature in air), growth of the carbon-centered polyenyl R1 (−·CH⁅CH=CH⁆, m ≥ 3), and the oxygen-centered dior tri-enyl R2 (−·OCH⁅CH=CH⁆m, m ≤ 3) residual radicals were measured for eight weeks. An X-band electron spin resonance (ESR) spectrometer was used for radical measurements. The initial relative radical concentrations (R2/R1) were found to be 10.13, 4.6 and 3.7 for the 65-kGy, 30-kGy and 100-kGy samples, respectively. R1 and R2 were both found to grow significantly in the 65-kGy samples while they grew only slightly in the 30-kGy and 100-kGy samples. In 65-kGy sample, R1 grew faster than R2 and the relative concentration R2/R1 was reduced from 10.13 to 2.9 for the 65-kGy sample while that for the 30-kGy and 100-kGy samples reduced only slightly, from 4.6 to 3.5 and 3.7 to 3.2, respectively. The behavior of the residual radicals can be explained by Raman spectroscopic data which suggest that the 65-kGy samples had a higher percentage of amorphous regions when compared to the 30-kGy or 100-kGy (21.7% compared to 15.7% or 17.9%) and also suggest a lower percentage of inter-phase regions (16.4% compared to 25.6% or 17.5%) and a lower level of structural disorder (0.26% compared to 0.44% or 0.27%).

Optical measurements of angle and axis of rotation

A carousel interferometer is designed to find the unknown angle and axis of rotation simultaneously. A set consisting of a compensator glass plate and a right-angle prism is placed in each of the two arms of the interferometer while located at the same rotational stage. When rotation takes place individual and relative optical path differences are generated in the beams that contribute toward finding out the angle and axis of rotation. Computer simulation shows that error remains less than a nanometer for a 1 m length of unknown radius and rotation range of +/-15 degrees .

Colorization and Automated Segmentation of Human T2 MR Brain Images for Characterization of Soft Tissues

Characterization of tissues like brain by using magnetic resonance (MR) images and colorization of the gray scale image has been reported in the literature, along with the advantages and drawbacks. Here, we present two independent methods; (i) a novel colorization method to underscore the variability in brain MR images, indicative of the underlying physical density of bio tissue, (ii) a segmentation method (both hard and soft segmentation) to characterize gray brain MR images. The segmented images are then transformed into color using the above-mentioned colorization method, yielding promising results for manual tracing. Our color transformation incorporates the voxel classification by matching the luminance of voxels of the source MR image and provided color image by measuring the distance between them. The segmentation method is based on single-phase clustering for 2D and 3D image segmentation with a new auto centroid selection method, which divides the image into three distinct regions (gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) using prior anatomical knowledge). Results have been successfully validated on human T2-weighted (T2) brain MR images. The proposed method can be potentially applied to gray-scale images from other imaging modalities, in bringing out additional diagnostic tissue information contained in the colorized image processing approach as described.

Ex Vivo Assessment of Carbon Tetrachloride (CCl 4 )-Induced Chronic Injury Using Polarized Light Spectroscopy

The liver performs various functions, such as the production and detoxification of chemicals; therefore, it is susceptible to hepatotoxins such as carbon tetrachloride (CCl4), which causes chronic injury. Thus, assessment of injury and its status of severity are of prime importance. Current work reports an ex vivo study for probing the severance of hepatic injury induced by CCl4 with polarized light over the spectral range 400–800 nm. Different concentrations of CCl4 were used to induce varying severity of hepatic injury in a rat model. Linear retardance, depolarization rates, and diagonal Mueller matrix elements (m22, m33, and m44), were successfully used as the distinguishing criterion for normal and different liver injuries. Our results show that linear retardance for injured liver samples with lower doses of CCl4 tends to increase when compared with normal liver samples, while samples injured at higher doses of CCl4 offer almost no retardance. Total, linear, and circular depolarizations follow decreasing trends with increased liver injury severity over the entire investigated wavelength range. Linear polarization states were observed to be better maintained as compared to circular polarization states for all samples. Furthermore, numerical values of diagonal elements of the experimentally measured Mueller matrix also increase with increasing doses of CCl4. Liver fibroses, change in transport albedo, and the relative refractive index of the extracellular matrix caused by CCl4 are responsible for the observed differences. These results will provide a pathway to gauge the severity of injury caused by toxic chemicals.

Cytotoxic and photocytotoxic effect of Photofrin® on human laryngeal carcinoma (Hep2c) cell line

Significant apoptotic effect in Hep2c cell line has been investigated, when diode laser (λ = 635 nm, red) are used as a source of illumination and initiation of photodynamic action. The optimal uptake time of Photofrin® for Hep2c cell line was investigated by means of spectrophotometric measurement. Quantification of the live cell population was determined by means of neutral red assay (NRA). The spectrometry measurements showed that after 46 h incubation, the maximal cellular uptake of Photofrin® was achieved and photocytotoxic assay showed that light dose of 120 J/cm2 give effective PDT outcome for Hep2c cell line incubated with 85 μg/ml of Photofrin®. No significant phototoxic and cytotoxic effects on Hep2c cells were observed due to light doses or photosensitize, when studied independently of each other and Photofrin® showed good anti tumor effects.