Y. Verma

Real-time in vivo imaging of adult Zebrafish brain using optical coherence tomography

We report noninvasive imaging of the brain of adult zebrafish (Danio rerio) using real time optical coherence tomography (OCT) capable of acquiring cross sectional 2D OCT images @ 8 frames/sec. Anatomic features such as telencephalon, tectum opticum, eminentia Granularis and cerebellum were clearly resolved in the OCT images. A 3D model of zebrafish brain was reconstructed, for the first time to our knowledge, using these 2D OCT images.

Effect of Helium-Neon Laser Irradiation on Hair Follicle Growth Cycle of Swiss Albino Mice

We report the results of a study carried out to investigate the effect of helium-neon (He-Ne) laser (632.8 nm) irradiation on the hair follicle growth cycle of testosterone-treated and untreated mice. Both histology and optical coherence tomography (OCT) were used for the measurement of hair follicle length and the relative percentage of hair follicles in different growth phases. A positive correlation (R = 0.96) was observed for the lengths of hair follicles measured by both methods. Further, the ratios of the lengths of hair follicles in the anagen and catagen phases obtained by both methods were nearly the same. However, the length of the hair follicles measured by both methods differed by a factor of 1.6, with histology showing smaller lengths. He-Ne laser irradiation (at ∼1 J/cm2) of the skin of both the control and the testosterone-treated mice was observed to lead to a significant increase (p < 0.05) in % anagen, indicating stimulation of hair growth. The study also demonstrates that OCT can be used to monitor the hair follicle growth cycle, and thus hair follicle disorders or treatment efficacy during alopecia.

Use of common path phase sensitive spectral domain optical coherence tomography for refractive index measurements

We report the use of a common path phase sensitive spectral domain optical coherence tomography setup for the measurement of the refractive index (RI) of a biomimetic material (glucose solution in water having intralipid as the scattering medium) and a single biological cell (keratinocyte). The RI of glucose solutions could be measured with a precision of ∼0.00015, which corresponds to a precision of ∼2 nm in the optical path length measurement in our setup. The precision obtained in the measurement of the RI of a single keratinocyte cell was ∼0.0004.

Non-invasive assessment of healing of bacteria infected and uninfected wounds using optical coherence tomography

Background/purpose: Bacterial infection is one of the main predisposing factors for the delay in wound healing. To facilitate a timely decision for correct therapy, it is important to accurately monitor the morphological changes in the infected wounds using noninvasive tools. In the present study, we have explored the use of optical coherence tomography (OCT) for monitoring the healing of superficial wounds infected with Staphylococcus aureus in mice under in vitro and in vivo conditions and studied the changes in collagen birefringence in the infected wounds.

BINARY TISSUE CLASSIFICATION STUDIES ON RESECTED HUMAN BREAST TISSUES USING OPTICAL COHERENCE TOMOGRAPHY IMAGES

We report the results of a comparative study of Fourier domain analysis (FDA) and texture analysis (TA) of optical coherence tomography (OCT) images of resected human breast tissues for binary classification between normal–abnormal classes and benign–malignant classes. With the incorporation of Fisher linear discriminant analysis (FLDA) in TA for feature extraction, the TA-based algorithm provided improved diagnostic performance as compared to the FDA-based algorithm in discriminating OCT images corresponding to breast tissues with three different pathologies. The specificity and sensitivity values obtained for normal–abnormal classification were both 100%, whereas they were 90% and 85%, respectively for benign–malignant classification.

Imaging of human breast tissue using polarization sensitive optical coherence tomography

We report a study on the use of polarization sensitive optical coherence tomography (PSOCT) for discriminating malignant (invasive ductal carcinoma), benign (fibroadenoma) and normal (adipocytes) breast tissue sites. The results show that while conventional OCT, that utilizes only the intensity of light back-scattered from tissue microstructures, is able to discriminate breast tissues as normal (adipocytes) and abnormal (malignant and benign) tissues, PS-OCT helps in discriminating between malignant and benign tissue sites also. The estimated values of birefringence obtained from the PSOCT imaging show that benign breast tissue samples have significantly higher birefringence as compared to the malignant tissue samples.

Effect of poly-L-lysine-chlorin P6-mediated antimicrobial photodynamic treatment on collagen restoration in bacteria-infected wounds.

OBJECTIVE The purpose of this work was to study the effect of poly-L-lysine-conjugated chlorin P6 (pl-cp6)-mediated antimicrobial photodynamic treatment (APDT) on collagen remodeling of murine excisional wounds infected with methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa (PAO). BACKGROUND DATA Bacterial infection of wounds leads to compromised collagen remodelling. APDT-induced inactivation of bacteria and bacterial proteases are expected to restore collagen remodeling in wounds. However, published reports on the effect of PDT on wound healing are somewhat contradictory. One of the reasons for these observations could be the random sampling of wound repair outcomes by invasive technques such as histology. METHODS Post-wounding time-dependent changes in collagen restoration were monitored noninvasively using polarization sensitive optical coherence tomography (PSOCT) and compared with histology and hydroxyproline level. Immunoblotting was performed to study matrix metalloproteinase (MMP) level. RESULTS As indicated by retardance measurements from PSOCT images and immunoblotting, bacteria-infected wounds showed slower collagen restoration and higher MMP-8, 9 expression, than did uninfected wounds. In contrast, in infected wounds treated with pl-cp6 and light, retardance was higher (approximately twofold) compared with wounds treated with pl-cp6 alone. These results were consistent with lower MMP-8, 9 level on day 5, more ordered collagen matrix, and higher hydroxyproline content (approximately threefold) on day 18, observed in photodynamically treated wounds, compared with that of untreated infected wounds. CONCLUSIONS APDT expedites healing in bacteria-infected wounds in mice by attenuating collagen degradation and by enhancing epithelialization, hydroxyproline content, and collagen remodelling.

Single mode fiber based polarization sensitive optical coherence tomography using a swept laser source

We report the development of a near real time single mode fiber-optic based polarization sensitive optical coherence tomography (PSOCT) setup utilizing a swept source. The setup has a polarization modulator (PM) and polarizer in a sample arm to serve as a polarization state generator and analyzer. Since only intensity information is used to retrieve the polarization parameters of the sample, the problem of phase jitters present in the swept source is avoided. Further, the use of polarization elements after the sample arm fiber makes the approach insensitive to the random birefringence of fibers. The swept source based PSOCT (SS-PSOCT) setup was calibrated by carrying out measurements on a quarter-wave plate whose fast axis orientation was rotated from 0° to 360° in steps of 10°. The setup has been used for imaging birefringence of mice tail tendon, thigh muscle ex vivo and human nail fold in vivo.

White light diffraction phase microscopy as profilometry tool

Abstract. A reflection type white light diffraction phase microscope for full field surface profiling of opaque samples is proposed. The system can extract surface profile from one recorded interferogram without any mechanical movement and the use of white light makes it free from speckle noise. We validated the performance of our system by measuring a known step sample and a high-quality plane sample. The step height of the step sample is found to be 88.5 nm with a standard deviation of 1.4 nm, and the surface peak to valley value of the plane sample is found to be 28.6 nm with a standard deviation of 3 nm.

Effect of Intraocular Pressure and Anisotropy on the Optical Properties of the Cornea: A Study Using Polarization Sensitive Optical Coherence Tomography.

PurposeWe hypothesize that because of the anisotropic properties of the cornea, there should be a nonuniform change in birefringence with an increase in intraocular pressure (IOP). In this in vitro study, anisotropic properties, stress distribution within the cornea, and the effect of IOP on changes in stress level were investigated. DesignButton inflation tests for deformation with polarization sensitive optical coherence tomography were used to demonstrate optical and material anisotropy on ex vivo human corneas. MethodsInflation tests were performed on human donor corneoscleral rims. Using a turntable and hydrostatic column, each corneoscleral rim was subjected to a hydrostatic pressure of 0, 10, 15, and 20 mm Hg. At each pressure step, 4 scans at 0, 45, 90, and 135 degrees were taken by a polarization sensitive optical coherence tomography system, and the birefringence images and normal intensity-based images were recorded; images were later compiled for analysis. ResultsThe retardation changed with the axis of orientation (P [T ⩽ t] 1-tailed = 0.025) and IOP (P [T ⩽ t] 1-tailed = 0.019). Optical thickness of the cornea decreased with increasing IOP. ConclusionsThe optical properties of the cornea are modified with change in IOP. This is not uniform because of distinct anisotropic properties. Anisotropic properties may unpredictably affect the optical quality of cornea during or after the surgeries. Changes in corneal birefringence can be also used as a tool for measuring the IOP of the eye.