Spectral-domain Low-coherence Interferometry Research Articles

A novel needle probe for deeper photoacoustic viscoelasticity measurement

We present for the first time, to the best of our knowledge, a needle probe for photoacoustic viscoelasticity (PAVE) measurements at a depth of 1 cm below the sample surface. The probe uses a gradient index rod lens, encased within a side-facing needle (0.7 mm outer diameter), to direct excitation light (532 nm) and detection light (1325 nm) focused on the sample, collecting and directing the returned detection light in a spectral domain low coherence interferometry system, which allows for obtaining optical phase differences due to photoacoustic oscillations. The feasibility of needle probe for PAVE depth characterization was investigated on gelatin phantoms and in vitro biological tissues. The experimental results in an in vivo animal model predict the great potential of this technique for in vivo tumor boundary detection.

Acousto-optic filtration in low-coherence spectral-domain interferometry

The basic principles of measurements in spectral-domain low coherence interferometry (optical coherence tomography, optical coherence microscopy) based on acousto-optic filtration are discussed. Relations for extracting information about sample’s spatial structure from a series of spectral interference images acquired with spectral tuning are given. The implementation of measurements in spectral domain using acousto-optic filtration is considered. The effect of the acousto-optic filter characteristics on depth measurement range and depth resolution is estimated. The results of modelling of the interference signal and experimental data obtained in the scheme with acousto-optic filtration of interfering beams at the output of Michelson interferometer are presented.

Spectral interferometric depth-resolved photoacoustic viscoelasticity imaging.

Viscoelasticity is closely related to the physiological characteristics of biological tissues. In this Letter, we propose a novel spectral interferometric depth-resolved photoacoustic viscoelasticity imaging (SID-PAVEI) method, to the best of our knowledge for the first time, which breaks the plight of surface viscoelasticity imaging and achieves an internal visible microscale SID-PAVEI in a noncontact fashion. In this work, we employ a high-sensitive and depth-resolved spectral domain low coherence interferometry (SDLCI) to remotely track photoacoustic-induced strain response of absorbers in situ. By decoupling the phase and amplitude of the photoacoustic-encoded spectral interference signal, the SID-PAVEI and scattering structure imaging (SSI) can be obtained simultaneously. Depth-resolved performance of the SID-PAVEI and the SSI in one scan were demonstrated by imaging biological tissues. The method opens new perspectives for three-dimensional microscale viscoelasticity imaging and provides a great potential in multi-parametric characterizing pathological information.

The influence of small amount of substances present in tissue on immunosuppressive drug optical spectrum

In this paper, we describe how commonly present in tissue substances - sodium chloride and glucose - affect the optical spectrum of an immunosuppressive drug (Cyclaid® by Apotex). Prepared samples were investigated using the spectrophotometer in the spectrum range from 250 nm to 1100 nm. The maximum wavelength shift calculated on the basis of measurement results is not bigger than the measurement wavelength step. So, it can be concluded, that the small amount of sodium chloride or glucose does not influence the measurement and it is possible to apply spectrophotometry in a point-of-care sensor of the Cyclaid® by Apotex level. Full Text: PDF ReferencesL. Taylor, C. J. E. Watson, and J. A. Bradley, "Immunosuppressive agents in solid organ transplantation: Mechanisms of action and therapeutic efficacy", Crit. Rev. Oncol. Hematol. 56, 23 (2005). CrossRef C. C. Mok, "Calcineurin inhibitors in systemic lupus erythematosus", Best Pract. Res. Clin. Rheumatol. 31, 429 (2017). CrossRef C. E. M. Griffiths et al., "Striae gravidarum in primiparae", Br. J. Dermatol. 155, 1 (2006). CrossRef F. Stucker and D. Ackermann, "Immunsuppressiva - Wirkungen, Nebenwirkungen und Interaktionen", Ther. Umschau. Rev. thérapeutique, 68 ,679 (2011). CrossRef A. Fahr, "Cyclosporin Clinical Pharmacokinetics", Clin. Pharmacokinet. 24, 472 (1993). CrossRef Cyclosporine – UpToDate, DirectLink P. Strakowska, R. Beutner, M. Gnyba et al., "Electrochemically assisted deposition of hydroxyapatite on Ti6A14V substrates covered by CVD diamond films – coating characterization and first cell biological results", Mater Sci Eng C Mater Biol Appl. 59, 624 (2016). CrossRef M. Gnyba, M. S. Wróbel, K. Karpienko et al., "Combined analysis of whole human blood parameters by Raman spectroscopy and spectral-domain low-coherence interferometry", Proc. SPIE 9537, 95371N (2015). CrossRef M. S. Wróbel, M. Gnyba, R. Urniaz et al., "Detection of propofol concentrations in blood by Raman spectroscopy", Proc. SPIE 9537, 95370Z (2015). CrossRef M. Gnyba, et al., "SAVE TO MY LIBRARY Raman spectroscopic investigation of blood and related materials", Proc. SPIE 9448, 944809 (2015). CrossRef H. S. Cho et al., "High frame-rate intravascular optical frequency-domain imaging in vivo", Biomed. Opt. Express 5, 223 (2013). CrossRef T. A. Valdez et al., "Multi-color reflectance imaging of middle ear pathology in vivo", Anal. Bioanal. Chem. 407, 3277 (2015). CrossRef M. Ali Ansari, S. Alikhani, and E. Mohajerani, "A hybrid imaging method based on diffuse optical tomography and optomechanical method to detect a tumor in the biological phantom", Opt. Commun. 342, 12 (2015). CrossRef M. S. Wróbel et al., "Multi-layered tissue head phantoms for noninvasive optical diagnostics", J. Innov. Opt. Health Sci. 08, 1541005 (2015). CrossRef D. A. Skoog, F. J. Holler, and S. R. Crouch, Principles of instrumental analysis, (Belmont, CA, Thomson Brooks/Cole 2007). CrossRef M. Hof, Basics of Optical Spectroscopy in Handbook of Spectroscopy, (Weinheim , Wiley-VCH Verlag GmbH & Co. KGaA 2005). CrossRef M. Marzejon et al,. "Optical-Spectrometry-Based Method for Immunosuppressant Medicine Level Detection in Aqueous Solutions", Sensors, 18, 2001 (2018). CrossRef UV-9000 Double Beam UV/VIS, http://en.metash.com/ProductShow_172.html CrossRef

Measurement of ocular axial length using full-range spectral-domain low-coherence interferometry

We demonstrate a system for measuring the ocular axial length (AL) with high sensitivity and high speed using spectral-domain low-coherence interferometry (SD-LCI). To address the limit in measuring such a large range by using SD-LCI, we propose a full-range method to recognize the positive and negative depths. The reference arm length is changed synchronously with the shift of the focal point of the probing beam. The system provides a composite depth range that is sufficient to cover the whole eye. We demonstrate the performance of the presented system by measuring the ALs of five volunteers. This system can provide the A-scan ocular biometric assessment of the corneal thickness and AL in 0.1 s.

Automatic Interference Term Retrieval From Spectral Domain Low-Coherence Interferometry Using the EEMD-EMD-Based Method

Low-coherence interferometry (LCI) has proved to be a useful tool in optical measurement and detection. However, the noise that is present in practical applications makes interference term retrieval (ITR) difficult. In this paper, we propose a novel technique based on ensemble empirical mode decomposition and empirical mode decomposition (EEMD-EMD) to achieve automatic ITR from the spectral domain LCI. In EEMD, the correlation coefficient of each intrinsic mode function (IMF) is calculated, and a characteristic parameter (CP) is introduced to recognize and remove the IMFs of noisy components. The remaining IMFs are used to reconstruct a new signal followed by EMD to extract the interference term. An experiment based on distributed polarization coupling detection in polarization-maintaining fibers (PMFs) was conducted; the PMFs having different lengths and coupling intensities were investigated. It was shown that by setting an appropriate CP, the interference term could be automatically extracted. The relative errors of the extracted coupling intensity were less than 2%. This suggests that our method may have potential applications in interferometric measurement.

Air etalon facilitated simultaneous measurement of group refractive index and thickness using spectral interferometry.

A simple method based on air etalons of a transparent cavity is proposed to simultaneously measure the group refractive index and thickness of a transparent optical plate by spectral domain low coherence interferometry. In this method, only a single beam path is needed in contrast to the two beam paths, the reference and sample arms, of the conventional Michelson interferometer. An empty cavity is first constructed in the beam path by two glass plates. Then the transparent plate under test is inserted into the cavity, so that two air gaps are formed in the cavity. A beam of light of low coherence length is then transmitted through the cavity in the normal direction. Measurements of the reflected waves by the air gaps before and after the sample plate is put into the cavity allow us to determine the group refractive index (ng) and thickness (d) of the sample simultaneously. The relative precision of the results for d and ng are both approximately 7×10-4.

On-line surface inspection using cylindrical lens-based spectral domain low-coherence interferometry.

We present a spectral domain low-coherence interferometry (SD-LCI) method that is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques by using cylindrical lenses as the objective lenses in a Michelson interferometric configuration to enable the measurement of long profiles. Combined with a modern high-speed CCD camera, general-purpose graphics processing unit, and multicore processors computing technology, fast measurement can be achieved. By translating the tested sample during the measurement procedure, real-time surface inspection was implemented, which is proved by the large-scale 3D surface measurement in this paper. ZEMAX software is used to simulate the SD-LCI system and analyze the alignment errors. Two step height surfaces were measured, and the captured interferograms were analyzed using a fast Fourier transform algorithm. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturer.

Improving axial resolution in spectral domain low-coherence interferometry through fast Fourier transform harmonic artifacts

Low-coherence interferometric setups in the Fourier domain can experience false structures after the Fourier transform procedure due to signal saturation; in fact, these structures are located at multiple frequencies of the original signal, also referred to as harmonics. This study aids in a better understanding of this phenomenon. The aim of the present work was to show that these features can be used to improve differential axial resolution in highly reflective samples. Using an optical coherence tomography system and calibrated step height standards, it was possible to achieve a resolution greater than the light source coherence length.

Spectral-domain low-coherence interferometry for phase-sensitive measurement of Faraday rotation at multiple depths.

We describe a method for differential phase measurement of Faraday rotation from multiple depth locations simultaneously. A polarization-maintaining fiber-based spectral-domain interferometer that utilizes a low-coherent light source and a single camera is developed. Light decorrelated by the orthogonal channels of the fiber is launched on a sample as two oppositely polarized circular states. These states reflect from sample surfaces and interfere with the corresponding states of the reference arm. A custom spectrometer, which is designed to simplify camera alignment, separates the orthogonal channels and records the interference-related oscillations on both spectra. Inverse Fourier transform of the spectral oscillations in k-space yields complex depth profiles, whose amplitudes and phase difference are related to reflectivity and Faraday rotation within the sample, respectively. Information along a full depth profile is produced at the camera speed without performing an axial scan for a multisurface sample. System sensitivity for the Faraday rotation measurement is 0.86 min of arc. Verdet constants of clear liquids and turbid media are measured at 687 nm.

Analysis of Pulsatile Retinal Movements by Spectral-Domain Low-Coherence Interferometry: Influence of Age and Glaucoma on the Pulse Wave

Recent studies have shown that ocular hemodynamics and eye tissue biomechanical properties play an important role in the pathophysiology of glaucoma. Nevertheless, better, non-invasive methods to assess these characteristics in vivo are essential for a thorough understanding of degenerative mechanisms. Here, we propose to measure ocular tissue movements induced by cardiac pulsations and study the ocular pulse waveform as an indicator of tissue compliance. Using a novel, low-cost and non-invasive device based on spectral-domain low coherence interferometry (SD-LCI), we demonstrate the potential of this technique to differentiate ocular hemodynamic and biomechanical properties. We measured the axial movement of the retina driven by the pulsatile ocular blood flow in 11 young healthy individuals, 12 older healthy individuals and 15 older treated glaucoma patients using our custom-made SD-OCT apparatus. The cardiac pulse was simultaneously measured through the use of an oximeter to allow comparison. Spectral components up to the second harmonic were obtained and analyzed. For the different cohorts, we computed a few parameters that characterize the three groups of individuals by analyzing the movement of the retinal tissue at two locations, using this simple, low-cost interferometric device. Our pilot study indicates that spectral analysis of the fundus pulsation has potential for the study of ocular biomechanical and vascular properties, as well as for the study of ocular disease.

Simultaneous Measurements of Refractive Index and Thickness by Spectral-Domain Low Coherence Interferometry Having Dual Sample Probes

We propose and demonstrate the novel method that enables simultaneous measurements of physical thickness and refractive group index without any prior knowledge on samples. The system is based on the spectral-domain optical low coherence interferometry with two sample probes facing each other. Owing to both side measurements schemes, thickness and group refractive index could be measured with not only transparent but also highly absorptive samples. The average errors were ~0.06% in both the physical thickness and the group refractive index measurements.

Spectral-domain differential interference contrast microscopy

We present a fiber-optic low-coherence imaging technique, termed spectral-domain differential interference contrast microscopy (SD-DIC), for quantitative DIC imaging of both reflective surfaces and transparent biological specimens. SD-DIC combines the common-path nature of a Nomarski DIC interferometer with the high sensitivity of spectral-domain low-coherence interferometry to obtain high-resolution, quantitative measurements of optical pathlength gradients from a single point on the sample. Full-field imaging can be achieved by scanning the sample. A reflected-light SD-DIC system was demonstrated using a USAF resolution target as the phase object. Live cardiomyocytes were also imaged, achieving a resolution of 36 pm for pathlength gradient measurements. The dynamics of cardiomyocyte contraction were recorded with high sensitivity at selected sites on the cells.

Development of a novel instrument to measure the pulsatile movement of ocular tissues

We demonstrate an optical instrument that can measure the axial displacement of different eye tissues, including the cornea and the fundus. The instrument is based on spectral-domain low-coherence interferometry, which extracts displacement information from sequential axial scans of the eye with 100 Hz sampling frequency and with a precision of 400 nm. Longitudinal retinal and corneal movements were successfully measured in vivo in live rats, and Fourier analysis of the signal revealed the signature of the respiratory and cardiac cycles at 1.0 and 3.5 Hz, respectively. The effective amplitudes of retinal and corneal displacements at the cardiac frequency were found to be about 1.10 and 1.37 μm, respectively. The synchrony and direction of these two movements relative to the systole and diastole were found to be nearly the same. This novel instrument can be applied to assess biomechanical properties of the eye, which could be important for early diagnosis and for understanding the pathophysiology of glaucoma and other ocular diseases.

Time-resolved simultaneous measurement of group index and physical thickness during photopolymerization of resin-based dental composite

Light-activated resin-based dental composites are increasingly replacing dental amalgam. However, these materials are limited by inefficient setting reactions as a function of depth that constrain the maximum extent of cure. Insufficient curing can contribute to an overall reduction in biocompatibility of the material. We demonstrate dynamic refractive index measurements of a commercial dental composite throughout cure using spectral domain low coherence interferometry. Our results show a linear relationship between the change in refractive index and polymerization-induced reduction in physical thickness during light-activated curing. This relationship between the optical and physical density demonstrates the potential of this technique as a unique noninvasive tool for measurement of the conversion degree of curing dental composite materials.

Toward noninvasive measurement of blood hematocrit using spectral domain low coherence interferometry and retinal tracking

We demonstrate in vivo measurements in human retinal vessels of an experimental parameter, the slope of the low coherence interferometry (LCI) depth reflectivity profile, which strongly correlates with the real value of blood hematocrit. A novel instrument that combines two technologies, spectral domain low coherence interferometry (SDLCI) and retinal tracking, has been developed and used for these measurements. Retinal tracking allows a light beam to be stabilized on retinal vessels, while SDLCI is used for obtaining depth-reflectivity profiles within the investigated vessel. SDLCI backscatter extinction rates are obtained from the initial slope of the A-scan profile within the vessel lumen. The differences in the slopes of the depth reflectivity profiles for different subjects are interpreted as the difference in the scattering coefficient, which is correlated with the number density of red blood cells (RBC) in blood. With proper calibration, it is possible to determine hematocrit in retinal vessels. Ex vivo measurements at various RBC concentrations were performed to calibrate the instrument. Preliminary measurements on several healthy volunteers show estimated hematocrit values within the normal clinical range.

Label-free measurement of microbicidal gel thickness using low-coherence interferometry

Spectral-domain low-coherence interferometry (LCI) was used to measure the thickness of microbicidal gels applied to a cylindrical calibration test socket. Microbicides are topical formulations containing active ingredients targeted to inhibit specific pathogens that are currently under development for application to the epithelial lining of the lower female reproductive tract to combat sexually transmitted infections such as HIV. Understanding the deployment and drug delivery of these formulations is vital to maximizing their effectiveness. Previously, in vivo measurements of microbicidal formulation thickness were assessed using fluorescence measurements of fluorescein-labeled gels via an optical endoscope-based device. Here we present an LCI-based device that measures the thickness of a formulation without the use of any exogenous agents by analyzing the interference pattern generated between the reflections from the front and back surface of the sample. Results are presented that validate the effectiveness and performance of the LCI measurement in a clinically relevant system as compared to an existing fluorescence-based method. The impact of the new LCI-based design on in vivo measurements is discussed.

Measuring dispersion between two modes of an optical fibre using time-domain and spectral-domain low-coherence interferometry

Group optical path difference (OPD) between two modes of an optical fibre excited by a low-coherence source characterized by a multimode spectrum is evaluated measuring both the visibility dependence in the Michelson interferometer configuration and the spectral modulation at the output of the optical fibre. Using the Fourier-transform method in processing the measured spectral modulations, a slight wavelength dependence in the group OPD between two modes of the optical fibre is resolved. Comparing the group OPD corresponding to a central wavelength of the measured spectral region with the group OPD obtained from the measured visibility dependence, good agreement between results of the measurements in the spectral domain and in the time domain is achieved.

Measuring dispersion between two modes of an optical fibre using time-domain and spectral-domain low-coherence interferometry

Measuring dispersion between two modes of an optical fibre using time-domain and spectral-domain low-coherence interferometry