A. Gh. Podoleanu

Optical coherence tomography.

The review provides a concise explanation of principles of operation of different optical coherence tomography methods. A comparative analysis of their advantages and disadvantages is presented in relation to specific applications. The review will assist the reader in making an educated choice on the most suitable optical coherence tomography method to be used in a particular application.

OCT en-face images from the retina with adjustable depth resolution in real time

A source with adjustable coherence length is devised and used to illuminate an OCT for en-face imaging of the retina of the human eye in vivo. Two modes of operation are described. The added capability of adjusting the depth resolution in real time while imaging patients is discussed. The utility of the OCT en-face imaging with adjustable coherence length for diagnostics is illustrated by images taken from the eye of a volunteer. Similar images with those produced by scanning laser ophthalmoscopes are produced for the first time in real time using OCT.

Image quality improvement in optical coherence tomography using Lucy–Richardson deconvolution algorithm

Optical coherence tomography (OCT) has the potential for skin tissue characterization due to its high axial and transverse resolution and its acceptable depth penetration. In practice, OCT cannot reach the theoretical resolutions due to imperfections of some of the components used. One way to improve the quality of the images is to estimate the point spread function (PSF) of the OCT system and deconvolve it from the output images. In this paper, we investigate the use of solid phantoms to estimate the PSF of the imaging system. We then utilize iterative Lucy-Richardson deconvolution algorithm to improve the quality of the images. The performance of the proposed algorithm is demonstrated on OCT images acquired from a variety of samples, such as epoxy-resin phantoms, fingertip skin and basaloid larynx and eyelid tissues.

Experimental Method to Find the Optimum Excitation Waveform to Quench Mechanical Resonances of Fabry–Pérot Tunable Filters Used in Swept Sources

We report experimental evidence of improving the nonlinearity of conventional wavelength swept laser sources based on a fiber Fabry-Perot tunable filter as a wavelength-selective element. Our solution is based on applying a nonsinusoidal, synthesized waveform to the tunable filter that can be identified experimentally. A significant improvement in the optical coherence tomography image quality has been obtained without any software recalibration method.

Ultrahigh-Resolution Combined Coronal Optical Coherence Tomography Confocal Scanning Ophthalmoscope (OCT/SLO): A pilot study

SummaryOBJECTIVE: To evaluate clinical images from a prototype ultrahigh resolution (UHR) combined coronal optical coherence tomography/confocal scanning ophthalmoscope (OCT/SLO) and to compare them to standard-resolution OCT/SLO images on the same patients. DESIGN: Cross-sectional pilot-study. PARTICIPANTS: Sixty-six eyes of 42 patients with various macular pathologies, such as age-related macular degeneration, macular edema, macular hole, central serous retinopathy, epiretinal membrane and posterior vitreous traction syndrome. METHODS: Each subject was first scanned with a standard-resolution OCT/SLO that has an axial resolution of ∼10 micron. Immediately following, patients were scanned with the prototype UHR OCT/SLO device. The UHR system employs a compact super luminescent diode (SLD) with a 150 nm bandwidth centered at 890 nm, which allows imaging of the retina with an axial resolution of 3 microns. Both coronal and longitudinal OCT scans were acquired with each system, and compared side-by-side. Scan quality was assessed for the observers ability to visualize the vitreo-retinal interface and retinal layers – in particular of the outer retina/RPE/choroidal interface, increased discrimination of pathological changes, and better signal intensity. MAIN OUTCOME MEASURES: Ultrahigh and standard-resolution coronal and longitudinal OCT/SLO images of macular pathologies. RESULTS: In the side-by-side comparison with the commercial standard-resolution OCT/SLO images, the scans in the Ultrahigh resolution OCT/SLO images were superior in 85% of cases. Relatively poor quality images were attributed to lower signal-to-noise ratio, limited focusing, or media opacities. Several images that had a better signal intensity in the standard-resolution OCT/SLO system were found to show more retinal detail in the UHR system. In general, intraretinal layers in the UHR OCT/SLO images were better delineated in both coronal and longitudinal scans. Enhanced details were also seen in the outer retina/RPE/choroidal complex. The UHR OCT/SLO system produced better definition of morphological changes in several macular pathologies. CONCLUSIONS: Broadband SLD-based UHR OCT/SLO offers a compact, efficient, and economic enhancement to the currently available clinical OCT imaging systems. UHR OCT/SLO imaging enhanced the quality of the OCT C-scans, facilitated appreciation of vitreo-retinal pathologies, and improved sensitivity to small changes in the retina, and the outer retina/RPE/choroidal interface.

Dynamic focus optical coherence tomography: feasibility for improved basal cell carcinoma investigation

Basal cell carcinoma (BCC) is the most common form of skin cancer. To improve the diagnostic accuracy, additional non-invasive methods of making a preliminary diagnosis have been sought. We have implemented an En-Face optical coherence tomography (OCT) for this study in which the dynamic focus was integrated into it. With the dynamic focus scheme, the coherence gate moves synchronously with the peak of confocal gate determined by the confocal interface optics. The transversal resolution is then conserved throughout the depth range and an enhanced signal is returned from all depths. The Basal Cell Carcinoma specimens were obtained from the eyelid a patient. The specimens under went analysis by DF-OCT imaging. We searched for remarkable features that were visualized by OCT and compared these findings with features presented in the histology slices.

Ex vivo optical coherence tomography imaging of larynx tissues using a forward-viewing resonant fiber-optic scanning endoscope

A miniature endoscope probe for forward viewing in a 50 kHz swept source optical coherence tomography (SS-OCT) configuration was developed. The work presented here is an intermediate step in our research towards in vivo endoscopic laryngeal cancer screening. The endoscope probe consists of a miniature tubular lead zirconate titanate (PZT) actuator, a single mode fiber (SMF) cantilever and a GRIN lens, with a diameter of 2.4 mm. The outer surface of the PZT actuator is divided into four quadrants that form two pairs of orthogonal electrodes (X and Y). When sinusoidal waves of opposite polarities are applied to one electrode pair, the PZT tube bends transversally with respect to the two corresponding quadrants, and the fiber optic cantilever is displaced perpendicular to the PZT tube. The cantilevers resonant frequency was found experimentally as 47.03 Hz. With the GRIN lens used, a lateral resolution of ~ 13 μm is expected. 2D en face spiral scanning pattern is achieved by adjusting the phase between the pairs of X and Y electrodes drive close to 90 degrees. Furthermore, we demonstrate the imaging capability of the probe by obtaining B-scan images of diseased larynx tissue and compare them with those obtained in a 1310 nm SS-OCT classical non-endoscopic system.

Talbot-like bands for a laser diode below threshold

We report on the problems encountered when replacing a tungsten filament lamp with a laser diode in a set-up for displaying Talbot bands using a diffraction grating. It is shown that the band pattern is rather complex and strong interference signals may exist in situations where Talbot bands are not normally expected to appear. In these situations, the period of the bands increases with the optical path difference (OPD). The visibility of bands as dependence on path imbalance is obtained by suitably obstructing halfway into the arms of a Michelson interferometer using opaque screens.

Novel software package to facilitate operation of any spectral (Fourier) OCT system

We present a novel software method (master-slave) to facilitate operation of any SDOCT system. This method relaxes constraints on dispersion compensation and k-domain re-sampling in SDOCT methods without requiring any changes in the hardware used.

Sensor-less aberration correction in optical imaging systems using blind optimization

The imperfection of optical devices in an optical imaging system deteriorates wavefront which results in aberration. This reduces the optical signal to noise ratio of the imaging system and the quality of the produced images. Adaptive optics composed of wavefront sensor (WFS) and deformable mirror (DM) is a straightforward solution for this problem. The need for a WFS in an AO system, raises the cost of the overall system, and there are also instances when they cannot be used, such as in microscopy. Moreover stray reflections from lens surfaces affect the performance of the WFS. In this paper, we describe a blind optimization technique with an in-expensive electronics without using the WFS to correct the aberration in order to achieve better quality images. The correction system includes an electromagnetic DM from Imagine, Mirao52d, with 52 actuators which are controlled by particle swarm optimization (PSO) algorithm. The results of the application of simulated annealing (SA), and genetic algorithm (GA) techniques that we have implemented in the sensor-less AO are used for comparison.