Daniel Ruminski

OCT angiography by absolute intensity difference applied to normal and diseased human retinas

We compare four optical coherence tomography techniques for noninvasive visualization of microcapillary network in the human retina and murine cortex. We perform phantom studies to investigate contrast-to-noise ratio for angiographic images obtained with each of the algorithm. We show that the computationally simplest absolute intensity difference angiographic OCT algorithm that bases only on two cross-sectional intensity images may be successfully used in clinical study of healthy eyes and eyes with diabetic maculopathy and branch retinal vein occlusion.

Multi-parametric imaging of murine brain using spectral and time domain optical coherence tomography

Abstract. Examination of brain functions in small animal models may help improve the diagnosis and treatment of neurological conditions. Transcranial imaging of small rodents’ brains poses a major challenge for optical microscopy. Another challenge is to reduce the measurement time. We describe methods and algorithms for three-dimensional assessment of blood flow in the brains of small animals, through the intact skull, using spectral and time domain optical coherence tomography. By introducing a resonant scanner to the optical setup of the optical coherence tomography (OCT) system, we have developed and applied a high-speed spectral OCT technique that allows us to vary the imaging range of flow and to shorten measurement time. Multi-parameter signal analysis enables us to obtain both qualitative and quantitative information about flow velocity from the same set of data.

OCT detection of neural activity in American cockroach nervous system

We show results of a project which focuses on detection of activity in neural tissue with Optical Coherence Tomography (OCT) methods. Experiments were performed in neural cords dissected from the American cockroach (Periplaneta americana L.). Functional OCT imaging was performed with ultrahigh resolution spectral / Fourier domain OCT system (axial resolution 2.5 μm). Electrical stimulation (voltage pulses) was applied to the sensory cercal nerve of the neural cord. Optical detection of functional activation of the sample was performed in the connective between the terminal abdominal ganglion and the fifth abdominal ganglion. Functional OCT data were collected over time with the OCT beam illuminating selected single point in the connectives (i.e. OCT M-scans were acquired). Phase changes of the OCT signal were analyzed to visualize occurrence of activation in the neural cord. Electrophysiology recordings (microelectrode method) were also performed as a reference method to demonstrate electrical response of the sample to stimulation.

Angiogram visualization and total velocity blood flow assessment based on intensity information analysis of OCT data

We propose two independent OCT data processing methods allowing visualization and analysis of the blood flow. These methods utilize variations in the OCT intensity images caused by flowing blood. The first method calculates standard deviation of intensity to generate retinal OCT angiograms. We present algorithm of this method and results of application for visualization of the microvasculature in the macular area of the human eye in vivo. The second method calculates cross power spectra of the volumetric intensity images to assess blood flow velocity in three dimensions. Validation of this method for OCT imaging was performed in a flow phantom.

Two-photon imaging of the mammalian retina with ultrafast pulsing laser

Noninvasive imaging of visual system components in vivo is critical for understanding the causal mechanisms of retinal diseases and for developing therapies for their treatment. However, ultraviolet light needed to excite endogenous fluorophores that participate in metabolic processes of the retina is highly attenuated by the anterior segment of the human eye. In contrast, 2-photon excitation fluorescence imaging with pulsed infrared light overcomes this obstacle. Reducing retinal exposure to laser radiation remains a major barrier in advancing this technology to studies in humans. To increase fluorescence intensity and reduce the requisite laser power, we modulated ultrashort laser pulses with high-order dispersion compensation and applied sensorless adaptive optics and custom image recovery software and observed an over 300% increase in fluorescence of endogenous retinal fluorophores when laser pulses were shortened from 75 fs to 20 fs. No functional or structural changes to the retina were detected after exposure to 2-photon excitation imaging light with 20-fs pulses. Moreover, wide bandwidth associated with short pulses enables excitation of multiple fluorophores with different absorption spectra and thus can provide information about their relative changes and intracellular distribution. These data constitute a substantial advancement for safe 2-photon fluorescence imaging of the human eye.

Anterior segment and retinal OCT imaging with simplified sample arm using focus tunable lens technology(Conference Presentation)

Availability of the long-depth-range OCT systems enables comprehensive structural imaging of the eye and extraction of biometric parameters characterizing the entire eye. Several approaches have been developed to perform OCT imaging with extended depth ranges. In particular, current SS-OCT technology seems to be suited to visualize both anterior and posterior eye in a single measurement. The aim of this study is to demonstrate integrated anterior segment and retinal SS-OCT imaging using a single instrument, in which the sample arm is equipped with the electrically tunable lens (ETL). ETL is composed of the optical liquid confined in the space by an elastic polymer membrane. The shape of the membrane, electrically controlled by a specific ring, defines the radius of curvature of the lens surface, thus it regulates the power of the lens. ETL can be also equipped with additional offset lens to adjust the tuning range of the optical power. We characterize the operation of the tunable lens using wavefront sensing. We develop the optimized optical set-up with two adaptive operational states of the ETL in order to focus the light either on the retina or on the anterior segment of the eye. We test the performance of the set-up by utilizing whole eye phantom as the object. Finally, we perform human eye in vivo imaging using the SS-OCT instrument with versatile imaging functionality that accounts for the optics of the eye and enables dynamic control of the optical beam focus.

Angio-OCT as a noninvasive tool for three-dimensional vascular network visualization in retinal diseases

In this paper we demonstrate applicability of intensity-based optical coherence tomography technique for noninvasive visualization of 3D retinal microcapillary network. The study was performed with ultra high resolution and high speed (180,000 Ascans/sec) spectral optical coherence tomography (SOCT). New scanning protocols and data processing algorithms have been introduced to visualize microcapillary network. Moreover, results obtained in the eyes of healthy volunteers and patients with eye diseases were compared with fluorescein angiography. Presented report shows that SOCT is well suited for visualization of 3D retinal capillary network in the healthy and pathologic eyes as well. Obtained results demonstrate high correspondence with fluorescein angiography, without using any contrast agents. Our data suggest that intensity-based SOCT has potential in the early diagnosis of the retinal vascular diseases.

Fourier domain OCT imaging of American cockroach nervous system

In this pilot study we demonstrate results of structural Fourier domain OCT imaging of the nervous system of Periplaneta americana L. (American cockroach). The purpose of this research is to develop an OCT apparatus enabling structural imaging of insect neural system. Secondary purpose of the presented research is to develop methods of the sample preparation and handling during the OCT imaging experiments. We have performed imaging in the abdominal nerve cord excised from the American cockroach. For this purpose we have developed a Fourier domain / spectral OCT system operating at 820 nm wavelength range.

Cortical blood flow imaging of mouse stroke model by high-speed Spectral OCT

We have developed and applied a high-speed Spectral OCT system to image small animal brains. OCT imaging with high spatial resolution and application of multi-parameter approach enabled cortical blood flow visualization. We imaged the brain vascular network of an anesthetized mouse stroke model. We demonstrated the impact of induced stroke on the brain vasculature. The preliminary studies have revealed local ischemia in the areas of the stroke.

Volumetric Doppler imaging of small animal brain using Spectral and Time domain Optical Coherence Tomography

In this paper we demonstrate applicability of Optical Coherence Tomography (OCT) for three-dimensional analysis of blood flow in brain of small animals. We proposed scanning protocols that enable receiving both qualitative and quantitative information about flow. Presented data are obtained with a laboratory high resolution and high speed Spectral OCT system. Data analysis is performed using joint Spectral and Time domain OCT.