Multimodal instrument for high-sensitivity autofluorescence and spectral optical coherence tomography of the human eye fundus

In this paper we present a multimodal device for imaging fundus of human eye in vivo which combines functionality of autofluorescence by confocal SLO with Fourier domain OCT. Native fluorescence of human fundus was excited by modulated laser beam (λ = 473 nm, 20 MHz) and lock-in detection was applied resulting in improving sensitivity. The setup allows for acquisition of high resolution OCT and high contrast AF images using fluorescence excitation power of 50-65 μW without averaging consecutive images. Successful functioning of constructed device have been demonstrated for 8 healthy volunteers of different age ranging from 24 to 83 years old.

Introduction to the BODA 2013 feature issue

The guest editors introduce a feature issue containing papers based on research presented at the BODA 2013 meeting.

Intravascular optical coherence tomography measurement of size and apposition of metallic stents

Effect of beam size and catheter position on the apparent size and apposition of metallic stent struts in IVOCT images were examined. Micro-CT data was employed to determine light - stent strut interactions. Simulated results suggest that location of the reflecting regions depend on relative orientation and position of stent struts to the IVOCT beam. Erroneous stent apposition measurements can occur when the IVOCT catheter is at an eccentric position. A method that mitigates stent strut apposition measurement errors is proposed.

Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

In phase-resolved OCT angiography blood flow is detected from phase changes in between A-scans that are obtained from the same location. In ophthalmology, this technique is vulnerable to eye motion. We address this problem by combining inter-B-scan phase-resolved OCT angiography with real-time eye tracking. A tracking scanning laser ophthalmoscope (TSLO) at 840 nm provided eye tracking functionality and was combined with a phase-stabilized optical frequency domain imaging (OFDI) system at 1040 nm. Real-time eye tracking corrected eye drift and prevented discontinuity artifacts from (micro)saccadic eye motion in OCT angiograms. This improved the OCT spot stability on the retina and consequently reduced the phase-noise, thereby enabling the detection of slower blood flows by extending the inter-B-scan time interval. In addition, eye tracking enabled the easy compounding of multiple data sets from the fovea of a healthy volunteer to create high-quality eye motion artifact-free angiograms. High-quality images are presented of two distinct layers of vasculature in the retina and the dense vasculature of the choroid. Additionally we present, for the first time, a phase-resolved OCT angiogram of the mesh-like network of the choriocapillaris containing typical pore openings.

Spatial Light Interference Microscopy (SLIM) using twisted-nematic liquid-crystal modulation

We report the use of a twisted nematic liquid-crystal spatial light modulator (TNLC-SLM) for quantitative phase imaging. The experimental setup is a new implementation of the SLIM principle, which is a phase shifting, white light method for quantitative phase imaging. The approach is based on switching between the phase and amplitude modulation modes of the SLM. Our system is able to deliver a 0.99 nm spatial and 1.33 nm temporal pathlength sensitivity while retaining the optical transverse resolution. The system is implemented as an additional module mounted to a conventional microscope, which makes the system very easy to deploy and integrate with other imaging modalities.

Axial response of high-resolution microendoscopy in scattering media

High-resolution microendoscopy (HRME) uses epi-fluorescence imaging with a coherent fiber-optic bundle to enable in vivo examination of cellular morphology. While the HRME platform has recently gained popularity as a simple alternative to confocal endomicroscopy, the axial response of HRME in thick, scattering tissue has yet to be described quantitatively. These details are important because when analyzing images collected by HRME, out-of-focus light may affect the accuracy of quantitative parameters such as nuclear-to-cytoplasm ratio, which has been proposed as a diagnostic indicator of dysplasia or cancer. In this study we investigated the imaging properties of the HRME system by using phantoms simulating scattering tissue with fluorescently labeled nuclei. We directly compared HRME imaging with confocal endomicroscopy in phantoms and in vivo human tissue. HRME images defocused (deep) objects with apparent diameters and intensity levels that are in agreement with a simple geometric model. Out-of-focus nuclei contribute a relatively low, uniform background level to images which neither leads to the erroneous appearance of large nuclei from deep layers, nor prevents accurate imaging of superficial nuclei with high contrast.

Real-time eye motion compensation for OCT imaging with tracking SLO

Fixational eye movements remain a major cause of artifacts in optical coherence tomography (OCT) images despite the increases in acquisition speeds. One approach to eliminate the eye motion is to stabilize the ophthalmic imaging system in real-time. This paper describes and quantifies the performance of a tracking OCT system, which combines a phase-stabilized optical frequency domain imaging (OFDI) system and an eye tracking scanning laser ophthalmoscope (TSLO). We show that active eye tracking minimizes artifacts caused by eye drift and micro saccades. The remaining tracking lock failures caused by blinks and large saccades generate a trigger signal which signals the OCT system to rescan corrupted B-scans. Residual motion artifacts in the OCT B-scans are reduced to 0.32 minutes of arc (~1.6 µm) in an in vivo human eye enabling acquisition of high quality images from the optic nerve head and lamina cribrosa pore structure.

Ultrasound modulation of coherent light in a multiple-scattering medium: experimental verification of nonzero average phase carried by light

We demonstrate the phase fluctuation introduced by oscillation of scattering centers in the focal volume of an ultrasound transducer in an optical tomography experiment has a nonzero mean. The conditions to be met for the above are: (i) the frequency of the ultrasound should be in the vicinity of the most dominant natural frequency of vibration of the ultrasound focal volume, (ii) the corresponding acoustic wavelength should be much larger than [Formula: see text], a modified transport mean-free-path applicable for phase decorrelation and (iii) the focal volume of the ultrasound transducer should not be larger than 4 - 5 times [Formula: see text]. We demonstrate through simulations that as the ratio of the ultrasound focal volume to [Formula: see text] increases, the average of the phase fluctuation decreases and becomes zero when the focal volume becomes greater than around [Formula: see text]; and through simulations and experiments that as the acoustic frequency increases from 100 Hz to 1 MHz, the average phase decreases to zero. Through experiments done in chicken breast we show that the average phase increases from around 110° to 130° when the background medium is changed from water to glycerol, indicating that the average of the phase fluctuation can be used to sense changes in refractive index deep within tissue.

Short-coherence off-axis holographic phase microscopy of live cell dynamics

We demonstrate a single-shot holographic phase microscope that combines short-coherence laser pulses with an off-axis geometry. By introducing a controlled pulse front tilt, ultrashort pulses are made to interfere over a large field-of-view without loss of fringe contrast. With this microscope, quantitative phase images of live cells can be recorded in a full-field geometry without moving parts. We perform phase imaging of HEK293 cells, to study the dynamics of cell volume regulation in response to an osmotic shock.

Multimodal optical studies of single and clustered colloidal quantum dots for the long-term optical property evaluation of quantum dot-based molecular imaging phantoms

Understanding the optical properties of clustered quantum dots (QDs) is essential to the design of QD-based optical phantoms for molecular imaging. Single and clustered core/shell colloidal QDs of dimers, trimers, and tetramers are self-assembled, separated, and preferentially collected using electrospray differential mobility analysis (ES-DMA) with electrostatic deposition. Multimodal optical characterization and analysis of their dynamical photoluminescence (PL) properties enables the long-term evaluation of the physicochemical and optical properties of QDs in a single or a clustered state. A multimodal time-correlated spectroscopic confocal microscope capable of simultaneously measuring the time evolution of PL intensity fluctuation, PL lifetime, and emission spectra reveals the long-term dynamic optical properties of interacting QDs in individual dimeric clusters of QDs. This new method will benefit research into the quantitative interpretation of fluorescence intensity and lifetime results in QD-based molecular imaging techniques. The process of photooxidation leads to coupling of the QDs in a dimer, leading to unique optical properties when compared to an isolated QD. These results guide the design and evaluation of QD-based phantom materials for the validation of the PL measurements for quantitative molecular imaging of biological samples labeled with QD probes.

Three-dimensional phantoms for curvature correction in spatial frequency domain imaging

The sensitivity to surface profile of non-contact optical imaging, such as spatial frequency domain imaging, may lead to incorrect measurements of optical properties and consequently erroneous extrapolation of physiological parameters of interest. Previous correction methods have focused on calibration-based, model-based, and computation-based approached. We propose an experimental method to correct the effect of surface profile on spectral images. Three-dimensional (3D) phantoms were built with acrylonitrile butadiene styrene (ABS) plastic using an accurate 3D imaging and an emergent 3D printing technique. In this study, our method was utilized for the correction of optical properties (absorption coefficient μ(a) and reduced scattering coefficient μ(s)') of objects obtained with a spatial frequency domain imaging system. The correction method was verified on three objects with simple to complex shapes. Incorrect optical properties due to surface with minimum 4 mm variation in height and 80 degree in slope were detected and improved, particularly for the absorption coefficients. The 3D phantom-based correction method is applicable for a wide range of purposes. The advantages and drawbacks of the 3D phantom-based correction methods are discussed in details.

Lymphatic abnormalities in the normal contralateral arms of subjects with breast cancer-related lymphedema as assessed by near-infrared fluorescent imaging

Current treatment of unilateral breast cancer-related lymphedema (BCRL) is only directed to the afflicted arm. Near-infrared fluorescent imaging (NIRF) of arm lymphatic vessel architecture and function in BCRL and control subjects revealed a trend of increased lymphatic abnormalities in both the afflicted and unafflicted arms with increasing time after lymphedema onset. These pilot results show that BCRL may progress to affect the clinically "normal" arm, and suggest that cancer-related lymphedema may become a systemic, rather than local, malady. These findings support further study to understand the etiology of cancer-related lymphedema and lead to better diagnostics and therapeutics directed to the systemic lymphatic system.

Introduction: feature issue on phantoms for the performance evaluation and validation of optical medical imaging devices

The editors introduce the Biomedical Optics Express feature issue on "Phantoms for the Performance Evaluation and Validation of Optical Medical Imaging Devices." This topic was the focus of a technical workshop that was held on November 7-8, 2011, in Washington, D.C. The feature issue includes 13 contributions from workshop attendees.

3D imaging of biofilms on implants by detection of scattered light with a scanning laser optical tomograph

Biofilms - communities of microorganisms attached to surfaces - are a constant threat for long-term success in modern implantology. The application of laser scanning microscopy (LSM) has increased the knowledge about microscopic properties of biofilms, whereas a 3D imaging technique for the large scale visualization of bacterial growth and migration on curved and non-transparent surfaces is not realized so far.Towards this goal, we built a scanning laser optical tomography (SLOT) setup detecting scattered laser light to image biofilm on dental implant surfaces. SLOT enables the visualization of living biofilms in 3D by detecting the wavelength-dependent absorption of non-fluorescent stains like e.g. reduced triphenyltetrazolium chloride (TTC) accumulated within metabolically active bacterial cells. Thus, the presented system allows the large scale investigation of vital biofilm structure and in vitro development on cylindrical and non-transparent objects without the need for fluorescent vital staining. We suggest SLOT to be a valuable tool for the structural and volumetric investigation of biofilm formation on implants with sizes up to several millimeters.

Multimodal photoacoustic and optical coherence tomography scanner using an all optical detection scheme for 3D morphological skin imaging

A noninvasive, multimodal photoacoustic and optical coherence tomography (PAT/OCT) scanner for three-dimensional in vivo (3D) skin imaging is described. The system employs an integrated, all optical detection scheme for both modalities in backward mode utilizing a shared 2D optical scanner with a field-of-view of ~13 × 13 mm(2). The photoacoustic waves were detected using a Fabry Perot polymer film ultrasound sensor placed on the surface of the skin. The sensor is transparent in the spectral range 590-1200 nm. This permits the photoacoustic excitation beam (670-680 nm) and the OCT probe beam (1050 nm) to be transmitted through the sensor head and into the underlying tissue thus providing a backward mode imaging configuration. The respective OCT and PAT axial resolutions were 8 and 20 µm and the lateral resolutions were 18 and 50-100 µm. The system provides greater penetration depth than previous combined PA/OCT devices due to the longer wavelength of the OCT beam (1050 nm rather than 829-870 nm) and by operating in the tomographic rather than the optical resolution mode of photoacoustic imaging. Three-dimensional in vivo images of the vasculature and the surrounding tissue micro-morphology in murine and human skin were acquired. These studies demonstrated the complementary contrast and tissue information provided by each modality for high-resolution 3D imaging of vascular structures to depths of up to 5 mm. Potential applications include characterizing skin conditions such as tumors, vascular lesions, soft tissue damage such as burns and wounds, inflammatory conditions such as dermatitis and other superficial tissue abnormalities.

Fiber optic microendoscopy for preclinical study of bacterial infection dynamics

We explore the use of fiber optic microendoscopy to image and quantify bacterial infection in the skin and lungs using an animal model. The contact probe fiber bundle fluorescence microendoscope has a 4 µm resolution, a 750 µm field of view, and a 1 mm outer diameter. Subcutaneous and intra-tracheal infections of fluorescent Mycobacterium bovis Bacillus Calmette-Guérin (BCG) bacteria were detected in situ from inocula down to 10(4) and 10(7) colony forming units, respectively.