Dual-band Fourier domain optical coherence tomography with depth-related compensations

Gold nanoparticles to enhance ophthalmic imaging

The use of gold nanoparticles as diagnostic tools is burgeoning, especially in the cancer community with a focus on theranostic applications to both cancer diagnosis and treatment. Gold nanoparticles have also demonstrated great potential for use in diagnostic and therapeutic approaches in ophthalmology. Although many ophthalmic imaging modalities are available, there is still a considerable unmet need, in particular for ophthalmic molecular imaging for the early detection of eye disease before morphological changes are more grossly visible. An understanding of how gold nanoparticles are leveraged in other fields could inform new ways they could be utilized in ophthalmology. In this paper, we review current ophthalmic imaging techniques and then identify optical coherence tomography (OCT) and photoacoustic imaging (PAI) as the most promising technologies amenable to the use of gold nanoparticles for molecular imaging. Within this context, the development of gold nanoparticles as OCT and PAI contrast agents are reviewed, with the most recent developments described in detail.

Spatiotemporal Tracking of Brain-Tumor-Associated Myeloid Cells in Vivo through Optical Coherence Tomography with Plasmonic Labeling and Speckle Modulation

By their nature, tumors pose a set of profound challenges to the immune system with respect to cellular recognition and response coordination. Recent research indicates that leukocyte subpopulations, especially tumor-associated macrophages (TAMs), can exert substantial influence on the efficacy of various cancer immunotherapy treatment strategies. To better study and understand the roles of TAMs in determining immunotherapeutic outcomes, significant technical challenges associated with dynamically monitoring single cells of interest in relevant live animal models of solid tumors must be overcome. However, imaging techniques with the requisite combination of spatiotemporal resolution, cell-specific contrast, and sufficient signal-to-noise at increasing depths in tissue are exceedingly limited. Here we describe a method to enable high-resolution, wide-field, longitudinal imaging of TAMs based on speckle-modulating optical coherence tomography (SM-OCT) and spectral scattering from an optimized contrast agent. The approach's improvements to OCT detection sensitivity and noise reduction enabled high-resolution OCT-based observation of individual cells of a specific host lineage in live animals. We found that large gold nanorods (LGNRs) that exhibit a narrow-band, enhanced scattering cross-section can selectively label TAMs and activate microglia in an in vivo orthotopic murine model of glioblastoma multiforme. We demonstrated near real-time tracking of the migration of cells within these myeloid subpopulations. The intrinsic spatiotemporal resolution, imaging depth, and contrast sensitivity reported herein may facilitate detailed studies of the fundamental behaviors of TAMs and other leukocytes at the single-cell level in vivo, including intratumoral distribution heterogeneity and roles in modulating cancer proliferation.

Improve depth of field of optical coherence tomography using finite energy Airy beam

We report a technique to break the depth of field (DOF) limit in optical coherence tomography (OCT) using a finite energy Airy beam. The Airy beam is generated using a phase mask in a Fourier transform schematic and provides the DOF improvement due to its low diffraction. We compare Airy beam OCT with conventional Gaussian beam OCT using lateral resolution and sensitivity. Experimental data from the polystyrene beads in water as well as lemon tissue confirm the extension of DOF up to 10 mm in Airy beam OCT, while the DOF of Gaussian beam OCT is less than 3.0 mm. We also demonstrate that a modified Airy beam can be effectively used in OCT by adjusting the truncating factor of the Airy beam via changing the pattern scale of the phase mask. This result provides a selection method for the use of a finite energy Airy beam in OCT.

The value of ultrahigh resolution OCT in dermatology - delineating the dermo-epidermal junction, capillaries in the dermal papillae and vellus hairs

Optical coherence tomography (OCT) imaging of the skin is gaining recognition and is increasingly applied to dermatological research. A key dermatological parameter inferred from an OCT image is the epidermal (Ep) thickness as a thickened Ep can be an indicator of a skin disease. Agreement in the literature on the signal characters of Ep and the subjacent skin layer, the dermis (D), is evident. Ambiguities of the OCT signal interpretation in the literature is however seen for the transition region between the Ep and D, which from histology is known as the dermo-epidermal junction (DEJ); a distinct junction comprised of the lower surface of a single cell layer in epidermis (the stratum basale) connected to an even thinner membrane (the basement membrane). The basement membrane is attached to the underlying dermis. In this work we investigate the impact of an improved axial and lateral resolution on the applicability of OCT for imaging of the skin. To this goal, OCT images are compared produced by a commercial OCT system (Vivosight from Michaelson Diagnostics) and by an in-house built ultrahigh resolution (UHR-) OCT system for dermatology. In 11 healthy volunteers, we investigate the DEJ signal characteristics. We perform a detailed analysis of the dark (low) signal band clearly seen for UHR-OCT in the DEJ region where we, by using a transition function, find the signal transition of axial sub-resolution character, which can be directly attributed to the exact location of DEJ, both in normal (thin/hairy) and glabrous (thick) skin. To our knowledge no detailed delineating of the DEJ in the UHR-OCT image has previously been reported, despite many publications within this field. For selected healthy volunteers, we investigate the dermal papillae and the vellus hairs and identify distinct features that only UHR-OCT can resolve. Differences are seen in tracing hairs of diameter below 20 μm, and in imaging the dermal papillae where, when utilising the UHR-OCT, capillary structures are identified in the hand palm, not previously reported in OCT studies and specifically for glabrous skin not reported in any other in vivo optical imaging studies.

Spatial convolution for mirror image suppression in Fourier domain optical coherence tomography

We developed a spatial convolution approach for mirror image suppression in phase-modulated Fourier domain optical coherence tomography, and demonstrated it in vivo for small animal imaging. Utilizing the correlation among neighboring A-scans, the mirror image suppression process was simplified to a three-parameter convolution. By adjusting the three parameters, we can implement different Fourier domain sideband windows, which is important but complicated in existing approaches. By properly selecting the window size, we validated the spatial convolution approach on both simulated and experimental data, and showed that it is versatile, fast, and effective. The new approach reduced the computational cost by 32% and improved the mirror image suppression by 10%. We adapted the spatial convolution approach to a GPU accelerated system for ultrahigh-speed processing in 0.1 ms. The advantage of the ultrahigh speed was demonstrated in vivo for small animal imaging in a mouse model. The fast scanning and processing speed removed respiratory motion artifacts in the in vivo imaging.

Contrast-enhanced optical coherence tomography with picomolar sensitivity for functional in vivo imaging

Optical Coherence Tomography (OCT) enables real-time imaging of living tissues at cell-scale resolution over millimeters in three dimensions. Despite these advantages, functional biological studies with OCT have been limited by a lack of exogenous contrast agents that can be distinguished from tissue. Here we report an approach to functional OCT imaging that implements custom algorithms to spectrally identify unique contrast agents: large gold nanorods (LGNRs). LGNRs exhibit 110-fold greater spectral signal per particle than conventional GNRs, which enables detection of individual LGNRs in water and concentrations as low as 250 pM in the circulation of living mice. This translates to ~40 particles per imaging voxel in vivo. Unlike previous implementations of OCT spectral detection, the methods described herein adaptively compensate for depth and processing artifacts on a per sample basis. Collectively, these methods enable high-quality noninvasive contrast-enhanced imaging of OCT in living subjects, including detection of tumor microvasculature at twice the depth achievable with conventional OCT. Additionally, multiplexed detection of spectrally-distinct LGNRs was demonstrated to observe discrete patterns of lymphatic drainage and identify individual lymphangions and lymphatic valve functional states. These capabilities provide a powerful platform for molecular imaging and characterization of tissue noninvasively at cellular resolution, called MOZART.

Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization

A tri-band spectroscopic optical coherence tomography (SOCT) system has been implemented for visualization of lipid and blood vessel distribution. The tri-band swept source, which covers output spectrum in 1.3, 1.5, and 1.6  μm wavelength windows, is based on a dual-band Fourier domain mode-locked laser and a fiber optical parametric amplifier. This tri-band SOCT can further differentiate materials, e.g., lipid and artery, qualitatively by contrasting attenuation coefficients difference within any two of these bands. Furthermore, ex vivo imaging of both porcine artery with artificial lipid plaque phantom and mice with coronary artery disease were demonstrated to showcase the capability of our SOCT.

Full-range Fourier domain Doppler optical coherence tomography based on sinusoidal phase modulation

A novel full-range Fourier domain Doppler optical coherence tomography (full-range FD-DOCT) using sinusoidal phase modulation for B-M scan is proposed. In this sinusoidal B-M scan, zero optical path difference (OPD) position does not move corresponding to lateral scanning points in contrast to linear B-M scan. Since high phase sensitivity arises around the zero OPD position, the proposed full-range FD-DOCT can achieve easily high velocity sensitivity without mirror image around the zero OPD position. Velocity sensitivity dependent on the OPD and the interval of scanning points is examined, and flow velocity detection capability is verified through Doppler imaging of a flow phantom and an in vivo biological sample.