We report on imaging of microcirculation by calculating the speckle variance of optical coherence tomography (OCT) structural images acquired using a Fourier domain mode-locked swept-wavelength laser. The algorithm calculates interframe speckle variance in two-dimensional and three-dimensional OCT data sets and shows little dependence to the Doppler angle ranging from 75 degrees to 90 degrees . We demonstrate in vivo detection of blood flow in vessels as small as 25 microm in diameter in a dorsal skinfold window chamber model with direct comparison with intravital fluorescence confocal microscopy. This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.

We demonstrate ultrahigh speed spectral / Fourier domain optical coherence tomography (OCT) using an ultrahigh speed CMOS line scan camera at rates of 70,000 -312,500 axial scans per second. Several design configurations are characterized to illustrate trade-offs between acquisition speed, resolution, imaging range, sensitivity and sensitivity roll-off performance. Ultrahigh resolution OCT with 2.5 -3.0 micron axial image resolution is demonstrated at ∼ 100,000 axial scans per second. A high resolution spectrometer design improves sensitivity roll-off and imaging range performance, trading off imaging speed to 70,000 axial scans per second. Ultrahigh speed imaging at >300,000 axial scans per second with standard image resolution is also demonstrated. Ophthalmic OCT imaging of the normal human retina is investigated. The high acquisition speeds enable dense raster scanning to acquire densely sampled volumetric three dimensional OCT (3D-OCT) data sets of the macula and optic disc with minimal motion artifacts. Imaging with ∼ 8 -9 micron axial resolution at 250,000 axial scans per second, a 512 × 512 × 400 voxel volumetric 3D-OCT data set can be acquired in only ∼ 1.3 seconds. Orthogonal registration scans are used to register OCT raster scans and remove residual axial eye motion, resulting in 3D-OCT data sets which preserve retinal topography. Rapid repetitive imaging over small volumes can visualize small retinal features without motion induced distortions and enables volume registration to remove eye motion. Cone photoreceptors in some regions of the retina can be visualized without adaptive optics or active eye tracking. Rapid repetitive imaging of 3D volumes also provides dynamic volumetric information (4D-OCT) which is shown to enhance visualization of retinal capillaries and should enable functional imaging. Improvements in the speed and performance of 3D-OCT volumetric imaging promise to enable earlier diagnosis and improved monitoring of disease progression and response to therapy in ophthalmology, as well as have a wide range of research and clinical applications in other areas. 1.IntroductionAn increasingly important tool for medical diagnosis and biomedical research, Optical Coherence Tomography (OCT) enables two and three dimensional visualization of the internal structure and morphology of tissue [1]. High sensitivity, large dynamic range, and micron level resolution imaging are achieved with OCT by interferometric detection of backscattered light from the sample. In ophthalmology, OCT can perform non-invasive structural and quantitative NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript imaging of the retina and anterior segment, which enables the identification of pathologies for disease diagnosis or monitoring responses to therapy [2].The earliest implementations of OCT used low coherence interferometry with time domain detection in which the echo delay of backscattered light was measured by mechanically sweeping a mirror in a reference arm [3,4,5]. Commercial ophtha...

We demonstrate swept source OCT utilizing vertical-cavity surface emitting laser (VCSEL) technology for in vivo high speed retinal, anterior segment and full eye imaging. The MEMS tunable VCSEL enables long coherence length, adjustable spectral sweep range and adjustable high sweeping rate (50–580 kHz axial scan rate). These features enable integration of multiple ophthalmic applications into one instrument. The operating modes of the device include: ultrahigh speed, high resolution retinal imaging (up to 580 kHz); high speed, long depth range anterior segment imaging (100 kHz) and ultralong range full eye imaging (50 kHz). High speed imaging enables wide-field retinal scanning, while increased light penetration at 1060 nm enables visualization of choroidal vasculature. Comprehensive volumetric data sets of the anterior segment from the cornea to posterior crystalline lens surface are also shown. The adjustable VCSEL sweep range and rate make it possible to achieve an extremely long imaging depth range of ~50 mm, and to demonstrate the first in vivo 3D OCT imaging spanning the entire eye for non-contact measurement of intraocular distances including axial eye length. Swept source OCT with VCSEL technology may be attractive for next generation integrated ophthalmic OCT instruments.

We describe methods and algorithms for rapid volumetric imaging of cortical vasculature with optical coherence tomography (OCT). By optimizing system design, scanning protocols, and algorithms for visualization of capillary flow, comprehensive imaging of the surface pial vasculature and capillary bed is performed in approximately 12 s. By imaging during hypercapnia and comparing with simultaneous CCD imaging, the sources of contrast of OCT angiography are investigated.Cortical microvasculature is typically visualized in vivo by fluorescent labeling of blood plasma or red blood cells (RBCs) and optical imaging. Recently, high-speed spectral/Fourier domain optical coherence tomography (OCT) was used to visualize major cortical vessels by using intrinsic scattering contrast alone [1]. Moving and stationary tissue were separated by high-pass filtering along the fast axis of a raster scan. However, this approach requires dwell times approaching the millisecond time scale in order to visualize capillary flows [2]. When quantitative flow measurements are not required, the Nyquist frequency for sampling of a single transverse location may be less than the Doppler frequency shift. In this case, angiography measurements can be parallelized, enabling significant improvements in flow sensitivity and imaging speed. In this Letter, we present an OCT system along with methods and algorithms for rapid, high-resolution, volumetric angiography of cortical vasculature.Animal protocols were approved by the animal care committee at Massachusetts General Hospital. Rats were prepared with cranial windows, immobilized stereotactically, and anesthetized with alphachloralose. A CCD camera with illumination at 570 nm (±5 nm) was employed for simultaneous imaging. A 1310 nm spectral/Fourier domain OCT microscope, shown in Fig. 1(A), was constructed for in vivo imaging of the rat cerebral cortex. The light source consisted of two superluminescent diodes combined by using a 50/50 fiber coupler to yield a bandwidth of 170 nm. The axial (depth) resolution was 4.7 µm in air (3.5 µm in tissue). The power on the sample was 4 mW, and the sensitivity was 105 dB. A spectrometer with a 1024 pixel InGaAs line scan camera operated at 47,000 axial scans/s. Either a 5× objective (7 µm transverse intensity profile FWHM at focus) or a 10× objective (3.5 µm transverse intensity profile FWHM at focus) was used. A line trigger from the InGaAs camera was used to synchronize the output of the galvanometer drive signals, ensuring that , the signal power due to a Doppler angle change of ΔΦ Doppler , we calculate a minimum detectable Doppler phase shift of (2−2α) 1/2 =0.2 rad, corresponding to an axial velocity of 1.4 µm/s. The minimum velocities that cause decorrelation comparable with the baseline level (α =0.98) are ~40 µm/ s (10× objective) and ~80 µm/s (5× objective) in the transverse direction and ~40 µm/s in the axial direction. In practice, these velocity sensitivities are achieved near the surface of the brain, where the shot-noise-limited signal-...

We introduce an integration of dynamic light scattering (DLS) and optical coherence tomography (OCT) for high-resolution 3D imaging of heterogeneous diffusion and flow. DLS analyzes fluctuations in light scattered by particles to measure diffusion or flow of the particles, and OCT uses coherence gating to collect light only scattered from a small volume for high-resolution structural imaging. Therefore, the integration of DLS and OCT enables high-resolution 3D imaging of diffusion and flow. We derived a theory under the assumption that static and moving particles are mixed within the OCT resolution volume and the moving particles can exhibit either diffusive or translational motion. Based on this theory, we developed a fitting algorithm to estimate dynamic parameters including the axial and transverse velocities and the diffusion coefficient. We validated DLS-OCT measurements of diffusion and flow through numerical simulations and phantom experiments. As an example application, we performed DLS-OCT imaging of the living animal brain, resulting in 3D maps of the absolute and axial velocities, the diffusion coefficient, and the coefficient of determination.