Masahiro Yamanari

Optical coherence angiography

Noninvasive angiography is demonstrated for the in vivo human eye. Three-dimensional flow imaging has been performed with high-speed spectral-domain optical coherence tomography. Sample motion is compensated by two algorithms. Axial motion between adjacent A-lines within one OCT image is compensated by the Doppler shift due to bulk sample motion. Axial displacements between neighboring images are compensated by a correlation-based algorithm. Three-dimensional vasculature of ocular vessels has been visualized. By integrating volume sets of flow images, two-dimensional images of blood vessels are obtained. Retinal and choroidal blood vessel images are simultaneously obtained by separating the volume set into retinal part and choroidal parts. These are corresponding to fluorescein angiogram and indocyanine angiogram.

In vivo high-contrast imaging of deep posterior eye by 1-μm swept source optical coherence tomography and scattering optical coherence angiography

Retinal, choroidal and scleral imaging by using swept-source optical coherence tomography (SS-OCT) with a 1-microm band probe light, and high-contrast and three-dimensional (3D) imaging of the choroidal vasculature are presented. This SS-OCT has a measurement speed of 28,000 A-lines/s, a depth resolution of 10.4 microm in tissue, and a sensitivity of 99.3 dB. Owing to the high penetration of the 1-microm probe light and the high sensitivity of the system, the in vivo sclera of a healthy volunteer can be observed. A software-based algorithm of scattering optical coherence angiography (S-OCA) is developed for the high-contrast and 3D imaging of the choroidal vessels. The S-OCA is used to visualize the 3D choroidal vasculature of the in vivo human macula and the optic nerve head. Comparisons of S-OCA with several other angiography techniques including Doppler OCA, Doppler OCT, fluorescein angiography, and indocyanine green angiography are also presented.

Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation

We present fiber-based polarization-sensitive swept-source optical coherence tomography (SS-OCT) based on continuous source polarization modulation. The light source is a frequency swept laser centered at 1.31 microm with a scanning rate of 20 kHz. The incident polarization is modulated by a resonant electro-optic modulator at 33.3 MHz, which is one-third of the data acquisition frequency. The zeroth- and first-order harmonic components of the OCT signals with respect to the polarization modulation frequency have the polarimetric information of the sample. By algebraic and matrix calculations of the signals, this system can measure the depth-resolved Jones matrices of the sample with a single wavelength scan. The phase fluctuations of the starting trigger of wavelength scan and the polarization modulation are cancelled by monitoring the OCT phase of a calibration mirror inserted into the sample arm. We demonstrate the potential of the system by the measurement of chicken breast muscle and the volumetric measurement of an in vivo human anterior eye segment. The phase retardation image shows an additional contrast in the fibrous tissue such as the collagen fiber in the trabecular meshwork and sclera.

Comprehensive in vivo micro-vascular imaging of the human eye by dual-beam-scan Doppler optical coherence angiography

Comprehensive angiography provides insight into the diagnosis of vascular-related diseases. However, complex microvascular networks of unstable in vivo organs such as the eye require micron-scale resolution in three dimensions and a high sampling rate to access a wide area as maintaining the high resolution. Here, we introduce dual-beam-scan Doppler optical coherence angiography (OCA) as a label-free comprehensive ophthalmic angiography that satisfies theses requirements. In addition to high resolution and high imaging speed, high sensitivity to motion for detecting tiny blood flow of microvessels is achieved by detecting two time-delayed signals with scanning of two probing beams separated on a sample. We present in vivo three-dimensional imaging of the microvasculature of the posterior part of the human eye. The demonstrated results show that this technique may be used for comprehensive ophthalmic angiography to evaluate the vasculature of the posterior human eye and to diagnose variety of vascular diseases.

Fiber-based polarization-sensitive Fourier domain optical coherence tomography using B-scan-oriented polarization modulation method

Fiber-based high-speed polarization-sensitive Fourier domain optical coherence tomography (PS-FD-OCT) is developed at 840 nm wavelength using polarization modulation method. The incident state of polarization is modulated along B-scan. The spectrometer has a polarizing beamsplitter and two line-CCD cameras operated at a line rate of 27.7 kHz. From the 0th and 1st orders of the spatial frequencies along the B-scanning, a depth-resolved Jones matrix can be derived. Since continuous polarization modulation along B-scan causes fringe washout, equivalent discrete polarization modulation is applied to biological measurements. For the demonstration, an in vitro chicken breast muscle, an in vivo finger pad, and an in vivo caries lesion of a human tooth are measured. Three dimensional phase retardation images show the potentials for applying the system to biological and medical studies.

Phase retardation measurement of retinal nerve fiber layer by polarization-sensitive spectral-domain optical coherence tomography and scanning laser polarimetry.

Phase retardation of in vivo human retinal nerve fiber layer (RNFL) is quantitatively measured by two methods--polarization-sensitive spectral-domain optical coherence tomography (PS-SD-OCT) and scanning laser polarimetry (SLP). An en face cumulative phase retardation map is calculated from the three-dimensional (3-D) phase retardation volume of healthy and glaucomatous eyes measured by PS-SD-OCT. It is shown that the phase retardation curves around the optic nerve head measured by PS-SD-OCT and SLP have similar values except near the retinal blood vessels. PS-SD-OCT can measure the cumulative phase retardation of RNFL as well as SLP, which will allow the evaluation of RNFL for glaucomatous eyes.

Visualization of sub-retinal pigment epithelium morphologies of exudative macular diseases by high-penetration optical coherence tomography.

PURPOSE To evaluate the clinical significance of the newly developed long-wavelength probe optical coherence tomography (LP-OCT) for the diagnosis of exudative macular diseases. METHODS Fourteen eyes of 13 participants were prospectively enrolled in the study. There were seven type I and five type II choroidal neovascularization (CNV) cases associated with age-related macular degeneration and idiopathic neovascularization and one case of polypoidal choroidal vasculopathy (PCV). A custom-built LP-OCT based on swept-source OCT (SS-OCT) technology was used. This new OCT uses a probe beam with a wavelength of 1060 nm that provides deeper penetration into the choroid and higher image contrast to the structures beneath the retinal pigment epithelium (RPE) and pathologic tissues than does conventional OCT. The depth resolution is 10.4 microm in tissue and the measurement speed is 28,000 depth scans/s. All the eyes were also examined by standard short wavelength probe OCT (SP-OCT). The image contrasts of the LP- and SP-OCT were qualitatively evaluated and analyzed by Wilcoxons paired signed rank test and Spearmans rank correlation test. RESULTS In 10 of 14 eyes, high-contrast visualization of the diseases beneath the RPE, CNV, or fibrin was attained. These diseases were almost invisible in the SP-OCT images. The LP-OCT of the remaining eyes also revealed significant improvement in the image contrasts beneath the RPE and CNV. Qualitative evaluation of the image contrasts and subsequent statistical test indicated statistically significant improvement in the image penetration to the choroid of LP-OCT to that of SP-OCT. CONCLUSIONS LP-OCT provided significant improvement in the image contrast of exudative macular diseases.

High-speed three-dimensional human retinal imaging by line-field spectral domain optical coherence tomography

Line-field spectral domain optical coherence tomography (LF-SDOCT) has been developed for very high-speed three-dimensional (3D) retinal imaging. By this technique, the A-line rate significantly improved to 823,200 A-lines/s for single frame imaging and 51,500 A-lines/s for continues frame imaging. The frame rate at continues frame imaging is 201 fps. This 3D acquisition speed is more than two fold higher acquisition speed than the standard flying spot SD-OCT. In this paper, the integration time of the camera was optimized for the in vivo retinal measurement and the degradation of the lateral resolution due to the ocular aberrations was suppressed by introducing the pupil stop. Owing to an optimal integration time, the motion artifact can be significantly suppressed. Also a pupil stop was employed in order to enhance the contrast of the OCT image for the effect of ocular aberrations. The in vivo 3D retinal imaging with 256 cross-sectional images (256 A-lines/image) was successfully performed in 1.3 seconds, corresponding to 0.8 volume/s. The maximum on-axis system sensitivity was measured to be 89.4 dB at a depth of 112 mum with an axial resolution of 7.4 mum in tissue. It is shown that LF-SDOCT might have a sensitivity advantage in comparison to the flying spot SD-OCT in the ultra high-speed acquisition mode.

Imaging Polarimetry in Age-Related Macular Degeneration

PURPOSE To evaluate the birefringence properties of eyes with age-related macular degeneration (AMD). To compare the information from two techniques--scanning laser polarimetry (GDx) and polarization-sensitive spectral-domain optical coherence tomography (OCT)--and investigate how they complement each other. METHODS The authors prospectively examined the eyes of two healthy subjects and 13 patients with exudative AMD. Using scanning laser polarimetry, they computed phase-retardation maps, average reflectance images, and depolarized light images. To obtain polarimetry information with improved axial resolution, they developed a fiber-based, polarization-sensitive, spectral-domain OCT system and measured the phase retardation associated with birefringence in the same eyes. RESULTS Both GDx and polarization-sensitive spectral-domain optical coherence tomography detected abnormal birefringence at the locus of exudative lesions. Polarization-sensitive, spectral-domain OCT showed that in the old lesions with fibrosis, phase-retardation values were significantly larger than in the new lesions (P = 0.020). Increased scattered light and altered polarization scramble were associated with portions of the lesions. CONCLUSIONS GDx and polarization-sensitive spectral-domain OCT are complementary in probing birefringence properties in exudative AMD. Polarimetry findings in exudative AMD emphasized different features and were related to the progression of the disease, potentially providing a noninvasive tool for microstructure in exudative AMD.

Generalized Jones matrix optical coherence tomography: performance and local birefringence imaging

Phase retardation imaging including local birefringence imaging of biological tissues is described by generalized Jones-matrix optical coherence tomography. The polarization properties of a local tissue can be obtained from two Jones matrices that are measured by backscattered lights from the front and back boundaries of the local tissue. The error in the phase retardation measurement due to background noise is analyzed theoretically, numerically, and experimentally. The minimum detectable phase retardation is estimated from numerical simulations. The theoretical analysis suggests that the measurements with two orthogonal input polarization states have the lowest retardation error. Local birefringence imaging is applied to the human anterior eye chamber and skin in vivo.