Young-Joo Hong

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.

Three-dimensional retinal and choroidal capillary imaging by power Doppler optical coherence angiography with adaptive optics

Retinal and choroidal vascular imaging is a key to the better understanding and diagnosis of eye diseases. To achieve comprehensive three-dimensional capillary imaging, we used an enhanced vascular imaging technique, so called adaptive optics optical coherence angiography (AO-OCA). AO-OCA enables in vivo high-resolution and high-contrast micro-vascular imaging by detecting Doppler frequency shifts. Using this technique, the retinal and choroidal vasculatures of healthy subjects were imaged. The results show that both intensity and Doppler power images have sufficient contrast to discriminate almost all vasculatures from the static tissue. However, the choriocapillaris, pre-arterioles, and post-venules in the Sattler layer were more contrasted by the Doppler technique. In conclusion, AO-OCA enables three-dimensional capillary imaging, and is especially useful for the detection of the choriocapillaris and choroidal capillary network.

Advanced multi-contrast Jones matrix optical coherence tomography for Doppler and polarization sensitive imaging.

An advanced version of Jones matrix optical coherence tomography (JMT) is demonstrated for Doppler and polarization sensitive imaging of the posterior eye. JMT is capable of providing localized flow tomography by Doppler detection and investigating the birefringence property of tissue through a three-dimensional (3-D) Jones matrix measurement. Owing to an incident polarization multiplexing scheme based on passive optical components, this system is stable, safe in a clinical environment, and cost effective. Since the properties of this version of JMT provide intrinsic compensation for system imperfection, the system is easy to calibrate. Compared with the previous version of JMT, this advanced JMT achieves a sufficiently long depth measurement range for clinical cases of posterior eye disease. Furthermore, a fine spectral shift compensation method based on the cross-correlation of calibration signals was devised for stabilizing the phase of OCT, which enables a high sensitivity Doppler OCT measurement. In addition, a new theory of JMT which integrates the Jones matrix measurement, Doppler measurement, and scattering measurement is presented. This theory enables a sensitivity-enhanced scattering OCT and high-sensitivity Doppler OCT. These new features enable the application of this system to clinical cases. A healthy subject and a geographic atrophy patient were measured in vivo, and simultaneous imaging of choroidal vasculature and birefringence structures are demonstrated.

High-penetration swept source Doppler optical coherence angiography by fully numerical phase stabilization

A high-penetration swept-source optical coherence tomography (HP-SS-OCT) system based on a 1-μm short cavity laser is developed. Doppler OCT processing is applied, along with a custom-made numerical phase stabilization algorithm; this process does not require additional calibration hardware. Thus, our phase stabilization method is simple and can be employed in a variety of SS-OCT systems. The bidirectional blood flow and vasculature in the deep choroid was successfully imaged via two Doppler modes that use different time intervals for Doppler processing. En face projection image of squared power of Doppler shift is compared to ICGA, and the utility of our method is verified.

Passive component based multifunctional Jones matrix swept source optical coherence tomography for Doppler and polarization imaging

We present a fiber based multifunctional Jones matrix swept source optical coherence tomography (SS-OCT) system for Doppler and polarization imaging. Jones matrix measurement without using active components such as electro-optic modulators is realized by incident polarization multiplexing based on independent delay of two orthogonal polarization states and polarization diversity detection. In addition to polarization sensitivity, this system measures Doppler flow without extra hardware for phase stabilized SS-OCT detection. An eighth-wave plate was measured to demonstrate the polarization detection accuracy. The optic nerve head of a retina was measured in vivo. Detailed vasculature and birefringent structures were investigated simultaneously.

Three-dimensional visualization of choroidal vessels by using standard and ultra-high resolution scattering optical coherence angiography

Scattering optical coherence angiography (S-OCA) is a noninvasive imaging method that is based on the high-speed standard 800nm band spectral-domain optical coherence tomography (SD-OCT) and the ultra-high-resolution SD-OCT which has the axial resolution of 6.1 mum and 2.9 mum in tissue, respectively. In this paper, we have demonstrated the use of this method for in vivo human retinal imaging. A three-dimensional view of the choroidal vasculature was obtained by segmenting the choroidal vessels; this was done using intensity threshold based binarization at each depth plane relative to the retinal pigment epithelium. A vascular projection image was obtained by integrating the segmented choroidal vasculature. In order to assess the feasibility of the proposed method, we compared these images with those obtained using existing invasive methods such as fluorescein angiography and indocyanine green angiography. Clinically worthful images are obtained from the application of S-OCA to the agerelated macular degeneration and polypoidal choroidal vasculopathy.

Noninvasive Investigation of Deep Vascular Pathologies of Exudative Macular Diseases by High-Penetration Optical Coherence Angiography

PURPOSE A newly developed high-penetration Doppler optical coherence angiography (HP-OCA) with a 1-μm probe beam for noninvasive investigation of vascular pathology of exudative macular diseases is introduced. A descriptive case series is presented to discuss the clinical utility of HP-OCA. METHODS Eleven eyes of 10 subjects with exudative macular disease, including two eyes with myopic choroidal neovascularization (mCNV); four eyes with AMD; and five eyes with polypoidal choroidal vasculopathy (PCV) were investigated. Two Doppler scanning modes (bidirectional and high-sensitive) of HP-OCA were used for the investigation. HP-OCA provides depth-resolved and en face angiograms and a structural OCT noninvasively. The HP-OCA images were compared with fluorescein angiography (FA); indocyanine green angiography (ICGA); and color fundus images. RESULTS The abnormal vasculature patterns observed with high-sensitive HP-OCA presented high similarity to the midphase of ICGA. Several abnormal Doppler signals were observed in the en face high-sensitive HP-OCA and were colocated with FA leakage. This colocation was found in one eye with mCNV, four eyes with AMD, and one eye with PCV. Doppler tomogram of the bidirectional mode showed abnormal Doppler signals in three of five PCV cases beneath the pigment epithelium detachment. With the high-sensitive mode, Doppler signals were found beneath the elevated retinal pigment epithelium in all untreated cases. CONCLUSIONS HP-OCA revealed depth-resolved abnormal vasculatures in exudative macular diseases. The en face HP-OCA images showed high similarity with FA and ICGA images. These results suggest HP-OCA can be used for noninvasive and three-dimensional angiography in a clinical routine.

Birefringence imaging of posterior eye by multi-functional Jones matrix optical coherence tomography

A clinical grade prototype of posterior multifunctional Jones matrix optical coherence tomography (JM-OCT) is presented. This JM-OCT visualized depth-localized birefringence in addition to conventional cumulative phase retardation imaging through local Jones matrix analysis. In addition, it simultaneously provides a sensitivity enhanced scattering OCT, a quantitative polarization uniformity contrast, and OCT-based angiography. The probe beam is at 1-μm wavelength band. The measurement speed and the depth-resolution were 100,000 A-lines/s, and 6.6 μm in tissue, respectively. Normal and pathologic eyes are examined and several clinical features are revealed, which includes high birefringence in the choroid and lamina cribrosa, and birefringent layered structure of the sclera. The theoretical details of the depth-localized birefringence imaging and conventional phase retardation imaging are formulated. This formulation indicates that the birefringence imaging correctly measures a depth-localized single-trip phase retardation of a tissue, while the conventional phase retardation can provide correct single-trip phase retardation only for some specific types of samples.

Three-dimensional Vascular Imaging of Proliferative Diabetic Retinopathy by Doppler Optical Coherence Tomography

PURPOSE To evaluate the 3-dimensional architecture of neovascularization in proliferative diabetic retinopathy using Doppler optical coherence tomography (OCT). DESIGN Prospective, nonrandomized clinical trial. METHODS Seventeen eyes of 14 patients with proliferative diabetic retinopathy were prospectively studied. Prototype Doppler OCT was used to evaluate the 3-dimensional vascular architecture at vitreoretinal adhesions. RESULTS Proliferative membranes were detected in all eyes with proliferative diabetic retinopathy by standard OCT images. Doppler OCT images detected blood flow by neovascularization of the disc in 12 eyes and neovascularization elsewhere in 11 eyes. Doppler OCT images showed the 3-dimensional extent of new vessels at various stages of neovascularization, and the extent of new vessels could be clearly confirmed at vitreoretinal adhesions. CONCLUSIONS Doppler OCT is useful for the detection and evaluation of the 3-dimensional vascular structure of neovascularization, and can assist in the noninvasive assessment of proliferative diabetic retinopathy.