Optical coherence tomography

About: Optical coherence tomography is a research topic. Over the lifetime, 19051 publications have been published within this topic receiving 477433 citations. The topic is also known as: optical coherent tomography.

Stable carrier generation and phase-resolved digital data processing in optical coherence tomography.

Abstract: We present a technique for improved carrier generation by eliminating the instability of a mechanical device in favor of an electro-optical phase modulator in the reference arm of an optical coherence tomography system. A greater than threefold reduction in the phase variance between consecutive A-line scans at a repetition rate of 1 kHz was achieved. Stable and reproducible interference fringe generation permits phase-resolved digital data processing. A correction algorithm was applied to the interferometric signal to compensate for the departure of the source spectrum from an ideal Gaussian shape, resulting in up to 8-dB sidelobe suppression at the expense of a 1-dB increase in the noise floor. In addition, we could eliminate completely the broadening effect of group-delay dispersion on the coherence function by introducing a quadratic phase shift in the Fourier domain of the interferometric signal.

Spatial distribution of posterior pole choroidal thickness by spectral domain optical coherence tomography.

Abstract: The choroid, a vascular meshwork between the retina and sclera, plays a major role in providing oxygen and nutrition to the outer layers of the retina.1 In recent years, increased awareness of its role in ocular development and its known association with many diseases of the posterior pole have stimulated a renewed focus on understanding choroidal anatomy and physiology.2 A number of methods, including histology3 and ultrasonography,4 have previously been used to quantify choroidal thickness (CT); however, the overall precision of these approaches is still lacking. Fortunately, the recent introduction of spectral domain optical coherence tomography (SD-OCT) and the description of “enhanced depth imaging” scanning protocols have afforded a new opportunity to improve the accuracy of quantitative choroidal assessment. As a result, changes in CT have now been studied using different OCT technologies over a wide range of ocular pathologies (e.g., glaucoma,5 inherited retinal diseases,6 high myopia,7 central serous chorioretinopathy,8 polypoidal choroidal vasculopathy,9 neovascular age-related macular degeneration [AMD],9 and Vogt Koyanagi Harada disease10). Although the use of OCT has provided many new insights into choroidal morphology, to date there exists a notable disparity between the CT measurements obtained in different studies. For example, several studies on the cross-sectional variation of CT measurements in “normal” subjects have shown CT to be greatest at the fovea, with decreasing thickness more nasally than temporally.9,11,12 Other results suggest that the foveal CT is thinner than the choroid superior to the fovea.13 These discrepancies may arise due to the use of different image acquisition methodologies, a generally limited field of view for scanning, and inconsistencies in choosing the exact locations for repeated CT measurement. Regardless, the exact spatial distribution of CT changes in the macular region of human eyes remains unclear. In addition, most OCT-derived studies have focused on assessment of CT in the macular region alone, examining the correlation between macular CT changes and disease expression. However, unlike the neurosensory retina, a complex and highly organized neural structure with the fovea as its unmistaken center, the choroid is a vascular layer with a potentially very different topography. Determination of choroidal spatial distribution may thus be difficult, and potentially inaccurate, in the context of macular scanning alone. In this report, we aim to address these issues by obtaining larger, two-dimensional (2D) maps of the spatial distribution of the choroid in the posterior pole and identifying its specific patterns in healthy volunteers using SD-OCT.

In vivo measurement of retinal physiology with high-speed ultrahigh-resolution optical coherence tomography.

Abstract: Noninvasive in vivo functional optical imaging of the intact retina is demonstrated by using high-speed, ultrahigh-resolution optical coherence tomography (OCT). Imaging was performed with 2.8 μm resolution at a rate of 24,000 axial scans per second. A white-light stimulus was applied to the dark-adapted rat retina, and the average reflectivities from different intraretinal layers were monitored as a function of time. A 10%-15% increase in the average amplitude reflectance of the photoreceptor outer segments was observed in response to the stimulus. The spatial distribution of the change in the OCT signal is consistent with an increase in backscatter from the photoreceptor outer segments. To our knowledge, this is the first in vivo demonstration of OCT functional imaging in the intact retina.

Pilot study of optical coherence tomography measurement of retinal blood flow in retinal and optic nerve diseases.

Abstract: The development of noninvasive methods such as magnetic resonance angiography1 and functional magnetic resonance imaging (MRI)2 to measure cerebral hemodynamics has greatly enhanced the study of neurologic diseases and functional neuroanatomy. Such methods would also be very helpful in the eye because the leading causes of blindness in the industrialized world—diabetic retinopathy, macular degeneration, and glaucoma—are all related to abnormal retinal3,4 or optic nerve blood flow.5 Unfortunately, MRI resolution is too coarse for quantitative imaging of retinal blood vessels, which have a very fine caliber. Although several techniques are being used for retinal blood flow evaluation, they all have serious limitations. Ultrasound color Doppler imaging has sufficient resolution to measure only the larger retrobulbar vessels.6 It can measure blood velocity but not vessel diameter; therefore, volumetric blood flow cannot be determined. Several types of laser Doppler techniques are able to measure flow in individual retinal vessels7–9 or capillary beds.10 Although it is possible to measure total retinal blood flow by adding measurements from individual vessels, this requires many measurements over a long session.8 These specialized instruments are generally available only in major research centers because they are expensive. Fluorescein and indocyanine green angiographies are widely used to visualize retinal and choroidal circulations. However, they do not provide quantitative measurements of blood flow and require the intravenous injection of dyes that have potential side effects.11 Optical coherence tomography (OCT)12 is commonly used in the diagnosis and management of retinal diseases.13–16 It has the requisite resolution to image retinal blood vessels.17 Because it is a coherent detection technique, OCT can detect the Doppler frequency shift of back-scattered light, which provides information on blood flow velocity.18,19 With the development of high-speed Fourier-domain OCT,20–22 it has become possible to capture the pulsatile dynamics of blood flow.23,24 Using Doppler Fourier-domain OCT, we developed a double circular scanning pattern (Fig. 1) that measures flow in all the blood vessels around the optic nerve head four to six times per second.25 Total retinal blood flow could be calculated with the data sampled within 2 seconds. We have demonstrated that flow measurements in normal subjects26 and in a patients with diabetic retinopathy27 can be reproducibly obtained. In this study, we used this new technique in a systematic investigation of blood flow abnormalities in retinal and optic nerve diseases. Figure 1. (a) Fundus photograph showing the double circular pattern of the OCT beam scanning retinal blood vessels emerging from the optic disc. (b) The relative position of a blood vessel in the two OCT cross-sections is used to calculate the Doppler angle θ ...