Imaging pulsatile retinal blood flow in human eye

Abstract

Abstract.A functional Fourier domain optical coherence tomography instrument offering spectral Doppler imaging of in vivo pulsatile human retinal blood flow was constructed. An improved phase-resolved algorithm was developed to correct bulk motion artifacts. Spectral Doppler imaging provides complementary temporal flow information to the spatially distributed flow information of the color Doppler image by providing direct visualization of the Doppler spectrum of the flow whose pattern can be further quantified with various velocity envelope curves and their corresponding flow indices. The coefficient of repeatability on resistance index measurement was assessed by analyzing 14 measurements on two vessels within two normal subjects. Previous studies suggest that retinal haemodynamics play an important role in glaucoma, 1 diabetic retinopathy, 2 and age-related macular degeneration.3 Therefore, it is desirable to assess retinal blood flow in vivo in order to investigate their role in major eye diseases. Although many flow measurement technologies have been developed, they do not provide adequate information for understanding the relationship between retinal blood flow and important ocular diseases.4 Doppler optical coherence tomography 5-11 ͑DOCT͒, a variation of optical coherence tomography ͑OCT͒ that combines coherence gating and laser Doppler effects, is an alternative that can overcome some limitations of the technologies mentioned above. 4 Because of the unknown Doppler angle between the blood flow and incident light beam and the absence of a quantification method that can generate interpretable results for clinicians, DOCT is not widely used in eye clinics. Conventional DOCT only generates a snapshot of pulsatile ocular blood flow that is projected along the light beam direction in a cardiac cycle. Most recent developments in quantifying blood flow information of the human eye utilizes 3-D vascular orientation information to estimate Doppler angle and the absolute flow velocity. 10,11 On the other hand, it is noteworthy to quantify the pulsatile flow pattern as an alternative method to investigate retinal flow dynamics. A simple projected ocular blood flow velocity ͑integration over the whole blood vessel͒ plot through a cardiac cycle was chosen by White 9 to demonstrate the pulsatile flow property, although it is possible to acquire much more hemodynamics information from the same raw data. The M-mode scanning method has been used to acquire temporal flow information in time-domain DOCT systems.12,13 The short-time fast Fourier transformation method from Doppler ultrasound 14 was used to generate Doppler spectrum wave forms 13 but without further quantification, which provides the most valuable information for clinicians. The purpose of this paper is to implement the full concept of spectral Doppler imaging, developed by scientists and clinicians in ultrasound medicine, in a Fourier-domain DOCT system and provide an alternative quantification method for an ocular blood flow pattern that may be further inves...

Phase-Resolved Doppler Optical Coherence Tomography

“…However these methods increase the computational complexity and time. The correction may also introduce artifacts when the blood vessels are large and take most of the pixels for an A-line [35,45]. We have shown that the Doppler variance method is not sensitive to bulk-motion and the method can be used without correcting the bulk-motion when the sample-movement-induced velocity changes gradually [42].…”

“…Although this correction artifact is not important in most imaging areas, the artifacts may cause erroneous blood vessel locations in the color Doppler image in regions with large blood vessels such as the optic disk. An improved phase-resolved algorithm has been proposed to correct this artifact [45]. Although effective, the improved algorithm increases the calculation time.…”

“…Because of its high spatial resolution and velocity sensitivity, Doppler OCT has been widely used for blood flow related biomedical applications [41][42][43][44][45][46][47][48]. These applications require imaging of blood flow in-vivo.…”

“…Blood flow related biomedical applications with PRODT have been demonstrated for imaging ocular blood flow, mapping cortical hemodynamics for brain research, drug screening, monitoring changes in image tissue morphology and hemodynamics following pharmacological intervention and photodynamic therapy, evaluating the efficacy of laser treatment in port wine stain (PWS) patients, assessing the depth of burn wounds, imaging tumor microenvironment, and quantifying cerebral blood flow [41][42][43][44][45][46][47][48]. There have been excellent review papers or book chapters about the advances of PRODT [2 and 50].…”

In vivo imaging of retinal hemodynamics with OCT angiography and Doppler OCT

“…However measurement of the absolute blood flow is still a challenge because of its pulsatile nature. Doppler optical coherence tomography (OCT) enables the imaging of retinal blood velocity in human eyes [7,8]. The principle of Doppler OCT is based on measuring the Doppler shift caused by the moving blood cells relative to the OCT probing light.…”