Abstract
We formulate a theory to show that the statistics of OCT signal amplitude and intensity are highly dependent on the sample reflectivity strength, motion, and noise power. Our theoretical and experimental results depict the lack of speckle amplitude and intensity contrasts to differentiate regions of motion from static areas. Two logarithmic intensity-based contrasts, logarithmic intensity variance (LOGIV) and differential logarithmic intensity variance (DLOGIV), are proposed for serving as surrogate markers for motion with enhanced sensitivity. Our findings demonstrate a good agreement between the theoretical and experimental results for logarithmic intensity-based contrasts. Logarithmic intensity-based motion and speckle-based contrast methods are validated and compared for in vivo human retinal vasculature visualization using high-speed swept-source optical coherence tomography (SS-OCT) at 1060 nm. The vasculature was identified as regions of motion by creating LOGIV and DLOGIV tomograms: multiple B-scans were collected of individual slices through the retina and the variance of logarithmic intensities and differences of logarithmic intensities were calculated. Both methods captured the small vessels and the meshwork of capillaries associated with the inner retina in en face images over 4 mm2 in a normal subject.
Highlights
The importance of retinal and choroidal vasculature visualization is paramount in diagnosing various eye diseases, such as diabetic retinopathy [1], age-related macular degeneration (AMD) [2], glaucoma [3], and anterior ischemic optic neuropathy (AION) [4].Color fundus photography (CF) and fluorescein angiography (FA) have served as valuable imaging methods for retinal vasculature network visualization [5]
We develop two methods, called logarithmic intensity variance (LOGIV) and differential logarithmic intensity variance (DLOGIV), which provide these surrogate markers for motion by acquiring more than one depth scan of the same retinal voxel and analyzing logarithmic intensity fluctuations at the same voxel
Our formulated theoretical description of the Fourier-domain optical coherence tomography (OCT) signal shows that the high sensitivity of amplitude and intensity speckle-based contrasts to static regions degrades microvasculature visualization
Summary
The importance of retinal and choroidal vasculature visualization is paramount in diagnosing various eye diseases, such as diabetic retinopathy [1], age-related macular degeneration (AMD) [2], glaucoma [3], and anterior ischemic optic neuropathy (AION) [4].Color fundus photography (CF) and fluorescein angiography (FA) have served as valuable imaging methods for retinal vasculature network visualization [5]. Smart scanning protocols enhance sensitivity to the smaller signals expected from the microvasculature by increasing the time separation between two OCT depth scans and relying on the acquired phase [12,15,16,17] of OCT signals for contrast. These methods [15,16,17] such as PC-OCT [12] are highly sensitive to the phase instability of the system and environment by relying on the phase information. The required bulk motion removal [18] and timing-induced phase error correction algorithms [19] as well as extra optical module [19] add to the complexity of the phase sensitive swept source (SS)-OCT software and hardware
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