Imaging of the parafoveal capillary network and its integrity analysis using fractal dimension

Abstract

Using a spectral domain OCT system, equipped with a broadband Ti:sapphire laser, we imaged the human retina with 5 µm x 1.3 µm transverse and axial resolution at acquisition rate of 100 kHz. Such imaging speed significantly reduces motion artifacts. Combined with the ultra-high resolution, this allows observing microscopic retinal details with high axial definition without the help of adaptive optics. In this work we apply our system to image the parafoveal capillary network. We demonstrate how already on the intensity level the parafoveal capillaries can be segmented by a simple structural high pass filtering algorithm. This data is then used to quantitatively characterize the capillary network of healthy and diseased eyes. We propose to use the fractal dimension as index for capillary integrity of pathologic disorders.

Quantifying the vascular response to ischemia with speckle variance optical coherence tomography

“…Vessel diameters have also been extracted [27], and the distribution provides insight into the contributions of vessels of various sizes to global measurements of length and density. Other parameters of interest include tortuosity and fractal dimension, which provide a measurement of vessel branching and architecture [27,58,61,62]. Although longitudinal changes in blood flow have been quantified in the HLI model using Doppler OCT [26] and optical microangiography techniques [49], assessment of vessel morphology has been limited to qualitative observations [26,49].…”

“…The latter can be applied to both periodic and non-periodic bulk motion, but the classifier algorithm requires a training set of manually segmented images [64]. There are also several methods available for addressing the challenge of motion artifacts in speckle variance OCT during acquisition, including the use of orthogonal scan patterns [34,66], short acquisition times [62], optimizing frame rates (field of view) and gate length [43]. However, additional scans increase acquisition time and data storage/processing, and acquiring faster scans may compromise field of view and sensitivity to slow flow.…”

“…Approaches range from intensity thresholding and band pass filtering [62] to clutter rejection [67] and directional filters (Gabor) [34]. Here, we chose to implement a Hessian filter [55][56][57] due to speed of computation and the multi-scale estimation of vessel-like structures that is compatible with segmenting the range of vessel sizes observed in the HLI model.…”

Optical coherence tomography today: speed, contrast, and multimodality

“…This has been successful for retinal vascular structures as well as for choroidal vasculature. [123][124][125] Employing dual-beam setups that probe the sample in parallel on laterally displaced positions enhances the sensitivity for contrasting vessels with a large range of velocities. Both beams scan the same spot after an adjustable time interval given by the lateral displacement and the scanning speed.…”

Stripe motion artifact suppression in phase-resolved OCT blood flow images of the human eye based on the frequency rejection filter

“…5(a) and (b), the stripe motion artifacts is substantially rejected and the signal-to-noise ratio (SNR) of the blood flow image is improved. [23] and Fig. 6(b) shows the filtered result of Fig.…”