Wide-field optical coherence tomography based microangiography for retinal imaging

Abstract

Optical coherence tomography angiography (OCTA) allows for the evaluation of functional retinal vascular networks without a need for contrast dyes. For sophisticated monitoring and diagnosis of retinal diseases, OCTA capable of providing wide-field and high definition images of retinal vasculature in a single image is desirable. We report OCTA with motion tracking through an auxiliary real-time line scan ophthalmoscope that is clinically feasible to image functional retinal vasculature in patients, with a coverage of more than 60 degrees of retina while still maintaining high definition and resolution. We demonstrate six illustrative cases with unprecedented details of vascular involvement in retinal diseases. In each case, OCTA yields images of the normal and diseased microvasculature at all levels of the retina, with higher resolution than observed with fluorescein angiography. Wide-field OCTA technology will be an important next step in augmenting the utility of OCT technology in clinical practice.

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels

“…Our previous experience with in vivo microvascular imaging suggests that the big blood vessels appear noticeably brighter than the small capillaries in the OMAG images [19,31]. This raises a question: whether or not the OMAG signal intensity is dependent on the vessel size.…”

“…1, the OMAG magnitude climbs to its full saturation with its slope much steeper for the faster flow velocity due to the faster decorrelation time. The OMAG magnitudes are fully saturated for all the velocities (0.1 mm/s to 8.0 mm/s) at a time scale beyond 3 ms (~333 Hz), a typical time interval often used for OCTA imaging [19,22,27]. Thus, it is reasonable to conclude that if B-scan rate is below ~333 Hz for OCTA imaging, there does not exist the dependency of OMAG value on the flow velocity that is faster than 0.1 mm/s (saturation velocity).…”

“…OMAG employs a differential operation based on complex OCT signals to utilize both intensity and phase information available in the system; hence it is a complex-based OCTA technique. In the past several years, OMAG has been successful in identifying disorder or dysfunction in the retinal and choroidal microvascular networks in vivo [18][19][20]. Despite many promising results of ocular blood flow using OMAG, the quantitative relationship between OMAG and flow remains unclear.…”

Challenges and advantages in wide-field optical coherence tomography angiography imaging of the human retinal and choroidal vasculature at 1.7-MHz A-scan rate

“…46 Some groups have reported wide-field OCTA with realtime motion tracking with a line scan ophthalmoscope for realtime stitching of narrow-field images. 42 Wide-field OCTA imaging in a single dataset was for the first time reported after the advent of FDML lasers operating at 1060-nm center wavelength and 1.7-MHz imaging speed. 38 In this paper, we demonstrate OCTA imaging of the posterior eye segment vasculature with an FDML laser operating at 1.7-MHz sweep rate, at 1065-nm center wavelength.…”

“…In the majority of these cases, extending the FOV beyond 10 deg (3 mm) without exceeding the imaging time beyond 5 to 7 s was achieved by undersampling in at least one scanning direction. 42,43 Some authors report reduction in the number of B-scans used for OCTA computations. 44,45 However, these two approaches may compromise visualization of finer vascular features.…”