Abstract
Purpose :
Optical coherence tomography angiography (OCT-A), a non-invasive technique for imaging the microvasculature of ocular tissue, is the dominant modality in ophthalmology. However, a limitation of OCT is its inability to penetrate optical opacities, such as monitoring the retinal flow with retinal prosthetic implants and the orbital vessels supplying the eye. In addition, OCTA has limited ability to depict the flow velocity. Owing to the importance of microvasculature in ocular tissue diseases, a new imaging technique with both high spatial resolution and deep penetration depth is desired.
Methods :
In this study, we have developed the super-resolution (SR) ultrasonic microvessel imaging technique utilizing a 18 MHz linear array and contrast microbubble (break the diffraction limit of conventional ultrasound imaging). Ultrafast compounding plane wave imaging technique was implemented to identify the motion filtered bubble signals followed by an optimal deconvolution based localization algorithm. Then the vessel density image or flow velocity can be reconstructed by accumulating or tracking localized bubble signal in successive frames. The performance of our imaging technique was first tested on a flow phantom with a 300 µm inner diameter and a designed velocity of 16.5 mm/s at depth of 20 mm. Then, an in vivo normal rabbit retinal/choroid model will be imaged.
Results :
The diameter of the reconstructed microvessel (295 ± 5.5 µm) is consisted with the designed value. Through tracking the microbubbles in successive frames, the average velocity was calculated to be 16.4 ± 0.5 mm/s, which is also comparable with the designed flow speed. These results demonstrate that SR imaging can provided resolution of approximately few micron while maintaining a 20 mm maximum penetration depth (see Fig. 1).
Conclusions :
SR ultrasonic microvessel imaging offers a new insight to obtain high resolution depiction of retinal or choroid vessel imaging. In this experiment, we focused on demonstrating the capability and accuracy of the SR microvessel imaging technique. We will soon apply this technique on some pre-clinical models such as eyes with retinal prosthetic implants.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.