Split-Spectrum Amplitude-Decorrelation Angiography with Optical Coherence Tomography

Abstract

 

Purpose:

 

Amplitude or speckle decorrelation measurement has been used to detect blood flow using ultrasound, laser scanning and optical coherence tomography (OCT) imaging systems. Its advantages are sensitivity to transverse flow and immunity to phase noise, in comparison to Doppler and other phase-based approaches. In this approach, the high resolution of OCT is advantageous for resolving microcirculation in 3 dimensions, but also introduces high sensitivity to bulk motion artifacts. In particular, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction, but relatively less sensitive to the flow signal, which in retinal and choroidal circulations is largely transverse to the probe beam. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio of flow detection.

 

Methods:

 

The full OCT spectrum is split into several narrower bands. These bands are used to generate OCT images of reduced axial resolution and reduced susceptibility to axial motion noise. Decorrelation between consecutive B-scans captured in the same location is used to detect flow. Decorrelation is computed using the spectral bands separately and then averaged to make full use of flow information in the entire spectrum.

 

Results:

 

The SSADA algorithm is tested on in vivo macular and optic nerve head scans using a 100 kHz swept-source OCT retinal scanner. Volumetric imaging of retinal, choroidal, and optic nerve head circulations were demonstrated. The SSADA algorithm showed significantly higher signal-to-noise ratio for flow detection, and captured significantly better connected microvascular network, when compared to amplitude-decorrelation calculations performed without splitting the spectrum, or using low-pass filtering by pixel averaging.

 

Conclusions:

 

SSADA represents a significant improvement in OCT angiography using the amplitude or speckle decorrelation approach.  

 

Keywords: blood supply • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: non-clinical