High speed, wide velocity dynamic range Doppler optical coherence tomography (Part IV): split spectrum processing in rotary catheter probes

Abstract

We report a technique for blood flow detection using split spectrum Doppler optical coherence tomography (ssDOCT) that shows improved sensitivity over existing Doppler OCT methods. In ssDOCT, the Doppler signal is averaged over multiple sub-bands of the interferogram, increasing the SNR of the Doppler signal. We explore the parameterization of this technique in terms of number of sub-band windows, width and overlap of the windows, and their effect on the Doppler signal to noise in a flow phantom. Compared to conventional DOCT, ssDOCT processing has increased flow sensitivity. We demonstrate the effectiveness of ssDOCT in-vivo for intravascular flow detection within a porcine carotid artery and for microvascular vessel detection in human pulmonary imaging, using rotary catheter probes. To our knowledge, this is the first report of visualizing in-vivo Doppler flow patterns adjacent to stent struts in the carotid artery.

Comparison of amplitude-decorrelation, speckle-variance and phase-variance OCT angiography methods for imaging the human retina and choroid

“…Poorer results of application of the split spectrum method may be caused by non-optimized splitting criteria. In general, higher separation of the centroids of the spectral bands and lesser overlap between them should provide better results [92]. Our conservative choice (wide and overlapping bands), may not be sufficient to observe significant improvement in the OCTA images.…”

Developing cross-correlation as a method for microvessel imaging using clinical intravascular optical coherence tomography systems

“…Thus, to pursue any of the CC approaches for a pullback mode requires that A-lines and images should be oversampled. Developments in IV-OCT technologies [11][12][13][14][15] promises that in future it may be possible to acquire coronary images with sufficiently high density and at high-speed.…”

“…A minimum ≈ 2 mm/s resolvable velocity was reported [10]. To improve the Doppler measurements a split-spectrum method was also applied [11]. Improved sensitivity and specificity of flow mapping was reported.…”

“…However, these improvements remain inadequate to resolve physiological microvascular flow velocities, which are typically around 200 µm/s. Also due to the low frame-rate (≤20 Hz) [9][10][11], this approach would have limited application within coronary arteries.…”

“…Thus, the systems generate undersampled cross-sectional images in the pullback direction [12]. Over-sampling by high-density imaging is required to enable accurate flow mapping and reduce noise effects, as demonstrated by the Doppler studies [9][10][11]. To increase image density, new catheter designs, involving distal-end high-speed micromotors (12,500-210,000 rpm) [12][13][14] or otherwise enhanced rotation speeds (21000 rpm) [15], have been reported.…”