Simultaneous Morphological and Flow Imaging Enabled by Megahertz Intravascular Doppler Optical Coherence Tomography.

Tianshi Wang,Wolfgang Wieser,A F W Van Der Steen,Tom Pfeiffer,Joost Daemen,Frits Mastik,Robert Huber,Gijs Van Soest

doi:10.1109/tmi.2019.2948258

Abstract

We demonstrate three-dimensional intravascular flow imaging compatible with routine clinical image acquisition workflow by means of megahertz (MHz) intravascular Doppler Optical Coherence Tomography (OCT). The OCT system relies on a 1.1 mm diameter motorized imaging catheter and a 1.5 MHz Fourier Domain Mode Locked (FDML) laser. Using a post processing method to compensate the drift of the FDML laser output, we can resolve the Doppler phase shift between two adjoining OCT A-line datasets. By interpretation of the velocity field as measured around the zero phase shift, the flow direction at specific angles can be qualitatively estimated. Imaging experiments were carried out in phantoms, micro channels, and swine coronary artery in vitro at a speed of 600 frames/s. The MHz wavelength sweep rate of the OCT system allows us to directly investigate flow velocity of up to 37.5 cm/s while computationally expensive phase-unwrapping has to be applied to measure such high speed using conventional OCT system. The MHz sweep rate also enables a volumetric Doppler imaging even with a fast pullback at 40 mm/s. We present the first simultaneously recorded 3D morphological images and Doppler flow profiles. Flow pattern estimation and three-dimensional structural reconstruction of entire coronary artery are achieved using a single OCT pullback dataset.

Highlights

C ORONARY artery disease is associated with the buildup of plaques in the artery wall, narrowing the artery lumen and decreasing the blood flow [1]–[4]
Large phase noise associated with cyclical fluctuations in groups of four sample points can be seen, which is due to the cluster output of the Fourier Domain Mode Locked (FDML) laser and the sampling offsets induced by the buffer stage
Since the phase shift of the stable coverslip surface is expected to be zero, root-mean-square error (RMSE) of the phase shift was calculated for evaluation, which was reduced from 1.60 rad to 0.01 rad using our compensation method

Summary

Introduction

C ORONARY artery disease is associated with the buildup of plaques in the artery wall, narrowing the artery lumen and decreasing the blood flow [1]–[4]. Visualizing the flow pattern and the morphology of the entire coronary artery may provide new insights into functional assessment of coronary artery lesions and enhance our understanding of the progression of atherosclerotic plaques. Previous studies have demonstrated that Magnetic Resonance Imaging and Doppler Ultrasound imaging can visualize carotid flow, as well as morphology, enabling early detection of carotid stenosis and its effects on hemodynamics [9], [10]. These techniques cannot fully capture the microscopic features of diseased coronary arteries, nor characterize their highly dynamic blood flow patterns in a lumen of only a few millimeters. A fast imaging technique that can simultaneously visualize the flow and morphology with high resolution is highly desired for research, diagnosis and treatment guidance of coronary artery disease

Methods

Results

Discussion

Conclusion