Abstract
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image. Recent ex vivo studies have demonstrated that birefringence mapping enables the characterization of collagen and smooth muscle concentration and distribution in vascular tissues. Instruments capable of applying these measurements percutaneously in vivo may provide new insights into coronary atherosclerosis and acute myocardial infarction. We have developed a polarization sensitive optical frequency domain imaging (PS-OFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter. The novel design of this system utilizes frequency multiplexing to simultaneously measure reflectance of two incident polarization states, overcoming concerns regarding temporal variations of the catheter fiber birefringence and spatial variations in the birefringence of the sample. We demonstrate circular cross-sectional birefringence imaging of a human coronary artery ex vivo through a flexible fiber-optic catheter with an A-line rate of 62 kHz and a ranging depth of 6.2 mm.
Highlights
Polarization sensitive optical coherence tomography (PS-OCT) [1,2,3,4] allows the determination of birefringence magnitude and orientation and polarization-dependent scattering and attenuation coefficients [2,3,4], information that is complementary to reflectance-based images provided by standard OCT
Polarization sensitive optical coherence tomography (PS-OCT) provides a cross-sectional image of birefringence in biological samples that is complementary in many applications to the standard reflectance-based image
We have developed a polarization sensitive optical frequency domain imaging (PSOFDI) system that enables high-speed intravascular birefringence imaging through a fiber-optic catheter
Summary
Polarization sensitive optical coherence tomography (PS-OCT) [1,2,3,4] allows the determination of birefringence magnitude and orientation and polarization-dependent scattering and attenuation coefficients [2,3,4], information that is complementary to reflectance-based images provided by standard OCT. In fiber-based systems, and especially when using endoscopic or catheter-based probes, it is impractical to maintain a pre-determined polarization state at the tissue surface as the probe bends or rotates This hurdle has been overcome by modulating the polarization state of the light at the sample so that it alternates between two states, which are perpendicular to each other on the Poincare sphere, on successive axial scans (A-lines) [4, 11, 12]. A novel frequency-multiplexing scheme, leveraging the unique features of OFDI, enables simultaneous illumination and detection of two perpendicular polarization states on the Poincare sphere This feature is relevant for catheter-based polarization sensitive imaging, which can be prone to artifacts arising from stress-induced changes of birefringence during catheter rotation or bending [16]. The large ranging depth of 6.2 mm of the system accommodates the varying distances between the fiber-optic probe and the vessel wall that are characteristic of catheter-based imaging
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