Conical scan polarization-sensitive optical coherence tomography

Abstract

We report on a new articular cartilage imaging technique with potential for clinical arthroscopic use, by supplementing the variable-incidence-angle polarization-sensitive optical coherence tomography method previously developed by us with a conical beam scan protocol. The technique is validated on bovine tendon by comparing experimental data with simulated data generated using the extended Jones matrix calculus. A unique capability of this new optical technique is that it can locate the "brushing direction" of collagen fibers in articular cartilage, which is structural information that extends beyond established methods such as split-line photography or birefringent fast-axis measurement in that it is uniquely defined over the full azimuthal-angle range of (-π, + π). The mapping of this direction over the cartilage surface may offer insights into the optimal design of tissue-engineering scaffolds for cartilage repair.

Keywords: (170.3880) Medical and biological imaging; (170.3890) Medical optics instrumentation; (170.4500) Optical coherence tomography; (260.1440) Birefringence; (260.5430) Polarization.

Figures

Fig. 1

Schematic diagram of the system. SS: wavelength-swept source, PC: polarization controller, IL-LP: in-line linear polarizer, PMC: polarization-maintaining coupler, QWP: quarter waveplate, PBS: polarization beamsplitter, H and V: balanced photo-detectors for horizontally and vertically polarized optical signals, respectively.

Fig. 2

Schematic diagram of conical scanning (left). Polar coordinate system (right).

Fig. 3

Measured phase retardance of the compensator as a function of set retardance values (left). (right) Measured phase retardance and optic axis orientation of the compensator as a function of set orientation values.

Fig. 4

Intensity (top) and phase retardance images (middle) obtained by CS-PS-OCT from a bovine tendon sample as a function of rotation angle with entire span of 360° and a 1° interval. (bottom): simulated results by using an EJMC model [20]. Image size is 1.4mm (axial) × 360° (transversal) in left column; polar radius is 1.4mm in right column.

Fig. 5

(a) Photo of the intact bovine cartilage samples used in this study. (b): Schematic presentation of proposed leaf-like mode of collagen architecture by Jeffery et al [15]. (c): A schematic of the cartilage zonal layered structure and the layer thickness used for the EJMC study. Also shown are the orientations of the polar angle of the collagen fast axis varying from 90° in the superficial zone to gradually becoming 0° in the radial zone.

Fig. 6

Intensity (top) and phase retardance images (middle) obtained by CS-PS-OCT from a bovine cartilage sample as a function of rotation angle with entire span of 360° and a 1° interval. (bottom): simulated results by using EJMC model [20]. Image size is 1.4mm (axial) × 360° (transversal) in left column; polar radius is 1.4mm in right column.