Needle guidance with Doppler-tracked polarization-sensitive optical coherence tomography

Abstract

We demonstrate that a simple, unscanned polarization-sensitive optical coherence tomography needle probe can be used to perform layer identification in biological tissues. Broadband light from a laser centered at 1310 nm was sent through a fiber that was embedded into a needle, and analysis of the polarization state of the returning light after interference coupled with Doppler-based tracking allowed the calculation of phase retardation and optic axis orientation at each needle location. Proof-of-concept phase retardation mapping was shown in Atlantic salmon tissue, while axis orientation mapping was demonstrated in white shrimp tissue. The needle probe was then tested on the ex vivo porcine spine, where mock epidural procedures were performed. Our imaging results demonstrate that unscanned, Doppler-tracked polarization-sensitive optical coherence tomography imaging successfully identified the skin, subcutaneous tissue, and ligament layers, before successfully reaching the target of the epidural space. The addition of polarization-sensitive imaging into the bore of a needle probe therefore allows layer identification at deeper locations in the tissue.

Figure 1:

Biological samples imaged in this work. a-b) Depiction of the sources of polarization-sensitive optical coherence tomography contrast in salmon (a) and shrimp (b) tissues. In salmon, highly oriented muscle induces large phase retardation of the incident light. In contrast, weakly oriented fat induces very little phase retardation. In shrimp, each muscle layer induces similarly high phase retardation, but the orientation of the fibers in each layer is distinct. c-d) Path of a needle during the epidural procedure. The needle must traverse the skin, subcutaneous tissue (fat), and three ligament layers (c) before reaching (d) the epidural space (layer 6). Care must be taken not to puncture the dura mater and the arachnoid mater, as reaching the subarachnoid space can result in a cerebral spinal fluid leak.

Figure 2:

Polarization-sensitive optical coherence tomography-based reconstructions of salmon tissue. a) Photo of the needle probe at its full insertion point in the salmon tissue. b-d) Needle-referenced map indicating the backscattered intensity (b), phase retardation (c), and optic axis orientation (d) of the salmon tissue. Time axis and needle insertion/retraction indicators apply to (b-d). e-g) Still frames from Video 1. Surface-referenced maps of intensity (e), phase retardation (f), and optic axis orientation (g). The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking.

Figure 3:

Polarization-sensitive optical coherence tomography-based reconstructions of shrimp tissue. a) Photo of the needle probe at its full insertion point in the shrimp tissue. b-d) Needle-referenced map indicating the backscattered intensity (b), phase retardation (c), and optic axis orientation (d) of the shrimp tissue. Time axis and needle insertion/retraction indicators apply to (b-d). e-g) Still frames from Video 2. Surface-referenced maps of intensity (e), phase retardation (f), and optic axis orientation (g). The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking.

Figure 4:

Polarization-sensitive optical coherence tomography-based reconstructions of porcine lower lumbar spine. a) Photo of the needle probe on top of the lower lumbar sample. The insertion was performed through the tissue. b-d) Needle-referenced map indicating the backscattered intensity (b), phase retardation (c), and optic axis orientation (d) of the spine tissue. Time axis and needle insertion/retraction indicators apply to (b-d). e-g) Still frames from Video 3. Surface-referenced maps of intensity (e), phase retardation (f), and optic axis orientation (g). The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking.