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

Abstract

Significance: Optical coherence tomography (OCT) can be integrated into needle probes to provide real-time navigational guidance. However, unscanned implementations, which are the simplest to build, often struggle to discriminate the relevant tissues.

Aim: We explore the use of polarization-sensitive (PS) methods as a means to enhance signal interpretability within unscanned coherence tomography probes.

Approach: Broadband light from a laser centered at 1310 nm was sent through a fiber that was embedded into a needle. The polarization signal from OCT fringes was combined with Doppler-based tracking to create visualizations of the birefringence properties of the tissue. Experiments were performed in (i) well-understood structured tissues (salmon and shrimp) and (ii) ex vivo porcine spine. The porcine experiments were selected to illustrate an epidural guidance use case.

Results: In the porcine spine, unscanned and Doppler-tracked PS OCT imaging data successfully identified the skin, subcutaneous tissue, ligament, and epidural spaces during needle insertion.

Conclusions: PS imaging within a needle probe improves signal interpretability relative to structural OCT methods and may advance the clinical utility of unscanned OCT needle probes in a variety of applications.

Keywords: birefringence; imaging coherence; lasers in medicine; polarization.

Fig. 1

Biological samples imaged in this work. (a), (b) Depiction of the sources of polarization-sensitive OCT 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.

Fig. 2

PS-OCT-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 thick black line represents the boundary between the tissue that the needle has already passed through (above) and the tissue that is still below the needle tip (below). Further description of the visualization in these movies is described in Fig. S1 in the Supplementary Material. The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking (Video 1, MP4, 808 KB [URL: https://doi.org/10.1117/1.JBO.28.10.102910.v1]).

Fig. 3

PS-OCT-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 thick black line represents the boundary between the tissue that the needle has already passed through (above) and the tissue that is still below the needle tip (below). The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking (Video 2, MP4, 788 KB [URL: https://doi.org/10.1117/1.JBO.28.10.102910.v2]).

Fig. 4

PS-OCT-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 thick black line represents the boundary between the tissue that the needle has already passed through (above) and the tissue that is still below the needle tip (below). The transformation from the needle reference frame to the surface reference frame was made possible by Doppler tracking (Video 3, MP4, 1.31 MB [URL: https://doi.org/10.1117/1.JBO.28.10.102910.v3]).