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. 2016 Apr 6;11(4):e0152539.
doi: 10.1371/journal.pone.0152539. eCollection 2016.

Electrophysiological and Anatomical Correlates of Spinal Cord Optical Coherence Tomography

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Free PMC article

Electrophysiological and Anatomical Correlates of Spinal Cord Optical Coherence Tomography

Mario E Giardini et al. PLoS One. .
Free PMC article

Abstract

Despite the continuous improvement in medical imaging technology, visualizing the spinal cord poses severe problems due to structural or incidental causes, such as small access space and motion artifacts. In addition, positional guidance on the spinal cord is not commonly available during surgery, with the exception of neuronavigation techniques based on static pre-surgical data and of radiation-based methods, such as fluoroscopy. A fast, bedside, intraoperative real-time imaging, particularly necessary during the positioning of endoscopic probes or tools, is an unsolved issue. The objective of our work, performed on experimental rats, is to demonstrate potential intraoperative spinal cord imaging and probe guidance by optical coherence tomography (OCT). Concurrently, we aimed to demonstrate that the electromagnetic OCT irradiation exerted no particular effect at the neuronal and synaptic levels. OCT is a user-friendly, low-cost and endoscopy-compatible photonics-based imaging technique. In particular, by using a Fourier-domain OCT imager, operating at 850 nm wavelength and scanning transversally with respect to the spinal cord, we have been able to: 1) accurately image tissue structures in an animal model (muscle, spine bone, cerebro-spinal fluid, dura mater and spinal cord), and 2) identify the position of a recording microelectrode approaching and inserting into the cord tissue 3) check that the infrared radiation has no actual effect on the electrophysiological activity of spinal neurons. The technique, potentially extendable to full three-dimensional image reconstruction, shows prospective further application not only in endoscopic intraoperative analyses and for probe insertion guidance, but also in emergency and adverse situations (e.g. after trauma) for damage recognition, diagnosis and fast image-guided intervention.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1
a) confocal image of a coronal hemisection of the spinal cord, with Glial Fibrillary Acidic Protein (GFAP, red), neurofilaments (green) distributed in the cytoplasm, and nuclei (blue); b) vignette to guide the eye, dotted lines delimiting the laminae; c) in-vivo cross sectional OCT image of the whole cord; d) laminar labelling superimposed over the OCT image in c). L2 means second lumbar myelomer and numbers from 1 to 6 refer to sensory laminae of the dorsal horn.
Fig 2
Fig 2. The mean spontaneous (left side) light (center) and high mechanical (right) threshold stimulus evoked mean neuronal activities.
Blue bars: with inactive OCT probing. Brick-red bars: same as above in the presence of OCT scanning. Statistical tests (Wilcoxon non-parametric ranksum test) reported no significance between normal recordings and those performed in conjunction with OCT scanning [p = 0.564 (spontaneous), p = 0.890 (light stimulation), p = 0.711 (high stimulation)].
Fig 3
Fig 3
: a), b), c), d), e): OCT sequence of images showing the trace of a needle probe being inserted in the spinal cord (arrow), and f): mutual relation between the OCT images, cord, dorsal vein and needle (not to scale). In a), the OCT probe was aligned orthogonally to the tip of the microelectrode that progressively meet the axis of the central vein. The color bar indicates the color distribution over the normalized dynamic range. The scale bar is 3 mm long.
Fig 4
Fig 4. Spike shapes randomly chosen within the recorded data during the spontaneous, low and high threshold stimulus activations with active and inactive OCT probing.
Fig 5
Fig 5. Local field potential spectral power in the same experimental conditions as above.
No significant change was observable with active and inactive OCT probing.

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Grant support

The authors acknowledge funding from the European Union Framework Programme 7 under grant agreements no. 225464 (ARAKNES—Array of Robots Augmenting the Kinematics of Endoluminal Surgery) and 224014 sub 2.16 (Photonics4Life—Fibre Optic Sensors as Guidance and Diagnostic Tools for Epiduroscopy). Part of the study was performed when MEG was employed at the University of St Andrews, UK, and significant sections of OCT software were written while NK was employed by the University of Sheffield. PON01_01297 and from the Ministero dell'Istruzione Universita' e Ricerca (MIUR).

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