Theranostic applications of optical coherence tomography in neurosurgery?

Abstract

In light of our own experiences, we value the existing literature to critically point out possible "near" future applications of optical coherence tomography (OCT) as an intraoperative neurosurgical guidance tool. "Pub Med", "Cochrane Library", "Crossref Metadata Search", and "IEEE Xplore" databases as well as the search engine "Google Scholar" were screened for "optical coherence tomography + neurosurgery", "optical coherence tomography + intraoperative imaging + neurosurgery", and "microscope integrated optical coherence tomography + neurosurgery". n = 51 articles related to the use of OCT as an imaging technique in the field of neurosurgery or neurosurgical research. n = 7 articles documented the intraoperative use of OCT in patients. n = 4 articles documented the use of microscope-integrated optical coherence tomography as a neurosurgical guidance tool. The Results demonstrate that OCT is the first imaging technique to study microanatomy in vivo. Postoperative analysis of intraoperative scans holds promise to enrich our physiological and pathophysiological understanding of the human brain. No data exists to prove that OCT-guided surgery minimizes perioperative morbidity or extends tumor resection. But results suggest that regular use of microscope-integrated OCT could increase security during certain critical microsurgical steps like, e.g., dural dissection at cavernous sinus, transtentorial approaches, or aneurysm clip placement. Endoscopy integration could aid surgery in regions which are not yet accessible to real-time imaging modalities like the ventricles or hypophysis. Theranostic instruments which combine OCT with laser ablation might gain importance in the emerging field of minimal invasive tumor surgery. OCT depicts vessel wall layers and its pathologies uniquely. Doppler OCT could further visualize blood flow in parallel. These abilities shed light on promising future applications in the field of vascular neurosurgery.

Keywords: Intraoperative imaging; Microscope integration; Neurosurgery; Optical coherence tomography.

Fig. 1

Recent technical developments in OCT. (1) Speckle-modulated OCT. Speckle artifacts limit the spatial to noise ratio in OCT imaging. These exemplary speckle-modulated OCT scans of the mouse cornea and retina show the increase of resolution in contrast to conventional OCT imaging. (1A) Conventional OCT scan of mouse cornea. (1B) Speckle modulated OCT scan of same mouse cornea, notice enhanced sectioning of histological layers. (1C, D) Enlarged excerpts (1D) notice enhanced delineation of histological structures like lamellae and enhanced delineation of the endothelium in speckle-modulated OCT. (1E) Histological section of cornea. (1F) Conventional OCT scan of mouse retina. (1G) Speckle-modulated OCT scan of mouse retina. (1H, I) Enlarged excerpts (1E) notice enhanced segregation of single retinal layers; see Yecies et al. [41]. (2) Polarization-sensitive OCT (ps-OCT). Through a set of hardware and software components, polarization-sensitive OCT (ps-OCT) is able to measure and correct the birefringence (“bi-refraction” of light) of local regions of tissue, leading to enhanced imaging of tissue with different optical densities and refraction indices. (2A) ps-OCT of a block of human cerebellar lobule. The folded cerebellar cortex is shown on orthogonal viewing planes (xy coronal; xz axial; yz sagittal). Note the ability to delineate the Purkinje cell layer. Volume rendering of segmented (2B) molecular layer, (2C) granual layer, and (2D) white matter (see Wang et al. [37]. (3) Doppler OCT. In vivo delineation of mouse cortical vasculature with Doppler OCT. (3A) Multi-photon laser scanning microscopy (MPM) of cerebral vasculature (3B) three-dimensional reconstruction of flow demonstrating the vasculature of the mouse cortex. (3C) Doppler OCT velocity projection map (see Gagnon et al. [13]. (4) Sensitivity contrast-enhanced OCT. Imaging of lymph vessels in ears pinnae in living mice. Injection of large gold nanorods LGNR is used for functional imaging. (4a) Delineation of blood vessels (red) by flow detection in OCT prior to LGNR injection. (4b) Injection of 815 nm LGNRs (green) and 925 nm LGNRS (cyan). (4c) Drainage of LGNRs and delineation of lymphatic vessels. (4d) Same imaging technique in a different mouse after injection of LGNRs (4e) enlarged excerpt displaying the relationship of blood and lymphatic vessels (4f) same area as in (4e) after injection of 925 nm LGNRs displaying the (arrow) junction of lymph vessels and mono directional flow (see Liba (2016))

Fig. 2

Microscope Integrated OCT. A Light microscopic image after right fronto-lateral craniotomy, during dissection of dura mater. Opened segment shows Sylvian fissure with superficial Sylvian veins and temporal as well as frontal brain cortex. Orange line indicates region of scan. B OCT scan of dura mater depicting the (1) outer endosteal and (2) inner meningeal layer. Strikingly, a (3) subdural space is present, enabling a clear definition of (2) the inner meningeal dural layer and the (4) arachnoid barrier cell membrane. Furthermore, (5) subarachnoid blood vessels, (6) subarachnoid space, (7) trabecular system, (8) brain cortex, and (9) reflection artifacts are depicted by the transdural OCT scan. Red line indicates the area of enlarged excerpt. C Enlarged excerpt demonstrating details of transdural OCT scan. D Schematic drawing of microstructures: (1) + (2) dura mater, (1) outer endosteal layer, (2) inner meningeal layer, (3) subdural space, (4) subarachnoid space (4) arachnoid barrier cell membrane, (5) subarachnoid blood vessels, (6) subarachnoid space, (7) trabecular system, (8) brain cortex, and (9) reflection artifacts; see Hartmann et al. [16], figure edited with permission from the authors. E OCT scan of frontal lobe at frontal operculum visualizing the collapsed SAS after CSF release, with adjacent internal blood vessels. Red rectangle shows enlarged details of the OCT-Scan; see Hartmann et al. [17, 18], figure edited with permission from the authors. F Light microscopic intraoperative image of parent vessel: right internal carotid artery. Orange horizontal line indicates area of OCT scan. G OCT scan of parent vessel. (1 Tunica externa; (2) tunica media; (3) tunica interna; (4) atherosclerotic plaque; (5) vasa vasorum. H Light microscopic intraoperative image of ramus communicans aneurysm seen from a left fronto-lateral approach. I OCT scan of the neck of the ramus communicans anterior aneurysm (CA) demonstrating the continuous fading transition from a 3-layered configuration of the parent vessel to the mono-layered appearance of the CA dome. (1) CA dome; (2) CA neck; (3) parent vessel. J Light microscopic intraoperative image of right proximal internal carotid artery aneurysm seen from a right fronto-lateral approach; orange lines indicate the area of OCT scan at the aneurysm dome with artherosclerotic plaque. K Longitudinal OCT scan at aneurysm dome demonstrating intra-aneurysmatic atherosclerotic plaque; see Hartmann et al. [17, 18], figures edited with permission from the authors