OCT imaging depends on the detection of back scattered near infrared light and is therefore harmless to biological tissue. Its physical properties allow for microscope integration. This leads to the possibility of contact free three-dimensional, real-time scanning of tissue in the field of view of the surgeon. Penetrating depth depends on optical tissue densities. With approximately 4000 μm in the human cerebral cortex it meets microsurgical requirements.
In particular OCT offers an unprecedented axial spatial resolution ranging from 1 - 15 μm –approaching the resolution of conventional histopathology. In vitro recent optical and image processing advancements like automatic serial sectioning of polarization sensitive OCT (asPSOCT) and speckle modulation further increased image quality to display cerebral cortical layers at single cell width.
A part from structural imaging adaptations of perfusion-dependent OCT offer the possibility of parallel functional brain mapping. Due to the capability of performing “optic biopsies” systems which combine catheter integrated OCT and laser ablation might demonstrate minimal invasive and precise theranostic instruments.
These versatile strengths shed light on future perspectives. Our team validates intraoperative use of microscope integrated OCT for progression of neurosurgical guidance.
Micro neurosurgery remains an exceedingly demanding and dexterous fine motor task. Microscope integrated three dimensional imaging techniques which delineate the microstructural composition in depth are missing so far.
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. C: Light microscopic image after dural opening depicting the frontal brain cortex, sylvian fissure and temporal brain cortex. Red line indicates the area of enlarged excerpt. D: Enlarged excerpt demonstrating details of transdural OCT scan. E: 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.
Brainfunction is based on the integrity of functional brain networks. Impairements of functional brain networks manifest in neurological deficits.
During our clinical routine we already use high resolution, contrast enhanced, perfusion- and diffusion based as well as task based magnet resonance imaging to delineate structural and functional correlates of neurological deficits. Measurements of spontanous activity at rest to delineate functional brain networks are missing so far. Though they now state the only technique to delineate functional brain networks.
During recent years resting state functional brain imaging gained importance for clinical applications in diseases like Autism, Schizophrenia, Alzheimer or Parkinson’s (Fox and Greicius et al. 2010). E g. in ADHS-Syndrom decreased functional connectivity of ACC (anterior cingulate cortex) and PCC (posterior cingulate cortex) could be described (Castellanos et al. 2008). The relevance of this technique as an objective diagnostic measurement is object of research.
Another future application is the delineation of eloquent brain areas for neurosurgical guidance. Up to date tasked based fMRI is used to delineate these - often individual or pathological relocated - brain areas (Petrella et al. 2006). In unconscious, impaired or pediatric patients task based approaches are limited. We here test for the relevance of resting state brain networks for the delineation of otherwise concealed eloquent brain networks (Nandakumar et al. 2019).
Fig. 3. Group differences in functional connectivity between early- and late-onset pianists. Early-onset pianists exhibited greater functional connectivity than late-onset pianists between the seed regions and a set of occipital and cortical sensorimotor areas, whereas functional connectivity to these areas was comparable between late-onset pianists and nonmusicians. The color of each patch indicates the seed region for which the area indicated greater functional connectivity. Barplot: functional connectivity across the seed regions (error bars indicate 2SE). Scatter plot indicates the correlation between functional connectivity and motor timing expertise (in ms; lower values correspond to greater expertise). Pianists who did not complete the scale playing task are omitted from the scatter plot. Analyses were performed in the volume but presented here on the cortical surface. VSi = ventral caudate/nucleus accumbens, VSs = ventral caudate, superior, DC = dorsal caudate, DCP = dorsocaudal putamen, DRP = dorsorostral putamen, VRP = ventrorostral putamen.