Abstract
A forward-imaging needle-type optical coherence tomography (OCT) probe with Doppler OCT (DOCT) capability has the potential to solve critical challenges in interventional procedures. A case in point is stereotactic neurosurgery where probes are advanced into the brain based on predetermined coordinates. Laceration of blood vessels in front of the advancing probe is an unavoidable complication with current methods. Moreover, cerebrospinal fluid (CSF) leakage during surgery can shift the brain rendering the predetermined coordinates unreliable. In order to address these challenges, we developed a forward-imaging OCT probe (740 μm O.D.) using a gradient-index (GRIN) rod lens that can provide real-time imaging feedback for avoiding at-risk vessels (8 frames/s with 1024 A-scans per frame for OCT/DOCT dual imaging) and guiding the instrument to specific targets with 12 μm axial resolution (100 frames/s with 160 A-scans per frame for OCT imaging only). The high signal-to-background characteristic of DOCT provides exceptional sensitivity in detecting and quantifying the blood flow within the sheep brain parenchyma in real time. The OCT/DOCT dual imaging also demonstrated its capability to differentiate the vessel type (artery/vein) on rat’s femoral vessels. We also demonstrated in ex vivo human brain that the location of the tip of the OCT probe can be inferred from micro-anatomical landmarks in OCT images. These findings demonstrate the suitability of OCT guidance during stereotactic procedures in the brain and its potential for reducing the risk of cerebral hemorrhage.
Highlights
Stereotactic procedures that require insertion of needle-based instruments into the brain serve important roles in neurosurgery. These procedures are employed in a variety of medical conditions from biopsy of suspected tumors [1] to cell-based and gene therapy [2,3] to the placement of electrodes that are used for deep brain stimulation (DBS) [4,5]
The major barrier to optimize the sensitivity is the high reflection from both surfaces of the GRIN rod lens
We tackled this problem by attaching a high refractive index cap (n = 1.56, which is close to the refractive index of GRIN lens n = 1.61) at the distal end, and using oblique illumination at the proximal end to minimize specular reflection
Summary
Stereotactic procedures that require insertion of needle-based instruments into the brain serve important roles in neurosurgery. A fundamental limitation of these stereotactic procedures is that they are blind procedures in that the operator does not have real-time feedback as to what lies immediately ahead of the advancing probe. Misplacement of electrodes by millimeters in the brain can seriously decrease the effectiveness of DBS [5] These two problems could be solved if the surgeon were able to visualize in real-time what is in front of the probe. We describe the design and demonstrate the imaging capability of a novel OCT probe for stereotactic neurosurgery that allows identification of blood vessels and anatomic landmarks in front of the advancing probe
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