Neurologic complications have been reported with spinal transforaminal injections. Causes include intraneural injection,
plus embolization occlusion of the radicular artery with subsequent spinal cord infarction. <sup>1</sup> Optical coherence
tomography (OCT) is a non-invasive imaging modality, which is used to image tissue microstructure with very high
resolution (less than 20 microns) in real-time. With a view toward needle tip OCT visualization of the spinal
neuroforamen, we conducted animal studies to explore OCT imaging of paraspinal neurovascular structures. With
institutional animal care committee approval, we performed ex-vivo and in situ OCT studies in a euthanized dog, pig,
and rabbit. Image data was gathered on spinal nerve roots, dura, and brachial plexus. Two systems were used: frequency
domain OCT imaging system developed at California Institute of Technology, and time domain Imalux NIRIS system
with a 2.7 mm diameter probe. In a euthanized pig, excised dura was punctured with a 17-gauge Tuohy needle. FDOCT
dural images of the puncture showed a subsurface cone-shaped defect. In a rabbit in situ study, puncture of the dura with
a 26-gauge needle is imaged as a discontinuity. FDOCT imaging of both small artery and large arteries will be
presented, along with H&E and OCT images of the brachial plexus.
We explored multiple image processing approaches by which to display the segmented adult brachial plexus in a three-dimensional manner. Magnetic resonance neurography (MRN) 1.5-Tesla scans with STIR sequences, which preferentially highlight nerves, were performed in adult volunteers to generate high-resolution raw images. Using multiple software programs, the raw MRN images were then manipulated so as to achieve segmentation of plexus neurovascular structures, which were incorporated into three different visualization schemes: rotating upper thoracic girdle skeletal frames, dynamic fly-throughs parallel to the clavicle, and thin slab volume-rendered composite projections.
Introduction: Optical coherence tomography (OCT) allows high-resolution imaging (less than 10 microns) of tissue structures. A pilot study with OCT and polarization-sensitive OCT (PS-OCT) was undertaken to image ex-vivo neurovascular structures (vessels, nerves) of the canine brachial plexus. Methods: OCT is an interferometry-based optical analog of B-mode ultrasound, which can image through non-transparent biological tissues. With approval of the USC Animal Care and Use Committee, segments of the supra- and infraclavicular brachial plexus were excised from euthanized adult dogs, and the ex-vivo specimens were placed in cold pH-buffered physiologic solution. An OCT beam, in micrometer translational steps, scanned the fixed-position bisected specimens in transverse and longitudinal views. Two-dimensional images were obtained from identified arteries and nerves, with specific sections of interest stained with hematoxylin-eosin for later imaging through a surgical microscope. Results: with the beam scan direction transverse to arteries, the resulting OCT images showed an identifiable arterial lumen and arterial wall tissue layers. By comparison, transverse beam OCT images of nerves revealed a multitude of smaller nerve bundles contained within larger circular-shaped fascicles. PS-OCT imaging was helpful in showing the characteristic birefringence exhibited by arrayed neural structures. Discussion: High-resolution OCT imaging may be useful in the optical identification of neurovascular structures during attempted regional nerve blockade. If incorporated into a needle-shaped catheter endoscope, such a technology could prevent intraneural and intravascular injections immediately prior to local anesthetic injection. The major limitation of OCT is that it can form a coherent image of tissue structures only to a depth of 1.5 - 2 mm.