Optical Devices for the Diagnosis and Management of Spinal Cord Injuries: A Review

Abstract

Throughout the central nervous system, the spinal cord plays a very important role, namely, transmitting sensory and motor information inwardly so that it can be processed by the brain. There are many different ways this structure can be damaged, such as through traumatic injury or surgery, such as scoliosis correction, for instance. Consequently, damage may be caused to the nervous system as a result of this. There is no doubt that optical devices such as microscopes and cameras can have a significant impact on research, diagnosis, and treatment planning for patients with spinal cord injuries (SCIs). Additionally, these technologies contribute a great deal to our understanding of these injuries, and they are also essential in enhancing the quality of life of individuals with spinal cord injuries. Through increasingly powerful, accurate, and minimally invasive technologies that have been developed over the last decade or so, several new optical devices have been introduced that are capable of improving the accuracy of SCI diagnosis and treatment and promoting a better quality of life after surgery. We aim in this paper to present a timely overview of the various research fields that have been conducted on optical devices that can be used to diagnose spinal cord injuries as well as to manage the associated health complications that affected individuals may experience.

Keywords: fiber Bragg grating; fluorescence imaging; neuroimaging; optical coherence tomography; photoacoustic imaging; plasmonic nanoparticles; spinal cord; spinal cord injury; wearable optical technology.

Figure 1

The primary working mechanism of the OCT imaging technique. Reproduced with permission from [34] (Copyright 2008, MDPI).

Figure 2

(a) The internal view of the lumber cistern after inserting a 16-gauge Tuohy needle into it, with yellow arrows indicating the position of the subarachnoid space visualized using a contrast agent; (b) the external view of inserting the OCT catheter (indicated with the red arrow) through the RHV and Tuohy needle into the lumbar cistern; (c) (i) the mobile unit to display captured OCT images; (ii) the OCT catheter with a large port that allows its connection to the docking system connected to the mobile unit (the blue arrow indicates the docking system and green arrow indicates the 5 mL syringe connected to catheter); and (iii) cross-sectional image of OCT probe performing a circumferential scan. Reproduced with permission from [36] (Copyright 2021, Spie. digitallibrary).

Figure 3

The OCT catheter’s progression into the lumber cistern through the L2/3 level (a,b). The yellow arrow indicates the Tuohy needle, blue arrow indicates the distal marker, the green arrow represents one lens marker, and the purple arrow indicates one proximal marker. The red pointer indicates the optical fiber catheter. (c) The catheter was seen to be advanced into the cervical spine, and (d) the catheter was navigated toward the sacrum (a large, triangular bone at the base of the spine) without difficulty. Reproduced with permission from [36] (Copyright 2021, Spie. digitallibrary).

Figure 4

Intrathecal cervical spine canal OCT imaging: (a,b) a white asterisk represents the location within the subarachnoid space, blue arrows represent the pile lining of the spinal cord, green arrows represent the arachnoid bands, and a lateral dentate ligament, yellow arrows represent the epidural veins and red arrow indicates the dura. White bars = 1 mm. Reproduced with permission from [36] (Copyright 2021, Spie. digitallibrary).

Figure 5

White light and cryo-fluorescence tomography (CFT) at the level of the vertebral spinal cord post-infusion of Qdots ICV. Reproduced with permission from [50] (Copyright 2023, MDPI).

Figure 6

Principles of light emission for wearable optical technology: (a) conventional optical fiber; (b) cladding perforation; (c) a macro-bent optical fiber.

Figure 7

Application of wearable sensors in the lumbar spine. Reproducing software and recorded kinematic data. Reproduced with permission from [59] (Copyright 2022, MDPI).

Figure 8

(a) Therapeutic semiconductor laser device with constant 810 nm wavelength: (i) button for emergency shutdown; (ii) interface for digital control; (iii) functional status indication lamp; (iv) power button; (v) interface for optical fibers. (b) (i–ii) light-emitting portion of an optical fiber; (ii–iii) remaining optical fiber components. Reproduced with permission from [96] (Copyright 2020, Wiley).

Figure 9

(a) The exposed T9 spinal cord; (b) the front end of the optical fibre was fixed to the spinous using absorbable sutures; (c) projection of light energy directly on the spinal cord surface; (d,e) the optical fibre was fixed tightly around the skin with absorbable suture; (f) the pig retained its motor ability after the operation; (g) schematic representation of implantation, fixation and irradiation using the optical fiber. Reproduced with permission from [96] (Copyright 2020, Wiley).

Figure 10

(a) An illustration of the longitudinal mid-cross-section of an instrumented spinal cord surrogate that incorporates an integrated fiber Bragg grating (FBG) sensor; (b) transverse view of the mechanical and optical setup of the instrumented spinal cord surrogate. Reproduced with permission from [110] (Copyright 2021, MDPI).

Figure 11

(a) An experimental setup for the characterization of a fiber Bragg grating (FBG) sensor and (b) the sensor’s reflection spectra (normalized with input power) for different transverse pressures on the spinal cord surrogate, obtained using the optical spectrum analyzer. Reproduced with permission from [110] (Copyright 2021, MDPI).

Figure 12

Using US and PA imaging techniques, researchers imaged an injection of AuNS-labeled MSCs into the spinal cord of a rat. (a–f) We were able to capture ultrasound and photoacoustic images in the same sequence after injecting 0, 1, 2, 3, 4, and 5 L of AuNS-labeled MSCs using the same protocol. A scale bar measuring 2 mm is shown in the figure; (g) the distribution of all photoacoustic absorbers after injecting 5L of AuNS-labeled MSCs into the spinal cord; (h) a photomicrograph showing transplanted AuNS-labeled MSCs in the gray matter of the spinal cord, with a scale bar of 2 mm; (i) a graph of the photoacoustic signal with an average amplitude of 700 nm throughout the experiment. Error bars are used to indicate the standard deviation of the data. Yellow arrows represent the needle shaft. Reproduced with permission from [129] (Copyright 2018, American Chemical Society).