Imaging Peripheral Nerves In Vivo with CT Neurogram Using Novel 2,4,6-Tri-Iodinated Lidocaine Contrast Agent

Abstract

Peripheral nerve injuries are a significant concern in surgical procedures, often leading to chronic pain and functional impairment. Despite advancements in imaging, preoperative and intraoperative visualization of peripheral nerves remains a challenge. This study introduces and evaluates a novel tri-iodinated lidocaine-based contrast agent for computed tomography neurography, aiming to enhance the intraoperative visibility of peripheral nerves in vivo. A tri-iodinated lidocaine analogue was synthesized and characterized for its radiodensity, sodium channel binding and nerve affinity. Sodium channel affinity was performed using molecular docking. In vitro contrast enhancement was assessed by comparing the agent's Hounsfield unit (HU) values with those of Omnipaque, a clinically approved contrast medium. In vivo imaging was conducted on rat sciatic nerves using micro-CT, followed by ex vivo validation. Nerve conduction blockade was assessed via electrical stimulation and histological analysis was performed to evaluate neurotoxicity. Experimental results revealed the tri-iodinated lidocaine analogue to have similar or higher affinity toward voltage-gated sodium channels than the parent lidocaine and a radiodensity comparable to the commercial CT contrast agent Omnipaque in vitro. In vivo, the contrast agent provided CT visualization of the sciatic nerve, with a significant increase in HU values compared to untreated nerves. Electrical stimulation confirmed transient nerve conduction blockade without observable histological damage, supporting its dual role as an imaging and nerve-blocking agent. This study presents a novel tri-iodinated lidocaine-based contrast agent that enables clear CT visualization of peripheral nerves while maintaining reversible nerve inhibition. These findings support its potential application in preoperative planning and intraoperative nerve protection to reduce surgical nerve injuries. Further studies are warranted to optimize imaging conditions and evaluate its clinical feasibility.

Keywords: nerve; nerve imaging; neurography.

Scheme 1

Synthesis of a 2,4,6 triiodo-substituted lidocaine performed by customer manufacturer Nanosyn Inc. 1—2,4,6-triiodo-phenylamine, 2—(2,4,6-triiodophenyl)-2-chloroacetamide, 3—2-(diethylamino)-N-(2,4,6-triiodophenyl)acetamide (final product).

Figure 1

Setup for imaging the sciatic nerve. (A) Bilateral Transgluteal Approach of the Sciatic nerve. (B) Placement inside the imaging nanoScan PET/CT [18].

Figure 2

Electrical stimulation of the exposed sciatic nerve using a CheckPoint electrical stimulator.

Figure 3

Measurements of the contrast between two optical clear straws in agar phantom filled with triiodo-lidocaine and Omnipaque: (A) Coronal view. (B) Transaxial view. Measurements of the Hounsfield unit (HU) density were taken for equivalent surface areas using the entire cross-section of the tube in the axial plane.

Figure 4

Molecular docking of lidocaine and triiodide lidocaine with a voltage-gated sodium channel, NavAb. The 3D structure of the NavAb voltage-gated sodium channel transport protein in a closed conformation (PDB: 5VB2) [16] was downloaded from the Protein Data Bank (https://www.rcsb.org/ (accessed on 11 April 2025)). (A) Top-down view of the channel, emphasizing the symmetrical arrangement of the helices around the central pore. Lidocaine is visible in the center. (B) A side view of the channel and the depth of lidocaine within the pore. (C) The surface presentation of the channel. Black arrow indicating the zoom-in section in the whole protein. (D) Zoomed view of the pore with an orientation of lidocaine inside the pore. (E) Top-down view of the channel, emphasizing the symmetrical arrangement of the helices around the central pore. Lidocaine is visible in the center. (F) A side view of the channel and the depth of triiodo-lidocaine within the pore. (G) The surface presentation of the channel. Black arrow indicating the zoom-in section in the whole protein. (H) Zoomed view of the pore with an orientation of triiodo-lidocaine inside the pore. Gray arrows show the positions of lidocaines within the channel. Locations and energies were calculated with the AutoDock Vina algorithm implemented in the PyRx Virtual Screening Tool. The surface plots use a jet color scheme, where the N-terminus is colored blue, and the C-terminus is colored red. The color gradient (blue → green → yellow → red) corresponds to the amino acid sequence progression, reflecting the residue numbering along the protein backbone.

Figure 5

CT scan from the in vivo and extracted rat sciatic nerves. (A) Transaxial view of the mouse. The yellow arrow shows the location of a non-treated sciatic nerve, and the blue arrow shows the location of the nerve treated with triiodo-lidocaine. (B) CT scan from the extracted contralateral non-treated nerve placed in an Eppendorf tube. No signal is noted (HU < 20). (C) CT scan from the extracted non-treated sciatic nerve placed in an Eppendorf tube showing strong contrast.

Figure 6

Histology of the sciatic nerves. Sciatic nerves from both the control and lidocaine derivative-treated sides were excised for histological analysis. These results demonstrate the normal architecture of the nerve after the treatment.

Figure 7

Lidocaine and iodinated derivative. The parent molecule has three domains: hydrophilic domain (a), linker (b) and lipophilic domain (c). In the current work, we used a novel compound: 2,4,6 tri-iodinated lidocaine. Blue circles represent iodine moieties.