Peripheral nerve magnetic resonance imaging

Preoperative visualization of the greater occipital nerve with magnetic resonance imaging in candidates for occipital nerve decompression for headaches

Occipital nerve decompression is effective in reducing headache symptoms in select patients with migraine and occipital neuralgia. Eligibility for surgery relies on subjective symptoms and responses to nerve blocks and Onabotulinum toxin A (Botox) injections. No validated objective method exists for detecting occipital headache pathologies. The purpose of the study is to explore the potential of high-resolution Magnetic Resolution Imaging (MRI) in identifying greater occipital nerve (GON) pathologies in chronic headache patients. The MRI protocol included three sequences targeting fat-suppressed fluid-sensitive T2-weighted signals. Visualization of the GON involved generating 2-D image slices with sequential rotation to track the nerve course. Twelve patients underwent pre-surgical MRI assessment. MRI identified four main pathologies that were validated against intra-operative examination: GON entanglement by the occipital artery, increased nerve thickness and hyperintensity suggesting inflammation compared to the non-symptomatic contralateral side, early GON branching with rejoining at a distal point, and a connection between the GON and the lesser occipital nerve. MRI possesses the ability to visualize the GON and identify suspected trigger points associated with headache symptoms. This case series highlights MRI's potential to provide objective evidence of nerve pathology. Further research is warranted to establish MRI as a gold standard for diagnosing extracranial contributors in headaches.

NerveTracker: a Python-based software toolkit for visualizing and tracking groups of nerve fibers in serial block-face microscopy with ultraviolet surface excitation images

Significance

Information about the spatial organization of fibers within a nerve is crucial to our understanding of nerve anatomy and its response to neuromodulation therapies. A serial block-face microscopy method [three-dimensional microscopy with ultraviolet surface excitation (3D-MUSE)] has been developed to image nerves over extended depths ex vivo. To routinely visualize and track nerve fibers in these datasets, a dedicated and customizable software tool is required.

Aim

Our objective was to develop custom software that includes image processing and visualization methods to perform microscopic tractography along the length of a peripheral nerve sample.

Approach

We modified common computer vision algorithms (optic flow and structure tensor) to track groups of peripheral nerve fibers along the length of the nerve. Interactive streamline visualization and manual editing tools are provided. Optionally, deep learning segmentation of fascicles (fiber bundles) can be applied to constrain the tracts from inadvertently crossing into the epineurium. As an example, we performed tractography on vagus and tibial nerve datasets and assessed accuracy by comparing the resulting nerve tracts with segmentations of fascicles as they split and merge with each other in the nerve sample stack.

Results

We found that a normalized Dice overlap (Dice norm ) metric had a mean value above 0.75 across several millimeters along the nerve. We also found that the tractograms were robust to changes in certain image properties (e.g., downsampling in-plane and out-of-plane), which resulted in only a 2% to 9% change to the meanDice norm values. In a vagus nerve sample, tractography allowed us to readily identify that subsets of fibers from four distinct fascicles merge into a single fascicle as we move ∼ 5    mm along the nerve's length.

Conclusions

Overall, we demonstrated the feasibility of performing automated microscopic tractography on 3D-MUSE datasets of peripheral nerves. The software should be applicable to other imaging approaches. The code is available at https://github.com/ckolluru/NerveTracker.

Multimodality imaging review of ulnar nerve pathologies

The ulnar nerve is the second most commonly entrapped nerve after the median nerve. Although clinical evaluation and electrodiagnostic studies remain widely used for the evaluation of ulnar neuropathy, advancements in imaging have led to increased utilization of these newer / better imaging techniques in the overall management of ulnar neuropathy. Specifically, high-resolution ultrasonography of peripheral nerves as well as MRI has become quite useful in evaluating the ulnar nerve in order to better guide treatment. The caliber and fascicular pattern identified in the normal ulnar nerves are important distinguishing features from ulnar nerve pathology. The cubital tunnel within the elbow and Guyon's canal within the wrist are important sites to evaluate with respect to ulnar nerve compression. Both acute and chronic conditions resulting in deformity, trauma as well as inflammatory conditions may predispose certain patients to ulnar neuropathy. Granulomatous diseases as well as both neurogenic and non-neurogenic tumors can also potentially result in ulnar neuropathy. Tumors around the ulnar nerve can also lead to mass effect on the nerve, particularly in tight spaces like the aforementioned canals. Although high-resolution ultrasonography is a useful modality initially, particularly as it can be helpful for dynamic evaluation, MRI remains most reliable due to its higher resolution. Newer imaging techniques like sonoelastography and microneurography, as well as nerve-specific contrast agents, are currently being investigated for their usefulness and are not routinely being used currently.

Response to "Validity of Quantitative, Multi-Parametric MRI in the Diagnosis of Polyneuropathies"

Level of Evidence

5

Technical Efficacy Stage

1

Multiparametric Quantitative MRI of Peripheral Nerves in the Leg: A Reliability Study

BACKGROUND

Patients with polyneuropathies typically have demyelination and/or axonal degeneration in peripheral nerves. Currently, there is a lack of imaging biomarkers to track the changes in these pathologies.

PURPOSE

To develop and evaluate the reliability of a multiparametric quantitative magnetic resonance imaging (qMRI) method of peripheral nerves in the leg.

STUDY TYPE

Prospective.

SUBJECTS

Seventeen healthy volunteers (36.2 ± 13.8 years old, 9 males) with 10 of them scanned twice for test-retest.

FIELD STRENGTH/SEQUENCE

3 T, three-dimensional gradient echo and diffusion tensor imaging.

ASSESSMENT

A qMRI protocol and processing pipeline was established for quantifying the following nerve parameters that are sensitive to myelin and axonal pathologies: magnetization transfer (MT) ratio (MTR), MT saturation index (MTsat), T2 *, T1 , proton density (PD), fractional anisotropy (FA), and mean/axial/radial diffusivities (MD, AD, and RD). The qMRI protocol also measures the volume of nerve fascicles (fVOL) and the fat fraction (FF) of muscles.

STATISTICAL TESTS

The intersession reproducibility and inter-rater reliability of each qMRI parameter were assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC). Pairwise Pearson correlation analyses were performed to investigate the intrinsic association between qMRI parameters. Distal-to-proximal variations were evaluated by paired t-tests with Bonferroni-Holm multiple comparison corrections. P < 0.05 was considered statistically significant.

RESULTS

The MTR, MTsat, T2 *, T1 , PD, FA, AD, and fVOL of the sciatic and tibial nerves, and the FF of leg muscles, had an overall good-to-excellent test-retest agreement (ICC varying from 0.78 to 0.99). All the qMRI parameters had good-to-excellent inter-rater reliability (ICC > 0.80). The data demonstrated a pattern of distal-to-proximal changes of an increased nerve MTsat and FA, and a decreased nerve T1 , PD, MD, and RD, as well as a significantly increased muscle FF.

DATA CONCLUSION

The proposed multiparametric qMRI method of the peripheral nerves is highly reproducible and provided healthy control data which will be used in developing monitoring biomarkers in patients with polyneuropathies.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 2.

Navigating the Frontier: Emerging Techniques for Detecting Microvascular Complications in Type 2 Diabetes Mellitus: A Comprehensive Review

This review comprehensively explores emerging techniques for detecting microvascular complications in Type 2 Diabetes Mellitus (T2DM), addressing the critical need for advancements in early detection and management. As T2DM continues to rise globally, microvascular complications, including retinopathy, nephropathy, and neuropathy, contribute significantly to the morbidity and mortality associated with the condition. The review synthesizes key findings, revealing various emerging technologies, from advanced imaging modalities to genomic and proteomic approaches. It underscores the potential for personalized medicine, emphasizing the importance of tailoring diagnostic strategies to individual patient profiles. Challenges, including the lack of standardized criteria and issues related to patient adherence, highlight the necessity for collaborative efforts. The conclusion issues a call to action, advocating for enhanced collaboration, increased research investment, patient empowerment through education, and seamless integration of emerging diagnostic techniques into routine clinical care. The review envisions a transformative shift in detecting and managing microvascular complications in T2DM, ultimately improving patient outcomes and contributing to a healthier future for individuals affected by this prevalent metabolic disorder.

Erector spinae plane block versus local infiltration anaesthesia for transforaminal percutaneous endoscopic discectomy: A prospective randomised controlled trial

BACKGROUND

Around 60%-80% of the population suffers from back pain, making it one of the most common health complaints. Transforaminal percutaneous endoscopic discectomy (TPED) is an effective treatment for low back pain that can be performed using different anaesthesia techniques. Our primary objective was to test the hypothesis that bilateral Erector spinae plane block (ESP) plus sedation is equally effective as traditional local infiltration anaesthesia plus sedation in TPED.

MATERIALS AND METHODS

Fifty-two patients undergoing TPED were randomly assigned to 2 groups: G1 - intravenous sedation with local infiltration anaesthesia; G2 - intravenous sedation with bilateral ESP.

PRIMARY OUTCOME

volume of fentanyl and propofol administered during surgery.

SECONDARY OUTCOMES

adverse events during sedation reported using the World Society of Intravenous Anaesthesia (SIVA) adverse sedation event tool, level of postoperative sedation measured on the Richmond Agitation-Sedation Scale (RASS), intensity of postoperative pain on a visual analogue scale (VAS), mechanical pain threshold (MPT) measured with von Frey monofilaments on both lower extremities, patient satisfaction with analgesia on 5-point Likert scale.

RESULTS

Volume of fentanyl, propofol, and level of postoperative sedation was significantly lower in G2 (p < 0.001). There was no difference between groups in intensity of pain, patient satisfaction with analgesia, and mechanical pain threshold after surgery. There were no adverse events in G2, but in G1 2 patients presented minimal risk descriptors, 5 presented minor risk descriptors, and 1 presented sentinel risk descriptors that required additional medication or rescue ventilation.

CONCLUSIONS

The ESP was equal to local infiltration anaesthesia in terms of intensity of pain, mechanical pain threshold after surgery, and patient satisfaction; however, ESP reduced the volume of intraoperative fentanyl and propofol, thereby reducing the adverse effects of sedation.

Development of an In Vitro Assessment Method for Chemotherapy-Induced Peripheral Neuropathy (CIPN) by Integrating a Microphysiological System (MPS) with Morphological Deep Learning of Soma and Axonal Images

Several anticancer drugs used in cancer therapy induce chemotherapy-induced peripheral neuropathy (CIPN), leading to dose reduction or therapy cessation. Consequently, there is a demand for an in vitro assessment method to predict CIPN and mechanisms of action (MoA) in drug candidate compounds. In this study, a method assessing the toxic effects of anticancer drugs on soma and axons using deep learning image analysis is developed, culturing primary rat dorsal root ganglion neurons with a microphysiological system (MPS) that separates soma from neural processes and training two artificial intelligence (AI) models on soma and axonal area images. Exposing the control compound DMSO, negative compound sucrose, and known CIPN-causing drugs (paclitaxel, vincristine, oxaliplatin, suramin, bortezomib) for 24 h, results show the somatic area-learning AI detected significant cytotoxicity for paclitaxel (* p < 0.05) and oxaliplatin (* p < 0.05). In addition, axonal area-learning AI detected significant axonopathy with paclitaxel (* p < 0.05) and vincristine (* p < 0.05). Combining these models, we detected significant toxicity in all CIPN-causing drugs (** p < 0.01) and could classify anticancer drugs based on their different MoA on neurons, suggesting that the combination of MPS-based culture segregating soma and axonal areas and AI image analysis of each area provides an effective evaluation method to predict CIPN from low concentrations and infer the MoA.

Imaging diagnosis in peripheral nerve injury

Peripheral nerve injuries (PNIs) can be caused by various factors, ranging from penetrating injury to compression, stretch and ischemia, and can result in a range of clinical manifestations. Therapeutic interventions can vary depending on the severity, site, and cause of the injury. Imaging plays a crucial role in the precise orientation and planning of surgical interventions, as well as in monitoring the progression of the injury and evaluating treatment outcomes. PNIs can be categorized based on severity into neurapraxia, axonotmesis, and neurotmesis. While PNIs are more common in upper limbs, the localization of the injured site can be challenging. Currently, a variety of imaging modalities including ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI) and positron emission tomography (PET) have been applied in detection and diagnosis of PNIs, and the imaging efficiency and accuracy many vary based on the nature of injuries and severity. This article provides an overview of the causes, severity, and clinical manifestations of PNIs and highlights the role of imaging in their management.

Nerve MR in the Differential Diagnosis of Neuropathies: A Case Series from a Single Center

In the present study, through a case series, we highlighted the role of magnetic resonance (MR) in the identification and diagnosis of peripheral neuropathies. MR neurography allows the evaluation of the course of nerves through 2D and 3D STIR sequences with an isotropic voxel, whereas the relationship between nerves, vessels, osteo-ligamentous and muscular structures can be appraised with T1 sequences. Currently, DTI and tractography are mainly used for experimental purposes. MR neurography can be useful in detecting subtle nerve alterations, even before the onset of symptoms. However, despite being sensitive, MR neurography is not specific in detecting nerve injury and requires careful interpretation. For this reason, MR information should always be supported by instrumental clinical tests.

Feasibility of in vivo multi-parametric quantitative magnetic resonance imaging of the healthy sciatic nerve with a unified signal readout protocol

Magnetic resonance neurography (MRN) has been used successfully over the years to investigate the peripheral nervous system (PNS) because it allows early detection and precise localisation of neural tissue damage. However, studies demonstrating the feasibility of combining MRN with multi-parametric quantitative magnetic resonance imaging (qMRI) methods, which provide more specific information related to nerve tissue composition and microstructural organisation, can be invaluable. The translation of emerging qMRI methods previously validated in the central nervous system to the PNS offers real potential to characterise in patients in vivo the underlying pathophysiological mechanisms involved in a plethora of conditions of the PNS. The aim of this study was to assess the feasibility of combining MRN with qMRI to measure diffusion, magnetisation transfer and relaxation properties of the healthy sciatic nerve in vivo using a unified signal readout protocol. The reproducibility of the multi-parametric qMRI protocol as well as normative qMRI measures in the healthy sciatic nerve are reported. The findings presented herein pave the way to the practical implementation of joint MRN-qMRI in future studies of pathological conditions affecting the PNS.

Diffusion-weighted MR is useful to assess peripheral nerve invasion of soft tissue tumor

To investigate the feasibility of readout-segmented diffusion-weighted (rsDW) magnetic resonance (MR) in assessing nerve invasion of soft tissue tumor. Forty-four patients with soft tissue mass in upper leg suspected of nerve invasion underwent rsDW MR. Nerve invasion by tumor was rated by 2 radiologists, respectively. Sensitivity and specificity of rsDW MR in identifying nerve invasion were calculated, with operation findings as reference of standard. Apparent diffusion coefficient and fraction of anisotropy of nerve were obtained using DW MR, and then were compared between invaded nerves and noninvasion cases. Inter-reader agreement in using rsDW MR to rate nerve invasion was excellent (kappa = 0.891 ± 0.043, P < 0.001). Sensitivity and specificity of rsDW MR in identifying nerve invasion were 89% and 88%, respectively. Apparent diffusion coefficient was significantly higher in invaded nerves versus normal nerves (1.45 ± 0.67 × 10-3 mm2/s vs 1.39 ± 0.46 × 10-3 mm2/s, P < 0.05). Fraction of anisotropy was significantly lower in invaded nerves versus normal nerves (0.22 ± 0.11 vs 0.37 ± 0.13, P < .05). Readout-segmented DW MR was feasible in assessing sciatic nerve invasion by soft tissue tumor in selected patients.

Methodologies and MR Parameters in Quantitative Magnetic Resonance Neurography: A Scoping Review Protocol

Magnetic resonance neurography (MRN), the MR imaging of peripheral nerves, is clinically used for assessing and monitoring peripheral neuropathies based on qualitative, weighted MR imaging. Recently, quantitative MRN has been increasingly reported with various MR parameters as potential biomarkers. An evidence synthesis mapping the available methodologies and normative values of quantitative MRN of human peripheral nerves, independent of the anatomical location and type of neuropathy, is currently unavailable and would likely benefit this young field of research. Therefore, the proposed scoping review will include peer-reviewed literature describing methodologies and normative values of quantitative MRN of human peripheral nerves. The literature search will include the databases MEDLINE (PubMed), EMBASE (Ovid), Web of Science, and Scopus. At least two independent reviewers will screen the titles and abstracts against the inclusion criteria. Potential studies will then be screened in full against the inclusion criteria by two or more independent reviewers. From all eligible studies, data will be extracted by two or more independent reviewers and presented in a diagrammatic or tabular form, separated by MR parameter and accompanied by a narrative summary. The reporting will follow the guidelines of the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Upon completion, the scoping review will provide a map of the available literature, identify possible gaps, and inform on possible future research. SCOPING REVIEW REGISTRATION: Open Science Framework 9P3ZM.

New insights into the evaluation of peripheral nerves lesions: a survival guide for beginners

PURPOSE

To perform a review of the physical basis of DTI and DCE-MRI applied to Peripheral Nerves (PNs) evaluation with the aim of providing readers the main concepts and tools to acquire these types of sequences for PNs assessment. The potential added value of these advanced techniques for pre-and post-surgical PN assessment is also reviewed in diverse clinical scenarios. Finally, a brief introduction to the promising applications of Artificial Intelligence (AI) for PNs evaluation is presented.

METHODS

We review the existing literature and analyze the latest evidence regarding DTI, DCE-MRI and AI for PNs assessment. This review is focused on a practical approach to these advanced sequences providing tips and tricks for implementing them into real clinical practice focused on imaging postprocessing and their current clinical applicability. A summary of the potential applications of AI algorithms for PNs assessment is also included.

RESULTS

DTI, successfully used in central nervous system, can also be applied for PNs assessment. DCE-MRI can help evaluate PN's vascularization and integrity of Blood Nerve Barrier beyond the conventional gadolinium-enhanced MRI sequences approach. Both approaches have been tested for PN assessment including pre- and post-surgical evaluation of PNs and tumoral conditions. AI algorithms may help radiologists for PN detection, segmentation and characterization with promising initial results.

CONCLUSION

DTI, DCE-MRI are feasible tools for the assessment of PN lesions. This manuscript emphasizes the technical adjustments necessary to acquire and post-process these images. AI algorithms can also be considered as an alternative and promising choice for PN evaluation with promising results.

Quantitative MR-Neurography at 3.0T: Inter-Scanner Reproducibility

Background

Quantitative MR-neurography (MRN) is increasingly applied, however, the impact of the MR-scanner on the derived parameters is unknown. Here, we used different 3.0T MR scanners and applied comparable MR-sequences in order to quantify the inter-scanner reproducibility of various MRN parameters of the sciatic nerve.

Methods

Ten healthy volunteers were prospectively examined at three different 3.0T MR scanners and underwent MRN of their sciatic nerve using comparable imaging protocols including diffusion tensor imaging (DTI) and T2 relaxometry. Subsequently, inter-scanner agreement was assessed for seven different parameters by calculating the intraclass correlation coefficients (ICCs) and the standard error of measurement (SEM).

Results

Assessment of inter-scanner reliability revealed good to excellent agreement for T2 (ICC: 0.846) and the quantitative DTI parameters, such as fractional anisotropy (FA) (ICC: 0.876), whereas moderate agreement was observed for proton spin density (PD) (ICC: 0.51). Analysis of variance identified significant inter-scanner differences for several parameters, such as FA (p < 0.001; p = 0.02), T2 (p < 0.01) and PD (p = 0.02; p < 0.01; p = 0.02). Calculated SEM values were mostly within the range of one standard deviation of the absolute mean values, for example 0.033 for FA, 4.12 ms for T2 and 27.8 for PD.

Conclusion

This study quantifies the measurement imprecision for peripheral nerve DTI and T2 relaxometry, which is associated with the use of different MR scanners. The here presented values may serve as an orientation of the possible scanner-associated fluctuations of MRN biomarkers, which can occur under similar conditions.

Computational modelling of nerve stimulation and recording with peripheral visceral neural interfaces

Objective.Neuromodulation of visceral nerves is being intensively studied for treating a wide range of conditions, but effective translation requires increasing the efficacy and predictability of neural interface performance. Here we use computational models of rat visceral nerve to predict how neuroanatomical variability could affect both electrical stimulation and recording with an experimental planar neural interface.Approach.We developed a hybrid computational pipeline,VisceralNerveEnsembleRecording andStimulation (ViNERS), to couple finite-element modelling of extracellular electrical fields with biophysical simulations of individual axons. Anatomical properties of fascicles and axons in rat pelvic and vagus nerves were measured or obtained from public datasets. To validate ViNERS, we simulated pelvic nerve stimulation and recording with an experimental four-electrode planar array.Main results.Axon diameters measured from pelvic nerve were used to model a population of myelinated and unmyelinated axons and simulate recordings of electrically evoked single-unit field potentials (SUFPs). Across visceral nerve fascicles of increasing size, our simulations predicted an increase in stimulation threshold and a decrease in SUFP amplitude. Simulated threshold changes were dominated by changes in perineurium thickness, which correlates with fascicle diameter. We also demonstrated that ViNERS could simulate recordings of electrically-evoked compound action potentials (ECAPs) that were qualitatively similar to pelvic nerve recording made with the array used for simulation.Significance.We introduce ViNERS as a new open-source computational tool for modelling large-scale stimulation and recording from visceral nerves. ViNERS predicts how neuroanatomical variation in rat pelvic nerve affects stimulation and recording with an experimental planar electrode array. We show ViNERS can simulate ECAPS that capture features of our recordings, but our results suggest the underlying NEURON models need to be further refined and specifically adapted to accurately simulate visceral nerve axons.

DTI and MTR Measures of Nerve Fiber Integrity in Pediatric Patients With Ankle Injury

Acute peripheral nerve injury can lead to chronic neuropathic pain. Having a standardized, non-invasive method to evaluate pathological changes in a nerve following nerve injury would help with diagnostic and therapeutic assessments or interventions. The accurate evaluation of nerve fiber integrity after injury may provide insight into the extent of pathology and a patient's level of self-reported pain. The aim of this investigation was to evaluate the extent to which peripheral nerve integrity could be evaluated in an acute ankle injury cohort and how markers of nerve fiber integrity correlate with self-reported pain levels in afferent nerves. We recruited 39 pediatric participants with clinically defined neuropathic pain within 3 months of an ankle injury and 16 healthy controls. Participants underwent peripheral nerve MRI using diffusion tensor (DTI) and magnetization transfer imaging (MTI) of their injured and non-injured ankles. The imaging window was focused on the branching point of the sciatic nerve into the tibial and fibular division. Each participant completed the Pain Detection Questionnaire (PDQ). Findings demonstrated group differences in DTI and MTI in the sciatic, tibial and fibular nerve in the injured ankle relative to healthy control and contralateral non-injured nerve fibers. Only AD and RD from the injured fibular nerve correlated with PDQ scores which coincides with the inversion-dominant nature of this particular ankle injuruy cohort. Exploratory analyses highlight the potential remodeling stages of nerve injury from neuropathic pain. Future research should emphasize sub-acute time frames of injury to capture post-injury inflammation and nerve fiber recovery.

Reliability and reproducibility of sciatic nerve magnetization transfer imaging and T2 relaxometry

Objectives

To assess the interreader and test-retest reliability of magnetization transfer imaging (MTI) and T2 relaxometry in sciatic nerve MR neurography (MRN).

Materials and methods

In this prospective study, 21 healthy volunteers were examined three times on separate days by a standardized MRN protocol at 3 Tesla, consisting of an MTI sequence, a multi-echo T2 relaxometry sequence, and a high-resolution T2-weighted sequence. Magnetization transfer ratio (MTR), T2 relaxation time, and proton spin density (PSD) of the sciatic nerve were assessed by two independent observers, and both interreader and test-retest reliability for all readout parameters were reported by intraclass correlation coefficients (ICCs) and standard error of measurement (SEM).

Results

For the sciatic nerve, overall mean ± standard deviation MTR was 26.75 ± 3.5%, T2 was 64.54 ± 8.2 ms, and PSD was 340.93 ± 78.8. ICCs ranged between 0.81 (MTR) and 0.94 (PSD) for interreader reliability and between 0.75 (MTR) and 0.94 (PSD) for test-retest reliability. SEM for interreader reliability was 1.7% for MTR, 2.67 ms for T2, and 21.3 for PSD. SEM for test-retest reliability was 1.7% for MTR, 2.66 ms for T2, and 20.1 for PSD.

Conclusions

MTI and T2 relaxometry of the sciatic nerve are reliable and reproducible. The values of measurement imprecision reported here may serve as a guide for correct interpretation of quantitative MRN biomarkers in future studies.

Key Points

• Magnetization transfer imaging (MTI) and T2 relaxometry of the sciatic nerve are reliable and reproducible.

• The imprecision that is unavoidably associated with different scans or different readers can be estimated by the here presented SEM values for the biomarkers T2, PSD, and MTR.

• These values may serve as a guide for correct interpretation of quantitative MRN biomarkers in future studies and possible clinical applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-08072-9.

Mapping the peripheral nervous system in the whole mouse via compressed sensing tractography

Objective.The peripheral nervous system (PNS) connects the central nervous system with the rest of the body to regulate many physiological functions and is therapeutically targeted to treat diseases such as epilepsy, depression, intestinal dysmotility, chronic pain, and more. However, we still lack understanding of PNS innervation in most organs because the large span, diffuse nature, and small terminal nerve bundle fibers have precluded whole-organism, high resolution mapping of the PNS. We sought to produce a comprehensive peripheral nerve atlas for use in future interrogation of neural circuitry and selection of targets for neuromodulation.Approach.We used diffusion tensor magnetic resonance imaging (DT-MRI) with high-speed compressed sensing to generate a tractogram of the whole mouse PNS. The tractography generated from the DT-MRI data is validated using lightsheet microscopy on optically cleared, antibody stained tissue.Main results.Herein we demonstrate the first comprehensive PNS tractography in a whole mouse. Using this technique, we scanned the whole mouse in 28 h and mapped PNS innervation and fiber network in multiple organs including heart, lung, liver, kidneys, stomach, intestines, and bladder at 70µm resolution. This whole-body PNS tractography map has provided unparalleled information; for example, it delineates the innervation along the gastrointestinal tract by multiple sacral levels and by the vagal nerves. The map enabled a quantitative tractogram that revealed relative innervation of the major organs by each vertebral foramen as well as the vagus nerve.Significance.This novel high-resolution nerve atlas provides a potential roadmap for future neuromodulation therapies and other investigations into the neural circuits which drive homeostasis and disease throughout the body.

Preliminary study on the influencing factors of shear wave elastography for peripheral nerves in healthy population

This study took shear wave elastography (SWE) technology to measure the shear wave velocity (SWV) of peripheral nerve in healthy population, which represents the stiffness of the peripheral nerves, and research whether these parameters (location, age, sex, body mass index (BMI), the thickness and cross-sectional area(CSA) of the nerve) would affect the stiffness of the peripheral nerves. 105 healthy volunteers were enrolled in this study. We recorded the genders and ages of these volunteers, measured height and weight, calculated BMI, measured nerve thickness and CSA using high-frequency ultrasound (HFUS), and then, we measured and compared the SWV of the right median nerve at the middle of the forearm and at the proximal entrance of the carpal tunnel. The SWV of the median nerve of the left side was measured to explore whether there exist differences of SWV in bilateral median nerve. Additionally, we also measured the SWV of the right tibial nerve at the ankle canal to test whether there is any difference in shear wave velocity between different peripheral nerves. This study found that there existed significant differences of SWV between different sites in one nerve and between different peripheral nerves. No significant difference was found in SWV between bilateral median nerves. Additionally, the SWV of peripheral nerves was associated with gender, while not associated with age or BMI. The mean SWV of the studied male volunteers in median nerve were significantly higher than those of female (p < 0.05). Peripheral nerve SWE measurement in healthy people is affected by different sites, different nerves and genders, and not associated with age, BMI, nerve thickness or CSA.

Initial findings in traumatic peripheral nerve injury and repair with diffusion tensor imaging

OBJECTIVE

Management of peripheral nerve injuries requires physicians to rely on qualitative measures from patient history, electromyography, and physical exam. Determining a successful nerve repair can take months to years for proximal injuries, and the resulting delays in clinical decision-making can lead to a negative impact on patient outcomes. Early identification of a failed nerve repair could prevent permanent muscle atrophy and loss of function. This study aims to test the feasibility of performing diffusion tensor imaging (DTI) to evaluate injury and recovery following repair of wrist trauma. We hypothesize that DTI provides a noninvasive and reliable assessment of regeneration, which may improve clinical decision-making and alter the clinical course of surgical interventions.

METHODS

Clinical and MRI measurements from subjects with traumatic peripheral nerve injury, carpal tunnel syndrome, and healthy control subjects were compared to evaluate the relationship between DTI metrics and injury severity.

RESULTS

Fractional anisotropy from DTI was sensitive to differences between damaged and healthy nerves, damaged and compressed nerves, and injured and healthy contralateral nerves. Longitudinal measurements in two injury subjects also related to clinical outcomes. Implications of other diffusion measures are also discussed.

INTERPRETATION

DTI is a sensitive tool for wrist nerve injuries and can be utilized for monitoring nerve recovery. Across three subjects with nerve injuries, this study has shown how DTI can detect abnormalities between injured and healthy nerves, measure recovery, and determine if re-operation was successful. Additional comparisons to carpal tunnel syndrome and healthy nerves show that DTI is sensitive to the degree of impairment.

Advances in imaging technologies for the assessment of peripheral neuropathies in rheumatoid arthritis

Peripheral neuropathy in patients with rheumatoid arthritis is associated with a maladaptive autoimmune response that may cause chronic pain and disability. Nerve conduction studies are the routine method performed when rheumatologists presume its presence. However, this approach is invasive, may not reveal subtle malfunctions in the early stages of the disease, and does not expose abnormalities in structures surrounding the nerves and muscles, limiting the possibility of a timely diagnosis. This work aims to present a narrative review of new technologies for the clinical assessment of peripheral neuropathy in Rheumatoid Arthritis. Through a bibliographic search carried out in five repositories, from 1990 to 2020, we identified three technologies that could detect peripheral nerve lesions and perform quantitative evaluations: (1) magnetic resonance neurography, (2) functional magnetic resonance imaging, and (3) high-resolution ultrasonography of peripheral nerves. We found these tools can overcome the main constraints imposed by the previous electrophysiologic methods, enabling early diagnosis.

Evaluation and Treatment of Foot Drop Using Nerve Transfer Techniques

Foot drop represents a complex pathologic condition, requiring a multidisciplinary approach for appropriate evaluation and treatment. Multiple etiologic factors require recognition before considering invasive/operative intervention. When considering surgical management for the treatment of foot drop, it is first and foremost imperative to establish the cause of the condition. Not all causes resulting in clinical foot drop have surgical options. Establishing a cause allows the provider to more appropriately curtail a multidisciplinary approach to working-up, and ultimately, treating the patient. The authors offer an algorithm for evaluating and treating foot drop conditions associated with lumbar spine radiculopathy and peripheral nerve lesions.

Techniques for Imaging Vascular Supply of Peripheral Nerves

Few studies have been developed to map the vascular structures feeding peripheral nerves, with the majority using cadaveric models and inadequate sample sizes. Preliminary evidence, while limited, indicates that the mapping of these vessels may allow or preclude certain procedures in nerve reconstruction due to the location of essential arterial inflow to the vasa nervorum. This review evaluates the evidence regarding historical, current, and emerging techniques for visualizing these vascular structures in vivo and considers their potential application in peripheral nerve vasculature.

Magnetic Resonance Neurography for Evaluation of Peripheral Nerves

Peripheral nerve injuries (PNIs) continue to present both diagnostic and treatment challenges. While nerve transections are typically a straightforward diagnosis, other types of PNIs, such as chronic or traumatic nerve compression, may be more difficult to evaluate due to their varied presentation and limitations of current diagnostic tools. As a result, diagnosis may be delayed, and these patients may go on to develop progressive symptoms, impeding normal activity. In the past, PNIs were diagnosed by history and clinical examination alone or techniques that raised concerns regarding accuracy, invasiveness, or operator dependency. Magnetic resonance neurography (MRN) has been increasingly utilized in clinical settings due to its ability to visualize complex nerve structures along their entire pathway and distinguish nerves from surrounding vasculature and tissue in a noninvasive manner. In this review, we discuss the clinical applications of MRN in the diagnosis, as well as pre- and postsurgical assessments of patients with peripheral neuropathies.

Demyelination in hereditary sensory neuropathy type-1C

OBJECTIVE

Sphingolipids are enriched in the nerves. Serine-palmitoyltransferase (SPT) catalyzes the key step of sphingolipids biosynthesis. Mutations in SPT subunits (SPTLC) lead to the excessive production of neurotoxic deoxysphingolipids (DoxSLs) in patients with Hereditary Sensory Neuropathy Type-1C (HSN1C). HSN1C is an autosomal dominant peripheral neuropathy characterized by sensory loss and distal muscle weakness. In this study, by leveraging a HSN1C family with a previously reported N177D mutation in SPTLC2, we aim to further define the spectrum of DoxSL species and the peripheral neve pathology of the disease.

METHODS

Next-generation sequencing along with Sanger confirmation was performed for family members and healthy controls. LC-MS was used for lipidomic analysis in participants' plasma. Quantitative magnetic resonance imaging (qMRI) was performed to study sciatic nerve pathologies.

RESULTS

A heterozygous N177D mutation in SPTLC2 was co-segregated in individuals with sensory-motor deficits in the limbs. Nerve conduction studies (NCS) revealed nonuniform slowing of conduction velocities. In line with the NCS, qMRI detected a pattern of nerve changes similar to those in acquired demyelinating polyneuropathies. Additionally, we detected a significant increase in multiple species of deoxysphingoid bases and deoxyceramides in patients' plasma.

INTERPRETATION

Mutations in the SPTLC2 cause a demyelinating phenotype resembling those in acquired demyelinating polyneuropathy. The species of increased DoxSLs in HSN1C may be more diverse than originally thought.