Diffusion tensor imaging to visualize axons in the setting of nerve injury and recovery (original) (raw)
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Journal of plastic, reconstructive & aesthetic surgery : JPRAS, 2020
Diagnosing the site and severity of peripheral nerve injuries can be challenging for clinicians. The current gold standards of evaluation with clinical examination and electrophysiology have respective limitations, particularly with determining the prognosis for spontaneous recovery. Current imaging techniques with ultrasound, computed tomography, and magnetic resonance imaging (MRI) may be used as adjuncts in the evaluation of peripheral nerve injuries but are limited in sensitivity and accuracy. Diffusion tensor imaging (DTI) is a recent advancement in MRI sequences that shows promise in evaluating peripheral nerve injuries. Unlike the qualitative traditional MRI, DTI captures the pattern of water diffusion along the nerves and provides quantitative information regarding the integrity of axons. Additionally, DTI images can be reconstructed into 3D images with tractography. This technique is well-established in the central nervous system but is only starting to be applied in the pe...
Diffusion tensor imaging and tractography of distal peripheral nerves at 3 T
Clinical Neurophysiology, 2005
Objective: We studied whether distal peripheral nerves could be imaged using quantitative diffusion tensor imaging (DTI) with a 3-T MRI scanner, and visualized using tractography. Methods: Altogether 6 healthy subjects were studied. The diffusion was quantified with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps, and the direction of main diffusivity was visualized with color-coded orientation maps and tractography. Results: We present the first DTI and tractography results of human distal peripheral nerves. The courses of median, ulnar, and radial nerves in the upper limb and of tibial and peroneal nerves in the lower limb were first analyzed quantifying ADC and FA, and then visualized in 3D with tractography. Tractography illustrated nicely the 3D courses of both upper and lower limb nerves which were reliably distinguished from the surrounding muscle tissue and ligaments. Conclusions: Quantitative DTI and tractography can be used to image and visualize distal peripheral nerves. Significance: DTI is a quantitative method that could provide useful information for the diagnosis and follow-up of nerve lesions, entrapments, and regeneration. Peripheral nerves as well-delineated structures also containing abundant branching into bundles of different diameters, could be used as 'living phantoms' for testing and validating different tractography methods.
Plastic and Aesthetic Research, 2015
Peripheral nerve injuries are a heterogeneous group of lesions that may occurs secondary to various causes. Several different classifications have been used to describe the pathophysiological mechanisms leading to the clinical deficit, from simple and reversible compression-induced demyelination, to complete transection of nerve axons. Neurophysiological data localize, quantify, and qualify (demyelination vs. axonal loss) the clinical and subclinical deficits. High-resolution ultrasound can demonstrate the morphological extent of nerve damage, fascicular echotexture (epineurium vs. perineurium, focal alteration of the cross-section of the nerve, any neuromas, etc.), and the surrounding tissues. High field magnetic resonance imaging provides high contrast neurography by fat suppression sequences and shows structural connectivity through the use of diffusion-weighted sequences. The aim of this review is to provide clinical guidelines for the diagnosis of nerve injuries, and the rationale for instrumental evaluation in the preoperative and postoperative periods. While history and clinical approach guide neurophysiological examination, nerve conduction and electromyography studies provide functional information on conduction slowing and denervation to assist in monitoring the onset of re-innervation. High-resolution nerve imaging complements neurophysiological data and allows direct visualization of the nerve injury while providing insight into its cause and facilitating surgical treatment planning. Indications and limits of each instrumental examination are discussed.
Functional MR Neurography in Evaluation of Peripheral Nerve Trauma and Postsurgical Assessment
RadioGraphics, 2019
Evaluation of traumatic peripheral nerve injuries has classically been based on clinical and electrophysiologic criteria. US and MRI have been widely used for morphologic assessment of nerve injury sites and concomitant lesions. In the past few years, morphologic MR neurography has significantly increased its clinical applications on the basis of three-dimensional or two-dimensional images with and without fat-suppression techniques. However, these sequences have a major drawback: absence of pathophysiologic information about functional integrity or axonal flow of peripheral nerves. In this scenario, functional MRI techniques such as diffusion-weighted imaging (DWI) or diffusion tensor imaging (DTI) can be used as a complementary tool in initial evaluation of peripheral nerve trauma or in assessment of trauma undergoing surgical repair. These approaches provide not only morphologic but also functional information about extent and degree of nerve impairment. Functional MR neurography can also be applied to selection, planning, and monitoring of surgical procedures that can be performed after traumatic peripheral nerve injuries, such as neurorrhaphy, nerve graft, or neurolysis, as it provides surgeons with valuable information about the functional status of the nerves involved and axonal flow integrity. The physical basis of DWI and DTI and the technical adjustments required for their appropriate performance for peripheral nerve evaluation are reviewed. Also, the clinical value of DWI and DTI in assessment of peripheral nerve trauma is discussed, enhancing their potential impact on selection, planning, and monitoring of surgical procedures employed for peripheral nerve repair.
Neurological Research
Background: Diffusion tensor tractography (DTT) has recently been shown to accurately detect nerve injury and regeneration. This study assesses whether 7-tesla (7T) DTT imaging is a viable modality to observe axonal outgrowth in a 4 cm rabbit sciatic nerve injury model fixed by a reverse autograft surgical technique. Methods: Transection injury of unilateral sciatic nerve (4 cm long) was performed in 25 rabbits and repaired using a reverse autograft (RA) surgical technique. Analysis of the nerve autograft was performed at 3, 6, and 11 weeks postoperatively and compared to normal contralateral sciatic nerve, used as control group. High-resolution DTT from ex vivo sciatic nerves were obtained using 3D diffusion-weighted spin-echo acquisitions at 7-T. Total axons and motor and sensory axons were counted at defined lengths along the graft. Results: At 11 weeks, histologically, the total axon count of the RA group was equivalent to the contralateral uninjured nerve control group. Similarly, by qualitative DTT visualization, the 11week RA group showed increased fiber tracts compared to the 3 and 6 weeks counterparts. Upon immunohistochemical evaluation, 11-week motor axon counts did not significantly differ between
Neurosurgical focus, 2015
OBJECT The majority of growing and/or symptomatic peripheral nerve tumors are schwannomas and neurofibromas. They are almost always benign and can usually be resected while minimizing motor and sensory deficits if approached with the proper expertise and techniques. Intraoperative electrophysiological stimulation and recording techniques allow the surgeon to map the surface of the tumor in an effort to identify and thus avoid damaging functioning nerve fibers. Recently, MR diffusion tensor imaging (DTI) techniques have permitted the visualization of axons, because of their anisotropic properties, in peripheral nerves. The object of this study was to compare the distribution of nerve fibers as revealed by direct electrical stimulation with that seen on preoperative MR DTI. METHODS The authors conducted a retrospective chart review of patients with a peripheral nerve or nerve root tumor between March 2012 and January 2014. Diffusion tensor imaging and intraoperative data had been pros...
Quantitative Imaging in Medicine and Surgery
Traumatic conditions of peripheral nerves and plexus have been classically evaluated by morphological imaging techniques and electrophysiological tests. New magnetic resonance imaging (MRI) studies based on 3D fat-suppressed techniques are providing high accuracy for peripheral nerve injury evaluation from a qualitative point of view. However, these techniques do not provide quantitative information. Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are functional MRI techniques that are able to evaluate and quantify the movement of water molecules within different biological structures. These techniques have been successfully applied in other anatomical areas, especially in the assessment of central nervous system, and now are being imported, with promising results for peripheral nerve and plexus evaluation. DWI and DTI allow performing a qualitative and quantitative peripheral nerve analysis, providing valuable pathophysiological information about functional integrity of these structures. In the field of trauma and peripheral nerve or plexus injury, several derived parameters from DWI and DTI studies such as apparent diffusion coefficient (ADC) or fractional anisotropy (FA) among others, can be used as potential biomarkers of neural damage providing information about fiber organization, axonal flow or myelin integrity. A proper knowledge of physical basis of these techniques and their limitations is important for an optimal interpretation of the imaging findings and derived data. In this paper, a comprehensive review of the potential applications of DWI and DTI neurographic studies is performed with a focus on traumatic conditions, including main nerve entrapment syndromes in both peripheral nerves and brachial or lumbar plexus.
Frontiers in Neurology
Objectives: Magnetic resonance-guided focused ultrasound (MRgFUS) is a non-invasive targeted tissue ablation technique that can be applied to the nervous system. Diffusion weighted imaging (DWI) can visualize and evaluate nervous system microstructure. Tractography algorithms can reconstruct fiber bundles which can be used for treatment navigation and diffusion tensor imaging (DTI) metrics permit the quantitative assessment of nerve microstructure in vivo. There is a need for imaging tools to aid in the visualization and quantitative assessment of treatment-related nerve changes in MRgFUS. We present a method of peripheral nerve tract reconstruction and use DTI metrics to evaluate the MRgFUS treatment effect.Materials and Methods: MRgFUS was applied bilaterally to the sciatic nerves in 6 piglets (12 nerves total). T1-weighted and diffusion images were acquired before and after treatment. Tensor-based and constrained spherical deconvolution (CSD) tractography algorithms were used to ...
PubMed, 2019
Peripheral nerves can be affected by a variety of benign and malignant tumour and tumour-like lesions. Besides clinical evaluation and electrophysiologic studies, MRI is the imaging modality of choice for the assessment of these soft tissue tumours. Conventional MR sequences, however, can fail to assess the histologic features of the lesions. Moreover, the precise topographical relationship between the peripheral nerve and the tumor must be delineated preoperatively for complete tumour resection minimizing nerve damage. Using Diffusion tensor imaging (DTI) and tractography, it is possible to obtain functional information on tumour and nerve structures, allowing the assess anatomy, function and biological features. In this article, we review the technical aspects and clinical application of DTI for the evaluation of peripheral nerve tumours.