Recognition of necrotic regions in MRI images of chronic spinal cord injury based on superpixel.

BACKGROUND AND OBJECTIVE: The cystic cavity and its surrounding dense glial scar formed in chronic spinal cord injury (SCI) hinder the regeneration of nerve axons. Accurate location of the necrotic regions formed by the scar and the cavity is conducive to eliminate the re-growth obstacles and promote SCI treatment. This work aims to realize the accurate and automatic location of necrotic regions in the chronic SCI magnetic resonance imaging (MRI). METHODS: In this study, a method based on superpixel is proposed to identify the necrotic regions of spinal cord in chronic SCI MRI. Superpixels were obtained by a simple linear iterative clustering algorithm, and feature sets were constructed from intensity statistical features, gray level co-occurrence matrix features, Gabor texture features, local binary pattern features and superpixel areas. Subsequently, the recognition effects of support vector machine (SVM) and random forest (RF) classification model on necrotic regions were compared from accuracy (ACC), positive predictive value (PPV), sensitivity (SE), specificity (SP), Dice coefficient and algorithm running time. RESULTS: The method is evaluated on T1- and T2-weighted MRI spinal cord images of 24 adult female Wistar rats. And an automatic recognition method for spinal cord necrosis regions was established based on the SVM classification model finally. The recognition results were 1.00±0.00 (ACC), 0.89±0.09 (PPV), 0.88±0.12 (SE), 1.00±0.00 (SP) and 0.88±0.07 (Dice), respectively. CONCLUSIONS: The proposed method can accurately and noninvasively identify the necrotic regions in MRI, which is helpful for the pre-intervention assessment and post-intervention evaluation of chronic SCI research and treatments, and promoting the clinical transformation of chronic SCI research.

Different macaque brain network remodeling after spinal cord injury and NT3 treatment.

Graph theory-based analysis describes the brain as a complex network. Only a few studies have examined modular composition and functional connectivity (FC) between modules in patients with spinal cord injury (SCI). Little is known about the longitudinal changes in hubs and topological properties at the modular level after SCI and treatment. We analyzed differences in FC and nodal metrics reflecting modular interaction to investigate brain reorganization after SCI-induced compensation and neurotrophin-3 (NT3)-chitosan-induced regeneration. Mean inter-modular FC and participation coefficient of areas related to motor coordination were significantly higher in the treatment animals than in the SCI-only ones at the late stage. The magnocellular part of the red nucleus may reflect the best difference in brain reorganization after SCI and therapy. Treatment can enhance information flows between regions and promote the integration of motor functions to return to normal. These findings may reveal the information processing of disrupted network modules.

MRI metrics at the epicenter of spinal cord injury are correlated with the stepping process in rhesus monkeys.

Clinical evaluations of long-term outcomes in the early-stage spinal cord injury (SCI) focus on macroscopic motor performance and are limited in their prognostic precision. This study was designed to investigate the sensitivity of the magnetic resonance imaging (MRI) indexes to the data-driven gait process after SCI. Ten adult female rhesus monkeys were subjected to thoracic SCI. Kinematics-based gait examinations were performed at 1 (early stage) and 12 (chronic stage) months post-SCI. The proportion of stepping (PS) and gait stability (GS) were calculated as the outcome measures. MRI metrics, which were derived from structural imaging (spinal cord cross-sectional area, SCA) and diffusion tensor imaging (fractional anisotropy, FA; axial diffusivity, λ//), were acquired in the early stage and compared with functional outcomes by using correlation analysis and stepwise multivariable linear regression. Residual tissue SCA at the injury epicenter and residual tissue FA/remote normal-like tissue FA were correlated with the early-stage PS and GS. The extent of lesion site λ///residual tissue λ// in the early stage after SCI was correlated with the chronic-stage GS. The ratios of lesion site λ// to residual tissue λ// and early-stage GS were predictive of the improvement in the PS at follow-up. Similarly, the ratios of lesion site λ// to residual tissue λ// and early-stage PS best predicted chronic GS recovery. Our findings demonstrate the predictive power of MRI combined with the early data-driven gait indexes for long-term outcomes. Such an approach may help clinicians to predict functional recovery accurately.

NT3 treatment alters spinal cord injury-induced changes in the gray matter volume of rhesus monkey cortex.

Spinal cord injury (SCI) may cause structural alterations in brain due to pathophysiological processes, but the effects of SCI treatment on brain have rarely been reported. Here, voxel-based morphometry is employed to investigate the effects of SCI and neurotrophin-3 (NT3) coupled chitosan-induced regeneration on brain and spinal cord structures in rhesus monkeys. Possible association between brain and spinal cord structural alterations is explored. The pain sensitivity and stepping ability of animals are collected to evaluate sensorimotor functional alterations. Compared with SCI, the unique effects of NT3 treatment on brain structure appear in extensive regions which involved in motor control and neuropathic pain, such as right visual cortex, superior parietal lobule, left superior frontal gyrus (SFG), middle frontal gyrus, inferior frontal gyrus, insula, secondary somatosensory cortex, anterior cingulate cortex, and bilateral caudate nucleus. Particularly, the structure of insula is significantly correlated with the pain sensitivity. Regenerative treatment also shows a protective effect on spinal cord structure. The associations between brain and spinal cord structural alterations are observed in right primary somatosensory cortex, SFG, and other regions. These results help further elucidate secondary effects on brain of SCI and provide a basis for evaluating the effects of NT3 treatment on brain structure.

Neural regeneration therapy after spinal cord injury induces unique brain functional reorganizations in rhesus monkeys.

PURPOSE: Spinal cord injury (SCI) destroys the sensorimotor pathway and induces brain plasticity. However, the effect of treatment-induced spinal cord tissue regeneration on brain functional reorganization remains unclear. This study was designed to investigate the large-scale functional interactions in the brains of adult female Rhesus monkeys with injured and regenerated thoracic spinal cord. MATERIALS AND METHODS: Resting-state functional magnetic resonance imaging (fMRI) combined with Granger Causality analysis (GCA) and motor behaviour analysis were used to assess the causal interaction between sensorimotor cortices, and calculate the relationship between causal interaction and hindlimb stepping in nine Rhesus monkeys undergoing lesion-induced spontaneous recovery (injured, n = 4) and neurotrophin-3/chitosan transplantation-induced regeneration (NT3-chitosan, n = 5) after SCI. RESULTS: The results showed that the injured and NT3-chitosan-treated animals had distinct spatiotemporal features of brain functional reorganization. The spontaneous recovery followed the model of "early intra-hemispheric reorganization dominant, late inter-hemispheric reorganization dominant", whereas regenerative therapy animals showed the opposite trend. Although the variation degree of information flow intensity was consistent, the tendency and the relationship between local neuronal activity properties and coupling strength were different between the two groups. In addition, the injured and NT3-chitosan-treated animals had similar motor adjustments but various relationship modes between motor performance and information flow intensity. CONCLUSIONS: Our findings show that brain functional reorganization induced by regeneration therapy differed from spontaneous recovery after SCI. The influence of unique changes in brain plasticity on the therapeutic effects of future regeneration therapy strategies should be considered. Key messagesNeural regeneration elicited a unique spatiotemporal mode of brain functional reorganization in the spinal cord injured monkeys, and that regeneration does not simply reverse the process of brain plasticity induced by spinal cord injury (SCI).Independent "properties of local activity - intensity of information flow" relationships between the injured and treated animals indicating that spontaneous recovery and regenerative therapy exerted different effects on the reorganization of the motor network after SCI.A specific information flow from the left thalamus to the right insular can serve as an indicator to reflect a heterogeneous "information flow - motor performance" relationship between injured and treated animals at similar motor adjustments.

Effect of b Value on Imaging Quality for Diffusion Tensor Imaging of the Spinal Cord at Ultrahigh Field Strength.

OBJECTIVE: To explore the optimal b value setting for diffusion tensor imaging of rats' spinal cord at ultrahigh field strength (7 T). METHODS: Spinal cord diffusion tensor imaging data were collected from 14 rats (5 healthy, 9 spinal cord injured) with a series of b values (200, 300, 400, 500, 600, 700, 800, 900, and 1000 s/mm2) under the condition that other scanning parameters were consistent. The image quality (including image signal-to-noise ratio and image distortion degree) and data quality (i.e., the stability and consistency of the DTI-derived parameters, referred to as data stability and data consistency) were quantitatively evaluated. The min-max normalization method was used to process the calculation results of the four indicators. Finally, the image and data quality under each b value were synthesized to determine the optimal b value. RESULTS: b = 200 s/mm2 and b = 900 s/mm2 ranked in the top two of the comprehensive evaluation, with the best image quality at b = 200 s/mm2 and the best data quality at b = 900 s/mm2. CONCLUSION: Considering the shortcomings of the ability of low b values to reflect the microstructure, b = 900 s/mm2 can be used as the optimal b value for 7 T spinal cord diffusion tensor scanning.

Importance of brain alterations in spinal cord injury.

Spinal cord injury (SCI) destroys the sensorimotor pathway and blocks the information flow between the peripheral nerve and the brain, resulting in autonomic function loss. Numerous studies have explored the effects of obstructed information flow on brain structure and function and proved the extensive plasticity of the brain after SCI. Great progress has also been achieved in therapeutic strategies for SCI to restore the "re-innervation" of the cerebral cortex to the limbs to some extent. Although no thorough research has been conducted, the changes of brain structure and function caused by "re-domination" have been reported. This article is a review of the recent research progress on local structure, functional changes, and circuit reorganization of the cerebral cortex after SCI. Alterations of structure and electrical activity characteristics of brain neurons, features of brain functional reorganization, and regulation of brain functions by reconfigured information flow were also explored. The integration of brain function is the basis for the human body to exercise complex/fine movements and is intricately and widely regulated by information flow. Hence, its changes after SCI and treatments should be considered.