Diffusion tensor imaging in pediatric spinal cord injury: preliminary examination of reliability and clinical correlation

A systematic review of repeatability and reproducibility studies of diffusion tensor imaging of cervical spinal cord

OBJECTIVES

Diffusion tensor imaging (DTI) techniques are being studied as a possible diagnostic and predictive tool for the evaluation of cervical spinal cord disease. This systematic review aims to evaluate the previous DTI studies that specifically investigated the repeatability and reproducibility of DTI in the cervical spinal cord.

METHODS AND MATERIALS

A search in the PubMed, Scopus, Web of Science and Ovid electronic databases was conducted for articles published between January 1990 and February 2022 that related to the repeatability and reproducibility of DTI in evaluating the cervical spinal cord using one of the following measurements: the intraclass correlation coefficient (ICC) and/or the coefficient of variation (CV), and/or Bland-Altman (BA) differences analysis methods. DTI studies that presented full statistical analysis of repeatability and/or reproducibility tests of the cervical spinal cord in peer-reviewed full-text publications published in journals were included. Articles that included at least one of the keywords within the titles or abstracts were identified. Additional full-text papers were found by searching the citations and reference lists of related articles. This review has followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidance. Risk of bias was evaluated with 13 criteria weighted toward methodological quality of reported studies using the QuADS assessment criteria. This assessment only included full-text articles written in English.

RESULTS

A total of 11 studies were included and assessed for different characteristics, including sample size,(3-34) re-test time interval (<1 h to >3 months), test-retest reproducibility scores and acquisition method. Six studies used ICC which ranged from poor (ICC<0.37) to excellent reproducibility (ICC 0.91-0.99). Four studies reported an overall CV lower than 40% for all DTI metrics. Three studies reported the Bland-Altman (BA) differences and reported a minimum percentage showing no strong differences between repeated measurements. Quantitative analysis was not undertaken due to heterogeneity of methods. Repeatability and reproducibility measures were generally found to be good.

CONCLUSION

This study revealed that the application of DTI and its related measures in a clinical setting in the assessment of cervical spinal cord changes is feasible and reproducible. However, cervical spinal cord DTI suffers from some existing limitations that prevent it from being routinely used in research and clinical settings.

ADVANCES IN KNOWLEDGE

DTI with its parametric maps provide broad evaluation of the tissue structure of axonal white matter and are being studied as a possible diagnostic and predictive tool for the assessment of cervical spinal cord (CSC) disease.

Porcine Model of the Growing Spinal Cord-Changes in Diffusion Tensor Imaging Parameters

Diffusion tensor imaging (DTI) is an advanced magnetic resonance imaging (MRI) technique that has promising applications for the objective assessment of the microstructure of the spinal cord. This study aimed to verify the parameters obtained using DTI change during the growth process. We also wanted to identify if the DTI values change on the course of the spinal cord. The model organism was a healthy growing porcine spinal cord (19 pigs, Polish White, weight 24-120 kg, mean 48 kg, median 48 kg, age 2.5-11 months, mean 5 months, median 5.5 months). DTI parameters were measured in three weight groups: up to 29 kg (five pigs), 30-59 kg (six pigs), and from 60 kg up (eight pigs). DTI was performed with a 1.5 Tesla magnetic resonance scanner (Philips, Ingenia). Image post-processing was done using the Fiber Track package (Philips Ingenia workstation) by manually drawing the regions of interest (nine ROIs). The measurements were recorded for three sections: the cervical, thoracolumbar and lumbar segments of the spinal cord at the C4/C5, Th13/L1, and L4/L5 vertebrae levels. In each case, one segment was measured cranially and one caudally from the above-mentioned places. The values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were obtained for each ROIs and compared. It is shown that there is a correlation between age, weight gain, and change in FA and ADC parameters. Moreover, it is noted that, with increasing weight and age, the FA parameter increases and ADC decreases, whereas the FA and ADC measurement values did not significantly change between the three sections of the spinal cord. These findings could be useful in determining the reference values for the undamaged spinal cords of animals and growing humans.

Electrical stimulation for the treatment of spinal cord injuries: A review of the cellular and molecular mechanisms that drive functional improvements

Spinal cord injury (SCI) is a devastating condition that causes severe loss of motor, sensory and autonomic functions. Additionally, many individuals experience chronic neuropathic pain that is often refractory to interventions. While treatment options to improve outcomes for individuals with SCI remain limited, significant research efforts in the field of electrical stimulation have made promising advancements. Epidural electrical stimulation, peripheral nerve stimulation, and functional electrical stimulation have shown promising improvements for individuals with SCI, ranging from complete weight-bearing locomotion to the recovery of sexual function. Despite this, there is a paucity of mechanistic understanding, limiting our ability to optimize stimulation devices and parameters, or utilize combinatorial treatments to maximize efficacy. This review provides a background into SCI pathophysiology and electrical stimulation methods, before exploring cellular and molecular mechanisms suggested in the literature. We highlight several key mechanisms that contribute to functional improvements from electrical stimulation, identify gaps in current knowledge and highlight potential research avenues for future studies.

Clinical characteristics and treatment of spinal cord injury in children and adolescents

Pediatric and adult spinal cord injuries (SCI) are distinct entities. Children and adolescents with SCI must suffer from lifelong disabilities, which is a heavy burden on patients, their families and the society. There are differences in Chinese and foreign literature reports on the incidence, injury mechanism and prognosis of SCI in children and adolescents. In addition to traumatic injuries such as car accidents and falls, the proportion of sports injuries is increasing. The most common sports injury is the backbend during dance practice. Compared with adults, children and adolescents are considered to have a greater potential for neurological improvement. The pathogenesis and treatment of pediatric SCI remains unclear. The mainstream view is that the mechanism of nerve damage in pediatric SCI include flexion, hyperextension, longitudinal distraction and ischemia. We also discuss the advantages and disadvantages of drugs such as methylprednisolone in the treatment of pediatric SCI and the indications and timing of surgery. In addition, the complications of pediatric SCI are also worthy of attention. New imaging techniques such as diffusion tensor imaging and diffusion tensor tractography may be used for diagnosis and assessment of prognosis. This article reviews the epidemiology, pathogenesis, imaging, clinical characteristics, treatment and complications of SCI in children and adolescents. Although current treatment cannot completely restore neurological function, patient quality of life can be enhanced. Continued developments and advances in the research of SCI may eventually provide a cure for children and adolescents with this kind of injury.

Role of diffusion tensor imaging and tractography in spinal cord injury

Spinal cord injuries pose grave medical and socioeconomic burdens warranting measures for early diagnosis, triaging, prognostication and therapeutics. Imaging has since long played a pivotal role in this regard, with continuing research and technological advancements opening newer frontiers. One such advanced Magnetic resonance (MR) technique is Diffusion tensor imaging (DTI) which assesses cord microstructure by tracking the movement of water molecules in biological tissues. DTI utilizes the principle of anisotropy exhibited by the normal compact white matter (WM) tracts of the cord, in which direction-dependent water molecular motion is seen along the axonal axis. Disruption of this complex structure in response to injury alters the movement of these molecules, interrupting anisotropy and thereby DTI metrics. Evaluation of DTI images can be done both by quantitative indices, of which fractional anisotropy (FA) and mean diffusivity (MD) are the most commonly used and by qualitative fiber tracking (tractography) methods in which three-dimensional WM tracts are reconstructed by algorithmic post-processing. Reduced FA is consistently seen at injury sites as a direct consequence of disturbance of anisotropy. Diffusivity values are however more variable with both high and low values recorded across studies. 3D tractography images allow visual assessment of cord integrity, morphology, and orientation. Significant correlation is found between DTI parameters and various spinal injury scores. Furthermore, DTI also helps in accurate lesion mapping and in assessing cord changes distant from injury epicenter providing a holistic evaluation. From its inception, consistent progress in the understanding and application of DTI has effectuated its clinical utility and impact. Incorporation into day-to-day diagnostics is however still challenging, due to suboptimal image acquisition, difficult post-processing, and lack of standardized protocols & image interpretation guidelines. Further research with technical validation, development of normative and disease data sets, and histological confirmation will help establish this novel technique in routine diagnostics.

Assessment of acute traumatic cervical spinal cord injury using conventional magnetic resonance imaging in combination with diffusion tensor imaging-tractography: a retrospective comparative study

PURPOSE

The application of conventional magnetic resonance imaging (MRI) in combination with diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) to diagnose acute traumatic cervical SCI has not been studied. This study explores the role of MRI with DTI-DTT in the diagnosis of acute traumatic cervical spinal cord injury (SCI).

METHODS

Thirty patients with acute traumatic cervical SCI underwent conventional MRI and DTI-DTT. Conventional MRI was used to detect the intramedullary lesion length (IMLL) and intramedullary hemorrhage length (IMHL). DTI was used to detect the spinal cord's fractional anisotropy (FA) and apparent diffusion coefficient value, and DTT detected the imaginary white matter fiber volume and the connection rates of fiber tractography (CRFT). Patients' neurological outcome was determined using the American Spinal Injury Association (ASIA) Impairment Scale (AIS) grades.

RESULTS

Patients were divided into group A (without AIS grade conversion) and group B (with AIS grade conversion). The IMLL and IMHL of group A were significantly higher than those of group B. The FA and CRFT of group A were significantly lower than those of group B. The final AIS grade was negatively correlated with the IMLL and IMHL, and positively correlated with the FA and CRFT. According to imaging features based on conventional MRI and DTI-DTT, we propose a novel classification and diagnostic procedure.

CONCLUSIONS

The combination of conventional MRI with DTI-DTT is a valid diagnostic approach for SCI. Lower IMLL and IMHL, and higher FA value and CRFT are linked to better neurological outcomes.

Clinical Utility of Diffusion Tensor Imaging as a Biomarker to Identify Microstructural Changes in Pediatric Spinal Cord Injury

Background

Lack of clarity about the neurological consequence of spinal cord injury (SCI) in children causes speculation about diagnoses, recovery potential, and treatment effectiveness. Diffusion tensor imaging (DTI) has shown promising results as a biomarker to evaluate spinal cord integrity at a microstructural level.

Objectives

To look at the difference between pediatric participants with and without SCI to determine which DTI metrics best categorize spinal cord tissue damage and to correlate DTI metrics with two clinical measures: Capabilities of the Upper Extremity Test (CUE-T) and Spinal Cord Independence Measure version III (SCIM-III).

Methods

This single-site, prospective study included pediatric participants with SCI (n = 26) and typically developed (TD) control subjects (n = 36). All participants underwent two magnetic resonance imaging (MRI) scans on a 3T MR scanner. Participants with SCI also completed the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), CUE-T, and SCIM-III outcomes measures.

Results

This study found significant strength of association between fractional anisotropy (FA) and upper extremity muscle strength (UEMS) in participants with SCI. Most DTI parameters showed a significant difference between participants with SCI and TD participants and a moderate correlation with the CUE-T total score. Regional effects on group differences were found to be significant.

Conclusion

This study demonstrates the strength of association between DTI parameters and clinical measures in the pedantic SCI population. It illustrates DTI as a potential biomarker of SCI location and severity in the pediatric SCI population.

Segmented quantitative diffusion tensor imaging evaluation of acute traumatic cervical spinal cord injury

OBJECTIVES

To evaluate segmented diffusion tensor imaging (DTI) white matter tract fractional anisotropy (FA) and mean diffusivity (MD) values in acute cervical spinal cord injury (CSCI).

METHODS

15 patients with acute CSCI and 12 control subjects were prospectively recruited and underwent axial DTI as part of the spine trauma MRI. Datasets were put through a semi-automated probabilistic segmentation algorithm that analyzed white matter, motor and sensory tracts. FA and MD values were calculated for white matter, sensory (spinal lemniscal) and motor tracts (ventral/lateral corticospinal) at the level of clinical injury, levels remote from injury and in normal controls.

RESULTS

There were significant differences in FA between the level of injury and controls for total white matter (0.65 ± .09 vs 0.68 ± .07; p = .044), motor tracts (0.64 ± .07 vs 0.7 ± .09; p = .006), and combined motor/sensory tracts (0.63 ± .09 vs 0.69 ± .08; p = .022). In addition, there were significant FA differences between the level of injury and one level caudal to the injury for combined motor tracts (0.64 ± .07 vs 0.69 ± .05; p = .002) and combined motor/sensory tracts (0.63 ± .09 vs 0.7 ± .07; p = .011). There were no significant differences for MD between the level of injury and one level caudal to the injury or normal controls.

CONCLUSION

Abnormalities in DTI metrics of DTI-segmented white matter tracts were detected at the neurological level of injury relative to normal controls and levels remote from the injury site, confirming its value in CSCI assessment.

ADVANCES IN KNOWLEDGE

Segmented DTI analysis can help identify microstructural spinal cord abnormalities in the setting of traumatic cervical spinal cord injury.

Reliability of pre-operative diffusion tensor imaging parameter measurements of the cervical spine in patients with cervical spondylotic myelopathy

The present study assessed test–retest and inter-observer reliability of diffusion tensor imaging (DTI) in cervical spondylotic myelopathy (CSM), as well as the agreement among measurement methods. A total 34 patients (12 men, 22 women; mean age, 58.7 [range 45–79] years) who underwent surgical decompression for CSM, with pre-operative DTI scans available, were retrospectively enrolled. Four observers independently measured fractional anisotropy (FA) values twice, using three different measurement methods. Test–retest and inter-observer reliability was assessed using intraclass correlation coefficients (ICCs). Overall, inter-observer agreements varied according to spinal cord level and the measurement methods used, and ranged from poor to excellent agreement (ICC = 0.374–0.821), with relatively less agreement for the sagittal region of interest (ROI) method. The radiology resident and neuro-radiologist group showed excellent test–retest reliability at almost every spinal cord level (ICC = 0.887–0.997), but inter-observer agreements varied from fair to good (ICC = 0.404–0.747). Despite excellent test–retest reliability of the ROI measurements, FA measurements in patients with CSM varied widely in terms of inter-observer reliability. Therefore, DTI parameter data should be interpreted carefully when applied clinically.

Dynamic correlation of diffusion tensor imaging and neurological function scores in beagles with spinal cord injury

Exploring the relationship between different structure of the spinal cord and functional assessment after spinal cord injury is important. Quantitative diffusion tensor imaging can provide information about the microstructure of nerve tissue and can quantify the pathological damage of spinal cord white matter and gray matter. In this study, a custom-designed spinal cord contusion-impactor was used to damage the T₁₀ spinal cord of beagles. Diffusion tensor imaging was used to observe changes in the whole spinal cord, white matter, and gray matter, and the Texas Spinal Cord Injury Score was used to assess changes in neurological function at 3 hours, 24 hours, 6 weeks, and 12 weeks after injury. With time, fractional anisotropy values after spinal cord injury showed a downward trend, and the apparent diffusion coefficient, mean diffusivity, and radial diffusivity first decreased and then increased. The apparent diffusion-coefficient value was highly associated with the Texas Spinal Cord Injury Score for the whole spinal cord (R = 0.919, P = 0.027), white matter (R = 0.932, P = 0.021), and gray matter (R = 0.882, P = 0.048). Additionally, the other parameters had almost no correlation with the score (P > 0.05). In conclusion, the highest and most significant correlation between diffusion parameters and neurological function was the apparent diffusion-coefficient value for white matter, indicating that it could be used to predict the recovery of neurological function accurately after spinal cord injury.

Test-Retest and Interreader Reproducibility of Semiautomated Atlas-Based Analysis of Diffusion Tensor Imaging Data in Acute Cervical Spine Trauma in Adult Patients

BACKGROUND AND PURPOSE

DTI is a tool for microstructural spinal cord injury evaluation. This study evaluated the reproducibility of a semiautomated segmentation algorithm of spinal cord DTI.

MATERIALS AND METHODS

Forty-two consecutive patients undergoing acute trauma cervical spine MR imaging underwent 2 axial DTI scans in addition to their clinical scan. The datasets were put through a semiautomated probabilistic segmentation algorithm that selected white matter, gray matter, and 24 individual white matter tracts. Regional and white matter tract volume, fractional anisotropy, and mean diffusivity values were calculated. Two readers performed the nonautomated steps to evaluate interreader reproducibility. The coefficient of variation and intraclass correlation coefficient were used to assess test-retest and interreader reproducibility.

RESULTS

Of 42 patients, 30 had useable data. Test-retest reproducibility of fractional anisotropy was high for white matter as a whole (coefficient of variation, 3.8%; intraclass correlation coefficient, 0.93). Test-retest coefficient-of-variation ranged from 8.0%-18.2% and intraclass correlation coefficients from 0.47-0.80 across individual white matter tracts. Mean diffusivity metrics also had high test-retest reproducibility (white matter: coefficient-of-variation, 5.6%; intraclass correlation coefficient, 0.86) with coefficients of variation from 11.6%-18.3% and intraclass correlation coefficients from 0.57-0.74 across individual tracts, with better agreement for larger tracts. The coefficients of variation of fractional anisotropy and mean diffusivity both had significant negative relationships with white matter volume (26%-27% decrease for each doubling of white matter volume, P < .01).

CONCLUSIONS

DTI spinal cord segmentation is reproducible in the setting of acute spine trauma, specifically for larger white matter tracts and total white or gray matter.

Diffusion Tensor Imaging of the Spinal Cord: Clinical Value, Investigational Applications, and Technical Limitations

Although diffusion-weighted imaging (DWI) has become a mainstay in modern brain imaging, it remains less utilized in the evaluation of the spinal cord. Many studies have shown promise in using DWI and diffusion-tensor imaging (DTI) for evaluation of the spinal cord; however, application has been stalled by technical obstacles and artifacts, and questions remain regarding its clinical utility on an individual examination level. This review discusses the background, concepts, and technical aspects of DWI and DTI, specifically for imaging of the spinal cord. The clinical and investigational applications of spinal cord DTI, as well as the practical difficulties and limitations of DWI and DTI for the evaluation of the spinal cord are examined.

Feasibility of Diffusion Tensor Imaging for Assessing Functional Recovery in Rats with Olfactory Ensheathing Cell Transplantation After Contusive Spinal Cord Injury (SCI)

Background

Olfactory ensheathing cell transplantation is a promising treatment for spinal cord injury. Diffusion tensor imaging has been applied to assess various kinds of spinal cord injury. However, it has rarely been used to evaluate the beneficial effects of olfactory ensheathing cell transplantation. This study aimed to explore the feasibility of diffusion tensor imaging in the evaluation of functional recovery in rats with olfactory ensheathing cell transplantation after contusive spinal cord injury.

Material/Methods

Immunofluorescence staining was performed to determine the purity of olfactory ensheathing cells. Rats received cell transplantation at week 1 after injury. Basso, Beattie, and Bresnahan score was used to assess the functional recovery. Magnetic resonance imaging was applied weekly, including diffusion tensor imaging. Diffusion tensor tractography was reconstructed to visualize the repair process.

Results

The results showed that olfactory ensheathing cell transplantation increased the functional and histological recovery and restrained the secondary injury process after the initial spinal cord injury. The fractional anisotropy values in rats with cell transplantation were significantly higher than those in the control group, while the apparent diffusion coefficient values were significantly lower. Basso, Beattie, and Bresnahan score was positively and linearly correlated with fractional anisotropy value, and it was negatively and linearly correlated with apparent diffusion coefficient value.

Conclusions

These findings suggest that diffusion tensor imaging parameters are sensitive biomarker indices for olfactory ensheathing cell transplantation interventions, and diffusion tensor imaging scan can reflect the functional recovery promoted by the olfactory ensheathing cell transplantation after contusive spinal cord injury.

Comparison of Preoperative Quantitative Magnetic Resonance Imaging and Clinical Assessment of Deep Pain Perception as Prognostic Tools for Early Recovery of Motor Function in Paraplegic Dogs with Intervertebral Disk Herniations

Background

Prognostic tools to predict early postoperative motor function recovery (MFR) after thoracolumbar intervertebral disk herniation (IVDH) in paraplegic dogs represent an opportunity to timely implement novel therapies that could shorten recovery times and diminish permanent neurological dysfunctions.

Hypothesis

Fractional anisotropy (FA) values obtained using diffusion tensor imaging have a higher prognostic value than a lesion extension ratio in T2‐weighted images (T2W‐LER) and clinical assessment of deep pain perception (DPP) for MFR.

Animals

Thirty‐five paraplegic dogs with diagnosis of acute or subacute thoracolumbar IVDH.

Methods

Prospective, descriptive observational study. At admission, absence or presence of DPP, T2W‐LER, and FA values was evaluated. MFR was assessed within 4 weeks after decompressive surgery. Values of T2W‐LER and FA of dogs with and without MFR were compared using t‐tests. All 3 methods were evaluated for their sensitivity and specificity as a prognostic factor.

Results

No differences were found between groups regarding T2W‐LER. FA values differed statistically when measured caudally of lesion epicenter being higher in dogs without MFR compared to dogs with MFR (P = .023). Logistic regression analysis revealed significance in FA values measured caudally of the lesion epicenter (P = .033, area under the curve = 0.72). Using a cutoff value of FA = 0.660, the technique had a sensitivity of 80% and a specificity of 55%. Evaluation of DPP had a sensitivity of 73.3% and specificity of 75% (P = .007).

Conclusions and Clinical Importance

Evaluation of DPP showed a similar sensitivity and a better specificity predicting early MFR than quantitative magnetic resonance imaging.

Manganese-enhanced MRI Offers Correlation with Severity of Spinal Cord Injury in Experimental Models

BACKGROUND

Spinal cord injuries (SCI) are clinically challenging, because neural regeneration after cord damage is unknown. In SCI animal models, regeneration is evaluated histologically, requiring animal sacrifice. Noninvasive techniques are needed to detect longitudinal SCI changes.

OBJECTIVE

To compare manganese-enhanced magnetic resonance imaging (MRI [MEMRI]) in hemisection and transection of SCI rat models with diffusion tensor imaging (DTI) and histology.

METHODS

Rats underwent T9 spinal cord transection (n=6), hemisection (n=6), or laminectomy without SCI (controls, n=6). One-half of each group received lateral ventricle MnCl₂ injections 24 hours later. Conventional DTI or T1-weighted MRI was performed 84 hours post-surgery. MEMRI signal intensity ratio above and below the SCI level was calculated. Fractional anisotropy (FA) measurements were taken 1 cm rostral to the SCI. The percentage of FA change was calculated 10 mm rostral to the SCI epicenter, between FA at the dorsal column lesion normalized to a lateral area without FA change. Myelin load (percentage difference) among groups was analyzed by histology.

RESULTS

In transection and hemisection groups, mean MEMRI ratios were 0.62 and 0.87, respectively, versus 0.99 in controls (P<0.001 and P<0.001, respectively); mean FA decreases were 67.5% and 40.1%, respectively, compared with a 6.1% increase in controls (P=0.002 and P=0.019, respectively). Mean myelin load decreased by 38.8% (transection) and 51.8% (hemisection) compared to controls (99.1%) (P<0.001 and P<0.001, respectively). Pearson's correlation coefficients were -0.94 for MEMRI ratio and FA changes and 0.87 for MEMRI and myelin load.

CONCLUSION

MEMERI results correlated to SCI severity measured by FA and myelin load. MEMRI is a useful noninvasive tool to assess neuronal damage after SCI.

Diffusion Tensor Imaging of the Normal Cervical and Thoracic Pediatric Spinal Cord

BACKGROUND AND PURPOSE

DTI data of the normal healthy spinal cord in children are limited compared with adults and are typically focused on the cervical spinal cord. The purpose of this study was the following: to investigate the feasibility of obtaining repeatable DTI parameters along the entire cervical and thoracic spinal cord as a function of age in typically developing pediatric subjects; to analyze the DTI parameters among different transverse levels of the cervical and thoracic spinal cord; and to examine the sex differences in DTI parameters along the cervical and thoracic spinal cord.

MATERIALS AND METHODS

Twenty-two subjects underwent 2 identical scans by using a 3T MR imaging scanner. Axial diffusion tensor images were acquired by using 2 overlapping slabs to cover the cervical and thoracic spinal cord. After postprocessing, DTI parameters were calculated by using ROIs drawn on the whole cord along the entire spinal cord for both scans.

RESULTS

An increase in fractional anisotropy and a decrease in mean diffusivity, axial diffusivity, and radial diffusivity were observed with age along the entire spinal cord. Significantly lower fractional anisotropy and higher mean diffusivity values were observed in the lower cervical cord compared with the upper cervical cord. Axial diffusivity values in the cervical cord were higher compared with the thoracic cord. No statistically significant sex differences were observed for all DTI parameters. There was a moderate-to-strong repeatability for all DTI parameters.

CONCLUSIONS

This study provides an initial understanding of DTI values of the spinal cord relevant to age and sex and shows that obtaining repeatable DTI values of the entire cord in children is feasible.

IVIg attenuates complement and improves spinal cord injury outcomes in mice

Objective

Traumatic spinal cord injury (SCI) elicits immediate neural cell death, axonal damage, and disruption of the blood–spinal cord barrier, allowing circulating immune cells and blood proteins into the spinal parenchyma. The inflammatory response to SCI involves robust complement system activation, which contributes to secondary injury and impairs neurological recovery. This study aimed to determine whether intravenous immunoglobulin (IVIg), an FDA‐approved treatment for inflammatory conditions, can scavenge complement activation products and improve recovery from contusive SCI.

Methods

We used functional testing, noninvasive imaging, and detailed postmortem analysis to assess whether IVIg therapy is effective in a mouse model of severe contusive SCI.

Results

IVIg therapy at doses of 0.5–2 g/kg improved the functional and histopathological outcomes from SCI, conferring protection against lesion enlargement, demyelination, central canal dilation, and axonal degeneration. The benefits of IVIg were detectable through noninvasive diffusion tensor imaging (DTI), with IVIg treatment counteracting the progressive SCI‐induced increase in radial diffusivity (RD) in white matter. Diffusion indices significantly correlated with the functional performance of individual mice and accurately predicted the degree of myelin preservation. Further experiments revealed that IVIg therapy reduced the presence of complement activation products and phagocytically active macrophages at the lesion site, providing insight as to its mechanisms of action.

Interpretation

Our findings highlight the potential of using IVIg as an immunomodulatory treatment for SCI, and the value of DTI to assess tissue damage and screen for the efficacy of candidate intervention strategies in preclinical models of SCI, both quantitatively and noninvasively.

Diffusion tensor imaging of the cervical spinal cord in children

PURPOSE

Obtaining fast, reliable, high-resolution diffusion tensor imaging (DTI) of the pediatric cervical spinal cord (CSC) is challenging, given the multitude of technical limitations involved. Overcoming these limitations may further potentiate DTI as a valuable quantitative tool in evaluating the pediatric CSC.

METHODS

Sixteen patients (9 girls and 7 boys) with hypoxic brain injury, craniocervical junction malformations, and head trauma were included in this retrospective study. Region of interests were placed from C1-C2 through C7-T1 consecutively at the cervical intervertebral disc levels. DTI metrics were compared with a pediatric DTI database of healthy controls. Clinical background and outcomes were tabulated.

RESULTS

Patients with hypoxic brain injury, Chiari I and II malformations, and head trauma demonstrated lower fractional anisotropy values than that of healthy controls at certain cervical intervertebral disc levels.

CONCLUSIONS

DTI may be a promising modality for providing additional information beyond that of conventional magnetic resonance imaging in pediatric central nervous system disorders.

Feasibility of 3.0 T diffusion-weighted nuclear magnetic resonance imaging in the evaluation of functional recovery of rats with complete spinal cord injury

Diffusion tensor imaging is a sensitive way to reflect axonal necrosis and degeneration, glial cell regeneration and demyelination following spinal cord injury, and to display microstructure changes in the spinal cord in vivo. Diffusion tensor imaging technology is a sensitive method to diagnose spinal cord injury; fiber tractography visualizes the white matter fibers, and directly displays the structural integrity and resultant damage of the fiber bundle. At present, diffusion tensor imaging is restricted to brain examinations, and is rarely applied in the evaluation of spinal cord injury. This study aimed to explore the fractional anisotropy and apparent diffusion coefficient of diffusion tensor magnetic resonance imaging and the feasibility of diffusion tensor tractography in the evaluation of complete spinal cord injury in rats. The results showed that the average combined scores were obviously decreased after spinal cord transection in rats, and then began to increase over time. The fractional anisotropy scores after spinal cord transection in rats were significantly lower than those in normal rats (P < 0.05); the apparent diffusion coefficient was significantly increased compared with the normal group (P < 0.05). Following spinal cord transection, fractional anisotropy scores were negatively correlated with apparent diffusion coefficient values (r = -0.856, P < 0.01), and positively correlated with the average combined scores (r = 0.943, P < 0.01), while apparent diffusion coefficient values had a negative correlation with the average combined scores (r = -0.949, P < 0.01). Experimental findings suggest that, as a non-invasive examination, diffusion tensor magnetic resonance imaging can provide qualitative and quantitative information about spinal cord injury. The fractional anisotropy score and apparent diffusion coefficient have a good correlation with the average combined scores, which reflect functional recovery after spinal cord injury.

Does diffusion tensor data reflect pathological changes in the spinal cord with chronic injury

Magnetic resonance diffusion tensor imaging has been shown to quantitatively measure the early pathological changes in chronic cervical spondylotic myelopathy. In this study, a novel spongy polyurethane material was implanted in the rat C_3–5 epidural space to establish a rat model of chronic cervical spondylotic myelopathy. Diffusion tensor data were used to predict pathological changes. Results revealed that the fractional anisotropy value gradually decreased at 4, 24, and 72 hours and 1 week after injury in rat spinal cord, showing a time-dependent manner. Average diffusion coefficient increased at 72 hours and 1 week after implantation. Hematoxylin-eosin staining and Luxol-fast-blue staining exhibited that the number of neurons in the anterior horn of the spinal cord gray matter and the nerve fiber density of the white matter gradually reduced with prolonged compression time. Neuronal loss was most significant at 1 week after injury. Results verified that the fractional anisotropy value and average diffusion coefficient reflected the degree of pathological change in the site of compression in rat models at various time points after chronic spinal cord compression injury, which potentially has a reference value in the early diagnosis of chronic cervical spondylotic myelopathy.

Framework for integrated MRI average of the spinal cord white and gray matter: the MNI-Poly-AMU template

The field of spinal cord MRI is lacking a common template, as existing for the brain, which would allow extraction of multi-parametric data (diffusion-weighted, magnetization transfer, etc.) without user bias, thereby facilitating group analysis and multi-center studies. This paper describes a framework to produce an unbiased average anatomical template of the human spinal cord. The template was created by co-registering T2-weighted images (N = 16 healthy volunteers) using a series of pre-processing steps followed by non-linear registration. A white and gray matter probabilistic template was then merged to the average anatomical template, yielding the MNI-Poly-AMU template, which currently covers vertebral levels C1 to T6. New subjects can be registered to the template using a dedicated image processing pipeline. Validation was conducted on 16 additional subjects by comparing an automatic template-based segmentation and manual segmentation, yielding a median Dice coefficient of 0.89. The registration pipeline is rapid (~15 min), automatic after one C2/C3 landmark manual identification, and robust, thereby reducing subjective variability and bias associated with manual segmentation. The template can notably be used for measurements of spinal cord cross-sectional area, voxel-based morphometry, identification of anatomical features (e.g., vertebral levels, white and gray matter location) and unbiased extraction of multi-parametric data.

Diffusion tensor imaging as a predictor of locomotor function after experimental spinal cord injury and recovery

Traumatic spinal cord injury (SCI) causes long-term disability with limited functional recovery linked to the extent of axonal connectivity. Quantitative diffusion tensor imaging (DTI) of axonal integrity has been suggested as a potential biomarker for prognostic and therapeutic evaluation after trauma, but its correlation with functional outcomes has not been clearly defined. To examine this application, female Sprague-Dawley rats underwent midthoracic laminectomy followed by traumatic spinal cord contusion of differing severities or laminectomy without contusion. Locomotor scores and hindlimb kinematic data were collected for 4 weeks post-injury. Ex vivo DTI was then performed to assess axonal integrity using tractography and fractional anisotropy (FA), a numerical measure of relative white matter integrity, at the injury epicenter and at specific intervals rostral and caudal to the injury site. Immunohistochemistry for tissue sparing was also performed. Statistical correlation between imaging data and functional performance was assessed as the primary outcome. All injured animals showed some recovery of locomotor function, while hindlimb kinematics revealed graded deficits consistent with injury severity. Standard T2 magnetic resonance sequences illustrated conventional spinal cord morphology adjacent to contusions while corresponding FA maps indicated graded white matter pathology within these adjacent regions. Positive correlations between locomotor (Basso, Beattie, and Bresnahan score and gait kinematics) and imaging (FA values) parameters were also observed within these adjacent regions, most strongly within caudal segments beyond the lesion. Evaluation of axonal injury by DTI provides a mechanism for functional recovery assessment in a rodent SCI model. These findings suggest that focused DTI analysis of caudal spinal cord should be studied in human cases in relationship to motor outcome to augment outcome biomarkers for clinical cases.

Diffusion tensor imaging of the cervical spinal cord in healthy adult population: normative values and measurement reproducibility at 3T MRI

BACKGROUND

Compared to diffusion tensor imaging (DTI) of the brain, there is a paucity of reports addressing the applicability of DTI in the evaluation of the spinal cord. Most normative data of cervical spinal cord DTI consist of relatively small and arbitrarily collected populations. Comprehensive normative data are necessary for clinical decision-making.

PURPOSE

To establish normal values for cervical spinal cord DTI metrics with region of interest (ROI)- and fiber tractography (FT)-based measurements and to assess the reproducibility of both measurement methods.

MATERIAL AND METHODS

Forty healthy adults underwent cervical spinal cord 3T MRI. Sagittal and axial conventional T2 sequences and DTI in the axial plane were performed. Whole cord fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were determined at different cervical levels from C2 to C7 using the ROI method. DTI metrics (FA, axial, and radial diffusivities based on eigenvalues λ1, λ2, and λ3, and ADC) of the lateral and posterior funicles were measured at C3 level. FA and ADC of the whole cord and the lateral and posterior funicles were also measured using quantitative tractography. Intra- and inter-observer variation of the measurement methods were assessed.

RESULTS

Whole cord FA values decreased and ADC values increased in the rostral to caudal direction from C2 to C7. Between the individual white matter funicles no statistically significant difference for FA or ADC values was found. Both axial diffusivity and radial diffusivity of both lateral funicles differed significantly from those of the posterior funicle. Neither gender nor age correlated with any of the DTI metrics. Intra-observer variation of the measurements for whole cord FA and ADC showed almost perfect agreement with both ROI and tractography-based measurements. There was more variation in measurements of individual columns. Inter-observer agreement varied from moderate to strong for whole cord FA and ADC.

CONCLUSION

Both ROI- and FT-based measurements are applicable methods yielding reproducible results for cervical spinal cord DTI metrics. Normative values for both measurement methods are presented.

Diffusion tensor imaging to guide surgical planning in intramedullary spinal cord tumors in children

INTRODUCTION

Intramedullary spinal cord neoplasms (ISCN) in children provide diagnostic, treatment and management dilemmas. Resection results in the best chance for disease control, but the greatest risk of neurologic deficit. We hypothesize that diffusion tensor imaging (DTI) and diffusion tensor-fiber tracking (DT-FT) can help characterize margins of pediatric ISCN to aid in surgical planning.

METHODS

This HIPAA compliant retrospective study was performed after Institutional Review Board approval. Patients with ISCN from a single tertiary care pediatric institution were identified, and patients with preoperative DTI were evaluated.

RESULTS

Ten patients (eight males and two females) with ISCN with preoperative DTI were identified. The mean age was 11.1 ± 6.2 years (range, 2-18 years). Eight tumors demonstrated DTI and DT-FT evidence of splayed cord tracts, and two demonstrated evidence of infiltration of cord tracts. The eight patients with splayed tracts underwent resection, with seven achieving gross-total resection and one subtotal resection. The two patients with infiltration of white matter tracts underwent biopsy of their lesion.

CONCLUSIONS

DTI of pediatric ISCN can aid in defining the margins of the tumor and relationship to the intrinsic white matter structures of the spinal cord. Splaying and displacement of fiber tracts appears to predict a discrete margin to the tumor and resectability, whereas infiltration of the white matter tracts suggests biopsy may be more advisable.

Hot topics in functional neuroradiology

Functional neuroradiology represents a relatively new and ever-growing subspecialty in the field of neuroradiology. Neuroradiology has evolved beyond anatomy and basic tissue signal characteristics and strives to understand the underlying physiologic processes of central nervous system disease. The American Society of Functional Neuroradiology sponsors a yearly educational and scientific meeting, and the educational committee was asked to suggest a few cutting-edge functional neuroradiology techniques (hot topics). The following is a review of several of these topics and includes "Diffusion Tensor Imaging of the Pediatric Spinal Cord"; "Diffusional Kurtosis Imaging"; "From Standardization to Quantification: Beyond Biomarkers toward Bioscales as Neuro MR Imaging Surrogates of Clinical End Points"; Resting-State Functional MR Imaging"; and "Current Use of Cerebrovascular Reserve Imaging."

Assessing the state of chronic spinal cord injury using diffusion tensor imaging

The aim of this study was to quantify the association between diffusion tensor imaging (DTI) parameters of the cervical spinal cord and neurological disability in patients with chronic traumatic spinal cord injury (SCI). A cervical spinal cord 3T magnetic resonance imaging (MRI) with DTI sequences was performed on 28 patients with chronic traumatic SCI and 40 healthy control subjects. DTI metrics, including fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD), and radial diffusivity (RD), were calculated within the normal-appearing spinal cord area at levels C2 or C3. Clinical assessment of the patients was performed according to the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) and the motor subscale of the Functional Independence Measure (FIM). The FA values of the patients with SCI were significantly lower than those of healthy control subjects (p<0.000001). In contrast, the ADC and RD values of these patients were significantly higher than those of control subjects (ADC p<0.0001, RD p<0.00001). In patients with SCI, the FA values were positively correlated with the motor (pr=0.56, p<0.01) and sensory (pr=0.66, p<0.001) scores of ISNCSCI and with the motor subscale of FIM (pr=0.51, p<0.01). DTI revealed spinal cord pathology, which was undetectable using conventional MRI. DTI changes in regions that were remote from the site of primary injury were most likely the result of secondary degeneration of white matter tracts. Decreased FA values were correlated with poorer motor and sensory function, as well as a lack of independence in daily living. DTI is a promising quantitative and objective tool that may be used in the clinical assessment of patients with SCI.

Longitudinal assessment of white matter pathology in the injured mouse spinal cord through ultra-high field (16.4 T) in vivo diffusion tensor imaging

This study examined the sensitivity of ultra-high field (16.4 T) diffusion tensor imaging (DTI; 70 μm in-plane resolution, 1mm slice thickness) to evaluate the spatiotemporal development of severe mid-thoracic contusive spinal cord injury (SCI) in mice. In vivo imaging was performed prior to SCI, then again at 2h, 1 day, 3 days, 7 days, and 30 days post-SCI using a Bruker 16.4 T small animal nuclear magnetic resonance spectrometer. Cross-sectional spinal cord areas were measured in axial slices and various DTI parameters, i.e. fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ||) and radial diffusivity (λ⊥), were calculated for the total spared white matter (WM), ventral funiculi (VF), lateral funiculi (LF) and dorsal columns (DCs) and then correlated with histopathology. Cross-sectional area measurements revealed significant atrophy (32% reduction) of the injured spinal cord at the lesion epicentre in the chronic phase of injury. Analysis of diffusion tensor parameters further showed that tissue integrity was most severely affected in the DCs, i.e. the site of immediate impact, which demonstrated a rapid and permanent decrease in FA and λ||. In contrast, DTI parameters for the ventrolateral white matter changed more gradually with time, suggesting that these regions are undergoing more delayed degeneration in a manner that may be amenable to therapeutic intervention. Of all the DTI parameters, λ⊥ was most closely correlated to myelin content whereas changes in FA and λ|| appeared more indicative of axonal integrity, Wallerian degeneration and associated presence of macrophages. We conclude that longitudinal DTI at 16.4T provides a clinically relevant, objective measure for assessing white matter pathology following contusive SCI in mice that may aid the translation of putative neuroprotective strategies into the clinic.

Diagnostic accuracy of diffusion tensor imaging for pediatric cervical spinal cord injury

STUDY DESIGN

Cross-sectional non-experimental study.

OBJECTIVES

To examine diagnostic accuracy of diffusion tensor imaging (DTI) for pediatric spinal cord injury (SCI).

SETTING

Pediatric Orthopedic Hospital.

METHODS

Thirty-five subjects, 10 SCI and 25 controls, mean age 13.38 years underwent two scans with 3.0 T MR scanner. Fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD) values were calculated. Subjects with SCI underwent examination of muscle strength, sensation and sacral sparing. Mean and s.d. values for FA, AD and RD were compared by group (controls, SCI with sacral sparing, SCI without sacral sparing) using analysis of variance for repeated measures. Comparisons were also made of DTI values at the injury site to values from cervical regions outside of the injury site. Specificity, sensitivity, receiver operating characteristics area under the curve (ROC AUC) and corresponding 95% confidence intervals were calculated. Resampling methods were used to validate the estimates from the final models.

RESULTS

FA values differed among SCI subjects with intact sacral sparing, absent sacral sparing and controls, P<0.003 (adjusted). DTI values in combination showed the strongest diagnostic accuracy for predicting the presence of anal contraction (AD, RD; ROC AUC=0.90), deep anal pressure (FA; ROC AUC=0.88), S4-5 sensation (FA, RD; ROC AUC=0.93), motor level (FA, AD, RD; ROC AUC=0.92) and MRI level (FA, AD, RD; ROC AUC=0.92). Bootstrap and Jackknife median values indicated consistency of the parameter estimates.

CONCLUSION

The predictive accuracy of DTI for sacral sparing end points and motor and MRI level of injury was good to strong.

The impact of post-processing on spinal cord diffusion tensor imaging

Diffusion tensor imaging (DTI) provides information about the microstructure in the brain and spinal cord. While new neuroimaging techniques have significantly advanced the accuracy and sensitivity of DTI of the brain, the quality of spinal cord DTI data has improved less. This is in part due to the small size of the spinal cord (ca. 1cm diameter) and more severe instrumental (e.g. eddy current) and physiological (e.g. cardiac pulsation) artefacts present in spinal cord DTI. So far, the improvements in image quality and resolution have resulted from cardiac gating and new acquisition approaches (e.g. reduced field-of-view techniques). The use of retrospective correction methods is not well established for spinal cord DTI. The aim of this paper is to develop an improved post-processing pipeline tailored for DTI data of the spinal cord with increased quality. For this purpose, we compared two eddy current and motion correction approaches using three-dimensional affine (3D-affine) and slice-wise registrations. We also introduced a new robust-tensor-fitting method that controls for whole-volume outliers. Although in general 3D-affine registration improves data quality, occasionally it can lead to misregistrations and biassed tensor estimates. The proposed robust tensor fitting reduced misregistration-related bias and yielded more reliable tensor estimates. Overall, the combination of slice-wise motion correction, eddy current correction, and robust tensor fitting yielded the best results. It increased the contrast-to-noise ratio (CNR) in FA maps by about 30% and reduced intra-subject variation in fractional anisotropy (FA) maps by 18%. The higher quality of FA maps allows for a better distinction between grey and white matter without increasing scan time and is compatible with any multi-directional DTI acquisition scheme.