MR diffusion tensor imaging and fiber tracking in spinal cord arteriovenous malformations: a preliminary study

Full cervical cord tractography: A new method for clinical use

Despite recent improvements in diffusion-weighted imaging, spinal cord tractography is not used in routine clinical practice because of difficulties in reconstructing tractograms, with a pertinent tri-dimensional-rendering, in a long post-processing time. We propose a new full tractography approach to the cervical spinal cord without extensive manual filtering or multiple regions of interest seeding that could help neurosurgeons manage various spinal cord disorders. Four healthy volunteers and two patients with either cervical intramedullary tumors or spinal cord injuries were included. Diffusion-weighted images of the cervical spinal cord were acquired using a Philips 3 Tesla machine, 32 diffusion directions, 1,000 s/mm²b-value, 2 × 2 × 2 mm voxel size, reduced field-of-view (ZOOM), with two opposing phase-encoding directions. Distortion corrections were then achieved using the FSL software package, and tracking of the full cervical spinal cord was performed using the DSI Studio software (quantitative anisotropy-based deterministic algorithm). A unique region of avoidance was used to exclude everything that is not of the nervous system. Fiber tracking parameters used adaptative fractional anisotropy from 0.015 to 0.045, fiber length from 10 to 1,000 mm, and angular threshold of 90°. In all participants, a full cervical cord tractography was performed from the medulla to the C7 spine level. On a ventral view, the junction between the medulla and spinal cord was identified with its pyramidal bulging, and by an invagination corresponding to the median ventral sulcus. On a dorsal view, the fourth ventricle—superior, middle, and inferior cerebellar peduncles—was seen, as well as its floor and the obex; and gracile and cuneate tracts were recognized on each side of the dorsal median sulcus. In the case of the intramedullary tumor or spinal cord injury, the spinal tracts were seen to be displaced, and this helped to adjust the neurosurgical strategy. This new full tractography approach simplifies the tractography pipeline and provides a reliable 3D-rendering of the spinal cord that could help to adjust the neurosurgical strategy.

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.

Effect of distortion corrections on the tractography quality in spinal cord diffusion-weighted imaging

PURPOSE

To assess the impact of a different distortion correction (DC) method and patient geometry (sagittal balance) on the quality of spinal cord tractography rendering according to different tractography approaches.

METHODS

Forty-four adults free of spinal cord diseases underwent cervical diffusion-weighted imaging. The phase-encoding direction was head→foot. Sequence with opposed polarities (foot→head) was acquired to perform DC. Eddy-current, motion effects, and susceptibility artifact correction methods were used for DC, and two deterministic and one probabilistic tractography approaches were evaluated using MRtrix and DSI Studio tractography software. Fiber length and number of fibers were extracted to evaluate the quality of the tractography rendering. For each subject, cervical lordosis was measured to assess patient geometry. The angle between the main direction of the spinal cord and the orientation of the acquisition box were computed at each spine level to assess acquisition geometry and define an angle threshold for which a tractography of good quality is no longer possible.

RESULTS

There was a significant improvement in tractography quality after performing DC with susceptibility artifact correction using a deterministic approach based on tensor. Before DC, the angle threshold was defined at C6 (15.2°) compared with C7 (21.9°) after corrections, demonstrating the importance of spinal cord angulation for DC.

CONCLUSION

The impact of DC on tractography quality is greatly impacted by acquisition geometry. To obtain a good-quality tractography, we propose as a future perspective to adapt the acquisition geometry to that of the patient by automatically adjusting the acquisition box.

Mapping the rest of the human connectome: Atlasing the spinal cord and peripheral nervous system

The emergence of diffusion, structural, and functional neuroimaging methods has enabled major multi-site efforts to map the human connectome, which has heretofore been defined as containing all neural connections in the central nervous system (CNS). However, these efforts are not structured to examine the richness and complexity of the peripheral nervous system (PNS), which arguably forms the (neglected) rest of the connectome. Despite increasing interest in an atlas of the spinal cord (SC) and PNS which is simultaneously stereotactic, interactive, electronically dissectible, scalable, population-based and deformable, little attention has thus far been devoted to this task of critical importance. Nevertheless, the atlasing of these complete neural structures is essential for neurosurgical planning, neurological localization, and for mapping those components of the human connectome located outside of the CNS. Here we recommend a modification to the definition of the human connectome to include the SC and PNS, and argue for the creation of an inclusive atlas to complement current efforts to map the brain's human connectome, to enhance clinical education, and to assist progress in neuroscience research. In addition to providing a critical overview of existing neuroimaging techniques, image processing methodologies and algorithmic advances which can be combined for the creation of a full connectome atlas, we outline a blueprint for ultimately mapping the entire human nervous system and, thereby, for filling a critical gap in our scientific knowledge of neural connectivity.

Reduced Field of View Diffusion Tensor Imaging and Fiber Tractography of the Pediatric Cervical and Thoracic Spinal Cord Injury

The aim of this study is to assess the utility and effectiveness of diffusion tensor imaging (DTI) and diffusion tensor tractography (DTT) of the entire pediatric cervical and thoracic spinal cord toward discrimination of typically developing (TD) controls and subjects with spinal cord injury (SCI). A total of 43 pediatric subjects, including 23 TD subjects ranging in age from 6 to 16 years old and 20 subjects with SCI ranging in age from 7 to 16 years, were recruited and scanned using a 3.0 Tesla magnetic resonance scanner. Reduced field of view diffusion tensor images were acquired axially to cover the entire spinal cord across two slabs. For DTI analysis, motion correction was performed by coregistration of the diffusion-weighted images to the reference image (b0). Streamline deterministic tractography results were generated from the preprocessed data. DTI and DTT parameters of the whole cord, including fractional anisotropy (FA), mean diffusivity (MD), tract length, and tract density, were calculated, averaged across the whole spinal cord, and compared between the TD and SCI groups. Statistically significant decreases have been shown in FA (TD = 0.46 ± 0.11; SCI = 0.37 ± 0.09; p < 0.0001) and tract density (TD = 405.93 ± 243.84; SCI = 268.90 ± 270.34; p < 0.0001). However, the mean length of tracts and MD did not show significant differences. When investigating differences in DTI and DTT parameters above and below the injury site, it was shown that the FA and tract density in patients with cervical SCI decreased significantly in the thoracic region. An identical trend was observed in the cervical region for patients with thoracic SCI as well. When comparing TD and SCI subjects, FA and tract density were the most sensitive parameters in detecting functional changes of the spinal cord in chronic pediatric SCI. The results show that both DTI and DTT have the potential to be imaging biomarkers in the diagnosis of SCI.

High-resolution diffusion tensor imaging in cervical spondylotic myelopathy: a preliminary follow-up study

Diffusion imaging is a promising technique as it can provide microstructural tissue information and thus potentially show viable changes in spinal cord. However, the traditional single-shot imaging method is limited as a result of various image artifacts. In order to improve measurement accuracy, we used a newly developed, multi-shot, high-resolution, diffusion tensor imaging (DTI) method to investigate diffusion metric changes and compare them with T₂ -weighted (T2W) images before and after decompressive surgery for cervical spondylotic myelopathy (CSM). T2W imaging, single-shot DTI and multi-shot DTI were employed to scan seven patients with CSM before and 3 months after decompressive surgery. High signal intensities were scored using the T2 W images. DTI metrics, including fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD), were quantified and compared pre- and post-surgery. In addition, the relationship between imaging metrics and neurological assessments was examined. The reproducibility of multi-shot DTI was also assessed in 10 healthy volunteers. Post-surgery, the mean grade of cervical canal stenosis was reduced from grade 3 to normal after 3 months. Compared with single-shot DTI, multi-shot DTI provided better images with lower artifact levels, especially following surgery, as a result of reduced artifacts from metal implants. The new method also showed acceptable reproducibility. Both FA and RD values from the new acquisition showed significant differences post-surgery (FA, p = 0.026; RD, p = 0.048). These changes were consistent with neurological assessments. In contrast, T2W images did not show significant changes before and after surgery. Multi-shot diffusion imaging showed improved image quality over single-shot DWI, and presented superior performance in diagnosis and recovery monitoring for patients with CSM compared with T2W imaging. DTI metrics can reflect the pathological conditions of spondylotic spinal cord quantitatively and may serve as a sensitive biomarker for potential CSM management.

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.

[Surgical treatment outcomes in children with tethered spinal cord syndrome. A prognosis on the basis of spinal 3T MRI tractography]

AIM

The study objective was to identify factors affecting surgical treatment outcomes in children with tethered cord syndrome (TCS).

MATERIAL AND METHODS

The study included 21 TCS patients aged 1 to 14 years who underwent tethered cord release. The preoperative and postoperative data of clinical and neurophysiological examination and high field (3T) MRI tractography of the caudal spinal cord were compared.

RESULTS

Regression of the TCS clinical and electrophysiological signs and the lack of pathological changes in the spinal cord tracts were observed in patients with filum terminale abnormalities and caudal lipomas after surgery. In patients with secondary spinal cord tethering caused by scar formation after lumbosacral myelomeningocele repair, a motor deficit was related to the interruption level of the spinal tracts, and surgical treatment did not lead to significant regression of the TCS clinical and electrophysiological signs.

CONCLUSION

We consider the absence of pathological changes in the caudal spinal cord, based on spinal MRI tractography, as a favorable prognostic factor in TCS surgical treatment.

Magnetic resonance diffusion tensor imaging and fiber-tracking diffusion tensor tractography in the management of spinal astrocytomas

Some specially imaging of magnetic resonance imaging, the diffusion-weighted imaging (DWI), the diffusion tensor imaging and fractional anisotropy (FA), are useful to described, detect, and map the extent of spinal cord lesions. FA measurements may are used to predicting the outcome of patients who have spinal cord lesions. Fiber tracking enable to visualizing the integrity of white matter tracts surrounding some lesions, and this information could be used to formulating a differential diagnosis and planning biopsies or resection. In this article, we will describe the current uses for DWI and fiber tracking and speculate on others in which we believe these techniques will be useful in the future.

Conus Medullaris Teratoma with Utilization of Fiber Tractography: Case Report

Objective Conus medullaris teratomas are very rare tumors. Traditional preoperative diagnosis depended on the findings from magnetic resonance imaging (MRI). Tractography is a novel technique that has recently been utilized to diagnose spinal cord lesions. This case report shows that fiber tractography has great potential in preoperative diagnosis and postoperative follow-up of teratomas of the conus medullaris.

Methods A 50-year-old man with a conus medullaris teratoma underwent tractography with the aim of visualizing the tumor in relation to the white matter tracts. The patient underwent a T12–L2 laminectomy, and the lesion was resected. The histopathology diagnosis was of a mature teratoma.

Study Design Case report.

Results Diffusion tensor imaging (DTI) and tractography provide more details about the white matter tracts in relation to space-occupying lesions that may be more sensitive than conventional MRI and have recently been utilized in spinal cord lesions. Fiber tracking has the ability to visualize the integrity of the white matter tracts at the level of the conus medullaris in relation to the lesion. The tracts appeared to be displaced by the lesion at the conus medullaris. Tractography also showed no white matter tracts within the lesion. Such findings are consistent with the characteristics of a benign lesion. Exploiting tractography in this case was helpful in predicting the nature of the lesion preoperatively and in planning the surgical intervention.

Conclusions Conus medullaris teratomas mostly affect adults. Patients generally present with a long history of clinical symptoms prior to diagnosis. Surgery is required for diagnosis, and the goal should be complete tumor excision without sacrificing any neurologic functions. The use of DTI and tractography, in addition to conventional MRI, has the potential to be very valuable for the diagnosis, surgical planning, and follow-up of patients with conus medullaris teratomas.

Correlation of diffusion tensor imaging and phase-contrast MR with clinical parameters of cervical spinal cord injuries

STUDY DESIGN

This is a cross-sectional study.

OBJECTIVES

The goal of this study was to characterize the diffusion properties across segments of the spinal cord and peak cerebrospinal fluid (CSF) velocities in the stenotic spinal canal, and to determine the correlation between these properties and clinical and electrophysiological parameters in patients with cervical spinal cord injury (SCI).

SETTING

This study was conducted in the University teaching hospital.

METHODS

The study involved 17 patients with cervical SCI. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the spinal cord and peak systolic and diastolic velocities of CSF were measured at the level of maximum compression (region 1) and at the levels above (region 2) and below (region 3) the level of injury with no signal change in conventional magnetic resonance imaging. Neurological and electrophysiological parameters were measured, including American Spinal Injury Association (ASIA) Impairment Scale (AIS), ASIA motor score, ASIA sensory score, Modified Barthel Index, Spinal Cord Independence Measure III (SCIM III), somatosensory evoked potentials (SSEP) and motor evoked potentials (MEP).

RESULTS

The ADC was significantly higher and the FA was significantly lower in regions 1, 2 and 3 of the SCI patients than in the normal controls (P<0.05 each). FA of the level below correlated with AIS, ASIA sensory score and SCIM III score, and FA of the level above correlated with SSEP latencies and MEP amplitudes (P<0.05 each). The reductions in FA correlated with CSF flow, functional measurements and evoked potentials.

CONCLUSIONS

Diffusion tensor imaging can be used to quantify the proximal and distal extents of spinal cord damage. Reductions in FA were correlated with CSF flow, functional measurements and evoked potentials.

MRI and MRA of spinal cord arteriovenous shunts

The purpose of this review is to describe the diagnostic criteria for spinal cord arteriovenous shunts (SCAVSs) when using magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA), and to discuss the extent to which the different MRI and MRA sequences and technical parameters provide the information that is required to diagnose these lesions properly. SCAVSs are divided into four groups according to location (paraspinal, epidural, dural, or intradural) and type (fistula or nidus); each type of lesion is described. SCAVSs are responsible for neurological symptoms due to spinal cord or nerve root involvement. MRI is usually the first examination performed when a spinal cord lesion is suspected. Recognition of the image characteristics of vascular lesions is mandatory if useful sequences are to be performed-especially MRA sequences. Because the treatment of SCAVSs relies mainly on endovascular therapies, MRI and MRA help with the planning of the angiographic procedure. We explain the choice of MRA sequences and parameters, the advantages and pitfalls to be aware of in order to obtain the best visualization, and the analysis of each lesion.

The current state-of-the-art of spinal cord imaging: applications

A first-ever spinal cord imaging meeting was sponsored by the International Spinal Research Trust and the Wings for Life Foundation with the aim of identifying the current state-of-the-art of spinal cord imaging, the current greatest challenges, and greatest needs for future development. This meeting was attended by a small group of invited experts spanning all aspects of spinal cord imaging from basic research to clinical practice. The greatest current challenges for spinal cord imaging were identified as arising from the imaging environment itself; difficult imaging environment created by the bone surrounding the spinal canal, physiological motion of the cord and adjacent tissues, and small crosssectional dimensions of the spinal cord, exacerbated by metallic implants often present in injured patients. Challenges were also identified as a result of a lack of "critical mass" of researchers taking on the development of spinal cord imaging, affecting both the rate of progress in the field, and the demand for equipment and software to manufacturers to produce the necessary tools. Here we define the current state-of-the-art of spinal cord imaging, discuss the underlying theory and challenges, and present the evidence for the current and potential power of these methods. In two review papers (part I and part II), we propose that the challenges can be overcome with advances in methods, improving availability and effectiveness of methods, and linking existing researchers to create the necessary scientific and clinical network to advance the rate of progress and impact of the research.

Spinal glomus (type II) arteriovenous malformations: a pooled analysis of hemorrhage risk and results of intervention

BACKGROUND

The natural history and treatment results for spinal glomus (type II) arteriovenous malformations (AVMs) remain relatively obscure.

OBJECTIVE

To calculate spinal glomus (type II) AVM hemorrhages rates and amalgamate results of intervention.

METHODS

We performed a pooled analysis via the PubMed database through May 2012, including studies with at least 3 cases. Data on individual patients were extracted and analyzed using a Cox proportional hazards regression model to obtain hazard ratios for hemorrhage risk factors.

RESULTS

The annual hemorrhage rate before treatment was 4% (95% confidence interval [confidence interval]: 3%-6%), increasing to 10% (95% CI: 7%-16%) for AVMs with previous hemorrhage. The hazard ratio for hemorrhage after hemorrhagic presentation was 2.25 (95% CI: 0.71-7.07), increasing to 13.0 within the first 10 years (95% CI: 1.44-118). The overall rates of complete obliteration were 78% (95% CI: 72%-83%) for surgery and 33% (95% CI: 24%-43%) for endovascular treatment. Long-term clinical worsening occurred in 12% of patients after surgical treatment (95% CI: 8%-16%) and in 13% after endovascular treatment (95% CI: 7%-21%). No hemorrhages occurred after complete obliteration. After partial surgical treatment, the annual hemorrhage rate was 3% (95% CI: 1%-6%); no hemorrhages were reported over 196 patient-years after partial endovascular treatment.

CONCLUSION

Spinal glomus (type II) AVMs with previous hemorrhage, particularly within 10 years, demonstrated a greater risk of hemorrhage. Complete obliteration and even partial endovascular treatment significantly decreased their hemorrhage rate.

Diffusion tensor imaging and tractography of the spinal cord: from experimental studies to clinical application

Diffusion-weighted magnetic resonance imaging provides detailed information about biological structures. In particular, diffusion tensor imaging and diffusion tensor tractography (DTT) are powerful tools for evaluating white matter fibers in the central nervous system. We previously established a reproducible spinal cord injury model in adult common marmosets and showed that DTT could be used to trace the neural tracts in the intact and injured spinal cord of these animals in vivo. Recently, many reports using DTT to analyze the spinal cord area have been published. Based on the findings from our experimental studies, we are now routinely performing DTT of the human spinal cord in the clinic. In this review we outline the basic principles of DTT, and describe the characteristics, limitations, and future uses of DTT to examine the spinal cord.

Spinal cord markers in ALS: diagnostic and biomarker considerations

Despite considerable involvement of the spinal cord in amyotrophic lateral sclerosis (ALS), current biomarker research is primarily centred on brain imaging and CSF proteomics. In clinical practice, spinal cord imaging in ALS is performed primarily to rule out alternative conditions in the diagnostic phase of the disease. Quantitative spinal cord imaging has traditionally been regarded as challenging, as it requires high spatial resolution while minimizing partial volume effects, physiological motion and susceptibility distortions. In recent years however, as acquisition and post-processing methods have been perfected, a number of exciting and promising quantitative spinal imaging and electrophysiology techniques have been developed. We performed a systematic review of the trends, methodologies, limitations and conclusions of recent spinal cord studies in ALS to explore the diagnostic and prognostic potential of spinal markers. Novel corrective techniques for quantitative spinal cord imaging are systematically reviewed. Recent findings demonstrate that imaging techniques previously used in brain imaging, such as diffusion tensor, functional and metabolic imaging can now be successfully applied to the human spinal cord. Optimized electrophysiological approaches make the non-invasive assessment of corticospinal pathways possible, and multimodal spinal techniques are likely to increase the specificity and sensitivity of proposed spinal markers. In conclusion, spinal cord imaging is an emerging area of ALS biomarker research. Novel quantitative spinal modalities have already been successfully used in ALS animal models and have the potential for development into sensitive ALS biomarkers in humans.

Diffusion tensor imaging of diffuse axonal injury in a rat brain trauma model

Diffusion tensor imaging (DTI) was used to study traumatic brain injury. The impact-acceleration trauma model was used in rats. Here, in addition to diffusivities (mean, axial and radial), fractional anisotropy (FA) was used, in particular, as a parameter to characterize the cerebral tissue early after trauma. DTI was implemented at 7 T using fast spiral k-space sampling and the twice-refocused spin echo radiofrequency sequence for eddy current minimization. The method was carefully validated on different phantom measurements. DTI of a trauma group (n = 5), as well as a sham group (n = 5), was performed at different time points during 6 h following traumatic brain injury. Two cerebral regions, the cortex and corpus callosum, were analyzed carefully. A significant decrease in diffusivity in the trauma group versus the sham group was observed, suggesting the predominance of cellular edema in both cerebral regions. No significant FA change was detected in the cortex. In the corpus callosum of the trauma group, the FA indices were significantly lower. A net discontinuity in fiber reconstructions in the corpus callosum was observed by fiber tracking using DTI. Histological analysis using Hoechst, myelin basic protein and Bielschowsky staining showed fiber disorganization in the corpus callosum in the brains of the trauma group. On the basis of our histology results and the characteristics of the impact-acceleration model responsible for the presence of diffuse axonal injury, the detection of low FA caused by a drastic reduction in axial diffusivity and the presence of fiber disconnections of the DTI track in the corpus callosum were considered to be related to the presence of diffuse axonal injury.

Diffusion tensor imaging and fiber tractography in cervical compressive myelopathy: preliminary results

OBJECTIVE

To assess diffusion tensor imaging (DTI) parameters in cervical compressive myelopathy (CCM) patients compared to normal volunteers, to relate them with myelopathy severity, and to relate tractography patterns with postoperative neurologic improvement.

SUBJECTS AND METHODS

Twenty patients suffering from CCM were prospectively enrolled (M:F = 13:7, mean age, 49.6 years; range 22-67 years) from September 2009 to March 2010. Sensitivity encoding (SENSE) single-shot echo-planar imaging (EPI) was used for the sagittal DTI. Twenty sex- and age-matched normal volunteers underwent the same scanning procedure. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values in the spinal cord were compared between the patients and normal volunteers and were related to myelopathy severity based on Japanese Orthopedic Association (JOA) scores. Tractography patterns were related to myelopathy severity and postoperative improvement.

RESULTS

There were significant differences between patients and normal volunteers in terms of FA (0.498 ± 0.114 vs. 0.604 ± 0.057; p = 0.001) and ADC (1.442 ± 0.389 vs. 1.169 ± 0.098; p = 0.001). DTI parameters and tractography patterns were not related to myelopathy severity. In ten patients in the neurologically worse group, postoperative neurologic improvement was seen in four of five patients with intact fiber tracts, but only one of five patients with interrupted fiber tracts exhibited neurologic improvement.

CONCLUSION

DTI parameters in CCM patients were significantly different from those in normal volunteers but were not significantly related to myelopathy severity. The patterns of tractography appear to correlate with postoperative neurologic improvement.

[Diffusion-weighted MR imaging of the spine and cord]

Due to its excellent sensitivity, MR imaging is invaluable for the evaluation of lesions of the cord and spine. Several studies dedicated to diffusion-weighted MR evaluation of the cord and spine have been published. While diffusion-weighted MR imaging of the brain is routinely performed, it is seldom performed when imaging the spine due to serious limitations. While anatomical limitations may not be changed, the voxel size, phase-encoding direction, mode of k-space filling, and acceleration factor are all parameters that can be optimized in order to routinely obtain diffusion-weighted imaging of the spine on 1.5T and 3T scanners.

Reproducibility of tract-specific magnetization transfer and diffusion tensor imaging in the cervical spinal cord at 3 tesla

Damage to specific white matter tracts within the spinal cord can often result in the particular neurological syndromes that characterize myelopathies such as traumatic spinal cord injury. Noninvasive visualization of these tracts with imaging techniques that are sensitive to microstructural integrity is an important clinical goal. Diffusion tensor imaging (DTI)- and magnetization transfer (MT)-derived quantities have shown promise in assessing tissue health in the central nervous system. In this paper, we demonstrate that DTI of the cervical spinal cord can reliably discriminate sensory (dorsal) and motor (lateral) columns. From data derived from nine healthy volunteers, two raters quantified column-specific parallel (lambda(||)) and perpendicular (lambda(perpendicular)) diffusivity, fractional anisotropy (FA), mean diffusivity (MD), and MT-weighted signal intensity relative to cerebrospinal fluid (MTCSF) over two time-points separated by more than 1 week. Cross-sectional means and standard deviations of these measures in the lateral and dorsal columns were as follows: lambda(||): 2.13 +/- 0.14 and 2.14 +/- 0.11 microm(2)/ms; lambda(perpendicular): 0.67 +/- 0.16 and 0.61 +/- 0.09 microm(2)/ms; MD: 1.15 +/- 0.15 and 1.12 +/- 0.08 microm(2)/ms; FA: 0.68 +/- 0.06 and 0.68 +/- 0.05; MTCSF: 0.52 +/- 0.05 and 0.50 +/- 0.05. We examined the variability and interrater and test-retest reliability for each metric. These column-specific MR measurements are expected to enhance understanding of the intimate structure-function relationship in the cervical spinal cord and may be useful for the assessment of disease progression.

Classification of Spinal Vascular Malformations

Spinal vascular malformations are rare diseases with a wide variety of neurological presentations. Their classification depends on the differentiation of shunting versus non-shunting lesions, the latter being the spinal cord cavernomas. In the shunting lesions, the next step in the proposed classification scheme is related to the feeding artery which can subdivide the dural vascular shunts from the pial vascular malformations: while those shunts that are fed by radiculomeningeal arteries (i.e. the counterparts of meningeal arteries in the brain) constitute the dural arteriovenous fistulas, the shunts that are fed by arteries that would normally supply the spinal cord (i.e. the radiculomedullary and radiculopial arteries) are the pial cord arteriovenous malformations (whose cranial counterparts are the brain AVMs). Depending on the type of transition between artery and vein the latter pial AVMs can be further subdivided into glomerular (plexiforme or nidus-type) AVMs with a network of intervening vessels in between the artery and vein and the fistulous pial AVMs. The last step in the classification then describes whether the type of fistula has a high or a low shunting volume which will differentiate the “Macro-” from the “Micro-”fistulae. The proposed classification is therefore based on a stepwise analysis of the shunt including its arterial anatomy, its nidus-architecture and its flow-volume evaluation. The major advantage of this approach is that it leads to a subclassification with direct implications on the choice of treatment, thereby constituting a simple and practical approach to evaluate these rare diseases.

Diffusion tensor imaging of ex vivo cervical spinal cord specimens: the immediate and long-term effects of fixation on diffusivity

Diffusion tensor imaging (DTI) is an emerging noninvasive method for evaluating tissue microstructure, but is highly susceptible to in vivo motion artifact. Ex vivo experiments on fixed tissues are needed to improve DTI techniques, which require fixed tissue specimens. Several efforts have been made to study the effect of fixation on both human and mouse tissue, with varying results. Four human cervical cords and three segments of pig cervical spinal cord specimens were imaged both before and after tissue fixation using 3D multishot diffusion weighted imaging (ms-DWEPI). Fixation caused a significant decrease in the longitudinal diffusivity whereas the relative anisotropy (RA) and radial diffusivity remained unaffected. Additionally, once adequately preserved, the diffusivity parameters of fixed tissue remain constant over time. Fixation has important effects on the diffusivity of tissue specimens. These findings have important implications for the determination of tissue microstructure and function using DTI technologies.

Diffusion-based tractography in neurological disorders: concepts, applications, and future developments

Diffusion-based tractography enables the graphical reconstruction of the white matter pathways in the brain and spinal cord of living humans. This technique has many potential clinical applications, including the investigation of stroke, multiple sclerosis, epilepsy, neurodegenerative diseases, and spinal cord disorders, and it enables hypotheses to be tested that could not previously be considered in living humans. This Review will outline the limitations of tractography, describe its current clinical applications in the most common neurological diseases, and highlight future opportunities.

Attenuation of lower-thoracic, lumbar, and sacral spinal cord motion: implications for imaging human spinal cord structure and function

BACKGROUND AND PURPOSE

Recent literature indicates that cervical and upper-thoracic spinal cord motion adversely affect both structural and functional MR imaging (fMRI; particularly diffusion tensor imaging [DTI] and spinal fMRI), ultimately reducing the reliability of these methods for both research and clinical applications. In the present study, we investigated motion of the lower-thoracic, lumbar, and sacral cord segments to evaluate the incidence of similar motion-related confounds in these regions.

MATERIALS AND METHODS

Recently developed methods, used previously for measuring cervical and upper-thoracic spinal cord motion, were employed in the present study to examine anteroposterior (A/P) and left-right (L/R) spinal cord motion in caudal regions. Segmented cinematic imaging was applied with a gradient-echo, turbo fast low-angle shot (turbo-FLASH) pulse sequence to acquire midline images of the cord at 24 cardiac phases throughout the lower-thoracic, lumbar, and sacral spinal cord regions.

RESULTS

The magnitude of A/P motion was found to be largest in rostral cord regions, whereas in caudal regions (at the level of the T4/T5 vertebrae and below), peak cord motion was uniformly small (routinely < or =0.10 mm). L/R motion, however, was found to be minimal throughout the thoracic, lumbar, and sacral regions.

CONCLUSION

Motion-related errors in spinal fMRI and DTI are expected to be significantly reduced throughout caudal regions of the spinal cord, thus yielding higher sensitivity and specificity compared with rostral regions. The paucity of such errors is expected to provide a means of observing the specific impact of motion (in rostral regions) and to enable the acquisition of uncorrupted DTI and fMRI data for studies of structure and function throughout lumbar and sacral regions.

Diffusion tensor magnetic resonance imaging and fiber tracking in spinal cord lesions: current and future indications

Diffusion-weighted imaging and fractional anisotropy may be more sensitive than other conventional magnetic resonance imaging techniques to detect, characterize, and map the extent of spinal cord lesions. Fiber tracking offers the possibility of visualizing the integrity of white matter tracts surrounding some lesions, and this information may help in formulating a differential diagnosis and in planning biopsies or resection. Fractional anisotropy measurements may also play a role in predicting the outcome of patients who have spinal cord lesions. In this article, we address several conditions in which diffusion-weighted imaging and fiber tracking is known to be useful and speculate on others in which we believe these techniques will be useful in the near future.