Diffusion-weighted echo planar imaging of the normal human cervical spinal cord

Imaging of Spinal Cord Injury: Acute Cervical Spinal Cord Injury, Cervical Spondylotic Myelopathy, and Cord Herniation

We review the pathophysiology and imaging findings of acute traumatic spinal cord injury (SCI), cervical spondylotic myelopathy, and briefly review the much less common cord herniation as a unique cause of myelopathy. Acute traumatic SCI is devastating to the patient and the costs to society are staggering. There are currently no "cures" for SCI and the only accepted pharmacologic treatment regimen for traumatic SCI is currently being questioned. Evaluation and prognostication of SCI is a demanding area with significant deficiencies, including lack of biomarkers. Accurate classification of SCI is heavily dependent on a good clinical examination, the results of which can vary substantially based upon the patient׳s condition or comorbidities and the skills of the examiner. Moreover, the full extent of a patients׳ neurologic injury may not become apparent for days after injury; by then, therapeutic response may be limited. Although magnetic resonance imaging (MRI) is the best imaging modality for the evaluation of spinal cord parenchyma, conventional MR techniques do not appear to differentiate edema from axonal injury. Recently, it is proposed that in addition to characterizing the anatomic extent of injury, metrics derived from conventional MRI and diffusion tensor imaging, in conjunction with the neurological examination, can serve as a reliable objective biomarker for determination of the extent of neurologic injury and early identification of patients who would benefit from treatment. Cervical spondylosis is a common disorder affecting predominantly the elderly with a potential to narrow the spinal canal and thereby impinge or compress upon the neural elements leading to cervical spondylotic myelopathy and radiculopathy. It is the commonest nontraumatic cause of spinal cord disorder in adults. Imaging plays an important role in grading the severity of spondylosis and detecting cord abnormalities suggesting myelopathy.

Diffusion tensor imaging of the spinal cord: insights from animal and human studies

Diffusion tensor imaging (DTI) provides a measure of the directional diffusion of water molecules in tissues. The measurement of DTI indexes within the spinal cord provides a quantitative assessment of neural damage in various spinal cord pathologies. DTI studies in animal models of spinal cord injury indicate that DTI is a reliable imaging technique with important histological and functional correlates. These studies demonstrate that DTI is a noninvasive marker of microstructural change within the spinal cord. In human studies, spinal cord DTI shows definite changes in subjects with acute and chronic spinal cord injury, as well as cervical spondylotic myelopathy. Interestingly, changes in DTI indexes are visualized in regions of the cord, which appear normal on conventional magnetic resonance imaging and are remote from the site of cord compression. Spinal cord DTI provides data that can help us understand underlying microstructural changes within the cord and assist in prognostication and planning of therapies. In this article, we review the use of DTI to investigate spinal cord pathology in animals and humans and describe advances in this technique that establish DTI as a promising biomarker for spinal cord disorders.

Characterization and limitations of diffusion tensor imaging metrics in the cervical spinal cord in neurologically intact subjects

PURPOSE

To characterize diffusion tensor imaging (DTI) metrics across all levels of the cervical spinal cord (CSC) and to study the impact of age and signal quality on these metrics.

MATERIALS AND METHODS

DTI metrics were calculated for gray matter (GM) and white matter (WM) funiculi throughout the CSC (C1-T1) in 25 healthy subjects (22-85 years old). Signal-to-noise ratios (SNRs) and mean DTI metrics were measured for the upper (C1-3), middle (C4-6) and lower (C7-T1) cervical segments. Age-related changes in DTI metrics were analyzed for the individual segment groups.

RESULTS

Fractional anisotropy (FA), mean diffusivity (MD) and transverse apparent diffusion coefficient (tADC) showed significant differences between GM and WM funiculi. Significant age-related changes were observed in FA in upper and middle CSC segments but not in the lower CSC. The median SNR was significantly lower in the middle and lower segment groups as compared to the upper levels, contributing to poor spatial resolution in these regions.

CONCLUSION

This study provides DTI data for GM and WM funiculi throughout the CSC. While DTI metrics may be used to define cord pathology, variations in metrics due to age and signal quality need to be accounted for before making definitive conclusions.

Diffusion tensor imaging of the spinal cord: a review

Diffusion tensor imaging (DTI) is a magnetic resonance technique capable of measuring the magnitude and direction of water molecule diffusion in various tissues. The use of DTI is being expanded to evaluate a variety of spinal cord disorders both for prognostication and to guide therapy. The purpose of this article is to review the literature on spinal cord DTI in both animal models and humans in different neurosurgical conditions. DTI of the spinal cord shows promise in traumatic spinal cord injury, cervical spondylotic myelopathy, and intramedullary tumors. However, scanning protocols and image processing need to be refined and standardized.

Diffusion tensor imaging of the spinal cord and its clinical applications

The identification of the extent of neural damage in patients with acute or chronic spinal cord injury is imperative for the accurate prediction of neurological recovery. The changes in signal intensity shown on routine MRI sequences are of limited value for predicting functional outcome. Diffusion tensor imaging (DTI) is a novel radiological imaging technique which has the potential to identify intact nerve fibre tracts, and has been used to image the brain for a variety of conditions. DTI imaging of the spinal cord is currently only a research tool, but preliminary studies have shown that it holds considerable promise in predicting the severity of spinal cord injury. This paper briefly reviews our current knowledge of this technique.

Diffusion tensor MR imaging in chronic spinal cord injury

BACKGROUND AND PURPOSE

Diffusion tensor MR imaging is emerging as an important tool for displaying anatomic changes in the brain after injury or disease but has been less widely applied to disorders of the spinal cord. The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo during the chronic stages of spinal cord injury (SCI). These data provide insight into the structural changes that occur as a result of long-term recovery from spinal trauma.

MATERIALS AND METHODS

Thirteen neurologically intact subjects and 10 subjects with chronic SCI (>4 years postinjury) were enrolled in this study. A single-shot twice-refocused spin-echo diffusion-weighted echo-planar imaging pulse sequence was used to obtain axial images throughout the entire spinal cord (C1-L1) in <60 minutes.

RESULTS

Despite heterogeneity in SCI lesion severity and location, diffusion characteristics of the chronic lesion were significantly elevated compared with those of uninjured controls. Fractional anisotropy was significantly lower at the chronic lesion and appeared dependent on the completeness of the injury. Conversely, mean diffusivity measurements in the upper cervical spinal cord in subjects with SCI were significantly lower than those in controls. These trends suggest that the entire neuraxis may be affected by long-term recovery from spinal trauma.

CONCLUSION

These results suggest that diffusion tensor imaging may be useful in the assessment of SCI recovery.

Diffusion tensor MR imaging of the neurologically intact human spinal cord

BACKGROUND AND PURPOSE

The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo. These data are essential for comparisons to pathologic conditions as well as for comparisons of different pulse sequence design parameters aimed to reduce scan time and more accurately determine diffusion coefficients.

MATERIALS AND METHODS

A total of 13 neurologically intact subjects were enrolled in this study. A single-shot, twice-refocused, spin-echo, diffusion-weighted, echo-planar imaging (EPI) pulse sequence was used to obtain axial images throughout the entire spinal cord (C1-L1) in 45 minutes.

RESULTS

Diffusion images indicated slight geometric distortions; however, gray and white matter contrast was observed. All measurements varied across the length of the cord. Whole cord diffusion coefficients averaged 0.5-1.3 x 10(-3) mm(2)/s depending on orientation, mean diffusivity (MD) averaged 0.83 +/- 0.06 x 10(-3) mm(2)/s, fractional anisotropy (FA) averaged 0.49 +/- 0.05, and volume ratio (VR) averaged 0.73 +/- 0.05.

CONCLUSION

This study provided normative diffusion values for the entire spinal cord for use in comparisons with pathologic conditions as well as improvements in pulse sequence design.

Morphology and morphometry of human chronic spinal cord injury using diffusion tensor imaging and fuzzy logic

Diffusion tensor imaging (DTI) was performed on regions rostral to the injury site in four human subjects with chronic spinal cord injury (SCI) and equivalent regions in four neurologically intact subjects. Apparent diffusion coefficients were measured and compared between subjects. A fuzzy logic tissue classification algorithm was used to segment gray and white matter regions for morphometric analysis, including comparisons of cross-sectional areas of gray and white matter along with frontal and sagittal diameters. Results indicated a general decrease in both longitudinal and transverse diffusivity in the upper cervical segments of subjects with chronic SCI. Further, a decrease in the cross-sectional area of the entire spinal cord was observed in subjects with SCI, consistent with severe atrophy of the spinal cord. These observations have implications in tracking the progression of SCI from the acute to the chronic stages. We conclude that DTI with fuzzy logic tissue classification has potential for monitoring morphological changes in the spinal cord in people with SCI.

Diffusion-weighted MR imaging (DWI) in the evaluation of epidural spinal lesions

INTRODUCTION

Epidural spinal cord compression is one of the most critical emergency conditions requiring medical attention and requires prompt and adequate treatment. The aim of our study was to assess the role of diffusion-weighted magnetic resonance (MR) imaging (DWI) in the diagnosis and differentiation of epidural spinal lesions.

METHODS

Three patients with epidural lymphoma, two with sarcoma and three with epidural metastatic disease were imaged on a 1.5T MRI unit. DWI was performed using navigated, interleaved, multi-shot echo planar imaging (IEPI). Three region of interest (ROI)-measurements were obtained on corresponding apparent diffusion coefficient (ADC) maps, and the mean ADC value was used for further analysis. The cellularity of tumors was determined as the N/C ratio (nucleus/cytoplasma ratio) from histological samples. The ADC values and N/C ratios of lesions were compared using a Kruskal-Wallis test.

RESULTS

The mean ADC of the lymphomas was 0.66 x 10(-3) mm2/s, that of the sarcomas was 0.85 x 10(-3) mm2/s and the ADC of the metastatic lesions was 1.05 x 10(-3) mm2/s; however, the differences were not statistically significant. Mean N/C ratios in the lymphoma, sarcomas and metastases were 4:1, 2:1, and 2.6:1, respectively, with a statistically significant difference between the groups (p < 0.025).

CONCLUSION

Although not statistically significant due to the small patient sample, our results clearly show a tendency toward decreased diffusivity in neoplastic lesions with higher cellularity. The data from our study suggest that DWI is a feasible and potentially useful technique for the evaluation of epidural lesions that cause spinal cord compression on a per-patient basis.

Examination of spinal cord tissue architecture with magnetic resonance diffusion tensor imaging

Magnetic resonance diffusion tensor imaging yields images with detailed information about tissue water diffusion. Diffusion-weighted imaging of the human spinal cord requires dedicated magnetic resonance pulse sequences that minimize the effects of subject motion, distortions, and artifacts from lipids and CSF flow. These problems are accentuated by the anatomic properties of the spinal cord (i.e., a small cross-sectional dimension and a location deep inside the body). The diffusion tensor (a simplified model for complex diffusion in structured tissues) can be estimated for each image pixel by measuring diffusion along a minimum of six independent directions. It can then be used to derive mean diffusivity, diffusion anisotropy, and the dominant orientation of the diffusion process. The observation that diffusion along nerve fibers is much higher than across fibers, allows a noninvasive reconstruction of the spinal cord nerve fiber architecture. This includes not only the primary cranio-caudad running connections, but also secondary, transverse running collateral fibers. With fiber tracking, the pixel-based diffusion information can be integrated to obtain a three-dimensional view of axonal fiber connectivity between the spinal cord and different brain regions. The development and myelination during infancy and early childhood is reflected in a gradual decrease of mean diffusivity and increase in anisotropy. There are several diseases that lead to either local or general changes in spinal cord water diffusion. For therapy research, such changes can be studied noninvasively and repeatedly in animal models.

Diffusion-weighted MR imaging (DWI) in spinal cord ischemia

INTRODUCTION

Spinal cord infarction is a rare clinical diagnosis characterized by a sudden onset of paralysis, bowel and bladder dysfunction, and loss of pain and temperature perception, with preservation of proprioception and vibration sense. Magnetic resonance imaging (MRI) usually demonstrates intramedullary hyperintensity on T2-weighted MR images with cord enlargement. However, in approximately 45% of patients, MR shows no abnormality. Diffusion-weighted MR imaging (DWI) has been widely used for the evaluation of a variety of brain disorders, especially for acute stroke. Preliminary data suggest that DWI has the potential to be useful in the early detection of spinal infarction.

METHODS

We performed DWI, using navigated, interleaved, multishot echo planar imaging (IEPI), in a series of six patients with a clinical suspicion of acute spinal cord ischemia.

RESULTS

In all patients, high signal was observed on isotropic DWI images with low ADC values (0.23 and 0.86x10(-3) cm(2)/s), indicative of restricted diffusion.

CONCLUSION

We analyzed the imaging findings from conventional MR sequences and diffusion-weighted MR sequences in six patients with spinal cord infarction, compared the findings with those in published series, and discuss the value of DWI in spinal cord ischemia based on current experience. Although the number of patients with described DWI findings totals only 23, the results of previously published studies and those of our study suggest that DWI has the potential to be a useful and feasible technique for the detection of spinal infarction.

Diffusion-weighted MRI and the evaluation of spinal cord axonal integrity following injury and treatment

Diffusion-based magnetic resonance imaging (MRI) (DWI) has been shown experimentally to detect both injury and functionally significant neuroprotection of injured spinal cord white matter that would otherwise go undetected with conventional MRI techniques. The diffusion of water in the central nervous system (CNS) is thought to be affected by both its location (intracellular or extracellular), and by diffusion barriers formed by cell membranes and myelin sheaths. There is, however, controversy concerning how to obtain, interpret, and present DWI data. Computer simulations and MR microscopy have been helpful in resolving some of these issues, as well as determining exact histologic correlates to DWI findings.

Diffusion-weighted MRI of the cervical cord in acute spinal cord injury with type II odontoid fracture

The authors present a case of acute spinal cord injury demonstrated by diffusion-weighted MRI (DWI) of the cervical cord. DWI taken 2 hours after injury showed intramedullary hyperintensity with a decrease of the apparent diffusion coefficient (ADC) value at C1-C2 vertebral levels. On T -weighted images obtained 1 month after injury, the lesion was hyperintense, indicating the existence of myelomalacia. DWI of the cervical cord provided satisfactory images and was a useful method for detecting and visualizing of the affected cord in the super-early stage.(2)

Diffusion-weighted imaging of the spinal cord

Spinal cord DWI may be useful in providing information not available with conventional MR imaging. More work, however, is required to explain what the qualitative and quantitative results actually represent. Computer simulations and detailed radiologic-histologic correlations will therefore be necessary.