Functional magnetic resonance imaging of the human cervical spinal cord with stimulation of different sensory dermatomes

Thermal stimulus task fMRI in the cervical spinal cord at 7 Tesla

Although functional magnetic resonance imaging (fMRI) is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B0 . Increasing field strength enables higher spatial resolution and improved sensitivity to blood oxygenation level-dependent (BOLD) signal, but amplifies the effects of B0 inhomogeneity. In this work, we present the first task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D echo-planar imaging (EPI) protocols, which differ in sensitivity to spatial and temporal B0 inhomogeneity. The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. All protocols used 3 mm slice thickness. For each protocol, the BOLD response to 13 10-s noxious thermal stimuli applied to the right thumb was acquired in a 10-min fMRI run. Image quality, temporal signal to noise ratio (SNR), and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols. Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed. Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment. PRACTITIONER POINTS: First stimulus task fMRI results in the spinal cord at 7 T. Single-shot 0.75 mm 2D EPI produced the highest mean z-statistic. Multi-shot 0.60 mm 2D EPI provided the best-localized activation and least distortion.

Thermal Stimulus Task fMRI in the Cervical Spinal Cord at 7 Tesla

PURPOSE

Although functional MRI is widely applied in the brain, fMRI of the spinal cord is more technically demanding. Proximity to the vertebral column and lungs results in strong spatial inhomogeneity and temporal fluctuations in B0. Increasing field strength enables higher spatial resolution and improved sensitivity to BOLD signal, but amplifies the effects of B0 inhomogeneity. In this work, we present the first stimulus task fMRI in the spinal cord at 7 T. Further, we compare the performance of single-shot and multi-shot 2D EPI protocols, as they differ in sensitivity to spatial and temporal B0 inhomogeneity.

METHODS

The cervical spinal cords of 11 healthy volunteers were scanned at 7 T using single-shot 2D EPI at 0.75 mm in-plane resolution and multi-shot 2D EPI at 0.75 and 0.6 mm in-plane resolutions. For each protocol, the BOLD response to thirteen 10-second noxious thermal stimuli applied to the right thumb was acquired in a 10-minute fMRI run. Image quality, temporal SNR, and BOLD activation (percent signal change and z-stat) at both individual- and group-level were evaluated between the protocols.

RESULTS

Temporal SNR was highest in single-shot and multi-shot 0.75 mm protocols. In group-level analyses, activation clusters appeared in all protocols in the ipsilateral dorsal quadrant at the expected C6 neurological level. In individual-level analyses, activation clusters at the expected level were detected in some, but not all subjects and protocols. Single-shot 0.75 mm generally produced the highest mean z-statistic, while multi-shot 0.60 mm produced the best-localized activation clusters and the least geometric distortion. Larger than expected within-subject segmental variation of BOLD activation along the cord was observed.

CONCLUSION

Group-level sensory task fMRI of the cervical spinal cord is feasible at 7 T with single-shot or multi-shot EPI. The best choice of protocol will likely depend on the relative importance of sensitivity to activation versus spatial localization of activation for a given experiment.

The current state of spinal cord functional magnetic resonance imaging and its application in clinical research

Since its development, spinal cord functional magnetic resonance imaging (fMRI) has utilized various methodologies and stimulation protocols to develop a deeper understanding of a healthy human spinal cord that lays a foundation for its use in clinical research and practice. In this review, we conducted a comprehensive literature search on spinal cord fMRI studies and summarized the recent advancements and resulting scientific achievements of spinal cord fMRI in the following three aspects: the current state of spinal cord fMRI methodologies and stimulation protocols, knowledge about the healthy spinal cord's functions obtained via spinal cord fMRI, and fMRI's exemplary usage in spinal cord diseases and injuries. We conclude with a discussion that, while technical challenges exist, novel fMRI technologies for and new knowledge about the healthy human spinal cord have been established. Empowered by these developments, investigations of pathological and injury states within the spinal cord have become the next important direction of spinal cord fMRI. Recent clinical investigations into spinal cord pathologies, for example, fibromyalgia, multiple sclerosis, spinal cord injury, and cervical spondylotic myelopathy, have already provided deep insights into spinal cord impairments and the time course of impairment-caused changes. We expect that future spinal cord fMRI advancement and research development will further enhance our understanding of various spinal cord diseases and provide the foundation for evaluating existing and developing new treatment plans.

Effects of variability in manually contoured spinal cord masks on fMRI co-registration and interpretation

Functional magnetic resonance imaging (fMRI) of the human spinal cord (SC) is a unique non-invasive method for characterizing neurovascular responses to stimuli. Group-analysis of SC fMRI data involves co-registration of subject-level data to standard space, which requires manual masking of the cord and may result in bias of group-level SC fMRI results. To test this, we examined variability in SC masks drawn in fMRI data from 21 healthy participants from a completed study mapping responses to sensory stimuli of the C7 dermatome. Masks were drawn on temporal mean functional image by eight raters with varying levels of neuroimaging experience, and the rater from the original study acted as a reference. Spatial agreement between rater and reference masks was measured using the Dice Similarity Coefficient, and the influence of rater and dataset was examined using ANOVA. Each rater's masks were used to register functional data to the PAM50 template. Gray matter-white matter signal contrast of registered functional data was used to evaluate the spatial normalization accuracy across raters. Subject- and group-level analyses of activation during left- and right-sided sensory stimuli were performed for each rater's co-registered data. Agreement with the reference SC mask was associated with both rater (F(7, 140) = 32.12, P < 2 × 10-16, η2 = 0.29) and dataset (F(20, 140) = 20.58, P < 2 × 10-16, η2 = 0.53). Dataset variations may reflect image quality metrics: the ratio between the signal intensity of spinal cord voxels and surrounding cerebrospinal fluid was correlated with DSC results (p < 0.001). As predicted, variability in the manually-drawn masks influenced spatial normalization, and GM:WM contrast in the registered data showed significant effects of rater and dataset (rater: F(8, 160) = 23.57, P < 2 × 10-16, η2 = 0.24; dataset: F(20, 160) = 22.00, P < 2 × 10-16, η2 = 0.56). Registration differences propagated into subject-level activation maps which showed rater-dependent agreement with the reference. Although group-level activation maps differed between raters, no systematic bias was identified. Increasing consistency in manual contouring of spinal cord fMRI data improved co-registration and inter-rater agreement in activation mapping, however our results suggest that improvements in image acquisition and post-processing are also critical to address.

Assessing the spatial distribution of cervical spinal cord activity during tactile stimulation of the upper extremity in humans with functional magnetic resonance imaging

Dermatomal maps are a mainstay of clinical practice and provide information on the spatial distribution of the cutaneous innervation of spinal nerves. Dermatomal deficits can help isolate the level of spinal nerve root involvement in spinal conditions and guide clinicians in diagnosis and treatment. Dermatomal maps, however, have limitations, and the spatial distribution of spinal cord sensory activity in humans remains to be quantitatively assessed. Here we used spinal cord functional MRI to map and quantitatively compare the spatial distribution of sensory spinal cord activity during tactile stimulation of the left and right lateral shoulders (i.e. C5 dermatome) and dorsal third digits of the hands (i.e., C7 dermatome) in healthy humans (n = 24, age = 36.8 ± 11.8 years). Based on the central sites for processing of innocuous tactile sensory information, we hypothesized that the activity would be localized more to the ipsilateral dorsal spinal cord with the lateral shoulder stimulation activity being localized more superiorly than the dorsal third digit. The findings demonstrate lateralization of the activity with the left- and right-sided stimuli having more activation in the ipsilateral hemicord. Contradictory to our hypotheses, the activity for both stimulation sites was spread across the dorsal and ventral hemicords and did not demonstrate a clear superior-inferior localization. Instead, the activity for both stimuli had a broader than expected distribution, extending across the C5, C6, and C7 spinal cord segments. We highlight the complexity of the human spinal cord neuroanatomy and several sources of variability that may explain the observed patterns of activity. While the findings were not completely consistent with our a priori hypotheses, this study provides a foundation for continued work and is an important step towards developing normative quantitative spinal cord measures of sensory function, which may become useful objective MRI-based biomarkers of neurological injury and improve the management of spinal disorders.

Imaging Cerebral Activity in Amyotrophic Lateral Sclerosis

Advances in neuroimaging, complementing histopathological insights, have established a multi-system involvement of cerebral networks beyond the traditional neuromuscular pathological view of amyotrophic lateral sclerosis (ALS). The development of effective disease-modifying therapy remains a priority and this will be facilitated by improved biomarkers of motor system integrity against which to assess the efficacy of candidate drugs. Functional MRI (FMRI) is an established measure of both cerebral activity and connectivity, but there is an increasing recognition of neuronal oscillations in facilitating long-distance communication across the cortical surface. Such dynamic synchronization vastly expands the connectivity foundations defined by traditional neuronal architecture. This review considers the unique pathogenic insights afforded by the capture of cerebral disease activity in ALS using FMRI and encephalography.

Ten Key Insights into the Use of Spinal Cord fMRI

A comprehensive review of the literature-to-date on functional magnetic resonance imaging (fMRI) of the spinal cord is presented. Spinal fMRI has been shown, over more than two decades of work, to be a reliable tool for detecting neural activity. We discuss 10 key points regarding the history, development, methods, and applications of spinal fMRI. Animal models have served a key purpose for the development of spinal fMRI protocols and for experimental spinal cord injury studies. Applications of spinal fMRI span from animal models across healthy and patient populations in humans using both task-based and resting-state paradigms. The literature also demonstrates clear trends in study design and acquisition methods, as the majority of studies follow a task-based, block design paradigm, and utilize variations of single-shot fast spin-echo imaging methods. We, therefore, discuss the similarities and differences of these to resting-state fMRI and gradient-echo EPI protocols. Although it is newly emerging, complex connectivity and network analysis is not only possible, but has also been shown to be reliable and reproducible in the spinal cord for both task-based and resting-state studies. Despite the technical challenges associated with spinal fMRI, this review identifies reliable solutions that have been developed to overcome these challenges.

Cervical spinal functional magnetic resonance imaging of the spinal cord injured patient during electrical stimulation

PURPOSE

To evaluate the spatial distribution and signal intensity changes following spinal cord activation in patients with spinal cord injury.

METHODS

This study used spinal functional magnetic resonance imaging (fMRI) based on signal enhancement by extra-vascular water protons (SEEP) to assess elicited responses during subcutaneous electrical stimulation at the right elbow and right thumb in the cervical spinal cord.

RESULTS

Seven healthy volunteers and seven patients with cervical spinal cord injury (SCI) were included in this study. Significant functional activation was observed mainly in the right side of the spinal cord at the level of the C5-C6 cervical vertebra in both the axial and sagittal planes. A higher percentage of signal changes (4.66 ± 2.08 % in injured subjects vs. 2.78 ± 1.66 % in normal) and more average activation voxels (4.69 ± 2.59 in injured subjects vs. 2.56 ± 1.13 in normal subject) in axial plane at the C5-C6 cervical vertebra with a statistically significant difference. The same trends were observed in the sagittal plane with higher percentage of signal changes and more average activation voxels, though no statistically significant difference compared with the control group.

CONCLUSIONS

Spinal SEEP fMRI is a powerful noninvasive method for the study of local neuronal activation in the human spinal cord, which may be of clinical value for evaluating the effectiveness of interventions aimed at promoting recovery of function using electrical stimulation.

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.

Plasticity of the injured human spinal cord: insights revealed by spinal cord functional MRI

Introduction

While numerous studies have documented evidence for plasticity of the human brain there is little evidence that the human spinal cord can change after injury. Here, we employ a novel spinal fMRI design where we stimulate normal and abnormal sensory dermatomes in persons with traumatic spinal cord injury and perform a connectivity analysis to understand how spinal networks process information.

Methods

Spinal fMRI data was collected at 3 Tesla at two institutions from 38 individuals using the standard SEEP functional MR imaging techniques. Thermal stimulation was applied to four dermatomes in an interleaved timing pattern during each fMRI acquisition. SCI patients were stimulated in dermatomes both above (normal sensation) and below the level of their injury. Sub-group analysis was performed on healthy controls (n = 20), complete SCI (n = 3), incomplete SCI (n = 9) and SCI patients who recovered full function (n = 6).

Results

Patients with chronic incomplete SCI, when stimulated in a dermatome of normal sensation, showed an increased number of active voxels relative to controls (p = 0.025). There was an inverse relationship between the degree of sensory impairment and the number of active voxels in the region of the spinal cord corresponding to that dermatome of abnormal sensation (R² = 0.93, p<0.001). Lastly, a connectivity analysis demonstrated a significantly increased number of intraspinal connections in incomplete SCI patients relative to controls suggesting altered processing of afferent sensory signals.

Conclusions

In this work we demonstrate the use of spinal fMRI to investigate changes in spinal processing of somatosensory information in the human spinal cord. We provide evidence for plasticity of the human spinal cord after traumatic injury based on an increase in the average number of active voxels in dermatomes of normal sensation in chronic SCI patients and an increased number of intraspinal connections in incomplete SCI patients relative to healthy controls.

A systematic review of spinal fMRI research: outlining the elements of experimental design

Object

Since the first published report of spinal functional MRI (fMRI) in humans in 1996, this body of literature has grown substantially. In the present article, the authors systematically review all spinal fMRI studies conducted in healthy individuals with a focus on the different motor and sensory paradigms used and the results acquired.

Methods

The authors conducted a systematic search of MEDLINE for literature published from 1990 through November 2011 reporting on stimulation paradigms used to assess spinal fMRI scans in healthy individuals.

Results

They identified 19 peer-reviewed studies from 1996 to the present in which a combination of different spinal fMRI methods were used to investigate the spinal cord in healthy individuals. Eight of the studies used a motor stimulation paradigm, 10 used a sensory stimulation paradigm, and 1 compared motor and sensory stimulation paradigms.

Conclusions

Despite differences in the results of various studies, even when similar stimulation paradigms were used, this body of literature underscores that spinal fMRI signals can be obtained from the human spinal cord. The authors intend this review to serve as an introduction to spinal fMRI research and what it may offer the field of spinal cord injury research.

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.

Measurement and characterization of the human spinal cord SEEP response using event-related spinal fMRI

Although event-related fMRI is able to reliably detect brief changes in brain activity and is now widely used throughout systems and cognitive neuroscience, there have been no previous reports of event-related spinal cord fMRI. This is likely attributable to the various technical challenges associated with spinal fMRI (e.g., imaging a suitable length of the cord, reducing image artifacts from the vertebrae and intervertebral discs, and dealing with physiological noise from spinal cord motion). However, with many of these issues now resolved, the largest remaining impediment for event-related spinal fMRI is a deprived understanding of the spinal cord fMRI signal time course. Therefore, in this study, we used a proton density-weighted HASTE sequence, with functional contrast based on signal enhancement by extravascular water protons (SEEP), and a motion-compensating GLM analysis to (i) characterize the SEEP response function in the human cervical spinal cord and (ii) demonstrate the feasibility of event-related spinal fMRI. This was achieved by applying very brief (1 s) epochs of 22°C thermal stimulation to the palm of the hand and measuring the impulse response function. Our results suggest that the spinal cord SEEP response (time to peak ≈8 s; FWHM ≈4 s; and probably lacking pre- and poststimulus undershoots) is slower than previous estimates of SEEP or BOLD responses in the brain, but faster than previously reported spinal cord BOLD responses. Finally, by detecting and mapping consistent signal-intensity changes within and across subjects, and validating these regions with a block-designed experiment, this study represents the first successful demonstration of event-related spinal fMRI.

Neuroimaging of the human visceral pain system–A methodological review

During the last decades there has been a tremendous development of non-invasive methods for assessment of brain activity following visceral pain. Improved methods for neurophysiological and brain imaging techniques have vastly increased our understanding of the central processing of gastrointestinal sensation and pain in both healthy volunteers as well as in patients suffering from gastrointestinal disorders. The techniques used are functional magnetic resonance imaging (fMRI), positron emission tomography (PET), electroencephalography (EEG)/evoked brain potentials (EPs), magnetoencephalography (MEG), single photon emission computed tomography (SPECT), and the multimodal combinations of these techniques. The use of these techniques has brought new insight into the complex brain processes underlying pain perception, including a number of subcortical and cortical regions, and paved new ways in our understanding of acute and chronic pain. The pathways are dynamic with a delicate balance between facilitatory and inhibitory pain mechanisms, and with modulation of the response to internal or external stressors with a high degree of plasticity. Hence, the ultimate goal in imaging of pain is to follow the stimulus response throughout the neuraxis.

Brain activity measured by fMRI is based on subtracting regional changes in blood oxygenation during a resting condition from the signal during a stimulus condition, and has high spatial resolution but low temporal resolution. SPECT and PET are nuclear imaging techniques where radiolabeled molecules are injected with visualization of the distribution, density and activity of receptors in the brain allowing not only assessment of brain activity but also study of receptor sites. EEG is based on assessment of electrical activity in the brain, and recordings of the resting EEG and evoked potentials following an external stimulus are used to study normal visceral pain processing, alterations of pain processing in different patient groups and the effect of pharmacological intervention. EEG has high temporal resolution, but relative poor spatial resolution, which however to some extent can be overcome by applying inverse modelling algorithms and signal decomposition procedures. MEG is based on recording the magnetic fields produced by electrical currents in the brain, has high spatial resolution and is especially suitable for the study cortical activation.

The treatment of chronic abdominal pain is often ineffective and dissapointing, which leads to search for optimized treatment achieved on the basis of a better understanding of underlying pain mechanisms. Application of the recent improvements in neuroimaging on the visceral pain system may likely in near future contribute substantially to our understanding of the functional and structural pathophysiology underlying chronic visceral pain disorders, and pave the road for optimized individual and mechanism based treatments.

The purpose of this review is to give a state-of-the-art overview of these methods, with focus on EEG, and especially the advantages and limitations of the single methods in clinical gastrointestinal pain esearch including examples from relevant studies.

Functional exploration of the human spinal cord during voluntary movement and somatosensory stimulation

Demonstrations of the possibility of obtaining functional information from the spinal cord in humans using functional magnetic resonance imaging (fMRI) have been growing in number and sophistication, but the technique and the results that it provides are still perceived by the scientific community with a greater degree of scepticism than fMRI investigations of brain function. Here we review the literature on spinal fMRI in humans during voluntary movements and somatosensory stimulation. Particular attention is given to study design, acquisition and statistical analysis of the images, and to the agreement between the obtained results and existing knowledge regarding spinal cord anatomy and physiology. A striking weakness of many spinal fMRI studies is the use of small numbers of subjects and of time-points in the acquired functional image series. In addition, spinal fMRI is characterised by large physiological noise, while the recorded functional responses are poorly characterised. For all these reasons, spinal fMRI experiments risk having low statistical power, and few spinal fMRI studies have yielded physiologically relevant information. Thus, while available evidence indicates that spinal fMRI is feasible, we are only approaching the stage at which the technique can be considered to have been rigorously established as a viable means of noninvasively investigating spinal cord functioning in humans.

Applying functional MRI to the spinal cord and brainstem

Functional magnetic resonance imaging of the spinal cord (spinal fMRI) has facilitated the noninvasive visualization of neural activity in the spinal cord (SC) and brainstem of both animals and humans. This technique has yet to gain the widespread usage of brain fMRI, due in part to the intrinsic technical challenges spinal fMRI presents and to the narrower scope of applications it fulfills. Nonetheless, methodological progress has been considerable and rapid. To date, spinal fMRI studies have investigated SC function during sensory or motor task paradigms in spinal cord injury (SCI), multiple sclerosis (MS) and neuropathic pain (NP) patient populations, all of which have yielded consistent and sensitive results. The most recent study in our laboratory has successfully used spinal fMRI to examine cervical SC activity in a SCI patient with a metallic fixation device spanning the C(4) to C(6) vertebrae, a critical step in realizing the clinical utility of the technique. The literature reviewed in this article suggests that spinal fMRI is poised for usage in a wide range of patient populations, as multiple groups have observed intriguing, yet consistent, results using standard, readily available MR systems and hardware. The next step is the implementation of this technique in the clinic to supplement standard qualitative behavioral assessments of SCI. Spinal fMRI may offer insight into the subtleties of function in the injured and diseased SC, and support the development of new methods for treatment and monitoring.

SSFSE sequence functional MRI of the human cervical spinal cord with complex finger tapping

PURPOSE

Functional MR imaging of the human cervical spinal cord was carried out on volunteers during alternated rest and a complex finger tapping task, in order to detect image intensity changes arising from neuronal activity.

METHODS

Functional MR imaging data using single-shot fast spin-echo sequence (SSFSE) with echo time 42.4 ms on a 1.5 T GE Clinical System were acquired in eight subjects performing a complex finger tapping task. Cervical spinal cord activation was measured both in the sagittal and transverse imaging planes. Postprocessing was performed by AFNI (Analysis of Functional Neuroimages) software system.

RESULTS

Intensity changes (5.5-7.6%) were correlated with the time course of stimulation and were consistently detected in both sagittal and transverse imaging planes of the cervical spinal cord. The activated regions localized to the ipsilateral side of the spinal cord in agreement with the neural anatomy.

CONCLUSION

Functional MR imaging signals can be reliably detected with finger tapping activity in the human cervical spinal cord using a SSFSE sequence with 42.4 ms echo time. The anatomic location of neural activity correlates with the muscles used in the finger tapping task.

Spinal-cord MRI in multiple sclerosis: conventional and nonconventional MR techniques

Multiple sclerosis is a diffuse disease of the central nervous system, and MRI of the spinal cord is highly recommended in the clinical evaluation of patients suspected of having multiple sclerosis. Within the new diagnostic criteria, spinal cord MRI increases sensitivity and possibly specificity for MS, but further work is needed to investigate other criteria that may give greater weight to the presence of cord lesions in patients with clinically isolated syndromes or suspected relapsing-remitting multiple sclerosis. Techniques should be further studied and validated in studies comparing these techniques with clinical status and histopathology, however.

Tactile-associated fMRI recruitment of the cervical cord in healthy subjects

Using spinal cord functional magnetic resonance imaging (fMRI), 12 right-handed healthy subjects were scanned during a tactile stimulation of the palm of the right hand. The task-related mean signal change was computed for all activated voxels within the cervical cord, and separately, in the four cord quadrants (right and left anterior, right and left posterior) from C5 to C8. The frequency of fMRI activity at each cord level was obtained by assigning a score of 25% at each active quadrant and by averaging the percentage of active quadrants at each level of all subjects. The difference in the occurrence of fMRI activity (a) in right versus left, and anterior versus posterior cord, and (b) among the different cord levels, was evaluated using a random effect logistic regression model, with the frequency of fMRI activity as the dependent variable and the subject as the grouping factor. The task-related mean signal change of all activated voxels of the cord was 3.2% (SD = 0.8%). During the tactile stimulation, subjects showed a higher occurrence of fMRI cord activity in the right than in the left cervical cord (odds ratio = 2.25, 95% confidence interval = 1.31-3.87, P = 0.003). A significant heterogeneity in frequency of fMRI activity between cord levels was also observed (P < 0.001), with the highest frequencies of fMRI activity detected at C6 and C7. Spinal cord fMRI enables to obtain reliable physiological information on the activity of human spinal circuits associated to tactile stimulation. This holds significant promise for a better planning and conduct of studies of people with diseased spinal cords.

Magnetic resonance imaging of the spine

Historically, magnetic resonance imaging has offered poor specificity in the diagnosis of back pain. Researchers currently are engaged in developing new techniques, and clinicians are successfully utilizing existing technologies (ie, diffusion-weighted imaging) that previously were not used to evaluate the spine. Magnetic resonance imaging may be used in several spinal applications: intervertebral disk and facet joint degeneration, spinal canal stenosis, suspected diskitis or osteomyelitis, suspected spinal column neoplasia, vascular disorders, trauma, and demyelinating disease.

Functional magnetic resonance imaging within the rat spinal cord following peripheral nerve injury

Functional magnetic resonance imaging (fMRI) was used to detect the effects of graded peripheral nerve injury at the spinal level. Graded peripheral nerve injury in rats was accomplished by transection of nerves entering the spinal cord at the L3 and L4 levels of the spinal cord segments. Electrical stimulation of the hindpaw was used to elicit activity within the spinal cord. The stimulation experimental paradigm consisted of 62 functional images, 5 slices each, with a total of 3 rest and 2 stimulation periods. A 9.4 T MRI system and a quadrature volume rf coil covering the lumbar spinal cord were used for the fMRI study. Sets of fast spin echo images were acquired repeatedly following sham preparatory surgery under control conditions and in rats following sham surgery (pre nerve cut), followed by L3 nerve and then L4 nerve section. In rats with sham surgery, there was a significant activation within the dorsal horn of slices corresponding to L3 and L4 spinal cord segments. Following section of the L3 nerve, there was a reduction in the number of active voxels in the L3 and L4 spinal cord segments. The activation was reduced further by sectioning of the L4 nerve. Thus, following an increasing loss of axonal connections to the spinal cord, there was a decreasing number of active voxels within the spinal cord. The results demonstrate that spinal fMRI in the rat has sufficient sensitivity to detect within the spinal cord the effects of a graded reduction in peripheral connectivity.

Functional magnetic resonance imaging of the human spinal cord during vibration stimulation of different dermatomes

INTRODUCTION

We investigated noninvasively areas of the healthy human spinal cord that become active in response to vibration stimulation of different dermatomes using functional magnetic resonance imaging (fMRI). The objectives of this study were to: (1) examine the patterns of consistent activity in the spinal cord during vibration stimulation of the skin, and (2) investigate the rostrocaudal distribution of active pixels when stimulation was applied to different dermatomes.

METHODS

FMRI of the cervical and lumbar spinal cord of seven healthy human subjects was carried out during vibration stimulation of six different dermatomes. In separate experiments, vibratory stimulation (about 50 Hz) was applied to the right biceps, wrist, palm, patella, Achilles tendon and left palm.

RESULTS

The segmental distribution of activity observed by fMRI corresponded well with known spinal cord neuroanatomy. The peak number of active pixels was observed at the expected level of the spinal cord with some activity in the adjacent segments. The rostrocaudal distribution of activity was observed to correspond to the dermatome being stimulated. Cross-sectional localization of activity was primarily in dorsal areas but also spread into ventral and intermediate areas of the gray matter and a distinct laterality ipsilateral to the stimulated limb was not observed.

CONCLUSION

We demonstrated that fMRI can detect a dermatome-dependent pattern of spinal cord activity during vibratory stimulation and can be used as a passive stimulus for the noninvasive assessment of the functional integrity of the human spinal cord. Demonstration of cross-sectional selectivity of the activation awaits further methodological and experimental refinements.

Potential clinical applications for spinal functional MRI

Functional MRI (fMRI) of the spinal cord is a noninvasive technique for obtaining information regarding spinal cord neuronal function. This article provides a brief overview of recent developments in spinal cord fMRI and outlines potential applications, as well as the limitations that must be overcome, for using spinal fMRI in the clinic. This technique is currently used for research purposes, but significant potential exists for spinal fMRI to become an important clinical tool.

Functional MRI of the cervical spinal cord during noxious and innocuous thermal stimulation in the alpha-chloralose- and halothane-anesthetized rat

Patterns of neuronal activity in the spinal cord using functional magnetic resonance imaging during noxious (48 degrees C) and innocuous (40 degrees C) thermal stimulation of the rat forepaw were examined. The patterns of functional activity elicited by thermal stimuli were compared in alpha-chloralose- and halothane-anesthetized rats. Although the locations of active pixels were similar during both types of stimulation, the mean percentage signal change was higher during noxious stimulation in both anesthetic groups. Ipsilateral dorsal horn activity was evident during both noxious and innocuous stimulation in all animals. The greatest consistency of ipsilateral dorsal horn activity occurred at the C3 to C5 spinal cord segments in all groups. Consistent contralateral dorsal horn activity appeared in segments C6 to C8 in all groups. C-fos immunohistochemical staining confirmed the presence of neural activity in the spinal cords of all animals.

Functional MR imaging of the cervical spinal cord by use of 20Hz functional electrical stimulation to median nerve

PURPOSE

Functional MR imaging of the human cervical spinal cord was carried out on volunteers by 20Hz functional electrical stimulation to median nerve, in order to detect signal changes arising concomitant to neuronal activity.

METHODS

Functional MR imaging data were acquired in six subjects with single-shot fast spin-echo sequence (SSFSE) on a 1.5T GE Clinical System. Cervical spinal cord activation was measured both in the sagittal and transverse imaging planes. Postprocessing was performed by AFNI (Analysis of Functional Neuroimages) software system.

RESULTS

Activation correlated with the time course of stimulation was consistently detected in both sagittal and transverse imaging planes of the cervical spinal cord. Regions of the spinal cord associated with motor and pain response were observed by 20Hz functional electrical stimulation to the median nerve.

CONCLUSION

The functional MR imaging signal can be detected in the human cervical spinal cord with functional electrical stimulation. Investigating the FES response in the spinal cord using the spinal fMRI will be helpful for the further discussion on the diagnosis and functional recovery to spinal cord diseases.

Functional MRI of the cervical spinal cord on 1.5 T with fingertapping: to what extent is it feasible?

INTRODUCTION

Until recently, functional magnetic resonance imaging (fMRI) with blood oxygen level-dependent (BOLD) contrast, was mainly used to study brain physiology. The activation signal measured with fMRI is based upon the changes in the concentration of deoxyhaemoglobin that arise from an increase in blood flow in the vicinity of neuronal firing. Technical limitations have impeded such research in the human cervical spinal cord. The purpose of this investigation was to determine whether a reliable fMRI signal can be elicited from the cervical spinal cord during fingertapping, a complex motor activity. Furthermore, we wanted to determine whether the fMRI signal could be spatially localized to the particular neuroanatomical location specific for this task.

METHODS

A group of 12 right-handed healthy volunteers performed the complex motor task of fingertapping with their right hand. T2*-weighted gradient-echo echo-planar imaging on a 1.5-T clinical unit was used to image the cervical spinal cord. Motion correction was applied. Cord activation was measured in the transverse imaging plane, between the spinal cord levels C5 and T1.

RESULTS

In all subjects spinal cord responses were found, and in most of them on the left and the right side. The distribution of the activation response showed important variations between the subjects. While regions of activation were distributed throughout the spinal cord, concentrated activity was found at the anatomical location of expected motor innervation, namely nerve root C8, in 6 of the 12 subjects.

CONCLUSION

fMRI of the human cervical spinal cord on an 1.5-T unit detects neuronal activity related to a complex motor task. The location of the neuronal activation (spinal cord segment C5 through T1 with a peak on C8) corresponds to the craniocaudal anatomical location of the neurons that activate the muscles in use.

Imaging intervertebral disc degeneration

Magnetic resonance imaging provides excellent anatomic detail of spinal tissues, but fails to provide the type of information that permits a definitive diagnosis in many patients with back pain. New imaging strategies that can be applied to the study of intervertebral disc degeneration include diffusion-weighted imaging, magnetic resonance imaging, diffusion tensor imaging, magnetic resonance spectroscopy, functional magnetic resonance imaging, dynamic computed tomography and magnetic resonance imaging, and T2 relaxometry. With dynamic imaging, the relative motions of normal and degenerated lumbar motion segments can be evaluated noninvasively. With further evaluation of the technique, hypermobile segments may be distinguishable from those with normal relative motion. T2 measurements obtained by T2 relaxometry appear to have important advantages with regard to spinal imaging because this modality provides a continuous and objective measure of the content of free water in the disc, which decreases with aging and degeneration. Anatomic imaging of the spine is highly accurate in the evaluation of nonmechanical causes of back pain and less beneficial in the evaluation of back pain that is due to mechanical causes. The development of functional imaging strategies of the spine will likely improve the management of patients with back pain. This article outlines the current magnetic resonance imaging protocols for intervertebral disc degeneration, indicates deficiencies in current imaging, and describes functional imaging strategies for the spine that will likely improve the evaluation of patients with back pain. It also reviews recent published articles on magnetic resonance imaging and computed tomographic imaging of the spine and details the results of studies that have explored the future potential of spine imaging.

Simultaneous functional magnetic resonance imaging in the rat spinal cord and brain

Functional magnetic resonance imaging (fMRI) method was developed to investigate the pattern and temporal relationship in neuronal pathways of brain and spinal cord. Signal intensity changes correlating with stimulation patterns were observed simultaneously in the rat spinal cord and brain using fMRI at 9.4 T. Electrical stimulation of the forepaw was used to elicit activity. A quadrature volume RF coil covering both brain and the cervical spinal cord was used. Sets of fast spin echo (FSE) images were acquire simultaneously for both brain and spinal cord fMRI. Experiments were repeated in single animal and across animals. Activities within the dorsal horn of the spinal cord and within the somatosensory cortex were observed consistently within each animal as well as across animals.

Functional MR imaging of the cervical spinal cord by use of electrical stimulation at LI4 (Hegu)

The purpose is to investigate the cervical spinal cord mapping on electrical stimulation at LI4 (Hegu) by using 'signal enhancement by extravascular water protons' (SEEP)-fMRI, and to establish the response of acupoint-stimulation in spinal cord. Three healthy volunteers were underwent low-frequency electrical stimulation at LI4. Meanwhile, a single-shot fast spin-echo (SSFSE) sequence was used to perform functional MR imaging on a 1.5 T GE Signa MR system. Cord activation was measured both in the sagittal and transverse imaging planes and then analyzed by AFNI (analysis of functional neuroimages) system. In the sagittal view, two subjects had an fMRI response in the cervical spinal cord upon electrical stimulation at LI4. The localizations of the segmental fMRI activation are both at C6 through T1 and C2/3 cervical spinal cord level. In the transverse imaging plane, significant fMRI responses could be measured in the last subjects locating at C6/7 segment, the cross-sectional localization of the activity measured in the spinal cord was most in terms of the ipsilateral posterior direction. It is concluded that the fMRI technique can be used for detecting with activity in the human cervical spinal cord by a single-shot fast spin-echo sequence on a 1.5 T GE clinical system. Investigating the acupoint-stimulation response in the spinal cord using the spinal fMRI will be helpful for the further discussion on the mechanisms of acupuncture to spinal cord diseases.

Spinal effects of acupuncture stimulation assessed by proton density-weighted functional magnetic resonance imaging at 0.2 T

Signal changes can be detected by proton density-weighted functional imaging in both the brain and the spinal cord. These are attributed to changes in extravascular water proton (signal enhancement by extravascular protons) density during neuronal activation. In this study, we used this technique to detect correlations between acupoint stimulation and neural activity in the spinal cord. Stimulation of acupoints associated with treatment of sensorimotor deficits (LI4 and LI11) was performed on 11 volunteers. During stimulation, 8 of the 11 subjects had consistent functional activations in C6/C7. A bilateral activation pattern was common. Our findings show that acupoint stimulation modulates activity in the spinal cord.

Magnetic resonance imaging of neuronal function in the spinal cord: spinal FMRI

A review of the current literature on magnetic resonance imaging of neuronal function in the spinal cord (spinal fMRI) is presented. The unique challenges of spinal fMRI are identified as being the small cross-sectional dimensions of the spinal cord, magnetic field inhomogeneity caused by the bone and cartilage in the spine, and motion of cerebrospinal fluid, blood, adjacent tissues and organs and of the spinal cord itself. Techniques have been developed to overcome or compensate for these challenges and the result is a fMRI method which is distinct from that used for mapping function in the brain. Evidence that the current spinal fMRI method provides accurate and sensitive maps of neuronal function is also discussed. Studies presented in the literature have demonstrated areas of neuronal activity corresponding with spinal cord neuroanatomy as a result of thermal and electrical stimuli and motor tasks with the hands, arms and legs. Signal intensity changes detected in active areas have also been demonstrated to depend on the intensity of the stimuli with both thermal stimulation and a motor task, providing evidence of the correspondence between spinal fMRI results and neuronal activity in the spinal cord.

Functional magnetic resonance imaging of the human lumbar spinal cord

PURPOSE

To determine whether consistent regions of activity could be observed in the lumbar spinal cord of single subjects with spin-echo functional MRI (fMRI) if several repeated experiments were performed within a single imaging session.

MATERIALS AND METHODS

Repeated fMRI experiments of the human lumbar spinal cord were performed at 1.5 T with a single-shot spin-echo technique (half-Fourier single-shot turbo spin-echo (HASTE)) as used by previous investigators, and a modified method (fluid-attenuated inversion recovery (FLAIR)-HASTE) that nulled the otherwise highly variable signal from the cerebrospinal fluid (CSF).

RESULTS

FLAIR-HASTE reduced the variability of the signal in the CSF region to background levels, and presumably reduced associated artifacts in the spinal cord. Consistent areas of activation in the spinal cord in response to a thermal stimulus just below the knee were not observed across the fMRI experiments with either method.

CONCLUSION

FLAIR-HASTE was useful for removing artifact in the spinal cord signal induced by variability in the CSF signal. However, with the techniques used in this study, we were not able to confirm the presence of a consistent fMRI response in the lumbar spinal cord because of the signal enhancement by extravascular protons (SEEP) effect during thermal stimulation of the hindlimb.

Interneuronal systems of the cervical spinal cord assessed with BOLD imaging at 1.5�T

The purpose of this study was to investigate if functional activity with spinal cord somatosensory stimulation can be visualized using BOLD fMRI. We investigated nine healthy volunteers using a somatosensory stimulus generator. The stimuli were applied in three different runs at the first, third, and fifth finger tip of the right hand, respectively, corresponding to dermatomes c6, c7, and c8. The stimuli gave an increase of BOLD signal (activation) in three different locations of the spinal cord and brain stem. First, activations could be seen in the spinal segment corresponding to the stimulated dermatome in seven out of nine volunteers for c6 stimulation, two out of eight for c7, and three out of eight for c8. These activations were located close to the posterior margin of the spinal cord, presumably reflecting synaptic transmission to dorsal horn interneurons. Second, activation in the medulla oblongata was evident in four subjects, most likely corresponding to the location of the nucleus cuneatus. The third location of activation, which was the strongest and most reliable observed was inside the spinal cord in the c3 and c4 segments. Activation at these spinal levels was almost invariably observed independently of the dermatome stimulated (9/9 for c6, 8/8 for c7, and 7/8 for c8 stimulation). These activations may pertain to an interneuronal system at this spinal level. The results are discussed in relation to neurophysiological studies on cervical spinal interneuronal pathways in animals and humans.

Issues about the fMRI of the human spinal cord

Noninvasive functional studies on human spinal cord by means of magnetic resonance imaging (MRI) are gaining attention because of the promising applications in the study of healthy and injured central nervous system. The findings obtained are generally consistent with the anatomic knowledge based on invasive methods, but the origin and specificity of functional contrast is still debated. In this paper, a review of current knowledge and major issues about functional MRI (fMRI) in the human spinal cord is presented, with emphasis on the main methodological and technical problems and on forthcoming applications as clinical tool.

Medical imaging of intervertebral disc degeneration: current status of imaging

STUDY DESIGN

The author reviewed literature and reports on spine imaging, selected key articles in which novel imaging strategies were described, and prepared a review of currently developing imaging strategies in intervertebral disc degeneration.

OBJECTIVES

To provide a review of imaging in intervertebral disc degeneration that covers the current methodology briefly and describes developing techniques in detail.

SUMMARY OF BACKGROUND DATA

Computed tomography and magnetic resonance imaging provide excellent anatomic images of the spine. However, anatomic imaging of the spine does not reliably identify the source of pain in patients with intervertebral disc degeneration. Many functional imaging techniques are suited to the study of the spine. Some of these techniques will improve our understanding of intervertebral disc degeneration and clinical symptomatology.

METHODS

The author selected reports in the current literature for further review and attempted to describe succinctly the material in the reports that are most relevant to spine imaging.

RESULTS

New and potentially useful imaging strategies for spine imaging include dynamic computed tomography, dynamic magnetic resonance imaging, functional magnetic resonance imaging, diffusion imaging, and magnetic resonance spectroscopy.

CONCLUSIONS

Technological advances in magnetic resonance imaging and computed tomography imaging continue to offer more opportunities to investigate and diagnose back pain and intervertebral disc degeneration.

Functional imaging and the neural systems of chronic pain

Pain remains a serious health care problem affecting millions of individuals, costing billions of dollars, and causing an immeasurable amount of human suffering. In designing improved therapies, there is still much to learn about peripheral nociceptor, nerves, and the spinal cord, and brain stem modulatory systems. Nevertheless, it is the brain that presents us with an incredible opportunity to understand the experience we call pain. Functional neuroimaging is helping to unlock the secrets of the sensory and emotional components of pain and its autonomic responses. These techniques are helping us to understand that pain is not a static disease with the pathologic findings localized to the periphery but is instead a highly plastic condition affecting multiple central neural systems. Functional neuroimaging is transforming our understanding of the neurobiology of pain and will be instrumental in helping us to design more rational treatments ultimately aimed at reducing the impact of pain on our patients. It is opening windows into the function of the brain that were previously closed.

Noninvasive assessment of the injured human spinal cord by means of functional magnetic resonance imaging

STUDY DESIGN

A magnetic resonance imaging technique that enables indirect detection of neuronal activity has been developed for the spinal cord. In the present study, this method, spinal functional magnetic resonance imaging (fMRI), is applied to the first study of the injured spinal cord, with the goal of better clinical assessment of the entire cord.

OBJECTIVES

The objectives of this project are: (1) to investigate the neuronal activity that can be detected in the spinal cord caudal to a chronic injury by means of spinal fMRI, and (2) to develop spinal fMRI as a clinical diagnostic tool.

SETTING

Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada.

METHODS

fMRI of the spinal cord was carried out in 27 volunteers with cervical or thoracic spinal cord injuries (SCIs). Of these volunteers, 18 had complete injuries, and nine had incomplete injuries. Spinal fMRI was carried out in a 1.5 T clinical MR system, using established methods. Thermal stimulation at 10 degrees C was applied to the fourth lumbar dermatome on each leg, and images were obtained of the entire lumbar spinal cord.

RESULTS

Areas of neuronal activity were consistently observed in the lumbar spinal cord in response to the thermal stimulation, even when the subjects had no awareness of the sensation. The pattern of activity was notably different compared with noninjured subjects. In general, subjects with complete SCI showed absent or diminished dorsal gray matter activity, but had enhanced ventral activity, particularly contralateral to the stimulation.

CONCLUSIONS

Spinal fMRI is able to provide a noninvasive assessment of the injured spinal cord that does not depend on the patient's perception of the stimulus being applied. This work was carried out on a standard clinical MRI system without modification, and so is readily applicable in most MR units.

SPONSORSHIP

This work was funded by a grant from the Canadian Institutes of Health Research (CIHR).

fMRI of the lumbar spinal cord during a lower limb motor task

This study applied spinal fMRI to the lumbar spinal cord during lower limb motor activity. During active ankle movement, activity was detected in the lumbar spinal cord motor areas and sensory areas bilaterally. During passive ankle movement, activity was detected in the motor and sensory areas in lower lumbar spinal cord segments and motor activity in higher lumbar spinal cord segments. Spinal fMRI detects patterns of activity consistent with known physiology and can be used to reliably assess activity in the lumbar spinal cord during lower limb motor stimulation. This study affirms spinal fMRI as an effective tool for assessing spinal cord function and increases its potential as a clinical tool.