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 (λ_||) and perpendicular (λ_?) 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: λ_||: 2.13 ± 0.14 and 2.14 ± 0.11 μm²/ms; λ_?: 0.67 ± 0.16 and 0.61 ± 0.09 μm²/ms; MD: 1.15 ± 0.15 and 1.12 ± 0.08 μm²/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. Copyright © 2009 John Wiley & Sons, Ltd.     

Tract‐specific and age‐related variations of the spinal cord microstructure: a multi‐parametric MRI study using diffusion tensor imaging (DTI) and inhomogeneous magnetization transfer (ihMT)

Being able to finely characterize the spinal cord (SC) microstructure and its alterations is a key point when investigating neural damage mechanisms encountered in different central nervous system (CNS) pathologies, such as multiple sclerosis, amyotrophic lateral sclerosis or myelopathy. Based on novel methods, including inhomogeneous magnetization transfer (ihMT) and dedicated SC probabilistic atlas post‐processing, the present study focuses on the in vivo characterization of the healthy SC tissue in terms of regional microstructure differences between (i) upper and lower cervical vertebral levels and (ii) sensory and motor tracts, as well as differences attributed to normal aging. Forty‐eight healthy volunteers aged from 20 to 70 years old were included in the study and scanned at 3 T using axial high‐resolution T₂*‐w imaging, diffusion tensor imaging (DTI) and ihMT, at two vertebral levels (C2 and C5). A processing pipeline with minimal user intervention, SC segmentation and spatial normalization into a reference space was implemented in order to assess quantitative morphological and structural parameters (cross‐sectional areas, scalar DTI and MT/ihMT metrics) in specific white and gray matter regions of interest. The multi‐parametric MRI metrics collected allowed upper and lower cervical levels to be distinguished, with higher ihMT ratio (ihMTR), higher axial diffusivity (λ_∥) and lower radial diffusivity (λ_⊥) at C2 compared with C5. Significant differences were also observed between white matter fascicles, with higher ihMTR and lower λ_∥ in motor tracts compared with posterior sensory tracts. Finally, aging was found to be associated with significant metric alterations (decreased ihMTR and λ_∥). The methodology proposed here, which can be easily transferred to the clinic, provides new insights for SC characterization. It bears great potential to study focal and diffuse SC damage in neurodegenerative and demyelinating diseases. Copyright © 2016 John Wiley & Sons, Ltd.     

Quantitative MRI in a non‐surgical model of cervical spinal cord injury

Quantitative T₂ (qT2), diffusion tensor imaging (DTI), and histology were used to investigate a cervical model of spinal cord injury (SCI) in the rat. While quantitative MRI can significantly increase the specificity in the presence of pathology, it must be validated for each type of injury or disease. In the case of traumatic SCI most models are difficult to image, either due to the location of the injury, or as a result of damage to surrounding tissues resulting from invasive surgical procedures. In this study a non‐surgical cervical model of SCI, produced using a combination of focused ultrasound and microbubbles, was used to produce pathology similar to that seen in models of contusive and compressive injuries. qT2 and DTI were performed at 24 h and 1 and 2 weeks following injury, and compared with H&E and luxol fast blue histology. In the injured spinal cord, in addition to intra/extracellular (I/E) water and myelin water in white matter, qT2 revealed a large component with very short T₂ of about 3 ms, which was highly correlated with the presence of hemorrhage in both gray and white matter at 24 h, and with the presence of hemosiderin in gray matter at 2 weeks following injury. The T₂ of the I/E water peak was also elevated at 24 h in both gray and white matter, which was correlated with the presence of vacuolation/edema on histology. Cystic cavities were only seen at the 1 or 2 week timepoints, and were correlated with the presence of a water peak with T₂ > 250 ms. No significant changes in diffusivity parameters were observed. Pathologies were often co‐occurring, with opposite effects on the average T₂ in a given voxel, reducing the visibility of injured tissue on standard T₂‐weighted MR images. Copyright © 2015 John Wiley & Sons, Ltd.     

The central canal of the human spinal cord: a computerised 3-D study

Knowledge of the structure and function of the central canal of the human spinal cord is important in understanding the pathogenesis of syringomyelia. Analysis of the morphology of the central canal is difficult using isolated histological sections. A 3-dimensional reconstruction technique using digitised histological sections was therefore developed to visualise the morphology of the central canal. The technique was used to study the canal in the conus medullaris and filum terminale of 1 sheep and 4 human spinal cords. A variety of morphological features were demonstrated including canal duplication, a terminal ventricle and openings from the canal lumen into the subarachnoid space. The findings suggest the possibility of a functionally important fluid communication in the caudal spinal cord which may have a sink function.     

Multi‐compartmental diffusion characterization of the human cervical spinal cord in vivo using the spherical mean technique

The purpose of this work was to evaluate the feasibility and reproducibility of the spherical mean technique (SMT), a multi‐compartmental diffusion model, in the spinal cord of healthy controls, and to assess its ability to improve spinal cord characterization in multiple sclerosis (MS) patients at 3 T. SMT was applied in the cervical spinal cord of eight controls and six relapsing‐remitting MS patients. SMT provides an elegant framework to model the apparent axonal volume fraction v_ax, intrinsic diffusivity D_ax, and extra‐axonal transverse diffusivity D_{ex_perp} (which is estimated as a function of v_ax and D_ax) without confounds related to complex fiber orientation distribution that reside in diffusion MRI modeling. SMT's reproducibility was assessed with two different scans within a month, and SMT‐derived indices in healthy and MS cohorts were compared. The influence of acquisition scheme on SMT was also evaluated. SMT's v_ax, D_ax, and D_{ex_perp} measurements all showed high reproducibility. A decrease in v_ax was observed at the site of lesions and normal appearing white matter (p < 0.05), and trends towards a decreased D_ax and increased D_{ex_perp} were seen. Importantly, a twofold reduction in acquisition yielded similarly high accuracy with SMT. SMT provides a fast, reproducible, and accurate method to improve characterization of the cervical spinal cord, and may have clinical potential for MS patients.     

Region‐specific impairment of the cervical spinal cord (SC) in amyotrophic lateral sclerosis: A preliminary study using SC templates and quantitative MRI (diffusion tensor imaging/inhomogeneous magnetization transfer)

In this preliminary study, our objective was to investigate the potential of high‐resolution anatomical imaging, diffusion tensor imaging (DTI) and conventional/inhomogeneous magnetization transfer imaging [magnetization transfer (MT)/inhomogeneous magnetization transfer (ihMT)] at 3 T, analyzed with template‐extracted regions of interest, to measure the atrophy and structural changes of white (WM) and gray (GM) matter spinal cord (SC) occurring in patients with amyotrophic lateral sclerosis (ALS). Ten patients with ALS and 20 age‐matched healthy controls were recruited. SC GM and WM areas were automatically segmented using dedicated templates. Atrophy indices were evaluated from T ₂*‐weighted images at each vertebral level from cervical C1 to C6. DTI and ihMT metrics were quantified within the corticospinal tract (CST), posterior sensory tract (PST) and anterior GM (aGM) horns at the C2 and C5 levels. Clinical disabilities of patients with ALS were evaluated using the Revised ALS Functional Rating Scale, upper motor neuron (UMN) and Medical Research Council scorings, and correlated with MR metrics. Compared with healthy controls, GM and WM atrophy was observed in patients with ALS, especially at lower cervical levels, where a strong correlation was also observed between GM atrophy and the UMN score (R  = ?0.75, p  = 0.05 at C6). Interestingly, a significant decrease in ihMT ratio was found in all regions of interest (p  < 0.0008), fractional anisotropy (FA) and MT ratios decreased significantly in CST, especially at C5 (p  < 0.005), and λ_// (axial diffusivity) decreased significantly in CST (p  = 0.0004) and PST (p  = 0.003) at C2. Strong correlations between MRI metrics and clinical scores were also found (0.47 < |R | < 0.87, p  < 0.05). Altogether, these preliminary results suggest that high‐resolution anatomical imaging and ihMT imaging, in addition to DTI, are valuable for the characterization of SC tissue impairment in ALS. In this study, in addition to an important SC WM demyelination, we also observed, for the first time in ALS, impairments of cervical aGM.     

Neurochemical profile of the human cervical spinal cord determined by MRS

MRS enables insight into the chemical composition of central nervous system tissue. However, technical challenges degrade the data quality when applied to the human spinal cord. Therefore, to date detection of only the most prominent metabolite resonances has been reported in the healthy human spinal cord. The aim of this investigation is to provide an extended metabolic profile including neurotransmitters and antioxidants in addition to metabolites involved in the energy and membrane metabolism of the human cervical spinal cord in vivo. To achieve this, data quality was improved by using a custom‐made, cervical detector array together with constructive averaging of a high number of echo signals, which is enabled by the metabolite cycling technique at 3T. In addition, the improved spinal cord spectra were extensively cross‐validated, in vivo, post‐mortem in situ and ex vivo. Reliable identification of up to nine metabolites was achieved in group analyses for the first time. Distinct features of the spinal cord neurochemical profile, in comparison with the brain neurotransmission system, include decreased concentrations of the sum of glutamate and glutamate and increased concentrations of aspartate, γ‐amino‐butyric acid, scyllo‐inositol and the sum of myo‐inositol and glycine.     

Glia to neuron ratio in the posterior aspect of the human spinal cord at thoracic segments relevant to spinal cord stimulation

Spinal cord stimulation (SCS) applied between T8 and T11 segments has been shown to be effective for the treatment of chronic pain of the lower back and limbs. However, the mechanism of the analgesic effect at these medullary levels remains unclear. Numerous studies relate glial cells with development and maintenance of chronic neuropathic pain. Glial cells are electrically excitable, which makes them a potential therapeutic target using SCS. The aim of this study is to report glia to neuron ratio in thoracic segments relevant to SCS, as well as to characterize the glia cell population at these levels. Dissections from gray and white matter of posterior spinal cord segments (T8, T9, intersection T9/T10, T10 and T11) were obtained from 11 human cadavers for histological analyses. Neuronal bodies and glial cells (microglia, astrocytes and oligodendrocytes) were immunostained, microphotographed and counted using image analysis software. Statistical analyses were carried out to establish significant differences of neuronal and glial populations among the selected segments, between the glial cells in a segment, and glial cells in white and gray matter. Results show that glia to neuron ratio in the posterior gray matter of the human spinal cord within the T8–T11 vertebral region is in the range 11 : 1 to 13 : 1, although not significantly different among vertebral segments. Glia cells are more abundant in gray matter than in white matter, whereas astrocytes and oligodendrocytes are more abundant than microglia (40 : 40 : 20). Interestingly, the population of oligodendrocytes in the T9/T10 intersection is significantly larger than in any other segment. In conclusion, glial cells are the predominant bodies in the posterior gray and white matter of the T8–T11 segments of the human spinal cord. Given the crucial role of glial cells in the development and maintenance of neuropathic pain, and their electrophysiological characteristics, anatomical determination of the ratio of different cell populations in spinal segments commonly exposed to SCS is fundamental to understand fully the biological effects observed with this therapy.     

Activation‐induced CD137 is a fast assay for identification and multi‐parameter flow cytometric analysis of alloreactive T cells

Detection and isolation of viable alloreactive T cells at the single‐cell level requires a cell surface marker induced specifically upon T cell receptor activation. In this study, a member of the tumour necrosis factor receptor (TNFR)‐family, CD137 (4‐1BB) was investigated for its potential to identify the total pool of circulating alloreactive T cells. Optimal conditions for sensitive and specific detection of allogeneic‐induced CD137 expression on circulating T cells were established. Thereafter, CD137⁺ alloreactive T cells were phenotypically and functionally characterized by multi‐parameter flow cytometry. Alloantigen‐induced CD137 expression identified both alloreactive CD8⁺ T cells (mean ± standard error of the mean: 0·21 ± 0·07%) and alloreactive CD4⁺ T cells (0·21 ± 0·05%). CD137⁺ alloreactive T cells were detected in different T cell subsets, including naive T cells, but were found preferentially in CD28⁺ T cells and not in the terminally differentiated T cell subset. Upon allogeneic (re‐)stimulation, the cytokine‐producing as well as proliferative capacity of T cells resided mainly within the CD137‐expressing fraction. About 10% of the CD137⁺ alloreactive T cells produced any combination of interferon (IFN)‐γ, interleukin (IL)‐2 and TNF‐α. Polyfunctional alloreactive T cells, defined by multiple cytokine expression, were observed infrequently. In conclusion, activation‐induced CD137 expression is a fast assay allowing for detection and functional analysis of the total alloreactive T cell compartment at the single‐cell level by multi‐parameter flow cytometry.     

Comparison of spoiled gradient echo and steady‐state free‐precession imaging for native myocardial T1 mapping using the slice‐interleaved T1 mapping (STONE) sequence

Cardiac T₁ mapping allows non‐invasive imaging of interstitial diffuse fibrosis. Myocardial T₁ is commonly calculated by voxel‐wise fitting of the images acquired using balanced steady‐state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B₁ and B₀ imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T₁ mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal‐to‐noise ratio (SNR) of GRE versus SSFP imaging. A slice‐interleaved T₁ mapping (STONE) sequence with SSFP readout (STONE–SSFP) has been recently proposed for native myocardial T₁ mapping, which allows longer recovery of magnetization (>8 R–R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T₁ mapping using STONE with GRE imaging readout (STONE–GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE–GRE and STONE–SSFP for native myocardial T₁ mapping at 1.5T. In numerical simulations, STONE–SSFP shows sensitivity to both T₂ and off resonance. Despite the insensitivity of GRE imaging to T₂, STONE–GRE remains sensitive to T₂ due to the dependence of the inversion pulse performance on T₂. In the phantom study, STONE–GRE had inferior accuracy and precision and similar repeatability as compared with STONE–SSFP. In in vivo studies, STONE–GRE and STONE–SSFP had similar myocardial native T₁ times, precisions, repeatabilities and subjective T₁ map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE–GRE provides similar native myocardial T₁ measurements, precision, repeatability, and subjective image quality when compared with STONE–SSFP at 1.5T.     

In vivo magnetic resonance spectroscopy detection of combined glutamate‐glutamine in healthy upper cervical cord at 3 T

The possibility of quantifying the superimposed signal of glutamate and glutamine (Glx) and its components by ¹ H magnetic resonance spectroscopy (MRS) in the spinal cord is an exciting challenge with important clinical applications in neurological conditions. The spinal cord is a particularly difficult region of interest due to its small volume, magnetic field inhomogeneities and physiological motion. In this study, we investigated for the first time the feasibility of obtaining quantitative measurements of Glx in healthy cervical spinal cord by ¹ H MRS at 3 T. The aim of this study was to compare two commercially available MRS sequences by spectral simulations and in vivo. A short echo time (TE) point resolved spectroscopy (PRESS) with TE = 30 ms and a stimulated echo acquisition mode (STEAM) with TE = 11 ms and mixing time (TM) = 17 ms were compared for reliability of Glx fit. Data allowed us to determine sample size estimates for future clinical studies for the first time. Results showed that PRESS provided a reliable fit for Glx in all cases (Cramér Rao lower bounds < 20%) whereas no reliable Glx fits were achieved using STEAM. Neither protocol provided reliable Glu quantification. The power calculations showed that a minimum sample size of 17 subjects per group was needed to detect Glx changes of > 20% using the PRESS sequence. This study proposed a clinically feasible MRS method for Glx detection in the human cervical cord in vivo including sample sizes needed for conclusive clinical studies. Copyright © 2012 John Wiley & Sons, Ltd.     

High‐resolution imaging of magnetisation transfer and nuclear Overhauser effect in the human visual cortex at 7 T

The aim of this study was to optimise a pulse sequence for high‐resolution imaging sensitive to the effects of conventional macromolecular magnetisation transfer (MT^m) and nuclear Overhauser enhancement (NOE), and to use it to investigate variations in these parameters across the cerebral cortex. A high‐spatial‐resolution magnetisation transfer‐prepared turbo field echo (MT‐TFE) sequence was designed to have high sensitivity to MT^m and NOE effects, whilst being robust to B₀ and B₁ inhomogeneities, and producing a good point spread function across the cortex. This was achieved by optimising the saturation and imaging components of the sequence using simulations based on the Bloch equations, including exchange and an image simulator. This was used to study variations in these parameters across the cortex. Using the sequence designed to be sensitive to NOE and MT^m, a variation in signals corresponding to a variation in MT^m and NOE across the cortex, consistent with a reduction in myelination from the white matter surface to the pial surface of the cortex, was observed. In regions in which the stria was visible on T₂*‐weighted images, it could also be detected in signals sensitive to MT^m and NOE. There was greater variation in signals sensitive to NOE, suggesting that the NOE signal is more sensitive to myelination. A sequence has been designed to image variations in MT^m and NOE at high spatial resolution and has been used to investigate variations in contrast in these parameters across the cortex. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamic 2D and 3D mapping of hyperpolarized pyruvate to lactate conversion in vivo with efficient multi‐echo balanced steady‐state free precession at 3 T

The aim of this study was to acquire the transient MRI signal of hyperpolarized tracers and their metabolites efficiently, for which specialized imaging sequences are required. In this work, a multi‐echo balanced steady‐state free precession (me‐bSSFP) sequence with Iterative Decomposition with Echo Asymmetry and Least squares estimation (IDEAL) reconstruction was implemented on a clinical 3 T positron‐emission tomography/MRI system for fast 2D and 3D metabolic imaging. Simulations were conducted to obtain signal‐efficient sequence protocols for the metabolic imaging of hyperpolarized biomolecules. The sequence was applied in vitro and in vivo for probing the enzymatic exchange of hyperpolarized [1–¹³C]pyruvate and [1–¹³C]lactate. Chemical shift resolution was achieved using a least‐square, iterative chemical species separation algorithm in the reconstruction. In vitro, metabolic conversion rate measurements from me‐bSSFP were compared with NMR spectroscopy and free induction decay‐chemical shift imaging (FID‐CSI). In vivo, a rat MAT‐B‐III tumor model was imaged with me‐bSSFP and FID‐CSI. 2D metabolite maps of [1–¹³C]pyruvate and [1–¹³C]lactate acquired with me‐bSSFP showed the same spatial distributions as FID‐CSI. The pyruvate‐lactate conversion kinetics measured with me‐bSSFP and NMR corresponded well. Dynamic 2D metabolite mapping with me‐bSSFP enabled the acquisition of up to 420 time frames (scan time: 180‐350 ms/frame) before the hyperpolarized [1–¹³C]pyruvate was relaxed below noise level. 3D metabolite mapping with a large field of view (180 × 180 × 48 mm³) and high spatial resolution (5.6 × 5.6 × 2 mm³) was conducted with me‐bSSFP in a scan time of 8.2 seconds. It was concluded that Me‐bSSFP improves the spatial and temporal resolution for metabolic imaging of hyperpolarized [1–¹³C]pyruvate and [1–¹³C]lactate compared with either of the FID‐CSI or EPSI methods reported at 3 T, providing new possibilities for clinical and preclinical applications.     

Evidence that dopamine‐beta‐hydroxylase immunoreactive neurons in the lateral reticular nucleus project to the spinal cord in the rat

The existence of noradrenergic projections from the lateral reticular nucleus (LRt) to the dorsal quadrant of cervical, thoracic, or lumbar spinal cord was investigated using a combined method of WGA‐apo‐HRP‐gold retrograde tracing and dopamine‐beta‐hydroxylase (DBH) immunocytochemistry. Preliminary retrograde tracing studies indicated that LRt neurons projecting to cervical, thoracic, or lumbar spinal cord were characteristically located near the perimeter of the LRt. Double‐labeling experiments demonstrated that a portion of these peripherally‐located, spinal‐projecting neurons were DBH‐immunoreactive. Double‐labeled neurons were also located at the parvocellular division of the contralateral LRt in the thoracic injection cases. Double‐labeled neurons were not observed at the subtrigeminal division in cervical, thoracic, or lumbar injection case. The results suggest the possibility that the noradrenergic LRt‐spinal pathway might be involved in a variety of pain processing and cardiovascular regulatory functions in the rat. Anat Rec 263:269–279, 2001. © 2001 Wiley‐Liss, Inc.     

电针对脊髓损伤早期caspase-3 mRNA及蛋白表达的影响

目的:探讨电针对脊髓损伤后caspase-3 mRNA及蛋白表达的影响。方法:成年雄性SD大鼠,随机分为模型组、电针(EA)治疗组、甲基强的松龙(MP)组及假手术组。采用改良的Allen's垂击法致大鼠T10脊髓损伤,应用原位杂交和免疫组织化学方法及图象定量分析法观察脊髓损伤后caspase-3 mRNA和蛋白的表达。结果:假手术组caspase-3 mRNA有中等数量的表达,脊髓损伤模型组caspase-3 mRNA表达增高;EA组与MP组caspase-3 mRNA的表达量低于模型组,与其比较有显著性差异;两治疗组间比较无显著性差异。假手术组caspase-3蛋白未见表达,脊髓损伤模型组caspase-3阳性细胞数增多;EA组与MP组caspase-3阳性细胞数低于模型组,与其比较有显著性差异;两治疗组间比较无显著性差异。结论:电针可下调caspase-3 mRNA及蛋白的表达,进而抑制细胞凋亡,保护神经细胞。     

Motion correction and frequency stabilization for MRS of the human spinal cord

Subject motion is challenging for MRS, because it can falsify results. For spinal cord MRS in particular, subject movement is critical, since even a small movement > 1 mm) can lead to a voxel shift out of the desired measurement region. Therefore, the identification of motion corrupted MRS scans is essential. In this investigation, MR navigators acquired simultaneously with the MRS data are used to identify a displacement of the spinal cord due to subject motion. It is shown that navigators are able to recognize substantial subject motion (>1 mm) without impairing the MRS measurement. In addition, navigators are easy to apply to the measurement, because no additional hardware and just a minor additional user effort are needed. Moreover, no additional scan time is required, because navigators can be applied in the deadtime of the MRS sequence. Furthermore, in this work, retrospective motion correction combined with frequency stabilization is presented by combining navigators with non‐water‐suppressed ¹H‐MRS, resulting in an improved spectral quality of the spinal cord measurements. Copyright © 2016 John Wiley & Sons, Ltd.     

Absence of connections between spinal nerves and the spinal cord in a twin fetus: a very rare malformation occasionally evidenced at autopsy

We describe a rare case of spinal cord malformation in a dichorionic diamniotic twin fetus aborted at 20 weeks' gestation due to acute chorioamnionitis with placental dysmaturity probably caused by a maternal viral infection. At autopsy, there were no connections between the spinal nerves and the spinal cord. The spinal cord lacked the posterior median fissure and gray matter; only a few neurons were present in the anterior and lateral gray columns. No chromosome anomalies were found. Although we cannot reconstruct the pathogenetic chain of events leading to this malformation, we believe that it is correlated with a maternal viral infection. We hypothesize that this viral infection altered the delicate balance between the factors inducing and those inhibiting fetal spinal neural differentiation.