Monoclonal antibodies conjugated with superparamagnetic iron oxide particles allow magnetic resonance imaging detection of lymphocytes in the mouse brain.

We investigated the potential of antibody-vectorialized superparamagnetic iron oxide (SPIO) particles as cellular specific magnetic resonance contrast agents to image lymphocyte populations within the central nervous system (CNS), with the final goal of obtaining a reliable tool for noninvasively detecting and tracking specific cellular populations in vivo. We used superparamagnetic particles bound to a monoclonal antibody. The particle is the contrast agent, by means of its T2* relaxation properties; the antibody is the targeting vector, responsible for homing the particle to target a surface antigen. To investigate the efficiency of particle vectorialization by these antibodies, we compared two types of antibody-vectorialized CD3-specific particles in vivo. We successfully employed vectorialized SPIO particles to image B220⁺ cells in a murine model of B-cell lymphoma. Likewise, we were able to identify CD3⁺ infiltrates in a murine model of multiple sclerosis. The specificity of the technique was confirmed by immunohistochemistry and electron microscopy of corresponding sections. Our findings suggest that indirect binding of the antibody to a streptavidinated particle allows for enhanced particle vectorialization compared to covalent binding of the antibody to the particle.

A modified damped Richardson-Lucy algorithm to reduce isotropic background effects in spherical deconvolution.

Spherical deconvolution methods have been applied to diffusion MRI to improve diffusion tensor tractography results in brain regions with multiple fibre crossing. Recent developments, such as the introduction of non-negative constraints on the solution, allow a more accurate estimation of fibre orientations by reducing instability effects due to noise robustness. Standard convolution methods do not, however, adequately model the effects of partial volume from isotropic tissue, such as gray matter, or cerebrospinal fluid, which may degrade spherical deconvolution results. Here we use a newly developed spherical deconvolution algorithm based on an adaptive regularization (damped version of the Richardson-Lucy algorithm) to reduce isotropic partial volume effects. Results from both simulated and in vivo datasets show that, compared to a standard non-negative constrained algorithm, the damped Richardson-Lucy algorithm reduces spurious fibre orientations and preserves angular resolution of the main fibre orientations. These findings suggest that, in some brain regions, non-negative constraints alone may not be sufficient to reduce spurious fibre orientations. Considering both the speed of processing and the scan time required, this new method has the potential for better characterizing white matter anatomy and the integrity of pathological tissue.

Ocular adnexal lymphoma: diffusion-weighted mr imaging for differential diagnosis and therapeutic monitoring.

PURPOSE: To describe the magnetic resonance (MR) imaging and diffusion-weighted (DW) imaging features of ocular adnexal lymphomas (OALs), to determine the diagnostic accuracy of apparent diffusion coefficient (ADC) for discriminating OALs from other orbital mass lesions, and to assess whether variations in ADC constitute a reliable biomarker of OAL response to therapy. MATERIALS AND METHODS: Institutional ethical committee approval and informed consent were obtained. In this prospective study, 114 white subjects (65 females and 49 males) were enrolled. Thirty-eight patients with histopathologically proved OAL underwent serial MR and DW imaging examination of the orbits. ADCs of OALs were compared with those of normal orbital structures, obtained in 18 healthy volunteers, and other orbital mass lesions, prospectively acquired in 58 patients (20 primary non-OAL neoplasms, 15 vascular benign lesions, 12 inflammatory lesions, 11 metastases). Interval change in ADC of OALs before and after treatment was analyzed in 29 patients. Analysis of covariance and a paired t test were used for statistical analysis. RESULTS: Baseline ADCs in OALs were lower than those in normal structures and other orbital diseases (P < .001). An ADC threshold of 775 x 10(-6) mm(2)/sec resulted in 96% sensitivity, 93% specificity, 88% positive predictive value, 98.2% negative predictive value, and 94.4% accuracy in OAL diagnosis. Following appropriate treatment, 10 (34%) of 29 patients showed OAL volumetric reduction, accompanied (n = 7) or preceded (n = 3) by an increase in ADC (P = .005). Conversely, a further reduction of ADC was observed in the seven patients who experienced disease progression (P < .05). CONCLUSION: ADC permits accurate diagnosis of OALs. Interval change in ADC after therapy represents a helpful tool for predicting therapeutic response.

Intraoperative use of diffusion tensor imaging fiber tractography and subcortical mapping for resection of gliomas: technical considerations.

Resection of lesions involving motor or language areas or pathways requires the intraoperative identification of functional cortical and subcortical sites for effectively and safe guidance. Diffusion tensor (DT) imaging and fiber tractography are MR imaging techniques based on the concept of anisotropic water diffusion in myelinated fibers, which enable 3D reconstruction and visualization of white matter tracts and provide information about the relationship of these tracts to the tumor mass. The authors routinely used DT imaging fiber tractography to reconstruct various tracts involved in the motor and/or language system in a large series of patients with lesions involving the motor and/or language areas or pathways. The DT imaging fiber tractography data were loaded into the neuronavigational system and combined intraoperatively with those obtained from direct electrical stimulation applied at the subcortical level. In this paper the authors report the results of their experience, describing the findings for each tract and discussing technical aspects of the combined use as well as the pitfalls.

Low power switched-resistor band-pass filter for neural recording channels in 130nm CMOS.

In this work, we present a low-power 2nd order band-pass filter for neural recording applications. The central frequency of the passband is set to 375Hz and the quality factor to 5 to properly process the neural signals related to the onset of epileptic seizure, and to strongly attenuate all the out of band biological signals and electrical disturbances. The biquad filter is based on a fully differential Tow Thomas architecture in which high-valued resistors are implemented through switched high-resistivity polysilicon resistors. A supply voltage as low as 0.8V and MOS transistors operating in the sub-threshold region are exploited to achieve a power consumption as low as 170nW, when driving a 1pF load capacitance. The filter exhibits a tuning range of the resonance frequency from 200Hz to 400Hz, and an area footprint of only 0.021 mm2. Very low power consumption and area occupation are key specifications for integrated, multiple-sensors, neural recording systems.

Monitoring disease evolution and treatment response in lysosomal disorders by the peripheral benzodiazepine receptor ligand PK11195.

Microglia activation and neuroinflammation play a pivotal role in the pathogenesis of lysosomal storage disorders (LSD) affecting the central nervous system (CNS), which are amenable to treatment by hematopoietic stem cell transplantation (HSCT). HSCT efficacy relies on replacing the intra- and extra-vascular hematopoietic cell compartments, including CNS microglia, with a cell population expressing the functional enzyme. Non-invasive and quantitative assessment of microglia activation and of its reduction upon HSCT might allow for evaluation of disease evolution and response to treatment in LSD. We here demonstrate that microglia activation can be quantified ex vivo and in vivo by PET using the peripheral benzodiazepine receptor ligand PK11195 in two models of LSD. Furthermore, we show a differential PBR binding following microglia replacement by donor cells in mice undergoing HSCT. Our data indicates that PBR ligands constitute valuable tools for monitoring the evolution and the response to treatment of LSD with CNS involvement, and enable us to evaluate whether the turnover between endogenous and donor microglia following HSCT could be adequate enough to delay disease progression.

Structural and functional MRI correlates of Stroop control in benign MS.

The objective of this study was to assess the functional and structural substrates of cognitive network changes in patients with benign multiple sclerosis (BMS), using an analysis of effective connectivity and MR tractography. Using a 3-Tesla scanner, we acquired dual-echo, diffusion tensor (DT) and functional MRI during the performance of the Stroop task from 15 BMS patients and 19 healthy controls. DT MRI tractography was used to calculate DT derived metrics from several white matter (WM) fiber bundles, thought to be involved in cognitive performance. DT MRI metrics from WM fiber bundles not directly related with cognitive performance were also derived. Effective connectivity analysis was performed using statistical parametric mapping. MS patients had significantly abnormal DT MRI metrics in all the structures analyzed. Compared with controls, MS patients had more significant activations of several areas of the cognitive network involved in Stroop performance, bilaterally. Compared with controls, BMS patients also had increased connectivity strengths between several cortical areas of the sensorimotor network and the right (R) inferior frontal gyrus and the R cerebellum, as well as decreased connectivity strengths with the anterior cingulate cortex. Coefficients of altered connectivity were moderately correlated with structural MRI metrics of tissue damage within intra- and inter-hemispheric cognitive-related WM fiber bundles, while no correlations were found with the remaining fiber bundles studied, suggesting that functional cortical changes in patients with BMS might represent an adaptive response driven by damage of specific WM structures.

Efficient in vitro labeling of human neural precursor cells with superparamagnetic iron oxide particles: relevance for in vivo cell tracking.

Recent studies have raised appealing possibilities of replacing damaged or lost neural cells by transplanting in vitro-expanded neural precursor cells (NPCs) and/or their progeny. Magnetic resonance (MR) tracking of superparamagnetic iron oxide (SPIO)-labeled cells is a noninvasive technique to track transplanted cells in longitudinal studies on living animals. Murine NPCs and human mesenchymal or hematopoietic stem cells can be efficiently labeled by SPIOs. However, the validation of SPIO-based protocols to label human neural precursor cells (hNPCs) has not been extensively addressed. Here, we report the development and validation of optimized protocols using two SPIOs (Sinerem and Endorem) to label human hNPCs that display bona fide stem cell features in vitro. A careful titration of both SPIOs was required to set the conditions resulting in efficient cell labeling without impairment of cell survival, proliferation, self-renewal, and multipotency. In vivo magnetic resonance imaging (MRI) combined with histology and confocal microscopy indicated that low numbers (5 x 10(3) to 1 x 10(4)) of viable SPIO-labeled hNPCs could be efficiently detected in the short term after transplantation in the adult murine brain and could be tracked for at least 1 month in longitudinal studies. By using this approach, we also clarified the impact of donor cell death to the MR signal. This study describes a simple protocol to label NPCs of human origin using SPIOs at optimized low dosages and demonstrates the feasibility of noninvasive imaging of labeled cells after transplantation in the brain; it also evidentiates potential limitations of the technique that have to be considered, particularly in the perspective of neural cell-based clinical applications.

Decreased parietal cortex activity during mental rotation in children with congenital hypothyroidism.

BACKGROUND: The ability to detect the spatial characteristics of objects and to rotate them mentally is frequently impaired in early treated congenital hypothyroidism (CH) children. AIMS: To explore the neural substrate of the visuospatial difficulty in children with CH, we studied 15 children with CH (8-10 years) and 13 age-matched control children with functional magnetic resonance imaging (fMRI) using a mental rotation task (VST). RESULTS: Performance at VST was significantly different between the two groups. Moreover, fMRI data showed greater activation in the superior parietal cortex in control children while children with CH had greater activation in the bilateral SMA and the opercular region of the precentral gyrus, the adjacent insula and the left somatosensory parietal cortex. Furthermore, children with CH deactivated the inferior parietal cortex (Brodmann area 40) more than controls. CONCLUSION: We suggest that the poorer performance of children with CH on VST task is related to the decreased activation in brain areas important for the mental representation of the objects' spatial characteristics, with increased recruitment of regions involved in the representation of somatosensory whole-body information. More studies will be necessary to understand if this different effectiveness in VST reflects immaturity of the neural system or its actual impairment.

Structural and metabolic changes in the brain of patients with upper motor neuron disorders: a multiparametric MRI study.

Our objective was to assess and compare the diagnostic sensitivity of conventional MRI (cMRI), magnetization transfer imaging (MTI), diffusion-weighted imaging (DWI), and proton magnetic resonance spectroscopic imaging ((1)H-MRSI) in patients with amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS). Thirty-eight ALS patients, nine PLS patients, and 22 healthy controls were enrolled. cMRI, MTI, DWI and (1)H-MRSI were obtained. ALS patients were classified as advanced phase (Ap)-ALS (definite+probable) and early phase (Ep)-ALS (possible+probable-laboratory supported). cMRI was highly sensitive in detecting corticospinal tract (CST) hyperintensities in Ap-ALS (63.4%) and PLS (71.9%), but it was poorly sensitive in Ep-ALS (17.1%). Hyperintensity on proton density-weighted images correlated with ALS severity (p=0.02). CST apparent diffusion coefficient was significantly increased in ALS (p<0.01) and PLS (p=0.02) versus controls. The N-acetylaspartate/creatine ratio was significantly reduced in the motor cortex of patients versus controls (p< or = 0.01 in PLS, p=0.02 in Ap-ALS). The study shows the utility of cMRI for diagnosing ALS. Nevertheless, MRI sensitivity is limited at the early stages of the disease. In these cases, DWI and (1)H-MRSI seem to have the potential to ameliorate the patients' work-up and estimate the nature and extent of the underlying pathological damage.

Syntax without language: neurobiological evidence for cross-domain syntactic computations.

Not all conceivable grammars are realized within human languages. Rules based on rigid distances, in which a certain word must occur at a fixed distance from another word, are never found in grammars of human languages. Distances between words are specified in terms of relative, non-rigid positions. The left inferior frontal gyrus (IFG) (Broca's area) has been found to be involved in the computation of non-rigid but not of rigid syntax in the language domain. A fundamental question is therefore whether the neural activity underlying this non-rigid architecture is language-specific, given that analogous structural properties can be found in other cognitive domains. Using event-related functional magnetic resonance imaging (fMRI) in sixteen healthy native speakers of Italian, we measured brain activity for the acquisition of rigid and non-rigid syntax in the visuo-spatial domain. The data of the present experiment were formally compared with those of a previous experiment, in which there was a symmetrical distinction between rigid and non-rigid syntax in the language domain. Both in the visuo-spatial and in the language domain, the acquisition of non-rigid syntax, but not the acquisition of rigid syntax, activated Brodmann Area 44 of the left IFG. This domain-independent effect was specifically modulated by performance improvement. Thus, in the human brain, one single "grammar without words" serves different higher cognitive functions.

Spectroscopic correlates of antidepressant response to sleep deprivation and light therapy: a 3.0 Tesla study of bipolar depression.

Glutamate is the primary excitatory neurotransmitter of the human brain, and recent findings suggest a role for the glutamatergic system in the pathophysiology and treatment of mood disorders. Single proton magnetic resonance spectroscopy (1H-MRS) was used to study the relative in vivo levels of brain neural metabolites. We evaluated the effect of antidepressant treatments on the relative concentration of unresolved glutamate and glutamine (Glx) with GABA contamination (2.35 ppm peak) using single voxel 1H-MRS at 3.0 Tesla. We studied 19 inpatients (7 males, 12 females) affected by bipolar disorder type I, current depressive episode without psychotic features, before and after 1 week of treatment with repeated total sleep deprivation (TSD) combined with light therapy (LT). Chronobiological treatment caused a significant amelioration in mood levels. Changes in the brain Glx/creatine ratio followed a general trend toward decrease, with individual variability. We observed that the decrease in the Glx/creatine ratio significantly correlated with the improvement of both objective and subjective measures of depression.

The mirror-neuron system and handedness: a "right" world?

To assess the relationship between the mirror-neuron system (MNS), an observation-execution matching system, and handedness, we acquired functional magnetic resonance imaging from 11 right-handed (RH) and eight left-handed (LH) subjects to identify regions involved in processing action (execution and observation) of the right and left upper limbs. During the execution tasks, LH subjects had a more bilateral pattern of activation than RH. An interaction between handedness and hand observed during the observation conditions was detected in several areas of the MNS and the motor system. The within- and between-groups analyses confirmed different lateralizations of the MNS and motor system activations in RH and LH subjects during the observation tasks of the dominant and nondominant limbs. The comparison of the execution vs. observation task demonstrated that during the execution task with their dominant limbs, RH subjects activated areas of the motor system in the left hemisphere, whereas LH subjects also activated areas of the MNS. During the execution task with the nondominant limbs, both groups activated regions of the MNS and motor system. Albeit this study is based on a small sample, the patterns of MNS activations observed in RH and LH subjects support the theory that suggests that this system is involved in brain functions lateralization. In LH people, this system might contribute to their adaptation to a world essentially built for right-handers through a mechanism of mirroring and imitation.

Magnetic-resonance-based tracking and quantification of intravenously injected neural stem cell accumulation in the brains of mice with experimental multiple sclerosis.

Eliciting the in situ accumulation and persistence patterns of stem cells following transplantation would provide critical insight toward human translation of stem cell-based therapies. To this end, we have developed a strategy to track neural stem/precursor cells (NPCs) in vivo using magnetic resonance (MR) imaging. Initially, we evaluated three different human-grade superparamagnetic iron oxide particles for labeling NPCs and found the optimal labeling to be achieved with Resovist. Next, we carried out in vivo experiments to monitor the accumulation of Resovist-labeled NPCs following i.v. injection in mice with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis. With a human MR scanner, we were able to visualize transplanted cells as early as 24 hours post-transplantation in up to 80% of the brain demyelinating lesions. Interestingly, continued monitoring of transplanted mice indicated that labeled NPCs were still present 20 days postinjection. Neuropathological analysis confirmed the presence of transplanted NPCs exclusively in inflammatory demyelinating lesions and not in normal-appearing brain areas. Quantification of transplanted cells by means of MR-based ex vivo relaxometry (R2*) showed significantly higher R2* values in focal inflammatory brain lesions from EAE mice transplanted with labeled NPCs as compared with controls. Indeed, sensitive quantification of low numbers of NPCs accumulating into brain inflammatory lesions (33.3-164.4 cells per lesion; r(2) = .998) was also obtained. These studies provide evidence that clinical-grade human MR can be used for noninvasive monitoring and quantification of NPC accumulation in the central nervous system upon systemic cell injection. Disclosure of potential conflicts of interest is found at the end of this article.

Neural and genetic correlates of antidepressant response to sleep deprivation: a functional magnetic resonance imaging study of moral valence decision in bipolar depression.

CONTEXT: Total sleep deprivation combined with light therapy causes rapid amelioration of bipolar depression. A polymorphism in the promoter for the serotonin transporter influences both antidepressant response and the structure and function of specific brain areas. OBJECTIVE: To determine whether antidepressant therapy or the genotype of the serotonin transporter influence the pattern of neural response to a task targeting the depressive biases in information processing (moral valence decision). DESIGN: Before-and-after trial studying the biologic correlates of response to treatment. SETTING: University hospital. Patients Twenty inpatients with bipolar depression. Intervention Repeated total sleep deprivation combined with light therapy for 1 week. MAIN OUTCOME MEASURES: Brain blood oxygen level-dependent functional magnetic resonance imaging using a 3.0-T scanner before and after treatment. Self-ratings and observer ratings of mood (visual analog scale 3 times daily and Hamilton Depression Rating Scale) before and after treatment. RESULTS: We found significant interactions of treatment (before and after), response to treatment (Hamilton Depression Rating Scale score <8), and moral valence of the stimuli (positive or negative) in the anterior cingulate cortex, dorsolateral prefrontal cortex, insula, and parietal cortex. In these areas, responders changed their blood oxygen level-dependent responses to emotional stimuli in a pattern opposite of that in nonresponders. Genotype of the promoter for the serotonin transporter predicted response to treatment and influenced baseline neural responses in the anterior cingulate cortex and the dorsolateral prefrontal cortex. CONCLUSION: Multiple factors that affect or are affected at the individual level by major depressive episodes in the course of bipolar disorder significantly interact in influencing brain cortical activity in specific areas.

Normal-appearing white and grey matter damage in MS. A volumetric and diffusion tensor MRI study at 3.0 Tesla.

The aims of this study were to improve, using a 3.0 Tesla (T) scanner and diffusion tensor (DT) magnetic resonance imaging (MRI) with sensitivity encoding, our understanding of: 1) the possible pathological substrates of normal-appearing white matter (NAWM) and grey matter (GM) damage in multiple sclerosis (MS) and 2) the factors associated to WM and GM atrophy in this condition. Conventional and DT MRI of the brain were acquired from 32 relapsing-remitting (RR) MS patients and 16 controls. Lesion load, WM (WMV), overall GM (GMV), and neocortical GM (NCV) volumes were measured. NAWM mean diffusivity (MD) and fractional anisotropy (FA), and GM MD were calculated. GMV and NCV were lower (p < or = 0.001) in MS patients than controls, whereas WMV did not differ significantly. MS patients had higher NAWM and GM average MD and lower NAWM average FA (p < or = 0.001) than controls. Moderate correlations were found between intrinsic lesion and tissue damage with both GM volumetric and diffusivity changes (-0.41 < or = r < or = 0.42, p < or = 0.04). DT MRI and volumetry measurements at 3.0 T confirm the presence of NAWM and GM abnormalities in RRMS patients. Although histopathology was not available, axonal and neuronal damage and consequent reactive glial proliferation are the most likely substrates of the changes observed.

A model-based deconvolution approach to solve fiber crossing in diffusion-weighted MR imaging.

A deconvolution approach is presented to solve fiber crossing in diffusion magnetic resonance imaging. In order to provide a direct physical interpretation of the signal generation process, we started from the classical multicompartment model and rewrote this in terms of a convolution process, identifying a significant scalar parameter alpha to characterize the physical system response. Deconvolution is performed by a modified version of the Richardson-Lucy algorithm. Simulations show the ability of this method to correctly separate fiber crossing, even in the presence of noisy data, with lower signal-to-noise ratio, and imprecision in the impulse response function imposed during deconvolution. The in vivo data confirms the efficacy of this method to resolve fiber crossing in real complex brain structures. These results suggest the usefulness of our approach in fiber tracking or connectivity studies.

Brain gray matter changes in migraine patients with T2-visible lesions: a 3-T MRI study.

BACKGROUND AND PURPOSE: In migraine patients, functional imaging studies have shown changes in several brain gray matter (GM) regions. However, 1.5-T MRI has failed to detect any structural abnormality of these regions. We used a 3-T MRI scanner and voxel-based morphometry (VBM) to assess whether GM density abnormalities can be seen in patients with migraine with T2-visible abnormalities and to grade their extent. METHODS: In 16 migraine patients with T2-visible abnormalities and 15 matched controls, we acquired a T2-weighted and a high-resolution T1-weighted sequence. Lesion loads were measured on T2-weighted images. An optimized version of VBM analysis was used to assess regional differences in GM densities on T1-weighted scans of patients versus controls. Statistical parametric maps were thresholded at P<0.001, uncorrected for multiple comparisons. RESULTS: Compared with controls, migraine patients had areas of reduced GM density, mainly located in the frontal and temporal lobes. Conversely, patients showed increased periacqueductal GM (PAG) density. Compared with patients without aura, migraine patients with aura had increased density of the PAG and of the dorsolateral pons. In migraine patients, reduced GM density was strongly related to age, disease duration, and T2-visible lesion load (r ranging from -0.84 to -0.73). CONCLUSIONS: Structural GM abnormalities can be detected in migraine patients with brain T2-visible lesions using VBM and a high-field MRI scanner. Such GM changes comprise areas with reduced and increased density and are likely related to the pathological substrates associated with this disease.

Cortical adaptation in patients with MS: a cross-sectional functional MRI study of disease phenotypes.

BACKGROUND: Movement-associated cortical reorganisation is known to occur in multiple sclerosis (MS). We aimed to define the development of such cortical reorganisation by comparing data from patients with different disease phenotypes. METHODS: We studied patients with different phenotypes of MS: 16 patients with a clinically isolated syndrome (CIS), 14 patients with relapsing-remitting MS (RRMS) and no disability, 15 patients with RRMS and mild clinical disability, and 12 patients with secondary progressive MS (SPMS). Patients did a simple motor task with their unimpaired dominant hand during MRI, which was compared across the phenotype groups. FINDINGS: Patients with a CIS activated more of the contralateral primary sensorimotor cortex than those with RRMS and no disability, whereas patients with RRMS and no disability activated more of the supplementary motor area than those with a CIS. Patients with RRMS and no disability activated more of the primary sensorimotor cortex, bilaterally, and more of the ipsilateral supplementary motor area than patients with RRMS and mild clinical disability. Conversely, patients with RRMS and mild clinical disability activated more of the contralateral secondary somatosensory cortex and inferior frontal gyrus, and the ipsilateral precuneus. Patients with RRMS and mild clinical disability activated more of the contralateral thalamus and of the ipsilateral secondary somatosensory cortex than those with SPMS. However, patients with SPMS activated more of the inferior frontal gyrus, bilaterally, the middle frontal gyrus, bilaterally, the contralateral precuneus, and the ipsilateral cingulate motor area and inferior parietal lobule. INTERPRETATION: Movement-associated cortical reorganisation in patients with MS seems to vary across individuals at different stages of disease. Our study suggests that early in the disease course more areas typically devoted to motor tasks are recruited. Then bilateral activation of these regions is seen, and late in the disease course, areas that healthy people recruit to do novel or complex tasks are activated.

Axonal injury and overall tissue loss are not related in primary progressive multiple sclerosis.

BACKGROUND: There is an increasing body of evidence that magnetic resonance imaging-occult tissue damage is an important component of primary progressive multiple sclerosis (PPMS) pathology. Proton magnetic resonance spectroscopy (1H-MRS) can be used to measure in vivo whole-brain N-acetylaspartate (WBNAA) concentrations, the decrease of whose levels is considered a marker of neuronal-axonal injury. OBJECTIVES: To study WBNAA 1H-MRS as a tool to provide information about irreversible brain damage in PPMS and to investigate the relationship between WBNAA and other magnetic resonance imaging measures of MS disease burden, including brain atrophy. METHODS: The following magnetic resonance pulse sequences of the brain were obtained from 32 patients with PPMS and 16 age-matched healthy subjects: (1) dual-echo turbo spin-echo; (2) T1-weighted spin-echo; and (3) 1H-MRS to measure WBNAA concentration. Brain total lesion volumes were measured. Normalized brain volumes were calculated using a fully automated technique. Absolute WBNAA amounts were calculated using a phantom replacement method and were then corrected for individual subjects' brain size. RESULTS: Levels of WBNAA concentrations and normalized brain volumes were significantly lower in patients with PPMS (mean values, 10.2 mm and 1500.0 mL, respectively) than in healthy controls (mean values, 12.9 mm and 1585.2 mL). Both WBNAA concentrations and normalized brain volumes were included as independent factors in the final model of a multivariable analysis predicting the subjects' condition. No significant correlations were found between WBNAA values and normalized brain volumes, WBNAA and T2-weighted or T1-weighted lesion volumes. CONCLUSIONS: Axonal-neuronal damage in the brain of patients with PPMS seems to occur, at least partially, independently of the burden of magnetic resonance imaging-visible lesions. Whole-brain N-acetylaspartate values and normalized brain volumes were unrelated in this cohort, thereby suggesting that 1H-MRS and atrophy assessment may provide in vivo complementary information about the actual extent of brain damage in PPMS.