Assessment of arcuate fasciculus with diffusion-tensor tractography may predict the prognosis of aphasia in patients with left middle cerebral artery infarcts

The role of language-related functional brain regions and white matter tracts in network plasticity of post-stroke aphasia

The neural mechanisms underlying language recovery after a stroke remain controversial. This review aimed to summarize the plasticity and reorganization mechanisms of the language network through neuroimaging studies. Initially, we discussed the involvement of right language homologues, perilesional tissue, and domain-general networks. Subsequently, we summarized the white matter functional mapping and remodeling mechanisms associated with language subskills. Finally, we explored how non-invasive brain stimulation (NIBS) promoted language recovery by inducing neural network plasticity. It was observed that the recruitment of right hemisphere language area homologues played a pivotal role in the early stages of frontal post-stroke aphasia (PSA), particularly in patients with larger lesions. Perilesional plasticity correlated with improved speech performance and prognosis. The domain-general networks could respond to increased "effort" in a task-dependent manner from the top-down when the downstream language network was impaired. Fluency, repetition, comprehension, naming, and reading skills exhibited overlapping and unique dual-pathway functional mapping models. In the acute phase, the structural remodeling of white matter tracts became challenging, with recovery predominantly dependent on cortical activation. Similar to the pattern of cortical activation, during the subacute and chronic phases, improvements in language functions depended, respectively, on the remodeling of right white matter tracts and the restoration of left-lateralized language structural network patterns. Moreover, the midline superior frontal gyrus/dorsal anterior cingulate cortex emerged as a promising target for NIBS. These findings offered theoretical insights for the early personalized treatment of aphasia after stroke.

Clinico-radiological factors associated with aphasia outcome in post stroke patients: A prospective follow up study from eastern part of India

BACKGROUND

Aphasia is a language disorder acquired secondary to brain damage. This study aims to evaluate clinical and radiological profile of patients with post stroke aphasia and factors affecting its recovery.

METHODS

We conducted a prospective study of patients with first left Middle or Anterior Cerebral Artery infarct or Intracerebral Hemorrhage (ICH) with aphasia admitted within 14 days of stroke onset. Aphasia Quotient (AQ) was assessed at 2 weeks (AQ1) and 3 months (AQ2) using Western Aphasia Battery-Hindi version. Magnetic Resonance Imaging of brain with Diffusion Tensor Imaging (DTI) of bilateral Arcuate Fasciculus (AF) and Corticospinal Tract was done at admission, and stroke volume, Laterality Indices of Fractional Anisotropy (LI-FA), Mean Diffusivity (LI-MD), Radial Diffusivity (LI-RD), Axial Diffusivity (LI-AD) and Apparent Diffusion Coefficient (LI-ADC) were obtained.

RESULTS

36 patients [8 ICH and 28 Acute Ischemic Stroke (AIS)] were included. AQ1 and AQ2 were significantly higher in subcortical stroke than cortical. AQ2 and increase in AQ scores (including its subscores) were significantly higher in ICH than AIS. National Institutes of Health Stroke Scale score at admission and volume of stroke had significant negative correlation with AQ1 and AQ2. Laterality Index of Fractional Anisotropy of Arcuate Fasciculus [LI-FA (AF)] had significant positive correlation with AQ2 and naming score at 3 months. Laterality Index of Mean Diffusivity of Arcuate Fasciculus [LI-MD (AF)] had significant negative correlation with AQ1, AQ2 and all subcomponents of AQ2. Significant positive correlation was seen between improvements in Modified Rankin Scale score and AQ.

CONCLUSION

The study shows that DTI can be used to predict severity of aphasia at follow up and recovery in language and motor functions occur in parallel.

Application of diffusion tensor imaging in the diagnosis of post-stroke aphasia: a meta-analysis and systematic review

Introduction

Diffusion Tensor Imaging (DTI) indicators of different white matter (WM) fibers and brain region lesions for post-stroke aphasia (PSA) are inconsistent in existing studies. Our study examines the consistency and differences between PSA tests performed with DTI. In addition, obtaining consistent and independent conclusions between studies was made possible by utilizing DTI in PSA assessment.

Methods

In order to gather relevant studies using DTI for diagnosing PSA, we searched the Web of Science, PubMed, Embase, and CNKI databases. Based on the screening and evaluation of the included studies, the meta-analysis was used to conduct a quantitative analysis. Narrative descriptions were provided for studies that met the inclusion criteria but lacked data.

Results

First, we reported on the left hemisphere. The meta-analysis showed that fractional anisotropy (FA) of the arcuate fasciculus (AF) and superior longitudinal fasciculus (SLF), inferior frontal-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), and uncinate fasciculus (UF) were decreased in the PSA group in comparison with the healthy controls (p < 0.00001). However, in the comparison of axial diffusivity (AD), there was no statistically significant difference in white matter fiber tracts in the dual-stream language model of the PSA group. Elevated radial diffusivity (RD) was seen only in the IFOF and ILF (PIFOF = 0.01; PILF = 0.05). In the classic Broca's area, the FA of the PSA group was decreased (p < 0.00001) while the apparent diffusion coefficient was elevated (p = 0.03). Secondly, we evaluated the white matter fiber tracts in the dual-stream language model of the right hemisphere. The FA of the PSA group was decreased only in the IFOF (p = 0.001). AD was elevated in the AF and UF (PAF < 0.00001; PUF = 0.009). RD was elevated in the AF and UF (PAF = 0.01; PUF = 0.003). The other fiber tracts did not undergo similar alterations.

Conclusion

In conclusion, DTI is vital for diagnosing PSA because it detects WM changes effectively, but it still has some limitations. Due to a lack of relevant language scales and clinical manifestations, diagnosing and differentiating PSA independently remain challenging.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/display_record.php?RecordID=365897.

Relationships of the arcuate fasciculus and nigrostriatal tract with language ability in intracerebral hemorrhage using a diffusion tensor imaging

We investigated the relationships of the arcuate fasciculus (AF) and the nigrostriatal tract (NST) with the language ability in patients with putaminal hemorrhage (PH) in the dominant hemisphere, using diffusion tensor tractography (DTT). Twenty-seven consecutive right-handed patients with PH and 27 age- and sex-matched normal control subjects were recruited. The aphasia quotient (AQ) score was used to evaluate the language ability at the early stage (within six weeks after onset). The fractional anisotropy (FA) value and tract volume (TV) of the ipsilesional AF and the ipsilesional NST were measured. The FA values and TVs of the ipsilesional AF and the ipsilesional NST of the patient group were lower than those of the control group (p < 0.05). The AQ score showed no significant correlation with the FA values of the ipsilesional AF and the ipsilesional NST (p > 0.05). By contrast, the AQ score showed a strong positive correlation with the TV of the ipsilesional AF (r = 0.868, p < 0.05). In addition, the AQ score revealed a moderate positive correlation with the TV of the ipsilesional NST (r = 0.577, p < 0.05). The states of the ipsilesional AF and the ipsilesional NST were closely related to the language ability at the early stages in patients with PH in the dominant hemisphere. Furthermore, the ipsilesional AF was more closely related to the language ability than the ipsilesional NST.

Early white matter connectivity and plasticity in post stroke aphasia recovery

A disruption of white matter connectivity is negatively associated with language (recovery) in patients with aphasia after stroke, and behavioral gains have been shown to coincide with white matter neuroplasticity. However, most brain-behavior studies have been carried out in the chronic phase after stroke, with limited generalizability to earlier phases. Furthermore, few studies have investigated neuroplasticity patterns during spontaneous recovery (i.e., not related to a specific treatment) in the first months after stroke, hindering the investigation of potential early compensatory mechanisms. Finally, the majority of previous research has focused on damaged left hemisphere pathways, while neglecting the potential protective value of their right hemisphere counterparts for language recovery. To address these outstanding issues, we present a longitudinal study of thirty-two patients with aphasia (21 males and 11 females, M = 69.47 years, SD = 10.60 years) who were followed up for a period of 1 year with test moments in the acute (1-2 weeks), subacute (3-6 months) and chronic phase (9-12 months) after stroke. Constrained Spherical Deconvolution-based tractography was performed in the acute and subacute phase to measure Fiber Bundle Capacity (FBC), a quantitative connectivity measure that is valid in crossing fiber regions, in the bilateral dorsal arcuate fasciculus (AF) and the bilateral ventral inferior fronto-occipital fasciculus (IFOF). First, concurrent analyses revealed positive associations between the left AF and phonology, and between the bilateral IFOF and semantics in the acute - but not subacute - phase, supporting the dual-stream language model. Second, neuroplasticity analyses revealed a decrease in connection density of the bilateral AF - but not the IFOF - from the acute to the subacute phase, possibly reflecting post stroke white matter degeneration in areas adjacent to the lesion. Third, predictive analyses revealed no contribution of acute FBC measures to the prediction of later language outcomes over and above the initial language scores, suggesting no added value ofthe diffusion measures for languageprediction. Our study provides new insights on (changes in) connectivity of damaged and undamaged language pathways in patients with aphasia in the first months after stroke, as well as if/how such measures are related to language outcomes at different stages of recovery. Individual results are discussed in the light of current frameworks of language processing and aphasia recovery.

White matter microstructural integrity pre- and post-treatment in individuals with chronic post-stroke aphasia

While previous studies have found that white matter damage relates to impairment severity in individuals with aphasia, further study is required to understand the relationship between white matter integrity and treatment response. In this study, 34 individuals with chronic post-stroke aphasia underwent behavioral testing and structural magnetic resonance imaging at two timepoints. Thirty participants within this sample completed typicality-based semantic feature treatment for anomia. Tractography of bi-hemispheric white matter tracts was completed via Automated Fiber Quantification. Associations between microstructural integrity metrics and behavioral measures were evaluated at the tract level and in nodes along the tract. Diffusion measures of the left inferior longitudinal, superior longitudinal, and arcuate fasciculi were related to aphasia severity and diffusion measures of the left inferior longitudinal fasciculus were related to naming and treatment response. This study also found preliminary evidence of left inferior longitudinal fasciculus microstructural changes following treatment.

The Recovery Mechanism of Standardized Aphasia in Intelligent Medical Treatment

A total of 35 patients with aphasia after cerebral infarct were included. Among them, 15 conjunctures were sensory (Wernicke's) aphasia and 20 cases were motor (Broca) aphasia. Perfusion Weighted Imaging (PWI) and Magnetic Resonance Spectroscopy (MRS) were performed on the attached hard area to measure the local cerebral blood flow (rCBF) and sectional cerebral blood compass (rCBV), mean conveyance tense (MTT), point delay (TTP), and N-acetylaspartate (NAA), choline (Cho), creatine (Cr)), and lactic acidic (lactate, Lac) and generally a relative analysis. Results. Among the patients with contaminative aphasia, rCBF was way diminished in the contralateral mirror extent. MTT and TTP were significantly longer than the contralateral mirror range, NAA and Cho were sullenness than the contralateral side, and the Lac peak appeared. The distinction was statistically taken (P < 0.05). Compared with the contralateral mirror circumference, motor aphasia was significantly reduced in rCBF and rCBV, and MTT and TTP were way prolonged. NAA and Cho were reduced compared with the contralateral side, and the Lac peak appeared. The dispute was statistically momentous (P < 0.05). Conclusion. After cerebral infarction, the language cosine extent of patients with aphasia bestows a rank of hypoperfusion and light metabolism, suggesting that it may be the pathogeny of aphasia.

A taxonomy of the brain's white matter: twenty-one major tracts for the 21st century

The functional and computational properties of brain areas are determined, in large part, by their connectivity profiles. Advances in neuroimaging and network neuroscience allow us to characterize the human brain noninvasively, but a comprehensive understanding of the human brain demands an account of the anatomy of brain connections. Long-range anatomical connections are instantiated by white matter, which itself is organized into tracts. These tracts are often disrupted by central nervous system disorders, and they can be targeted by neuromodulatory interventions, such as deep brain stimulation. Here, we characterized the connections, morphology, traversal, and functions of the major white matter tracts in the brain. There are major discrepancies across different accounts of white matter tract anatomy, hindering our attempts to accurately map the connectivity of the human brain. However, we are often able to clarify the source(s) of these discrepancies through careful consideration of both histological tract-tracing and diffusion-weighted tractography studies. In combination, the advantages and disadvantages of each method permit novel insights into brain connectivity. Ultimately, our synthesis provides an essential reference for neuroscientists and clinicians interested in brain connectivity and anatomy, allowing for the study of the association of white matter's properties with behavior, development, and disorders.

Recovery of an injured arcuate fasciculus via transcallosal fiber in a stroke patient: A case report

RATIONALE

We report on a patient whose arcuate fasciculus (AF) and corticobulbar tract (CBT) recovered following an infarct in the middle cerebral artery (MCA) territory, demonstrated on serial diffusion tensor tractography (DTT).

PATIENT CONCERNS

The patient showed moderate conduction aphasia on the Western Aphasia Battery with an aphasia quotient of 46.5‰ (spontaneous speech: 35.0‰, auditory comprehension: 36.0‰, and naming: 53.1‰) at 1 month after onset. His aphasia improved with an aphasia quotient of 49‰ (spontaneous speech: 71.0‰, auditory comprehension: 52.0‰, and naming: 59.0‰) at 10 months after onset.

DIAGNOSIS

A 44-year-old right-handed male patient presented with aphasia and quadriplegia, which occurred at the onset of an infarct in the left MCA territory.

INTERVENTION

Diffusion tensor imaging data were acquired twice (1 month and 10 months after onset).

OUTCOMES

On one-month DTT, the discontinuation of the left AF and severe narrowing of the right CBT were observed. However, on ten-month DTT, the left AF was connected to the opposite AF by a new tract that passed through the splenium of corpus callosum, and the right CBT had become thicker.

LESSONS

We believe that our results suggest a recovery mechanism of injured AF and CBT in stroke patients.

Naming errors and dysfunctional tissue metrics predict language recovery after acute left hemisphere stroke

Language recovery following acute left hemisphere (LH) stroke is notoriously difficult to predict. Global language measures (e.g., overall aphasia severity) and gross lesion metrics (e.g., size) provide incomplete recovery predictions. In this study, we test the hypothesis that the types of naming errors patients produce, combined with dysfunctional brain tissue metrics, can provide additional insight into recovery following acute LH stroke. One hundred forty-eight individuals who were hospitalized with a new LH stroke completed clinical neuroimaging and assessments of naming and global language skills. A subset of participants again completed language testing at subacute, early (5-7 months post-stroke), and late (≥11 months post-stroke) chronic phases. At each time point, we coded naming errors into four types (semantic, phonological, mixed and unrelated) and determined error type totals and proportions. Dysfunctional tissue measures included the percentage of damage to language network regions and hypoperfusion in vascular territories. A higher proportion of semantic errors was associated with better acute naming, but higher proportions of other error types was related to poorer accuracy. Naming and global language skills significantly improved over time , but naming error profiles did not change. Fewer acute unrelated errors and less damage to left angular gyrus resulted in optimal naming and language recovery by the final testing time point, yet patients with more acute errors and damage to left middle temporal gyrus demonstrated the greatest increases in language over time. These results illustrate that naming error profiles, particularly unrelated errors, add power to predictions of language recovery after stroke.

A Review on Treatment-Related Brain Changes in Aphasia

Numerous studies have investigated brain changes associated with interventions targeting a range of language problems in patients with aphasia. We strive to integrate the results of these studies to examine (1) whether the focus of the intervention (i.e., phonology, semantics, orthography, syntax, or rhythmic-melodic) determines in which brain regions changes occur; and (2a) whether the most consistent changes occur within the language network or outside, and (2b) whether these are related to individual differences in language outcomes. The results of 32 studies with 204 unique patients were considered. Concerning (1), the location of treatment-related changes does not clearly depend on the type of language processing targeted. However, there is some support that rhythmic-melodic training has more impact on the right hemisphere than linguistic training. Concerning (2), we observed that language recovery is not only associated with changes in traditional language-related structures in the left hemisphere and homolog regions in the right hemisphere, but also with more medial and subcortical changes (e.g., precuneus and basal ganglia). Although it is difficult to draw strong conclusions, because there is a lack of systematic large-scale studies on this topic, this review highlights the need for an integrated approach to investigate how language interventions impact on the brain. Future studies need to focus on larger samples preserving subject-specific information (e.g., lesion effects) to cope with the inherent heterogeneity of stroke-induced aphasia. In addition, recovery-related changes in whole-brain connectivity patterns need more investigation to provide a comprehensive neural account of treatment-related brain plasticity and language recovery.

Relationship between Visual Perception and Microstructural Change of the Superior Longitudinal Fasciculus in Patients with Brain Injury in the Right Hemisphere: A Preliminary Diffusion Tensor Tractography Study

Right hemisphere brain damage often results in visual-spatial deficits. Because various microstructural changes of the superior longitudinal fasciculus (SLF) after a stroke in the right hemisphere affect visual perception, including neglect, the present study investigates the relationship between both microstructural change and lateralization of SLF and visual perception, using diffusion tensor imaging (DTI) in patients with lesions in the right hemisphere. Eight patients with strokes (five patients with intracranial hemorrhage, and three patients with infarction; mean age of 52.5 years) and 16 mean-age-matched healthy control subjects were involved in this study. The visual perception of all eight patients was assessed with the motor-free visual perception test (MVPT), and their SLFs were reconstructed using DTI. The results showed that there was a significant difference between the DTI parameters of the patients and the control subjects. Moreover, patients with microstructural damage to the right SLF showed impairment of visual perception. In patients with damage to both the dorsal and ventral pathways of the right SLF, spatial neglect was present. However, although a leftward SLF asymmetry was revealed in our patients, this lateralization did not show a relationship with visual perception. In conclusion, the microstructural changes of the right SLF play an important role in visual perception, and both pathways contribute to spatial neglect, but leftward lateralization of the right SFL activity after a stroke does not contribute to general visual perception.

The role of microstructural integrity of major language pathways in narrative speech in the first year after stroke

BACKGROUND AND PURPOSE

Left hemisphere stroke often results in a variety of language deficits due to varying patterns of damage to language networks. The Cookie Theft picture description task, a classic, quick bedside assessment, has been shown to quantify narrative speech reliably. In this study, we utilized diffusion tensor imaging (DTI) to assess language network white matter tract correlates of lexical-semantic and syntactic impairments longitudinally.

METHODS

Twenty-eight patients with mild to severe language impairments after left hemispheric lobar and/or subcortical ischemic stroke underwent the Cookie Theft picture description test and DTI up to three different time points: within the first three months, six months and twelve months after stroke. Dorsal and ventral stream language pathways were segmented to obtain DTI integrity metrics of both hemispheres. Multivariable regression models and partial correlation analyses adjusted for age, education, and lesion load were conducted to evaluate the temporal DTI profile of the white matter microstructural integrity of the language tracts as neural correlates of narrative speech within the first year after stroke.

RESULTS

Among all the major language white matter pathways, the integrity of the left arcuate (AF), inferior fronto-occipital, and inferior longitudinal fasciculi (ILF) were related to picture description performance. After FDR correction, left ILF fractional anisotropy correlated with syntactic cohesiveness (r=0.85,p=0.00087) within the first three months after stroke, whereas at one year post-stroke, the strongest correlations were found between lexical-semantic performance and left AF radial diffusivity (r = -0.71, p = 0.00065).

CONCLUSION

Our study provides a temporal profile of associations between the integrity of the main language pathways and lexical semantics and syntactic impairments in left hemispheric strokes.

Clinical and neuroimaging factors associated with aphasia severity in stroke patients: diffusion tensor imaging study

This study investigated factors associated with aphasia severity at both 2 weeks and 3 months after stroke using demographic and clinical variables, brain diffusion tensor imaging (DTI) parameters, and lesion volume measurements. Patients with left hemisphere stroke were assessed at 2 weeks (n = 68) and at 3 months (n = 20) after stroke. Demographic, clinical, and neuroimaging data were collected; language functions were assessed using the Western Aphasia Battery. For neuroimaging, DTI parameters, including the laterality index (LI) of fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity, mean diffusivity and fibre density (FD) of the arcuate fasciculus (AF), and lesion volume, were measured. Lesion volume, cortical involvement, and the National Institutes of Health Stroke Scale score significantly predicted aphasia severity at 2 weeks after stroke, whereas the aphasia quotient and presence of depression during the early subacute stage were significant predictors at 3 months after stroke. According to Pearson correlation, LI-AD and LI-FD were significantly correlated with the aphasia quotient 2 weeks after ischaemic stroke, and the LI-FA was significantly correlated with the aphasia quotient 2 weeks after haemorrhagic stroke, suggesting that the extent and mechanism of AF injuries differ between ischaemic and haemorrhagic strokes. These differences may contribute to aphasia severity.

Single Word Repetition Predicts Long-Term Outcome of Aphasia Caused by an Ischemic Stroke

PURPOSE

Better understanding of clinical predictors of aphasia outcome is of the utmost importance, in patients' rehabilitation planning, expectation management, and further physiopathology understanding. We aimed to identify clinical predictors of long-term poststroke aphasia's outcome.

METHODS

We conducted a prospective longitudinal observation study of patients with left-Middle Cerebral Artery stroke with aphasia. Patients were evaluated at baseline, day 7 and 6 months with National Institutes of Health Stroke Scale (NIHSS) and Aphasia Rapid Test Other demographic variables and vascular risk factors were collected. A linear regression was performed to identify best predictors of aphasia at 6 months.

FINDINGS

We included 113 patients with a left hemisphere stroke, with 81 reaching the final evaluation. Aphasia Handicap Score at 6 months was predicted by baseline total NIHSS (β = .077, 95%CI = [.026, .127]. P = .004), infarct volume on CT-scan (β = .009, 95%CI = [.003, .015]. P = .003), single word repetition at baseline (β = .188, 95%CI = [.040, .335]. P = .013), and infection during hospitalization (β = .759, 95%CI = [.263, 1.255]. P = .003).

CONCLUSIONS

Aphasia's outcome in patients with stroke is predicted by a single word repetition task at baseline. Infection during hospitalization has a negative impact on aphasia's outcome at 6 months.

Acute Diffusivity Biomarkers for Prediction of Motor and Language Outcome in Mild-to-Severe Stroke Patients

Background and Purpose—

Early severity of stroke symptoms—especially in mild-to-severe stroke patients—are imperfect predictors of long-term motor and aphasia outcome. Motor function and language processing heavily rely on the preservation of important white matter fasciculi in the brain. Axial diffusivity (AD) from the diffusion tensor imaging model has repeatedly shown to accurately reflect acute axonal damage and is thus optimal to probe the integrity of important white matter bundles and their relationship with long-term outcome. Our aim was to investigate the independent prognostic value of the AD of white matter tracts in the motor and language network evaluated at 24 hours poststroke for motor and aphasia outcome at 3 months poststroke.

Methods—

Seventeen (motor cohort) and 28 (aphasia cohort) thrombolyzed patients with initial mild-to-severe stroke underwent a diffusion tensor imaging sequence at 24 hours poststroke. Motor and language outcome were evaluated at 3 months poststroke with a composite motor score and the aphasia handicap scale. We first used stepwise regression to determine which classic (age, initial motor or aphasia severity, and lesion volume) and imaging (ratio of affected/unaffected AD of motor and language fasciculi) factors were related to outcome. Second, to determine the specificity of our a priori choices of fasciculi, we performed voxel-based analyses to determine if the same, additional, or altogether new regions were associated with long-term outcome.

Results—

The ratio of AD in the corticospinal tract was the sole predictor of long-term motor outcome, and the ratio of AD in the arcuate fasciculus—along with age and initial aphasia severity—was an independent predictor of 3-month aphasia outcome. White matter regions overlapping with these fasciculi naturally emerged in the corresponding voxel-based analyses.

Conclusions—

AD of the corticospinal tract and arcuate fasciculus are effective biomarkers of long-term motor and aphasia outcome, respectively.

Predictive role of subcomponents of the left arcuate fasciculus in prognosis of aphasia after stroke: A retrospective observational study

The relationship between the left arcuate fasciculus (AF) and stroke-related aphasia is unclear. In this retrospective study, we aimed to investigate the role of subcomponents of the left AF in predicting prognosis of aphasia after stroke. Twenty stroke patients with aphasia were recruited and received language assessment as well as diffusion tensor tractography scanning at admission. According to injury of the left AF, the participants were classified into four groups: group A (4 cases), the AF preserved intactly; group B (6 cases), the anterior segment injured; group C (4 cases), the posterior segment injured; and group D (6 cases), completely injured. After a consecutive speech therapy, language assessment was performed again. Changes of language functions among the groups were compared and the relation between these changes with segments injury of the AF was analyzed. After therapy, relatively high increase score percentage changes in terms of all the subcategories of language assessment were observed both in group A and C; by contrast, only naming in group B, and spontaneous speech in group D. Although no statistical difference was demonstrated among the four groups. In addition, there was no significant correlation between improvement of language function with segments injury of the AF. The predictive role of subcomponents of the left AF in prognosis of aphasia is obscure in our study. Nevertheless, it indicates the importance of integrity of the left AF for recovery of aphasia, namely that preservation of the left AF on diffusion tensor tractography could mean recovery potential of aphasia after stroke.

Brain networks and their relevance for stroke rehabilitation

Stroke has long been regarded as focal disease with circumscribed damage leading to neurological deficits. However, advances in methods for assessing the human brain and in statistics have enabled new tools for the examination of the consequences of stroke on brain structure and function. Thereby, it has become evident that stroke has impact on the entire brain and its network properties and can therefore be considered as a network disease. The present review first gives an overview of current methodological opportunities and pitfalls for assessing stroke-induced changes and reorganization in the human brain. We then summarize principles of plasticity after stroke that have emerged from the assessment of networks. Thereby, it is shown that neurological deficits do not only arise from focal tissue damage but also from local and remote changes in white-matter tracts and in neural interactions among wide-spread networks. Similarly, plasticity and clinical improvements are associated with specific compensatory structural and functional patterns of neural network interactions. Innovative treatment approaches have started to target such network patterns to enhance recovery. Network assessments to predict treatment response and to individualize rehabilitation is a promising way to enhance specific treatment effects and overall outcome after stroke.

Current Clinical Applications of Diffusion-Tensor Imaging in Neurological Disorders

Diffusion-tensor imaging (DTI) is a noninvasive medical imaging tool used to investigate the structure of white matter. The signal contrast in DTI is generated by differences in the Brownian motion of the water molecules in brain tissue. Postprocessed DTI scalars can be used to evaluate changes in the brain tissue caused by disease, disease progression, and treatment responses, which has led to an enormous amount of interest in DTI in clinical research. This review article provides insights into DTI scalars and the biological background of DTI as a relatively new neuroimaging modality. Further, it summarizes the clinical role of DTI in various disease processes such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's dementia, epilepsy, ischemic stroke, stroke with motor or language impairment, traumatic brain injury, spinal cord injury, and depression. Valuable DTI postprocessing tools for clinical research are also introduced.

Contributions of Neuroimaging to Understanding Language Deficits in Acute Stroke

Advances in structural and functional imaging techniques have provided new insights into our understanding of brain and language relationships. In this article, we review the various structural and functional imaging methods currently used to study language deficits in acute stroke. We also discuss the advantages and the limitations of each imaging modality and the applications of each modality in the clinical and research settings in the study of language deficits.

Recovery of injured Broca's portion of arcuate fasciculus in the dominant hemisphere in a patient with traumatic brain injury

RATIONALE

Recovery of injured AF in patients with traumatic brain injury (TBI) has not been reported. In this study, we report on a patient with TBI who recovered from an injury to Broca's portion of AF in the dominant hemisphere, diagnosed by diffusion tensor tractography (DTT).

PATIENT CONCERNS

A 28-year-old right-handed male patient suffered head trauma resulting from sliding while riding a motorcycle.

DIAGNOSES

He was diagnosed with a traumatic contusional hemorrhage in the left frontal lobe, subarachnoid hemorrhage, and subdural hemorrhage in the left fronto-temporal lobe.

INTERVENTIONS

He underwent craniectomy on the left fronto-temporal area, and hematoma removal for the subdural hemorrhage in the neurosurgery department of a university hospital. Two weeks after the injury, he was transferred to the rehabilitation department of another university hospital. He showed severe aphasia and brain MRI showed leukomalactic lesion in the left frontal lobe.

OUTCOMES

The result WAB for the patient showed severe aphasia, with an aphasia quotient of 45.3 percentile. However, his aphasia improved rapidly by 9 months with an aphasia quotient at the 100.0 percentile. 2-week DTT detected discontinuity in the subcortical white matter at the branch to Broca's area of left AF. By contrast, on 9-month DTT, the discontinued portion of left AF was elongated to the left Broca's area.

LESSONS

Recovery of injured Broca's portion of AF in the dominant hemisphere along with excellent improvement of aphasia was demonstrated in a patient with TBI. This study has important implications in brain rehabilitation because the mechanism of recovery from aphasia following TBI has not been elucidated.

Reduced Diffusion Tensor Fractional Anisotropy in the Left Arcuate Fasciculus of Patients with Aphasia Caused by Acute Cerebral Infarct

Background

Magnetic resonance diffusion tensor imaging (DTI) is a new technique that evaluates neural fiber integrity within the brain. We conducted DTI in patients exhibiting aphasia during the acute stage post-infarct and investigated the neural tracts responsible by comparison with DTI data from age-matched controls.

Methods

Fractional anisotropy (FA) maps were generated from diffusion tensor brain images obtained from aphasic patients 14-21 days following their first infarct. Tract-based spatial statistics (TBSS) analysis was then applied. In addition, regions of interest (ROIs) were set within the right and left arcuate fasciculus, and mean FA values were extracted from individual TBSS data. The ratios between FA values in the left and right hemispheres were compared with those of the control group.

Results

The study examined 10 aphasic patients and 21 age-matched controls. Brain maps from TBSS analysis revealed significantly reduced FA in the left arcuate fasciculus of the patient group compared with that in the control group. Further ROI analyses confirmed significantly lower left/right arcuate fasciculus FA ratios in aphasic patients versus controls (median [range]: 0.955 [0.739-1.023] vs. 1.006 [0.982-1.088]; P = 0.0001 by Wilcoxon rank sum test).

Conclusions

These results suggest that FA in the left arcuate fasciculus decreased in association with aphasia after cerebral infarct. Because patients in the acute stage have not yet experienced the neural recovery that occurs in the chronic stage, the findings indicate that the left arcuate fasciculus is a crucial neural structure in aphasia.

Injury of the Arcuate Fasciculus in the Nondominant Hemisphere by Subfalcine Herniation in Patients with Intracerebral Hemorrhage : Two Case Reports and Literature Review

Using diffusion tensor tractography (DTT), we demonstrated injury of the arcuate fasciculus (AF) in the nondominant hemisphere in two patients who showed subfalcine herniation after intracerebral hemorrhage (ICH) in the dominant hemisphere. Two patients (patient 1 and patient 2) with ICH and six age-matched control patients who have ICH on the left corona radiata and basal ganglia without subfalcine herniation were recruited for this study. DTT was performed at one month after onset in patient 1 and patient 2. AFs of both hemispheres in both patients were disrupted between Wernicke's and Broca's areas. The fractional anisotropy value and tract numbers of the right AFs in both patients were found to be more than two standard deviations lower than those of control patients. In contrast, the apparent diffusion coefficient value was more than two standard deviations higher than those of control patients. Using the configuration and parameters of DTT, we confirmed injury of the AF in the nondominant hemisphere in two patients with subfalcine herniation following ICH in the dominant hemisphere. Therefore, DTT would be a useful tool for detection of underlying injury of the AF in the nondominant hemisphere in patients with subfalcine herniation.

Diffusion-tensor imaging of major white matter tracts and their role in language processing in aphasia

A growing literature is pointing towards the importance of white matter tracts in understanding the neural mechanisms of language processing, and determining the nature of language deficits and recovery patterns in aphasia. Measurements extracted from diffusion-weighted (DW) images provide comprehensive in vivo measures of local microstructural properties of fiber pathways. In the current study, we compared microstructural properties of major white matter tracts implicated in language processing in each hemisphere (these included arcuate fasciculus (AF), superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus (ILF), inferior frontal-occipital fasciculus (IFOF), uncinate fasciculus (UF), and corpus callosum (CC), and corticospinal tract (CST) for control purposes) between individuals with aphasia and healthy controls and investigated the relationship between these neural indices and language deficits. Thirty-seven individuals with aphasia due to left hemisphere stroke and eleven age-matched controls were scanned using DW imaging sequences. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) values for each major white matter tract were extracted from DW images using tract masks chosen from standardized atlases. Individuals with aphasia were also assessed with a standardized language test in Russian targeting comprehension and production at the word and sentence level. Individuals with aphasia had significantly lower FA values for left hemisphere tracts and significantly higher values of MD, RD and AD for both left and right hemisphere tracts compared to controls, all indicating profound impairment in tract integrity. Language comprehension was predominantly related to integrity of the left IFOF and left ILF, while language production was mainly related to integrity of the left AF. In addition, individual segments of these three tracts were differentially associated with language production and comprehension in aphasia. Our findings highlight the importance of fiber pathways in supporting different language functions and point to the importance of temporal tracts in language processing, in particular, comprehension.

Injury of the Arcuate Fasciculus in the Dominant Hemisphere in Patients With Mild Traumatic Brain Injury: A Retrospective Cross-Sectional Study

Little is known about injury of the arcuate fasciculus (AF) in patients with mild traumatic brain injury (TBI). We investigated injury of the AF in the dominant hemisphere in patients with mild TBI, using diffusion tensor tractography (DTT). We recruited 25 patients with injury of the left AF among 64 right-handed consecutive patients with mild TBI and 20 normal control subjects. DTTs of the left AF were reconstructed, and fractional anisotropy (FA), apparent diffusion coefficient (ADC), and fiber number of the AF were measured. Among 64 consecutive patients, 25 (39%) patients showed injury of the left AF. The patient group showed lower FA value and fiber number with higher ADC value than the control group (P < 0.05). On K-WAB evaluation, aphasia quotient and language quotient were 95.9 ± 4.1 (range 85-100) and 95.0 ± 5.4 (range 80-100), respectively. However, 23 (92.0%) of 25 patients complained of language-related symptoms after TBI; paraphasia in 12 (48.0%) patients, deficits of comprehension in 4 (16.0%) patients, deficits of speech production in 1 (4.0%) patient, and >2 language symptoms in 6 (24.0%) patients. We found that a significant number (39%) of patients with mild TBI had injury of the AF in the dominant hemisphere and these patients had mild language deficit. These results suggest that DTT could provide useful information in detecting injury of the AF and evaluation of the AF using DTT would be necessary even in the case of a patient with mild TBI who complains of mild language deficit.

Brodmann's Area Template Based Region of Interest Setting and Probabilistic Pathway Map Generation in Diffusion Tensor Tractography: Application to the Arcuate Fasciculus Fiber Tract in the Human Brain

The purpose of this study is to acquire accurate diffusion tensor tractography (DTT) results for arcuate fasciculus (AF) fiber tract using Brodmann's area (BA) template for region of interest (ROI) setting. Thirteen healthy subjects were participated in this study. Fractional anisotropy (FA) map of each subject was calculated using diffusion tensor data, and T1w template was co-registered to FA map. The BA template was also co-registered using the transformation matrix. The ROIs were drawn in the co-registered BA template, and AF fiber tract was extracted. To generate the probabilistic pathway map, a binary mask image was generated based on the fiber tract image and co-registered to T1w template image. We also measured relative location of the AF fiber tract. The location of the probabilistic pathway map of each subject's AF fiber tract was well defined in the brain. By using this probabilistic map, the mediolateral position ratio of AF was measured 18%, and the anteroposterior position ratio of AF was measured 35%, respectively. This study demonstrated that the AF fiber tract can be extracted using BA template for ROI setting and probabilistic pathway of fiber tract. Our results and analytical approaches can helpful for accurate fiber tracking and application of perspective clinical researches.

Contributions of bilateral white matter to chronic aphasia symptoms as assessed by diffusion tensor MRI

Language reorganisation following stroke has been studied widely. However, while studies of brain activation and grey matter examined both hemispheres, studies of white matter changes have mostly focused on the left hemisphere. Here we examined the relationship between bilateral hemispheric white matter and aphasia symptoms. 15 chronic stroke patients with aphasia and 18 healthy adults were studied using Diffusion Weighted Imaging data. By applying histogram analysis, Tract-Based Spatial Statistics, tractography and lesion-tract overlap methods, it was found that damage to the left hemisphere in general, and to the arcuate fasciculus in particular, correlated with impairments on word repetition, object naming, sentence comprehension and homophone and rhyme judgement. However, no such relationship was found in the right hemisphere. It is suggested that while some language function in aphasia can be explained by damage to the left arcuate fasciculus, it cannot be explained by looking at the contra-lesional tract.

Community Integration and Quality of Life in Aphasia after Stroke

PURPOSE

To examine community integration and contributing factors in people with aphasia (PWA) following stroke and to investigate the relationship between community integration and quality of life (QOL).

MATERIALS AND METHODS

Thirty PWA and 42 age-and education-matched control subjects were involved. Main variables were as follows: socioeconomic status, mobility, and activity of daily living (ADL) (Modified Barthel Index), language function [Frenchay Aphasia Screening Test (FAST)], depression [Geriatric Depression Scale (GDS)], Community Integration Questionnaire (CIQ) and Stroke and Aphasia Quality of Life Scale-39 (SAQOL-39). Differences between aphasia and control groups and factors affecting community integration and QOL were analyzed.

RESULTS

Home and social integration and productive activity were significantly decreased in the aphasia group compared to the control group; 8.5 and 18.3 points in total CIQ score, respectively. Amount of time spent outside the home and frequency of social contact were also significantly reduced in the aphasia group. Total mean score on the SAQOL-39 was 2.75±0.80 points and was significantly correlated with economic status, gait performance, ADL, depressive mood, and social domain score on the CIQ. Depression score measured by GDS was the single most important factor for the prediction of QOL, but the FAST score was significantly correlated only with the communication domain of the SAQOL-39.

CONCLUSION

Community activities of PWA were very limited, and depression was highly associated with decreased community integration and QOL. Enhancing social participation and reducing emotional distress should be emphasized for rehabilitation of PWA.

Aphasia severity in chronic stroke patients: a combined disconnection in the dorsal and ventral language pathways

BACKGROUND

The contribution of lesion size and location in poststroke aphasia is debated, especially the extent to which aphasia severity is affected by damage to specific white matter areas.

OBJECTIVE

To identify specific white matter areas critical for poststroke aphasia global severity and to determine whether injury to these areas had more impact on aphasia severity than the infarct volume.

METHODS

Twenty-three chronic poststroke aphasic patients were assessed with the Aphasia Rapid Test (ART) and the Boston Diagnosis Aphasia Examination (BDAE) global severity scales and underwent diffusion tensor and structural imaging. Voxel-based diffusion tensor imaging regression analysis was used to determine in which areas fractional anisotropy (FA) abnormalities were correlated with ART and BDAE severity scales. The relationships between aphasia severity, FA values, and infarct volumes were investigated using global and partial correlations.

RESULTS

We found a critical area associated with aphasia severity overlapping with the arcuate and the inferior fronto-occipital fasciculi, resulting in a combined disconnection of the dorsal and ventral pathways. ART scores were inversely correlated with FA values in this region, with greater severity present with lower FA values (correlation coefficient = -0.833, P < .0001). The proportion of variance explained by the FA value was higher than the proportion of variance explained by the infarct volume (R (2) = 68% vs 27%, P = .01). The impact of infarct volume on aphasia severity disappeared when damage to this critical white matter area was taken into account (P = .38).

CONCLUSION

The assessment of the integrity of this region may potentially have a clinical impact in neurorehabilitation and acute decision making.

Relation between aphasia and arcuate fasciculus in chronic stroke patients

Background

The role of the arcuate fasciculus (AF) in the dominant hemisphere in stroke patients with aphasia has not been clearly elucidated. We investigated the relation between language function and diffusion tensor tractography (DTT) findings for the left AF in chronic stroke patients with aphasia.

Method

Twenty five consecutive right-handed stroke patients with aphasia following lesions in the left hemisphere were recruited for this study. The aphasia quotient (AQ) of Korean-Western Aphasia Battery was used for assessment of language function. We measured values of fractional anisotropy (FA), apparent diffusion coefficient (ADC), voxel number of the left AF. We classified patients into three groups: type A - the left AF was not reconstructed, type B - the left AF was discontinued between Wernicke’s and Broca’s areas, and type C – the left AF was preserved around the stroke lesion.

Results

Moderate positive correlation was observed between AQ and voxel number of the left AF (r = 0.471, p < 0.05). However, no correlation was observed between AQ and FA (r = 0.275, p > 0.05) and ADC values (r = -0.286, p > 0.05). Significant differences in AQ scores were observed between the three types (p < 0.05); the AQ score of type C was higher than those of type A and B, and that of type B was also higher than that of type A (p < 0.05).

Conclusion

According to our findings, the remaining volume of the left AF, irrespective of directionality and diffusivity, showed moderate positive correlation with language function in chronic stroke patients with aphasia. Discontinuation or non-construction of the left AF was also an important factor for language function.

Predicting speech fluency and naming abilities in aphasic patients

There is a need to identify biomarkers that predict degree of chronic speech fluency/language impairment and potential for improvement after stroke. We previously showed that the Arcuate Fasciculus lesion load (AF-LL), a combined variable of lesion site and size, predicted speech fluency in patients with chronic aphasia. In the current study, we compared lesion loads of such a structural map (i.e., AF-LL) with those of a functional map [i.e., the functional gray matter lesion load (fGM-LL)] in their ability to predict speech fluency and naming performance in a large group of patients. The fGM map was constructed from functional brain images acquired during an overt speaking task in a group of healthy elderly controls. The AF map was reconstructed from high-resolution diffusion tensor images also from a group of healthy elderly controls. In addition to these two canonical maps, a combined AF-fGM map was derived from summing fGM and AF maps. Each canonical map was overlaid with individual lesion masks of 50 chronic aphasic patients with varying degrees of impairment in speech production and fluency to calculate a functional and structural lesion load value for each patient, and to regress these values with measures of speech fluency and naming. We found that both AF-LL and fGM-LL independently predicted speech fluency and naming ability; however, AF lesion load explained most of the variance for both measures. The combined AF-fGM lesion load did not have a higher predictability than either AF-LL or fGM-LL alone. Clustering and classification methods confirmed that AF lesion load was best at stratifying patients into severe and non-severe outcome groups with 96% accuracy for speech fluency and 90% accuracy for naming. An AF-LL of greater than 4 cc was the critical threshold that determined poor fluency and naming outcomes, and constitutes the severe outcome group. Thus, surrogate markers of impairments have the potential to predict outcomes and can be used as a stratifier in experimental studies.

Predictive value of fractional anisotropy of the arcuate fasciculus for the functional recovery of language after brain tumor resection: a preliminary study

OBJECTIVE

The arcuate fasciculus has been recognized as an important pathway for language processing. Brain tumors located in proximity to the fasciculus frequently cause preoperative language impairment, and in some cases, no language recovery occurs after tumor resection. No predictive value has been presented for possible postoperative language recovery after tumor resection. The aim of this study is to analyze the preoperative state of the arcuate fasciculus in the patients with brain tumor from the perspective of its usefulness as a predictive factor for postoperative recovery of language functions.

METHODS

For 12 right-handed patients with brain tumors in the left hemisphere, preoperative arcuate fasciculi were analyzed with fractional anisotropy (FA) of the diffusion tensor imaging (DTI) tractography. Language functions were evaluated pre- and postoperatively by using the Western Aphasia Battery (WAB). The preoperative value of the FA of the arcuate fasciculus on the lesion side was examined in relation with the language recovery.

RESULTS

There was a positive relationship between preoperative increasing values of the FA of the left arcuate fasciculus and improvement of the postoperative total WAB score (p=0.0056), and the scores of the naming (p=0.018), reading (p=0.029), and writing subcategories (p=0.012) CONCLUSION: The preoperative increasing value of the FA of the arcuate fasciculus in the dominant hemisphere could be a predictor for postoperative language recovery following tumor resection. Meticulous procedure should be performed especially in the cases with higher FA of the arcuate fasciculus harboring high possibility of language recovery.

Changes in white matter connectivity following therapy for anomia post stroke

BACKGROUND

The majority of studies investigating the neural mechanisms underlying treatment-induced recovery in aphasia have focused on the cortical regions associated with language processing. However, the integrity of the white matter connecting these regions may also be crucial to understanding treatment mechanisms.

OBJECTIVE

This study investigated the integrity of the arcuate fasciculus (AF) and uncinate fasciculus (UF) before and after treatment for anomia in people with aphasia.

METHOD

Eight people with aphasia received 12 treatment sessions to improve naming; alternating between phonologically-based and semantic-based tasks, with high angular resolution diffusion imaging conducted pre and post treatment. The mean generalized fractional anisotropy (GFA), a measure of fiber integrity, and number of fibers in the AF and UF were compared pre and post treatment, as well as with a group of 14 healthy older controls.

RESULTS

Pre treatment, participants with aphasia had significantly fewer fibers and lower mean GFA in the left AF compared with controls. Post treatment, mean GFA increased in the left AF to be statistically equivalent to controls. Additionally, mean GFA in the left AF pre and post treatment positively correlated with maintenance of the phonologically based treatment. No differences were found in the right AF, or the UF in either hemisphere, between participants with aphasia and controls, and no changes were observed in these tracts following treatment.

CONCLUSIONS

Anomia treatments may improve the integrity of the white matter connecting cortical language regions. These preliminary results add to the understanding of the mechanisms underlying treatment outcomes in people with aphasia post stroke.

Damage to the left ventral, arcuate fasciculus and superior longitudinal fasciculus-related pathways induces deficits in object naming, phonological language function and writing, respectively

The anatomic localization of brain functions can be characterized via diffusion tensor imaging in patients with brain tumors and neurological symptoms. The goal of the present study was to evaluate the function of the ventral, arcuate fasciculus (AF) and the superior longitudinal fasciculus (SLF)-related language pathways using these techniques by analyzing 9 patients treated in our hospital between 2007 and 2011. In cases 1-3, the left ventral pathways, namely, the inferior longitudinal fasciculus, uncinate fasciculus or inferior fronto-occipital fasciculus, were mainly damaged, and the common dysfunction experienced by these patients was a deficit in object naming. In cases 4-6, the left SLF was mainly damaged, and the common deficit was dysgraphia. In cases 7-9, the left AF was mainly damaged, and almost all language functions related to phonology were abnormal. These results suggest that the left ventral, AF and SLF-related pathways are closely related to visual, auditory and hand-related language function, respectively.

The role of MRI as a prognostic tool in ischemic stroke

Magnetic resonance imaging (MRI) is an invaluable tool used in the diagnosis of ischemic stroke. Ongoing technological advances in MRI technology and advent of new imaging sequences has now made it possible to use MRI as a prognostic tool both in the acute and chronic stages of cerebral ischemia. This review summarizes the role of MRI in estimating final tissue outcome, specifically by providing information on severity and location of ischemic insult, cerebral blood flow dynamics, vascular status, and cerebral reserve. All of these predictions can then be used to make projections regarding clinical outcome, and can be refined by other prognostic models to estimate recovery and risk of further ischemic events. These algorithms, in the end, can ultimately help the clinician in tailoring therapies on an individual basis and optimize the risk-benefit ratio of therapeutic approaches used in the acute and chronic stages of ischemic stroke. The implementation of such prognostic algorithms to clinical imaging workstations and calculation of all the possible projections within minutes after completion of imaging are likely to become an integral part of clinical practice in the near future.

Prediction of aphasia outcome using diffusion tensor tractography for arcuate fasciculus in stroke

BACKGROUND AND PURPOSE

The AF is an important neural tract in language function. We investigated aphasia outcome according to DTT findings for AF in the early stage of stroke.

MATERIALS AND METHODS

Twenty-five consecutive patients with aphasia and stroke and 12 control subjects were recruited. The AQ of K-WAB was used for the assessment of aphasia in the early stage of stroke (10-30 days) and at approximately 6 months after onset. We classified the patients into 3 groups according to the severity of left AF injury: type A, the AF was not reconstructed; type B, the AF was disrupted; and type C, the AF was preserved around the lesion.

RESULTS

When comparing AQ among AF types at early evaluation, the type C score (32.84±18.05) was significantly higher than type A (3.60±2.73) (P<.05). However, no significant difference was observed between types A and B (18.02±17.19) or between types B and C (P>.05). At late evaluation, the AQ values of types B (52.43±25.75) and C (68.08±15.76) were higher than that of type A (10.98±3.90) (P<.05). However, there was no significant difference between types B and C.

CONCLUSIONS

The aphasia outcome of the patients whose left AF could be reconstructed was better than that in patients whose left AF could not be reconstructed, irrespective of its integrity. We believe that evaluation of the left AF by using DTT in the early stage of stroke could be helpful in predicting aphasia outcome in patients with stroke.

Elevated mean diffusivity in the left hemisphere superior longitudinal fasciculus in autism spectrum disorders increases with more profound language impairment

BACKGROUND AND PURPOSE

Language impairments are observed in a subset of individuals with ASD. To examine microstructural brain white matter features associated with language ability in ASD, we measured the DTI parameters of language-related white matter tracts (SLF) as well as non-language-related white matter tracts (CST) in children with ASD/+LI and ASD/-LI) and in TD.

MATERIALS AND METHODS

Eighteen children with ASD/-LI (age range, 6.7-17.5 years), 17 with ASD/+LI (age range, 6.8-14.8 years), and 25 TD (age range, 6.5-18 years) were evaluated with DTI and tractography. Primary DTI parameters considered for analysis were MD and FA.

RESULTS

There was a main effect of diagnostic group on age-corrected MD (P < .05) with ASD/+LI significantly elevated compared with TD. This was most pronounced for left hemisphere SLF fiber tracts and for the temporal portion of the SLF. There was significant negative correlation between left hemisphere SLF MD values and the clinical assessment of language ability. There was no main effect of diagnostic group or diagnostic group X hemisphere interaction for FA. Although there was a main effect of diagnostic group on values of MD in the CST, this did not survive hemispheric subanalysis.

CONCLUSIONS

Abnormal DTI parameters (specifically significantly elevated MD values in ASD) of the SLF appear to be associated with language impairment in ASD. These elevations are particularly pronounced in the left cerebral hemisphere, in the temporal portion of the SLF, and in children with clinical language impairment.

Diffusion tensor imaging: exploring the motor networks and clinical applications

With the advances in diffusion magnetic resonance (MR) imaging techniques, diffusion tensor imaging (DTI) has been applied to a number of neurological conditions because DTI can demonstrate microstructures of the brain that are not assessable with conventional MR imaging. Tractography based on DTI offers gross visualization of the white matter fiber architecture in the human brain in vivo. Degradation of restrictive barriers and disruption of the cytoarchitecture result in changes in the diffusion of water molecules in various pathological conditions, and these conditions can also be assessed with DTI. Yet many factors may influence the ability to apply DTI clinically, so these techniques have to be used with a cautious hand.

Impairment of speech production predicted by lesion load of the left arcuate fasciculus

BACKGROUND AND PURPOSE

Previous studies have suggested that patients' potential for poststroke language recovery is related to lesion size; however, lesion location may also be of importance, particularly when fiber tracts that are critical to the sensorimotor mapping of sounds for articulation (eg, the arcuate fasciculus) have been damaged. In this study, we tested the hypothesis that lesion loads of the arcuate fasciculus (ie, volume of arcuate fasciculus that is affected by a patient's lesion) and of 2 other tracts involved in language processing (the extreme capsule and the uncinate fasciculus) are inversely related to the severity of speech production impairments in patients with stroke with aphasia.

METHODS

Thirty patients with chronic stroke with residual impairments in speech production underwent high-resolution anatomic MRI and a battery of cognitive and language tests. Impairment was assessed using 3 functional measures of spontaneous speech (eg, rate, informativeness, and overall efficiency) as well as naming ability. To quantitatively analyze the relationship between impairment scores and lesion load along the 3 fiber tracts, we calculated tract-lesion overlap volumes for each patient using probabilistic maps of the tracts derived from diffusion tensor images of 10 age-matched healthy subjects.

RESULTS

Regression analyses showed that arcuate fasciculus lesion load, but not extreme capsule or uncinate fasciculus lesion load or overall lesion size, significantly predicted rate, informativeness, and overall efficiency of speech as well as naming ability.

CONCLUSIONS

A new variable, arcuate fasciculus lesion load, complements established voxel-based lesion mapping techniques and, in the future, may potentially be used to estimate impairment and recovery potential after stroke and refine inclusion criteria for experimental rehabilitation programs.

Recent developments in functional and structural imaging of aphasia recovery after stroke

BACKGROUND: Functional and structural neuroimaging techniques can increase our knowledge about the neural processes underlying recovery from post-stroke language impairments (aphasia). AIMS: In the present review we highlight recent developments in neuroimaging research of aphasia recovery. MAIN CONTRIBUTION: We review (a) cross-sectional findings in aphasia with regard to local brain functions and functional connectivity, (b) structural and functional imaging findings using longitudinal (intervention) paradigms, (c) new adjunct treatments that are guided by functional imaging techniques (e.g., electrical brain stimulation) and (d) studies related to the prognosis of language recovery and treatment responsiveness after stroke. CONCLUSIONS: More recent developments in data acquisition and analysis foster better understanding and more realistic modelling of the neural substrates of language recovery after stroke. Moreover, the combination of different neuroimaging protocols can provide converging evidence for neuroplastic brain remodelling during spontaneous and treatment-induced recovery. Researchers are also beginning to use sophisticated imaging analyses to improve accuracy of prognosis, which may eventually improve patient care by allowing for more efficient treatment planning. Brain stimulation techniques offer a new and exciting way to improve the recovery potential after stroke.

MR tractography: a review of its clinical applications

Magnetic resonance tractography based on diffusion-tensor imaging was first introduced to the medical imaging community a decade ago. It has been successfully applied to a number of neurological conditions and most commonly used for preoperative planning for brain tumors and vascular malformations. Areas of active research include stroke, and dementia, where it provides valuable information not available through other imaging techniques. This technique was first introduced using the deterministic streamline algorithm and has evolved to use more sophisticated probabilistic approaches. We will review the past, present, and future of tractography, focusing primarily on its clinical applications.