Probabilistic Diffusion Tensor Tractography Research Articles

Tractography patterns of pedunculopontine nucleus deep brain stimulation

Deep brain stimulation of the pedunculopontine nucleus is a promising surgical procedure for the treatment of Parkinsonian gait and balance dysfunction. It has, however, produced mixed clinical results that are poorly understood. We used tractography with the aim to rationalise this heterogeneity. A cohort of eight patients with postural instability and gait disturbance (Parkinson’s disease subtype) underwent pre-operative structural and diffusion MRI, then progressed to deep brain stimulation targeting the pedunculopontine nucleus. Pre-operative and follow-up assessments were carried out using the Gait and Falls Questionnaire, and Freezing of Gait Questionnaire. Probabilistic diffusion tensor tractography was carried out between the stimulating electrodes and both cortical and cerebellar regions of a priori interest. Cortical surface reconstructions were carried out to measure cortical thickness in relevant areas. Structural connectivity between stimulating electrode and precentral gyrus (r = 0.81, p = 0.01), Brodmann areas 1 (r = 0.78, p = 0.02) and 2 (r = 0.76, p = 0.03) were correlated with clinical improvement. A negative correlation was also observed for the superior cerebellar peduncle (r = −0.76, p = 0.03). Lower cortical thickness of the left parietal lobe and bilateral premotor cortices were associated with greater pre-operative severity of symptoms. Both motor and sensory structural connectivity of the stimulated surgical target characterises the clinical benefit, or lack thereof, from surgery. In what is a challenging region of brainstem to effectively target, these results provide insights into how this can be better achieved. The mechanisms of action are likely to have both motor and sensory components, commensurate with the probable nature of the underlying dysfunction.

Post-Traumatic Stress Symptoms after Pediatric Injury: Relation to Pre-Frontal Limbic Circuitry.

Pre-frontal limbic circuitry is vulnerable to effects of stress and injury. We examined microstructure of pre-frontal limbic circuitry after traumatic brain injury (TBI) or extracranial injury (EI) and its relation to post-traumatic stress symptoms (PTSS). Participants aged 8 to 15 years who sustained mild to severe TBI (n = 53) or EI (n = 26) in motor vehicle incidents were compared with healthy children (n = 38) in a prospective longitudinal study. At the seven-week follow-up, diffusion tensor imaging was obtained in all groups; injured children completed PTSS ratings using a validated scale. Using probabilistic diffusion tensor tractography, pathways were seeded from bilateral amygdalae and hippocampi to estimate the trajectory of white matter connecting them to each other and to targeted pre-frontal cortical (PFC) regions. Microstructure was estimated using fractional anisotropy (FA) in white matter and mean diffusivity (MD) in gray matter. Pre-frontal limbic microstructure was similar across groups, except for reduced FA in the right hippocampus to orbital PFC pathway in the injured versus healthy group. We examined microstructure of components of pre-frontal limbic circuitry with concurrently obtained PTSS cluster scores in the injured children. Neither microstructure nor PTSS scores differed significantly in the TBI and EI groups. Across PTSS factors, specific symptom clusters were related positively to higher FA and MD. Higher hyperarousal, avoidance, and re-experiencing symptoms were associated with higher FA in amygdala to pre-frontal and hippocampus to amygdala pathways. Higher hippocampal MD had a central role in hyperarousal and emotional numbing symptoms. Age moderated the relation of white and gray matter microstructure with hyperarousal scores. Our findings are consistent with models of traumatic stress that implicate disrupted top-down PFC and hippocampal moderation of overreactive subcortical threat arousal systems. Alterations in limbic pre-frontal circuitry and PTSS place children with either brain or body injuries at elevated risk for both current and future psychological health problems.

Laterality of cerebellar afferent and efferent pathways in a healthy right-handed population: A diffusion tensor imaging study.

The cerebellum communicates with the cerebral cortex through the cortico-ponto-cerebellar tract (CPCT, cerebellar afferent) and the dentato-rubro-thalamo-cortical tract (DRTCT, cerebellar efferent). This study explored the laterality of CPCT and DRTCT in a right-handed population. Forty healthy right-handed subjects (18 males and 22 females with age range of 26-79years old) who underwent diffusion tensor imaging (DTI) were retrospectively enrolled. Bilateral CPCT, DRTCT, and the corticospinal tract (CST) were reconstructed using probabilistic diffusion tensor tractography (DTT). Tract volume (TV) and fractional anisotropy (FA) were compared between dominant and non-dominant tracts. Subjects were divided into age groups (20-40, 41-60, and 61-80years), and the DTI-derived parameters of the groups were compared to determine age-related differences. TV and FA of non-dominant CPCT were higher than those of dominant CPCT, and the dominant CST was higher than the non-dominant CST. The TV and FA of DRTCT showed no side-to-side difference. The 61-80years age group had the highest TV of the dominant and non-dominant DRTCT among the three groups and the highest FA of the non-dominant CPCT and DRTCT. The results revealed the structural characteristics of CPCT and DRTCT using probabilistic DTT. Normal asymmetric patterns and age-related changes in cerebellar white matter tracts may be important to researchers investigating cerebro-cerebellar structural connectivity.

Structural neural connectivity of the vestibular nuclei in the human brain: a diffusion tensor imagingS study.

Many animal studies have reported on the neural connectivity of the vestibular nuclei (VN). However, little is reported on the structural neural connectivity of the VN in the human brain. In this study, we attempted to investigate the structural neural connectivity of the VN in 37 healthy subjects using diffusion tensor tractography. A seed region of interest was placed on the isolated VN using probabilistic diffusion tensor tractography. Connectivity was defined as the incidence of connection between the VN and each brain region. The VN showed 100% connectivity with the cerebellum, thalamus, oculomotor nucleus, trochlear nucleus, abducens nucleus, and reticular formation, irrespective of thresholds. At the threshold of 5 streamlines, the VN showed connectivity with the primary motor cortex (95.9%), primary somatosensory cortex (90.5%), premotor cortex (87.8%), hypothalamus (86.5%), posterior parietal cortex (75.7%), lateral prefrontal cortex (70.3%), ventromedial prefrontal cortex (51.4%), and orbitofrontal cortex (40.5%), respectively. These results suggest that the VN showed high connectivity with the cerebellum, thalamus, oculomotor nucleus, trochlear nucleus, abducens nucleus, and reticular formation, which are the brain regions related to the functions of the VN, including equilibrium, control of eye movements, conscious perception of movement, and spatial orientation.

Symmetrical Location Characteristics of Corticospinal Tract Associated With Hand Movement in the Human Brain: A Probabilistic Diffusion Tensor Tractography.

The purpose of this study is to elucidate the symmetrical characteristics of corticospinal tract (CST) related with hand movement in bilateral hemispheres using probabilistic fiber tracking method.Seventeen subjects were participated in this study. Fiber tracking was performed with 2 regions of interest, hand activated functional magnetic resonance imaging (fMRI) results and pontomedullary junction in each cerebral hemisphere. Each subject's extracted fiber tract was normalized with a brain template. To measure the symmetrical distributions of the CST related with hand movement, the laterality and anteriority indices were defined in upper corona radiata (CR), lower CR, and posterior limb of internal capsule.The measured laterality and anteriority indices between the hemispheres in each different brain location showed no significant differences with P < 0.05. There were significant differences in the measured indices among 3 different brain locations in each cerebral hemisphere with P < 0.001. Our results clearly showed that the hand CST had symmetric structures in bilateral hemispheres.The probabilistic fiber tracking with fMRI approach demonstrated that the hand CST can be successfully extracted regardless of crossing fiber problem. Our analytical approaches and results seem to be helpful for providing the database of CST somatotopy to neurologists and clinical researches.

Acute infarcts cause focal thinning in remote cortex via degeneration of connecting fiber tracts.

To study remote effects distant from acute ischemic infarcts by measuring longitudinal changes of cortical thickness in connected brain regions as well as changes in microstructural integrity in connecting fiber tracts. Thirty-two patients (mean age 71 years) underwent a standardized protocol including multimodal MRI and clinical assessment both at stroke onset and 6 months after the event. Cortex connected to acute infarcts was identified by probabilistic diffusion tensor tractography starting from the acute lesion. Changes of cortical thickness were measured using the longitudinal stream of FreeSurfer. Microstructural damage in white matter tracts was assessed by changes of mean diffusivity. We found focal cortical thinning specifically in areas connected to acute infarcts (p < 0.001). Thinning was more pronounced in regions showing a high probability of connectivity to infarcts. Microstructural damage in white matter tracts connecting acute infarcts with distant cortex significantly correlated with thickness changes in that region (ρ = -0.39, p = 0.028). There was no indication of an influence of cavitation status or infarct etiology on the observed changes in cortex and white matter. These findings identify secondary degeneration of connected white matter tracts and remote cortex as key features of acute ischemic infarcts. Our observations may have implications for the understanding of structural and functional reorganization after stroke.

Common cerebral networks associated with distinct deep brain stimulation targets for cluster headache

Several centers have reported efficacious cluster headache suppression with deep brain stimulation (DBS) of the hypothalamic region using a variety of targets. While the connectivity of some of these targets has individually been studied, commonalities across these targets, especially with respect to network-level connectivity, have not previously been explored. We examined the anatomic connectivity of the four distinct DBS targets reported in the literature using probabilistic diffusion tensor tractography in normal subjects. Despite being described as hypothalamic, the DBS targets localized in the midbrain tegmentum posterior to the hypothalamus. Common tracts across DBS targets and subjects included projections to the ipsilateral hypothalamus, reticular formation, and cerebellum. Although DBS target coordinates are not located within the hypothalamus, a strong connection between DBS targets and the hypothalamus likely exists. Moreover, a common projection to the medial ipsilateral cerebellum was identified. Understanding the common connectivity of DBS-targeted regions may elucidate anatomic pathways that are involved in modulating cluster headache attacks and facilitate more precise patient-specific targeting of DBS.

A crucial role of altered fractional anisotropy in motor problems of very preterm children

BackgroundVery preterm children (<32 weeks of gestation) are characterized by impaired white matter development as measured by fractional anisotropy (FA). This study investigates whether altered FA values underpin the widespread motor impairments and higher incidence of developmental coordination disorder (DCD) in very preterm children at school-age. MethodsThirty very preterm born children (mean (SD) age of 8.6 (0.3) years) and 47 term born controls (mean [SD] age 8.7 [0.5] years) participated. Motor development was measured using the Movement Assessment Battery for Children. A score below the 15th percentile was used as a research diagnosis of DCD. FA values, as measure of white matter abnormalities, were determined for 18 major white matter tracts, obtained using probabilistic diffusion tensor tractography. ResultsLarge-sized reductions in FA of the cingulum hippocampal tract right (d = 0.75, p = .003) and left (d = 0.76, p = .001), corticospinal tract right (d = 0.56, p = .02) and left (d = 0.65, p = .009), forceps major (d = 1.04, p < .001) and minor (d = 0.54, p = .02) were present in very preterms, in particular with a research diagnosis of DCD. Reduced FA values moderately to strongly related to motor impairments. A ROC curve for average FA, as calculated from tracts that significantly discriminated between very preterm children with and without a research diagnosis of DCD, showed an area under curve of 0.87 (95% CI 0.74–1.00, p = .001). ConclusionsThis study provides clear evidence that reduced FA values are strongly underpinning motor impairment and DCD in very preterm children at school-age. In addition, outcomes demonstrate that altered white matter FA values can potentially be used to discriminate between very preterm children at risk for motor impairments, although future studies are warranted.

Anatomical location of transcallosal sensorimotor fibers in the human brain: Diffusion tensor tractography study

AbstractMany diffusion tensor tractography (DTT) studies have reported on the topography of transcallosal fibers (TCF). However, little detailed anatomical information on TCF that can be easily applied for clinical purposes is known. Using probabilistic DTT, we attempted to determine the anatomical location of the TCF for motor and sensory function in the human brain. A total of 51 healthy subjects were recruited for this study. Diffusion tensor images (DTIs) were obtained at 1.5 T, and four TCF for the premotor cortex (PMC), the primary motor cortex (M1) for hand and leg, and the primary somatosensory cortex (S1) were obtained using FMRIB software. Locations of the TCF were defined as the highest probabilistic location on the midsagittal slice of the corpus callosum. We measured distances between the most anterior and posterior points of the corpus callosum. The relative mean distances of the highest probabilistic location for the precentral knob PMC (Brodmann area 6 anterior to the precentral knob), hand M1, leg M1, and precentral knob S1 (postcentral gyrus posterior to the precentral knob) TCF were 48.99%, 59.78%, 67.93%, and 73,48% from the most anterior point of the CC, respectively. According to our findings, the precentral knob PMC, hand M1, leg M1, and precentral knob S1 TCF were located at the anterior body, posterior body, posterior body, and isthmus according to Witelson’s classification, respectively.

Predicting Behavioral Deficits in Pediatric Traumatic Brain Injury Through Uncinate Fasciculus Integrity

Behavioral dysregulation is a common and detrimental consequence of traumatic brain injury (TBI) in children that contributes to poor academic achievement and deficits in social development. Unfortunately, behavioral dysregulation is difficult to predict from either injury severity or early neuropsychological evaluation. The uncinate fasciculus (UF) connects orbitofrontal and anterior temporal lobes, which are commonly implicated in emotional and behavioral regulation. Using probabilistic diffusion tensor tractography (DTT), we examined the relationship between the integrity of the UF 3 months post-injury and ratings of executive functions 12 months post-injury in children with moderate to severe TBI and a comparison group with orthopedic injuries. As expected, fractional anisotropy of the UF was lower in the TBI group relative to the orthopedic injury group. DTT metrics from the UF served as a biomarker and predicted ratings of emotional and behavior regulation, but not metacognition. In contrast, the Glasgow Coma Scale score was not related to either UF integrity or to executive function outcomes. Neuroanatomical biomarkers like the uncinate fasciculus may allow for early identification of behavioral problems and allow for investigation into the relationship of frontotemporal networks to brain-behavior relationships.