Early Diffusion Tensor Imaging Research Articles

Post SRS Target Diffusion Metrics for Response Prognostication in Idiopathic Trigeminal Neuralgia

Diffusion tensor imaging (DTI) is used to measure the movement of water molecules in biological tissue, which permits a thorough characterization of white matter microstructure through quantitative diffusivity metrics. The most commonly used diffusivity metric, fractional anisotropy (FA), provides insight into the overall white matter microstructural properties, whereas radial diffusivity (RD), axial diffusivity (AD), and mean diffusivity (MD) suggest changes in myelination, axonal integrity & underlying neuro-inflammation and edema respectively. Study purpose is to find whether trigeminal nerve diffusivity metrics at a single, early time point after frameless SRS is predictive of long-term pain relief in patients with TN.Study cohort comprised of 44 pts with inclusion criteria were: 1) diagnosis of classic, type 1 TN 2) SRS treatment with no prior surgical procedures for TN; 3) 3 tesla MRI scans at 6 months posttreatment (range 5-7 months); and 4) at least 12 months of clinical follow-up. Patients with TN secondary to multiple sclerosis, cranial tumors, or vertebrobasilar dolichoectasia compressing the brainstem were excluded from the study. For each patient, diffusivity metrics (FA, MD, RD, and AD) were extracted from both the affected and unaffected trigeminal nerves at 6 months posttreatment 6 months diffusivity metrics were compared with long-term clinical outcome. Patients were identified as long-term responders if they achieved at least 75% reduction in preoperative pain for 12 months or longer following SRS. Average microstructural diffusivity differences (within group - pre and post treatment; across group - responder & non-responders) were analyzed using paired / Independent T test.Trigeminal nerve diffusivity at 6 months post-SRS was predictive of long-term clinical effectiveness, where long-term responders (n = 36) showed significantly lower fractional anisotropy at the radiosurgical target of their affected nerve compared to their contralateral, unaffected nerve and to nonresponders. Radial diffusivity and mean diffusivity, correlates of myelin alterations and inflammation, were also significantly higher in the affected nerve of long-term responders compared to their unaffected nerve. Nonresponders (n = 8) did not exhibit any characteristic diffusivity changes after SRS.DTI, FA specifically, appears to be a strong, objective measure to assess the effects of radiation on a nerve. Incorporating early DTI assessment can provide prognostic information that supplements clinical measures.

Correlating early motor skills to white matter abnormalities in preterm infants using diffusion tensor imaging.

Diffusion tensor imaging (DTI) can detect injury to specific white matter (WM) tracts involved with sensorimotor processing and may provide sensitive measures for latent or nascent motor skills. We hypothesized that DTI measures of WM fractional anisotropy (FA) could predict early motor scores on a standardized assessment in a cohort of preterm infants at risk for WM injury. In this prospective study, preterm infants (n= 26, 11 female, 15 male, mean gestational age 29.1 ± 2.5) underwent the Test of Infant Motor Performance (TIMP) at term and at 12 weeks corrected age (CA) and underwent an non-sedated magnetic resonance imaging (MRI) with DTI at a mean of 42 ± 1.5 weeks CA. Fractional anisotropy (FA) was measured by Voxelwise statistical analysis using Tract-Based Spatial Statistics (TBSS) in the specific regions of interest. Significant differences were found between infants with poor versus average performance on motor assessments at 12-weeks and FA values in several left hemispheric WM tracts (p< 0.05). High FA of the left anterior limb of the internal capsule (ALIC) predicted mean increase in TIMP scores on specific items for head lift in prone and head lift turn to sound (p= 0.045 and p= 0.002). Subtle WM injury, as indicated by low FA in left WM tracts, can predict outcomes of early motor skills performance testing at 3 months. Early DTI may identify infants with silent WM injury who need early intervention. Further studies may establish if individual tract FA improve after targeted treatment.

Loss of Consciousness Is Related to White Matter Injury in Mild Traumatic Brain Injury

To study the relation of loss of consciousness (LOC) to white matter integrity after mild traumatic brain injury (mTBI), we acquired diffusion tensor imaging (DTI) at 3 Tesla in 79 participants with mTBI and normal computed tomography (age 18 to 50 years) whom we imaged after a mean post-injury interval of 25.9 h (standard deviation = 12.3) and at 3 months. For comparison, 64 participants with orthopedic injury (OI) underwent DTI at similar intervals. Quantitative tractography was used to measure fractional anisotropy (FA) and mean diffusivity (MD) in the left and right uncinate fasciculus (UF), left and right inferior frontal occipital fasciculus (IFOF), and the genu of the corpus callosum. Generalized estimating equation models assessed the association between LOC and both MD and FA across time after mTBI and compared their DTI metrics with the OI group. LOC was significantly related to MD in UF and IFOF (p values ranged from p < 0.0001 to 0.0270) and to FA in left UF (p = 0.0104) and right UF (p = 0.0404). Between-group differences in MD were significant for left UF, left and right IFOF, and the genu of the corpus callosum on initial DTI, but not at 3 months post-injury, and these differences were specific to the mTBI subgroup with LOC. Groups did not differ in FA at either occasion. Early DTI may provide a biomarker for mTBI with LOC, even in patients whose consciousness recovers by arrival in the emergency department. MD better differentiates mTBI from OI than FA on early DTI, but this is specific to mTBI with LOC. DTI findings support a continuum of white matter injury in early mTBI.

Neonatal DTI early after birth predicts motor outcome in preterm infants with periventricular hemorrhagic infarction.

To determine the association between early neonatal diffusion tensor imaging (DTI) and the development of unilateral spastic cerebral palsy (USCP) in preterm infants with periventricular hemorrhagic infarction (PVHI). Preterm infants with PVHI were assessed with early (≤4 wk after birth) and term-equivalent age MRI-DTI. Involvement of corticospinal tracts was assessed by visual assessment of the posterior limb of the internal capsule (PLIC) on DTI (classified asymmetrical, equivocal, or symmetrical) and by an atlas-based approach calculating fractional anisotropy asymmetry index in the PLIC. Motor outcome was assessed at ≥15 mo corrected age. Seven out of 23 infants with PVHI developed USCP. Their PLIC was visually scored as asymmetrical in 6 and equivocal in 1 on the early DTI. Thirteen out of 16 infants with a symmetrical motor development had a symmetrical PLIC on early DTI, the remaining 3 were equivocal. All infants with USCP had a fractional anisotropy asymmetry index of >0.05 (optimal cut-off value) on early DTI. In infants with a symmetrical motor development (n = 16), 14 had an asymmetry index ≤0.05 while 2 had an index >0.05. DTI in preterm infants with PVHI within a few weeks after birth is associated with later motor development.

Early diffusion tensor imaging findings in animal models of acute diffuse axonal injury

Objective To establish animal models of diffuse axonal injury (DAI) and discuss the early functional MRI findings.Methods Twenty-five adult white rabbits were divided into control group (n =5),mild DAI group and severe DAI group (n =6) according to random number.Mild DAI group was subdivided into mild DAI 3 h (n =6),1 day (n =4) and 1 week (n =4) groups.Routine MRI and diffusion tensor imaging (DTI) were performed.Parameters measured were fractional anisotropy (FA),apparent diffusion coefficient (ADC),axial diffusivity (AD) and radical diffusivity (RD).Results Significantly increased FA (P＜0.01) and decreased ADC (P＜0.05) and RD (P＜0.01) were detected in severe DAI group compared to control group,but there was no significant variation in AD between the two groups (P ＞ 0.05).Each parameter remained almost unchanged in mild DAI 3 h group and mild DAI 1 week group,but FA was increased (P ＜ 0.01) and RD decreased (P ＜ 0.05) in mild DAI 1 day group,with no changes of ADC and AD.Conclusion DTI is a sensitive way to detect the occurrence and development of DAI and can provide referential images for early DAI diagnosis. Key words: Brain injuries; Diffuse axonal injuries; Diffusion tensor imaging; Rabbits

Prediction of neurodevelopmental outcome after hypoxic–ischemic encephalopathy treated with hypothermia by diffusion tensor imaging analyzed using tract-based spatial statistics

Objective biomarkers are needed to assess neuroprotective therapies after perinatal hypoxic-ischemic encephalopathy (HIE). We tested the hypothesis that, in infants who underwent therapeutic hypothermia after perinatal HIE, neurodevelopmental performance was predicted by fractional anisotropy (FA) values in the white matter (WM) on early diffusion tensor imaging (DTI) as assessed by means of tract-based spatial statistics (TBSS). We studied 43 term infants with HIE. Developmental assessments were carried out at a median (range) age of 24 (12-28) mo. As compared with infants with favorable outcomes, those with unfavorable outcomes had significantly lower FA values (P < 0.05) in the centrum semiovale, corpus callosum (CC), anterior and posterior limbs of the internal capsule, external capsules, fornix, cingulum, cerebral peduncles, optic radiations, and inferior longitudinal fasciculus. In a second analysis in 32 assessable infants, the Griffiths Mental Development Scales (Revised) (GMDS-R) showed a significant linear correlation (P < 0.05) between FA values and developmental quotient (DQ) and all its component subscale scores. DTI analyzed by TBSS provides a qualified biomarker that can be used to assess the efficacy of additional neuroprotective therapies after HIE.

Diffusion tensor imaging of early changes in corpus callosum after acute cerebral hemisphere lesions in newborns

The main purpose was to investigate any early diffusion tensor imaging (DTI) changes in corpus callosum (CC) associated with acute cerebral hemisphere lesions in term newborns. We retrospectively analysed 19 cases of term newborns acutely affected by focal or multi-focal lesions: hypoxic-ischemic encephalopathy, hypoglycaemic encephalopathy, focal ischemic stroke and deep medullary vein associated lesions. DTI was acquired at 1.5 Tesla with dedicated neonatal coil. DTI metrics (apparent diffusion coefficient (ADC), fractional anisotropy (FA), axial λ(∐) and radial λ(⟂) diffusivity) were measured in the hemisphere lesions and in the CC. The control group included seven normal newborns. The following significant differences were found between patients and normal controls in the CC: mean ADC was lower in patients (0.88 SD 0.23 versus 1.18 SD 0.07 μm(2)/s) and so was mean FA (0.50 SD 0.1 versus 0.67 SD 0.05) and mean λ(∐) value (1.61 SD 0.52 versus 2.36 SD 0.14 μm(2)/s). In CC the percentage of ADC always diminished independently of lesion age (with one exception), whereas in hemisphere lesions, it was negative in earlier lesions, but exceeded normal values in the older lesions. CC may undergo early DTI changes in newborns with acute focal or multi-focal hemisphere lesions of different aetiology. Although a direct insult to CC cannot be totally ruled out, DTI changes in CC (in particular λ(∐)) may also be compatible with very early Wallerian degeneration or pre-Wallerian degeneration.

Age‐related differences in multiple measures of white matter integrity: A diffusion tensor imaging study of healthy aging

Diffusion tensor imaging (DTI) measures diffusion of molecular water, which can be used to calculate indices of white matter integrity. Early DTI studies of aging primarily focused on two global measures of integrity; the average rate (mean diffusivity, MD) and orientation coherence (fractional anisotropy, FA) of diffusion. More recent studies have added measures of water movement parallel (axial diffusivity, AD) and perpendicular (radial diffusivity, RD) to the primary diffusion direction, which are thought to reflect the neural bases of age differences in diffusion (i.e., axonal shrinkage and demyelination, respectively). In this study, patterns of age differences in white matter integrity were assessed by comparing younger and healthy older adults on multiple measures of integrity (FA, AD, and RD). Results revealed two commonly reported patterns (Radial Increase Only and Radial/Axial Increase), and one relatively novel pattern (Radial Increase/Axial Decrease) that varied by brain region and may reflect differential aging of microstructural (e.g., degree of myelination) and macrostructural (e.g., coherence of fiber orientation) properties of white matter. In addition, larger age differences in FA in frontal white matter were consistent with the anterior-posterior gradient of age differences in white matter integrity. Together, these findings complement other recent studies in providing information about patterns of diffusivity that are characteristic of healthy aging.

Diffusion tensor imaging in a case of Kearns–Sayre syndrome: Striking brainstem involvement as a possible cause of oculomotor symptoms

Kearns–Sayre syndrome (KSS) is a rare autosomal dominant mitochondrial disorder affecting the central nervous system. Progressive external ophthalmoplegia is an early and characteristic clinical symptom of the disease. We describe a 22-year-old female patient with a typical KSS including early and severe external ophthalmoplegia. Conventional MRI and diffusion tensor imaging (DTI) was performed to investigate the early involvement of the central nervous system (CNS). DTI revealed substantial white matter alterations that were primarily confined to the brainstem. These early DTI changes support the hypothesis that regional affection of the brainstem may play a role in the pathogenesis of the early oculomotor symptoms. DTI might be helpful to detect an early involvement of the CNS in KSS.

Developmental Changes and Injury Induced Disruption of the Radial Organization of the Cortex in the Immature Rat Brain Revealed by In Vivo Diffusion Tensor MRI

During brain development, morphological changes modify the cortex from its immature radial organization to its mature laminar appearance. Applying in vivo diffusion tensor imaging (DTI), the microstructural organization of the cortex in the immature rat was analyzed and correlated to neurohistopathology. Significant differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were detected between the external (I-III) and deep (IV-VI) cortical layers in postnatal day 3 (P3) and P6 pups. With cortical maturation, ADC was reduced in both cortical regions, whereas a decrease in FA was only seen in the deep layers. A distinct radial organization of the external cortical layers with the eigenvectors perpendicular to the pial surface was observed at both ages. Histology revealed maturational differences in the cortical architecture with increased neurodendritic density and reduction in the radial glia scaffolding. Early DTI after hypoxia-ischemia at P3 shows reduced ADC and FA in the ipsilateral cortex that persisted at P6. Cortical DTI eigenvector maps reveal microstructural disruption of the radial organization corresponding to regions of neuronal death, radial glial disruption, and astrocytosis. Thus, the combined use of in vivo DTI and histopathology can assist in delineating normal developmental changes and postinjury modifications in the immature rodent brain.

Diffusion tensor imaging detects early Wallerian degeneration of the pyramidal tract after ischemic stroke

We used diffusion tensor imaging (DTI) to assess Wallerian degeneration of the pyramidal tract within the first 2 weeks after ischemic stroke, and correlated the extent of Wallerian degeneration with the motor deficit. Nine patients with middle cerebral artery stroke were examined 2–16 days after stroke by DTI and T2-weighted MRI. We measured fractional anisotropy (FA), averaged diffusivity (Dav), eigenvalues of the diffusion tensor and T2-weighted signal in the cerebral peduncle and compared these values between the affected and the unaffected side and between patients and six controls. FA was significantly reduced on the affected side compared to the unaffected side and compared to the control group. The largest eigenvalue was reduced, whereas the smallest eigenvalue was elevated on the affected side. There was no significant difference in T2-weighted signal and Dav. The decrease of anisotropy correlated positively with the motor deficit at the time of DTI study and 90 days after stroke. The reduction of anisotropy mirrors the disintegration of axonal structures, as it occurs in the early phase of Wallerian degeneration. DTI detects changes of water diffusion related to beginning pyramidal tract degeneration within the first 2 weeks after stroke that are not yet visible in conventional T2-weighted or orientationally averaged diffusion weighted MRI. We demonstrated for the first time a correlation of early DTI findings of pyramidal tract damage with the motor deficit. DTI can help prognosing recovery of motor function after stroke within the early subacute phase.