Diffusion Tensor Imaging Evaluation Research Articles

Optimization of large-scale mouse brain connectome via joint evaluation of DTI and neuron tracing data

Tractography based on diffusion tensor imaging (DTI) data has been used as a tool by a large number of recent studies to investigate structural connectome. Despite its great success in offering unique 3D neuroanatomy information, DTI is an indirect observation with limited resolution and accuracy and its reliability is still unclear. Thus, it is essential to answer this fundamental question: how reliable is DTI tractography in constructing large-scale connectome? To answer this question, we employed neuron tracing data of 1772 experiments on the mouse brain released by the Allen Mouse Brain Connectivity Atlas (AMCA) as the ground-truth to assess the performance of DTI tractography in inferring white matter fiber pathways and inter-regional connections. For the first time in the neuroimaging field, the performance of whole brain DTI tractography in constructing a large-scale connectome has been evaluated by comparison with tracing data. Our results suggested that only with the optimized tractography parameters and the appropriate scale of brain parcellation scheme, can DTI produce relatively reliable fiber pathways and a large-scale connectome. Meanwhile, a considerable amount of errors were also identified in optimized DTI tractography results, which we believe could be potentially alleviated by efforts in developing better DTI tractography approaches. In this scenario, our framework could serve as a reliable and quantitative test bed to identify errors in tractography results which will facilitate the development of such novel tractography algorithms and the selection of optimal parameters.

Visual–motor deficits relate to altered gray and white matter in young adults born preterm with very low birth weight

Individuals born preterm and at very low birth weight (birth weight≤1500g) are at an increased risk of perinatal brain injury and neurodevelopmental deficits over the long term. This study examined whether this clinical group has more problems with visual–motor integration, motor coordination, and visual perception compared to term-born controls, and related these findings to cortical surface area and thickness and white matter fractional anisotropy. Forty-seven preterm-born very low birth weight individuals and 56 term-born controls were examined at 18–22years of age with a combined cognitive, morphometric MRI, and diffusion tensor imaging evaluation in Trondheim, Norway. Visual–motor skills were evaluated with the Beery–Buktenica Developmental Test of Visual–Motor Integration—V (VMI) copying test and its supplemental tests of motor coordination and visual perception. 3D T1-weighted MPRAGE images and diffusion tensor imaging were done at 1.5T. Cortical reconstruction generated in FreeSurfer and voxelwise maps of fractional anisotropy calculated with Tract-Based Spatial Statistics were used to explore the relationship between MRI findings and cognitive results. Very low birth weight individuals had significantly lower scores on the copying and motor coordination tests compared with controls. In the very low birth weight group, VMI scores showed significant positive relationships with cortical surface area in widespread regions, with reductions of the superior temporal gyrus, insula, and medial occipital lobe in conjunction with the posterior ventral temporal lobe. Visual perception scores also showed positive relationships with cortical thickness in the very low birth weight group, primarily in the lateral occipito-temporo-parietal junction, the superior temporal gyrus, insula, and superior parietal regions. In the very low birth weight group, visual–motor performance correlated positively with fractional anisotropy especially in the corpus callosum, inferior fronto-occipital fasciculus bilaterally, and anterior thalamic radiation bilaterally, driven primarily by an increase in radial diffusivity. VMI scores did not demonstrate a significant relationship to cortical surface area, cortical thickness, or diffusion measures in the control group. Our results indicate that visual–motor integration problems persist into adulthood for very low birth weight individuals, which may be due to structural alterations in several specific gray–white matter networks. Visual–motor deficits appear related to reduced surface area of motor and visual cortices and disturbed connectivity in long association tracts containing visual and motor information. We conjecture that these outcomes may be due to perinatal brain injury or aberrant cortical development secondary to injury or due to very preterm birth.

Regional differences in fiber tractography predict neurodevelopmental outcomes in neonates with infantile Krabbe disease.

BackgroundKrabbe disease is a fatal neurodegenerative disease caused by rapid demyelination of the central and peripheral nervous systems. The only available treatment, unrelated umbilical cord blood transplantation, is effective only if performed before clinical symptoms appear. Phenotypic expressions of disease-causing mutations vary widely, but genotype–phenotype relationships are unclear. Therefore, we evaluated diffusion tensor imaging (DTI) tractography with volumetric analysis as a biomarker of early white matter changes and functional disability in presymptomatic infants.MethodsWe obtained DTI and structural scans of newborns with early-infantile Krabbe disease (n = 9) diagnosed by family history or newborn screening. We compared white matter fiber tract properties to those of normal controls (n = 336) and assessed the ability of tract-based properties to predict longitudinal development in four functional domains (cognitive, fine motor, gross motor, adaptive behavior) after treatment with unrelated umbilical cord blood transplantation. We also assessed the relationship between the standard evaluation (modified Loes score) and DTI results, and the volumetric differences between the Krabbe subjects and normal controls.FindingsReductions in fractional anisotropy were significant in the corticospinal tract in the Krabbe patients compared to controls, which strongly correlated with motor and cognitive outcomes after transplantation. Significant regional differences were observed in the splenium and uncinate fasciculus in Krabbe patients and these differences correlated only with cognitive outcomes. Regional brain volumes of Krabbe patients were slightly larger than controls. Loes scores did not correlate with DTI results.InterpretationNeonatal microstructural abnormalities correlate with neurodevelopmental treatment outcomes in patients treated for infantile Krabbe disease. DTI with quantitative tractography is an excellent biomarker for evaluating infants with Krabbe disease identified through newborn screening.

Diffusion tensor imaging in evaluation of thigh muscles in patients with polymyositis and dermatomyositis.

To explore the diffusion tensor imaging (DTI) characteristics of thigh muscles in patients with polymyositis (PM) and dermatomyositis (DM). 12 patients with known PM/DM and 10 healthy volunteers were enrolled in this study. Both DTI and conventional MR sequences were performed on both thighs of all subjects. Apparent diffusion coefficient (ADC), fractional anisotropy (FA) and three eigenvalues were compared between the PM/DM group and the healthy group. One-way analysis of variance and Student's t-test were used for statistical analyses with a significance of p < 0.05. In the healthy group, the vastus intermedius muscle showed the highest ADC value and the gracilis (GA) muscle showed the lowest ADC value. These results were statistically significant when compared with other muscles (p < 0.05). The GA, semi-tendinosus and semi-membranosus muscles showed higher FA values than the other three thigh muscles (p < 0.05). The mean ADC value and three eigenvalues of oedematous muscles in the PM/DM group were higher on average and showed a statistically significant difference when compared with unaffected (non-oedematous muscles in patients) and normal muscles (p < 0.05). There was no statistical difference in the mean FA value between oedematous and normal muscles. The mean ADC, FA and three eigenvalues in unaffected muscles (in patients) showed no statistical differences from those in normal muscles (p > 0.05). DTI can be used to quantitatively evaluate the anisotropic diffusion characteristics of muscles in patients with PM/DM. A new application of DTI is proposed for inflammatory myopathies. The results show that ADC and the three eigenvalues were significantly different between diseased and normal muscles, a finding of potential value in both diagnosis and treatment monitoring of myopathies.

Detection of central white matter injury underlying vestibulopathy after mild traumatic brain injury.

To determine if central axonal injury underlies vestibulopathy and ocular convergence insufficiency after mild traumatic brain injury (TBI) by using tract-based spatial statistics (TBSS) analysis of diffusion-tensor imaging (DTI). The institutional review board approved this study, and the requirement to obtain informed consent was waived. Diffusion-tensor images were retrospectively reviewed in 30 patients with mild TBI and vestibular symptoms and 25 patients with mild TBI and ocular convergence insufficiency. Control subjects consisted of 39 patients with mild TBI without vestibular abnormalities and 17 patients with mild TBI and normal ocular convergence. Fractional anisotropy (FA) maps were generated as a measure of white matter integrity and were analyzed with TBSS regression analysis by using a general linear model. DTI abnormalities were correlated with symptom severity, neurocognitive test scores, and time to recovery with the Pearson correlation coefficient. Compared with control subjects, patients with mild TBI and vestibular symptoms had decreased neurocognitive test scores (P < .05) and FA values in the cerebellum and fusiform gyri (P < .05). Patients with ocular convergence insufficiency had diminished neurocognitive test scores (P < .05) and FA values in the right anterior thalamic radiation and right geniculate nucleus optic tracts (P < .0001). Cerebellar injury showed an inverse correlation with recovery time (R = -0.410, P = .02). Anterior thalamic radiation injury showed correlation with decreased processing speed (R = 0.402, P < .05). DTI findings in patients with mild TBI and vestibulopathy support the hypothesis that posttraumatic vestibulopathy has a central axonal injury component. Peripheral vestibular structures were not assessed, and a superimposed peripheral contribution may exist. DTI evaluation of central vestibular structures may provide a diagnostic imaging tool in these patients and a quantitative biomarker to aid in prognosis.

Determination of the ideal rat model for spinal cord injury by diffusion tensor imaging

Four different spinal cord injury (SCI) models (hemisection, contusion, transection, and segment resection) were produced in male Sprague–Dawley rats to determine the most suitable animal model of SCI by analyzing the changes in diffusion tensor imaging (DTI) parameters both qualitatively and quantitatively in vivo. Radiological examinations were performed before surgery and weekly within 4 weeks after surgery to obtain DTI tractography, MRI routine images, and DTI data of fractional anisotropy (FA) and apparent diffusion coefficient (ADC). The Basso, Beattie, and Bresnahan scale was used to evaluate the locomotor outcomes. We found that DTI tractography tracked nerve fibers and showed conspicuous changes in the injured spinal cord in all the model groups, which confirmed that our modeling was successful. A decrease in FA values and an increase in ADC were observed in all the model groups after surgery. There were significant differences in FA and ADC between weeks 1 and 4 in both hemisection and contusion groups (P<0.05), whereas the differences in the transection and segment resection groups were not as remarkable (P>0.05). Basso, Beattie, and Bresnahan scores further proved the results because of a significant, positive correlation of the scores with FA (R=0.899, P<0.01) and a significant, negative correlation of the scores with ADC (R=−0.829, P<0.01). Therefore, the transection model, which is more quantified and stable within 4 weeks after injury according to the DTI and behavioral evaluation, should be used as the standard model for SCI animal testing.

Diffusion-Tensor MR Imaging of the Breast: Hormonal Regulation

To investigate the parameters obtained with magnetic resonance (MR) diffusion-tensor imaging (DTI) of the breast throughout the menstrual cycle phases, during lactation, and after menopause, with and without hormone replacement therapy (HRT). All protocols were approved by the internal review board, and signed informed consent was obtained from all participants. Forty-five healthy volunteers underwent imaging by using T2-weighted and DTI MR sequences at 3 T. Premenopausal volunteers (n = 16) underwent imaging weekly, four times during one menstrual cycle. Postmenopausal volunteers (n = 19) and lactating volunteers (n = 10) underwent imaging once. The principal diffusion coefficients (λ1, λ2, and λ3), apparent diffusion coefficient (ADC), fractional anisotropy (FA), and maximal anisotropy (λ1-λ3) were calculated pixel by pixel for the fibroglandular tissue in the entire breast. In all premenopausal volunteers, the DTI parameters exhibited high repeatability, remaining almost equal along the menstrual cycle, with a low mean within-subject coefficient of variance of λ1, λ2, λ3, and ADC (1%-2% for all) and FA (5%), as well as a high intraclass correlation of 0.92-0.98. The diffusion coefficients were significantly lower (a) in the group without HRT use as compared with the group with HRT use (P < .01) and premenopausal volunteers (P < .01) and (b) in the lactating volunteers as compared with the premenopausal volunteers (P < .005). No significant differences in DTI parameters were found between premenopausal volunteers free of oral contraceptives and those who used oral contraceptives (P = .28-0.82) and between premenopausal volunteers and postmenopausal volunteers who used HRT (P = .31-0.93). DTI parameters are not sensitive to menstrual cycle changes, while menopause, long-term HRT, and presence of milk in lactating women affected the DTI parameters. Therefore, the timing for performing breast DTI is not restricted throughout the menstrual cycle, whereas the modulations in diffusion parameters due to HRT and lactation should be taken into account in DTI evaluation.

Preliminary experience with diffusion tensor imaging before and after re-irradiation treatments in children with progressive diffuse pontine glioma

The purpose of this study is to evaluate quantitative changes in diffusion tensor imaging (DTI) tractography and fractional anisotropy (FA) of the pons along with clinical correlation, in patients who receive re-irradiation for progressive diffuse intrinsic pontine glioma (DIPG). A retrospective case review of children with progressive DIPG who received re-irradiation at our institution from 2007 to 2011 after approval from the Institutional Review Board was performed. Tractography analysis and FA were analyzed pre and post-re-irradiation, and correlation with clinical features and MR imaging was performed. DTI analysis showed reduced values of FA on tumor progression. Increase in the FA values was noted after re-irradiation in these patients. This correlated with clinical improvement. These changes were concordant with the 3D tractography analysis which showed better visualization of the corticospinal tracts as they course through brainstem and posterior transverse pontine fibers following re-irradiation. Serial changes in the FA values using DTI could provide clinically more correlative information in patients with progressive DIPG, who receive re-irradiation. Though the use and results of this modality has been reported in the newly diagnosed DIPG before, evaluation of DTI in children who receive re-irradiation for progressive DIPG has not been reported earlier. Though limited by the small sample size and treatment variability, this study for the first time shows the preliminary experience, potential, and likely efficacy of complementing DTI analysis to routine neuroimaging also in patients re-irradiated for progressive DIPG to better assess treatment response.

Oligodendrocyte Lineage and Subventricular Zone Response to Traumatic Axonal Injury in the Corpus Callosum

Traumatic brain injury frequently causes traumatic axonal injury (TAI) in white matter tracts. Experimental TAI in the corpus callosum of adult mice was used to examine the effects on oligodendrocyte lineage cells and myelin in conjunction with neuroimaging. The injury targeted the corpus callosum over the subventricular zone, a source of neural stem/progenitor cells. Traumatic axonal injury was produced in the rostral body of the corpus callosum by impact onto the skull at the bregma. During the first week after injury, magnetic resonance diffusion tensor imaging showed that axial diffusivity decreased in the corpus callosum and that corresponding regions exhibited significant axon damage accompanied by hypertrophic microglia and reactive astrocytes. Oligodendrocyte progenitor proliferation increased in the subventricular zone and corpus callosum. Oligodendrocytes in the corpus callosum shifted toward upregulation of myelin gene transcription. Plp/CreERT:R26IAP reporter mice showed normal reporter labeling of myelin sheaths 0 to 2 days after injury but labeling was increased between 2 and 7 days after injury. Electron microscopy revealed axon degeneration, demyelination, and redundant myelin figures. These findings expand the cell types and responses to white matter injuries that inform diffusion tensor imaging evaluation and identify pivotal white matter changes after TAI that may affect axon vulnerability vs. recovery after brain injury.

Utility of Diffusion Tensor Imaging in Evaluation of the Peritumoral Region in Patients with Primary and Metastatic Brain Tumors

In the brain, diffusion tensor imaging is a useful tool for defining white matter anatomy, planning a surgical approach to space-occupying lesions, and characterizing tumors, including distinguishing primary tumors from metastases. Recent studies have attempted, with varying success, to use DTI to define the extent of tumor microinfiltration beyond the apparent borders on T2-weighted imaging. In the present review, we discuss the current state of research on the utility of DTI for evaluating the peritumoral region of brain tumors.

Osteoporosis detection by 3T diffusion tensor imaging and MRI spectroscopy in women older than 60 years

Aim of this study was to evaluate the cancellous bone quality of postmenopausal women (age >60 years) by diffusion tensor imaging (DTI) using mean diffusivity (MD) and fractional anisotropy (FA) in combination with proton magnetic resonance spectroscopy (1H-MRS). 20 postmenopausal women older than 60 years were introduced to dual-energy X-ray absorptiometry (DXA) examination in femoral neck and to an MRI spectroscopy and DTI evaluation at 3T. We observed that fat fraction (FF) can discriminate healthy and osteoporotic patients. Water mean diffusivity (MD) and FA can discriminate the healthy group from osteopenic and osteoporotic group. MD/FF vs FA/FF graph extracted from the femoral neck identifies all healthy individuals, according to DXA results. DTI and spectroscopy protocol performed in the femoral neck could be highly sensitive and specific in identifying healthy subjects.

Diffusion tensor imaging of the median nerve before and after carpal tunnel release in patients with carpal tunnel syndrome: feasibility study

To evaluate diffusion tensor imaging (DTI) indices of the median nerve pre and postoperatively in patients with carpal tunnel syndrome (CTS) to determine whether indices acquired prior to surgery differ from those acquired postoperatively. Following IRB approval, ten patients with a diagnosis of CTS were prospectively recruited. Eight patients completed the study (seven women, one man). All had bilateral asymmetric symptoms, with subsequent carpal tunnel release on the more symptomatic side. DTI of both wrists were performed using single-shot spin-echo echo-planar imaging (TR/TE, 7,000/103ms; b value 1,025s/mm(2)) preoperatively, 6weeks and 6months after carpal tunnel release. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the median nerve at the level of the distal radioulnar joint and pisiform were determined by one investigator blinded to clinical data, side, and time relative to surgery. All patients had resolution of symptoms on the surgical side at 6months. A significant increase in FA (p = 0.018) and decrease in ADC (p = 0.017) were found proximally at 6months compared to baseline on the operative side. A significant increase in FA was observed on the operative side distally at 6weeks (p = 0.012) and 6months (p = 0.017). There was a significant difference in the percentage change in FA values from baseline to 6months on the operative side in comparison with the non-operative side (p = 0.017). A significant increase in FA and decrease in ADC of the median nerve are seen following decompression surgery in patients with CTS.

Early white matter changes in childhood multiple sclerosis

Aims: Loss of integrity in nonlesional white matter occurs as a fundamental feature of multiple sclerosis (MS) in children and adults. The purpose of our study was to evaluate diffusion tensor imaging (DTI)-derived measures of white matter integrity in children with multiple sclerosis compared to age- and gender-matched controls.

Diffusion Tensor Imaging in NAWM and NADGM in MS and CIS: Association with Candidate Biomarkers in Sera

The aim of this study was to evaluate diffusion tensor imaging (DTI) indices in the corpus callosum and pyramidal tract in normal-appearing white matter (NAWM) and the caudate nucleus and thalamus in deep grey matter (NADGM) in all MS subtypes and clinically isolated syndrome (CIS). Furthermore, it was determined whether these metrics are associated with clinical measures and the serum levels of candidate immune biomarkers. Apparent diffusion coefficients (ADC) values were significantly higher than in controls in all six studied NAWM regions in SPMS, 4/6 regions in RRMS and PPMS and 2/6 regions in CIS. In contrast, decreased fractional anisotropy (FA) values in comparison to controls were detected in 2/6 NAWM regions in SPMS and 1/6 in RRMS and PPMS. In RRMS, the level of neurological disability correlated with thalamic FA values (r = 0.479, P = 0.004). In chronic progressive subtypes and CIS, ADC values of NAWM and NADGM were associated with the levels of MIF, sFas, and sTNF-α. Our data indicate that DTI may be useful in detecting pathological changes in NAWM and NADGM in MS patients and that these changes are related to neurological disability.

Magnetic Resonance Diffusion Tensor Imaging for Evaluation of Histopathological Changes in a Rat Model of Diabetic Nephropathy

The aim of this study was to investigate whether magnetic resonance (MR) diffusion tensor imaging (DTI) allows assessment of renal pathologies in a rat model of diabetic nephropathy. Twenty-one male Sprague-Dawley rats were divided into 3 groups: (1) untreated controls, (2) diabetes (DM), (3) diabetes with uninephrectomy (DM UNX) to accelerate renal impairment. Eight weeks after diabetes induction with streptozotocin, MR imaging was performed in a 1.5-T scanner using an 8-channel wrist coil. Morphological proton density images and echoplanar DTI were obtained (b = 0 and 300 s/mm, 6 diffusion directions). Renal apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were calculated for each of the different anatomical layers of the kidney. Imaging results, laboratory parameters of diabetic state and kidney function, and renal histopathological changes (glomerulosclerosis, tubular dilatation, and renal fibrosis) were compared between groups. Correlations between FA and histopathological changes were evaluated. All diabetic animals developed hyperglycemia and hypoinsulinemia. Uremia, albuminuria, and histopathological changes were most pronounced in DM UNX animals. Fractional anisotropy was significantly reduced in DM UNX animals in the cortex (CO) (0.167; confidence interval [CI], 0.151-0.184; P < 0.001), outer stripe of the outer medulla (OS) (0.254; CI, 0.225-0.283; P = 0.038), and inner medulla (IM) (0.459; CI, 0.395-0.523; P = 0.008) compared with control animals (CO, 0.251; CI, 0.224-0.277; OS, 0.309; CI, 0.267-0.350; IM, 0.559; CI, 0.515-0.603). In DM-without-UNX animals, only cortical FA was significantly lower than in controls (P < 0.001). Between groups, ADC values were not different, except for cortical ADC, which was higher in DM UNX animals than in controls. Significant negative correlations were observed between the FA of different anatomical layers and the extent of glomerulosclerosis (CO, P = 0.003, r = -0.65; and OS, P = 0.022, r = -0.52), tubulointerstitial fibrosis (IM, P = 0.028, r = -0.50), and tubular dilatation (CO, P = 0.015, r = -0.55; and IM, P = 0.006, r = -0.61), respectively. Magnetic resonance DTI by reduction of FA identified renal pathologies of diabetic nephropathy such as glomerulosclerosis, interstitial fibrosis, and tubular damage. Representing different stages of disease, DM and DM UNX animals could be differentiated. Thus, MR DTI may be valuable for noninvasive detection and monitoring of renal pathology in patients with diabetes.

Diffusion Tensor Imaging as a Prognostic Investigation in Cervical Myelopathy-Comparison of Pre- and Postsurgical Decompression DTI Indices and Tractography in 56 subjects

Introduction We present the first study in literature that documents the changes in diffusion tensor imaging (DTI) indices and tractography after surgical decompression in patients with cervical myelopathy. DTI, an established tool for tracking nerve fibers in brain, is now widely evaluated for its usefulness in spine pathologies. Although there are many studies directly comparing DTI indices of control and cervical myelopathic patients, there are no studies that have evaluated the prognostic applicability of DTI indices. The present study analyzes the pre- and postdecompression DTI indices and tractography in cervical myelopathic patients and its prognostic value. Materials and Methods Total 56 subjects including 16 cervical myelopathy patients who required surgical decompression (mean age: 53.5 ± 12.3 years, males: 15, females: (1) and forty normal controls (mean age: 38.18 ± 13.74 years, males: 20, females: 20) were included in the study. DTI of cervical spine was obtained using an axial single shot echo-planar parallel diffusion-weighted imaging sequence in a 1.5 tesla magnetic resonance imaging (MRI). Apparent diffusion coefficient (ADC), fractional anisotropy (FA), and Eigen values (E1, E2, and E3) were obtained at each region of interest (cervical disk level) from C1-C2 to C7-T1. The DTI indices of myelopathic patients were compared with normal volunteers after matching was done based on sex, cord level, and cord size. Postoperatively, the patients were followed up after 6 months and DTI scan was performed again. The clinical improvement and the DTI indices observed at the follow-up were compared with the preoperative values. Results Analysis showed significant differences between the controls and patients in all the indices (p&lt;0.05) at the site of compression. At the compressed levels, FA decreased while all the other indices increased as compared to the controls. The mean DTI indices of myelopathic patients before surgery at the sites of spinal cord compression were as follows: FA (0.49 ± 0.092), ADC (1.8 ± 0.32 µm2/ms), E1 (2.80 ± 0.44 µm2/ms), E2 (1.63 ± 0.45 µm2/ms), E3 (0.95 ± 0.23 µm2/ms). The average DTI indices of matched controls were as follows: FA (0.55 ± 0.033), ADC (1.47 ± 0.066 µm2/ms), E1 (2.49 ± 0.150 µm2/ms), E2 (1.16 ± 0.050 µm2/ms), E3 (0.77 ± 0.058 µm2/ms. The Nurick grading distribution in patients before surgery was as follows: Grade 2 = 2, Gr 3 = 8, Gr 4 = 2, Gr 5 = 4. Postoperatively, all the patients had improvement of neurology by at least one Nurick grade except for one patient who had no improvement. The Nurick grading distribution in patients during 6 months follow-up after surgery was as follows: Grade 0 = 3, Gr 1 = 6, Gr 2 = 2, Gr 3 = 3, Gr 4 = 2. Mean postoperative values of ADC, E1, and E2 showed improvement towards normal values especially in patients with preoperative Nurick grade 2 and 3 (Table 1). Patients with Nurick grade 4 and 5 did not show any significant change. The mean FA and E3 values worsened when compared to preoperative DTI indices. The postoperative DTI indices for the patients who had neurological improvement are as follows: FA (0.45 ± 0.087), ADC (1.73 ± 0.31 µm2/ms), E1 (2.59 ± 0.28 µm2/ms), E2 (1.56 ± 0.38 µm2/ms), E3 (1.07 ± 0.31 µm2/ms. Tractography also showed interruption of nerve fibre tract continuity at the level of severe compression in patients with myelopathy. At levels of moderate compression over the spinal cord, the changes in direction of nerve fibres due to bulging disc-osteophytes were evident as changes in color coding of the tracts. After surgical decompression, the restitution of fibre tract pathways was clearly demonstrated in DT tractography. Conclusion For the first time, the prognostic applicability of DTI by comparing pre- and postoperative indices of cervical myelopathy patients has been described. All preoperative DTI indices at compressed levels showed significant differences from controls indicating abnormality in neuronal integrity. All but one of the patients showed clinical improvement at 6 months. The postoperative DTI values (ADC, E1 and E2) of patients with Nurick grading 2 and 3 were observed to approach normal values indicating restoration of linear diffusion in neuronal tracts. DTI indices in patients with Nurick grade 4 and 5 remained same or worsened more. This could probably indicate persistent axonal damage. At 6 months postsurgery, DTI indices show evidence of improvement towards normal values, even though the values did not match the true extent of clinical improvement. Further DTI evaluation at 12 months and 2 years is required to analyze the extent of usefulness of DTI indices in evaluating cervical myelopathy. The results suggest that DTI indices, especially ADC and Eigen vectors can be promising indicators in the evaluation and prognostic assessment of myelopathy patients. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared

Diffusion Tensor Imaging Detected Optic Nerve Injury Correlates with Decreased Compound Action Potentials after Murine Retinal Ischemia

This study evaluated the function of mouse optic nerves after transient retinal ischemia using in vitro electrophysiologic recordings of compound action potentials (CAPs) correlated with diffusion tensor imaging (DTI) injury markers with confirmation by immunohistochemistry-determined pathology. Retinal ischemia was induced in 7- to 8-week-old female C57BL/6 mice by elevating intraocular pressure to 110 mm Hg for 60 minutes. At 3 and 7 days after retinal ischemia, optic nerves were removed for CAP measurements. The CAP amplitude was recorded using suction electrodes in isolated control and injured optic nerves followed by ex vivo DTI evaluation. After DTI, optic nerves were embedded in paraffin and cut for immunohistochemical analyses. Consistent with previous in vivo DTI measurements, a 25% decrease in axial diffusivity with normal radial diffusivity was seen at 3 days after retinal ischemia, suggesting axonal injury without myelin damage. At 7 days, there was no additional change in axial diffusivity compared with that at 3 days, but radial diffusivity significantly increased by 50%, suggestive of significant myelin damage due to sustained axonal injury. The relative anisotropy (RA) progressively decreased after retinal ischemia when compared with that of the controls. The CAP amplitude in injured nerves also progressively decreased after retinal ischemia, which correlated with the reduced RA (r = 0.80). This study suggests that CAP amplitude reflects both axonal and myelin integrity and RA is an optimal parameter for functional assessment compared with axial or radial diffusivity alone in murine optic nerves after retinal ischemia.

Diffusion tensor imaging evaluation of white matter in adolescents with myelomeningocele and Chiari II malformation

Macrostructural abnormalities in cerebral white matter in patients with myelomeningocele are well known, but microstructural abnormalities are not as well studied. The aim of this study was to evaluate cerebral white matter in adolescents with myelomeningocele using diffusion tensor imaging (DTI), and to investigate the effects of ventricular dilation and CSF shunt presence on white matter microstructure in these patients. DTI and T1-weighted 3-D (T1-3-D) MRI were performed on nine adolescents with myelomeningocele and Chiari II malformation and nine age-matched controls. The fractional anisotropy (FA) and mean diffusivity (MD) values were measured and compared. Significantly decreased FA and increased MD values were observed in most white matter regions and fibers in adolescents with myelomeningocele compared to controls. Further analysis in patients revealed significant changes in DTI parameters in hemispheres with enlarged lateral ventricles compared to those with normal ventricle size. In addition, a significant difference in FA values in the posterior limb of the internal capsule was found in the comparison of hemispheres in patients with or without CSF shunt catheters. This study revealed widespread microstructural abnormalities in white matter in adolescents with myelomeningocele and Chiari II malformation. Ventricular dilation may have additional effects on white matter microstructure in this patient population. CSF shunt diversion effects on white matter may be multifactorial and need further investigation.

Wallerian degeneration after spinal cord lesions in cats detected with diffusion tensor imaging

One goal of in vivo neuroimaging is the detection of neurodegenerative processes and anatomical reorganizations after spinal cord (SC) injury. Non-invasive examination of white matter fibers in the living SC can be conducted using magnetic resonance diffusion-weighted imaging. However, this technique is challenging at the spinal level due to the small cross-sectional size of the cord and the presence of physiological motion and susceptibility artifacts. In this study, we acquired in vivo high angular resolution diffusion imaging (HARDI) data at 3T in cats submitted to partial SC injury. Cats were imaged before, 3 and 21 days after injury. Spatial resolution was enhanced to 1.5 × 1.5 × 1 mm(3) using super-resolution technique and distortions were corrected using the reversed gradient method. Tractography-derived regions of interest were generated in the dorsal, ventral, right and left quadrants, to evaluate diffusion tensor imaging (DTI) and Q-Ball imaging metrics with regards to their sensitivity in detecting primary and secondary lesions. A three-way ANOVA tested the effect of session (intact, D3, D21), cross-sectional region (left, right, dorsal and ventral) and rostrocaudal location. Significant effect of session was found for FA (P<0.001), GFA (P<0.05) and radial diffusivity (P<0.001). Post-hoc paired T-test corrected for multiple comparisons showed significant changes at the lesion epicenter (P<0.005). More interestingly, significant changes were also found several centimeters from the lesion epicenter at both 3 and 21 days. This decrease was specific to the type of fibers, i.e., rostrally to the lesion on the dorsal aspect of the cord and caudally to the lesion ipsilaterally, suggesting the detection of Wallerian degeneration.

Diffusion Tensor Imaging for Evaluation of the Childhood Brain and Pediatric White Matter Disorders

Magnetic resonance (MR) imaging has been used by investigators and clinicians to assess the development of the brain in childhood to understand both patterns of normal growth and patterns by which a maturing brain may deviate from normal. Advanced MR techniques such as diffusion tensor imaging (DTI) have gained prominence as a means of assessing brain development. This review explains the sequence of brain maturation and the means by which DTI can be used to assess it in normal children.