Serial Diffusion Tensor Imaging Research Articles

Serial Diffusion Tensor Imaging and Rate of Ventricular Blood Clearance in Patients with Intraventricular Hemorrhage.

We developed a noninvasive biomarker to quantify the rate of ventricular blood clearance in patients with intracerebral hemorrhage and extension to the ventricles-intraventricular hemorrhage. We performed magnetic resonance imaging in 26 patients at 1, 14, 28, and 42days of onset and measured their hematoma volume (HV), ventricular blood volume (VBV), and two diffusion metrics: fractional anisotropy (FA), and mean diffusivity (MD). The ipasilesional ventricular cerebral spinal fluid's FA and MD were associated with VBV and stroke severity scores (National Institute of Health Stroke Scale [NIHSS]). A subcohort of 14 patients were treated with external ventricular drain (EVD). A generalized linear mixed model was applied for statistical analysis. At day 1, the average HVs and NIHSS scores were 14.6 ± 16.7 cm3 and16 ± 8, respectively. A daily rate of 2.1% and 1.3% blood clearance/resolution were recorded in HV and VBV, respectively. Ipsilesional ventricular FA (vFA) and ventricular MD (vMD) were simultaneously decreased (vFA = 1.3% per day, posterior probability [PP] > 99%) and increased (vMD = 1.5% per day, PP > 99%), respectively. Patients with EVD exhibited a faster decline in vFA (1.5% vs. 1.1% per day) and an increase in vMD (1.8% vs. 1.5% per day) as compared with patients without EVD. Temporal change in vMD was associated with VBV; a 1.00-cm3 increase in VBV resulted in a 5.2% decrease in vMD (PP < 99%). VBV was strongly associated with NIHSS score (PP = 97-99%). A larger cerebral spinal fluid drained volume was associated with a greater decrease (PP = 83.4%) in vFA, whereas a smaller volume exhibited a greater increase (PP = 94.8%) in vMD. In conclusion, vFA and vMD may serve as biomarkers for VBV status.

Factors influencing diffusion tensor imaging of knee cartilage in children ages 6-12years: a prospective study.

Magnetic resonance diffusion tensor imaging (DTI) has recently been used to evaluate the developing cartilage of children, but the influencing factors have not been well studied. The objective of this study was to investigate the influence of the diffusion gradient strength (b value), diffusion gradient direction, age and sex on knee cartilage DTI in healthy children aged 6-12years. A total of 30 healthy child volunteers, with an average age of 8.9 ± 1.6 (mean ± standard deviation) years, were enrolled in this study. They were categorized into three groups according to their age range: 6-8years, 8-10years and 10-12years, ensuring equal sex distribution in each group (5 boys and 5 girls). These volunteers underwent routine left knee joint magnetic resonance imaging (MRI) and serial DTI scans. DTI parameters were altered as follows: when b value = 600s/mm2, diffusion gradient direction was set to 6, 15, 25, 35 and 45; and when diffusion gradient direction = 25, b value was set to 300, 600, 900 and 1200s/mm2. The values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were separately acquired using image post-processing techniques. The correlation between various b values, diffusion gradient directions, age and sex on the one hand and FA and ADC values on the other, was investigated. (1) When diffusion gradient direction was fixed and the b value was varied, both FA and ADC exhibited a decreasing trend as the b value increased (P < 0.001). (2) When the b value was fixed and diffusion gradient direction was varied, the FA of knee cartilage showed a decreasing trend with increasing diffusion gradient direction (P < 0.001). (3) The FA value increased with age (P < 0.05). The b value, diffusion gradient direction value and age exert a significant impact on both FA and ADC values in MR DTI of knee cartilage in children aged 6-12years. In order to obtain a stable DTI, it is recommended to select a b value ≥ 600s/mm2 and a diffusion gradient direction ≥ 25 during scanning.

Serial deep gray nuclear DTI changes in Parkinson's disease over twelve years.

Deep gray nuclear pathology relates to motor deterioration in idiopathic Parkinson's disease (PD). Inconsistent deep nuclear diffusion tensor imaging (DTI) findings in cross-sectional or short-term longitudinal studies have been reported. Long-term studies in PD are clinically challenging; decade-long deep nuclear DTI data are nonexistent. We investigated serial DTI changes and clinical utility in a case-control PD cohort of 149 subjects (72 patients/77 controls) over 12 years. Participating subjects underwent brain MRI at 1.5T; DTI metrics from segmented masks of caudate, putamen, globus pallidus and thalamus were extracted from three timepoints with 6-year gaps. Patients underwent clinical assessment, including Unified Parkinson Disease Rating Scale Part 3 (UPDRS-III) and Hoehn and Yahr (H&Y) staging. A multivariate linear mixed-effects regression model with adjustments for age and gender was used to assess between-group differences in DTI metrics at each timepoint. Partial Pearson correlation analysis was used to correlate clinical motor scores with DTI metrics over time. MD progressively increased over time and was higher in the putamen (p < 0.001) and globus pallidus (p = 0.002). FA increased (p < 0.05) in the thalamus at year six, and decreased in the putamen and globus pallidus at year 12. Putaminal (p = 0.0210), pallidal (p = 0.0066) and caudate MD (p < 0.0001) correlated with disease duration. Caudate MD (p < 0.05) also correlated with UPDRS-III and H&Y scores. Pallido-putaminal MD showed differential neurodegeneration in PD over 12 years on longitudinal DTI; putaminal and thalamic FA changes were complex. Caudate MD could serve as a surrogate marker to track late PD progression.

Microstructural brain tissue changes contribute to cognitive and mood deficits in adults with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) patients show brain tissue changes in mood and cognitive regulatory sites, but the nature and extent of tissue injury and their associations with symptoms are unclear. Our aim was to examine brain tissue damage in T2DM over controls using mean diffusivity (MD) computed from diffusion tensor imaging (DTI), and assess correlations with mood and cognitive symptoms in T2DM. We collected DTI series (MRI), mood, and cognitive data, from 169 subjects (68 T2DM and 101 controls). Whole-brain MD-maps were calculated, normalized, smoothed, and compared between groups, as well as correlated with mood and cognition scores in T2DM subjects. Type 2 diabetes patients showed altered cognitive and mood functions over control subjects. Multiple brain sites in T2DM patients showed elevated MD values, indicating chronic tissue changes, including the cerebellum, insula, and frontal and prefrontal cortices, cingulate, and lingual gyrus. Associations between MD values and mood and cognition scores appeared in brain sites mediating these functions. Type 2 diabetes patients show predominantly chronic brain tissue changes in areas mediating mood and cognition functions, and tissue changes from those regions correlate with mood and cognitive symptoms suggesting that the microstructural brain changes may account for the observed functional deficits.

Bevacizumab is associated with cerebral microstructural alterations: a DTI study in high-grade glioma.

For recurrent high-grade glioma, especially glioblastoma, no standard of care treatment exists. Due to the prolongation of progression-free survival and a cortiocosteroid-sparing effect, bevacizumab is often used in this condition. Despite initial clinical responses, there is growing evidence that bevacizumab may potentiate microstructural alterations which may cause cognitive decline, mostly affecting learning and memory. To investigate bevacizumab-associated microstructural damage of defined regions of interest (ROIs) in the white matter, diffusion tensor imaging (DTI) was performed in 10 patients with a case history or third-party report for neurological dysfunction concerning cognitive performance. Serial DTI data before and under bevacizumab were collected and longitudinal changes of fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) were assessed in mesiotemporal (hippocampal), frontal, and occipital regions. The longitudinal DTI data under bevacizumab compared to DTI prior to bevacizumab demonstrated a significant decrease in FA and increase in AD and RD both in mesiotemporal (hippocampal) regions and in frontal regions, whereas occipital regions showed no significant alterations in DTI metrics. The regionally impaired microstructure in mesiotemporal (hippocampal) regions and in frontal regions is in line with the fact that neurocognitive impairment in learning and memory is mostly related to hippocampal integrity and attentional control in frontal regions. Further studies could investigate the potential of DTI to assess bevacizumab-associated microstructural damages in vulnerable brain regions.

Machine learning approach for obstructive sleep apnea screening using brain diffusion tensor imaging.

Patients with obstructive sleep apnea (OSA) show autonomic, mood, cognitive, and breathing dysfunctions that are linked to increased morbidity and mortality, which can be improved with early screening and intervention. The gold standard and other available methods for OSA diagnosis are complex, require whole-night data, and have significant wait periods that potentially delay intervention. Our aim was to examine whether using faster and less complicated machine learning models, including support vector machine (SVM) and random forest (RF), with brain diffusion tensor imaging (DTI) data can classify OSA from healthy controls. We collected two DTI series from 59 patients with OSA [age: 50.2 ± 9.9 years; body mass index (BMI): 31.5 ± 5.6 kg/m2 ; apnea-hypopnea index (AHI): 34.1± 21.2 events/h 23 female] and 96 controls (age: 51.8± 9.7 years; BMI: 26.2± 4.1kg/m2 ; 51 female) using a 3.0-T magnetic resonance imaging scanner. Using DTI data, mean diffusivity maps were calculated from each series, realigned and averaged, normalised to a common space, and used to conduct cross-validation for model training and selection and to predict OSA. The RF model showed 0.73 OSA and controls classification accuracy and 0.85 area under the curve (AUC) value on the receiver-operator curve. Cross-validation showed the RF model with comparable fitting over SVM for OSA and control data (SVM; accuracy, 0.77; AUC, 0.84). The RF ML model performs similar to SVM, indicating the comparable statistical fitness to DTI data. The findings indicate that RF model has similar AUC and accuracy over SVM, and either model can be used as a faster OSA screening tool for subjects having brain DTI data.

Can diffusion tensor imaging (DTI) outperform standard magnetic resonance imaging (MRI) investigations in post-COVID-19 autoimmune encephalitis?

BackgroundNeurological and psychiatric manifestations related to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection are widely recognised. Standard magnetic resonance imaging (MRI) investigations are normal in 40–80% of symptomatic patients, eventually delaying appropriate treatment when MRI is unrevealing any structural changes. The aim of this study is to investigate white matter abnormalities during an early stage of post-COVID-19 (coronavirus disease 2019) encephalitis while conventional MRI was normal.MethodsA patient with post-COVID-19 autoimmune encephalitis was investigated by serial MRIs and diffusion tensor imaging (DTI). Ten healthy control individuals (HC) were utilised as a control group for the DTI analysis. Major projection, commissural and association white matter pathways were reconstructed, and multiple diffusion parameters were analysed and then compared to the HC average using a z-test for serial examinations.ResultsEleven days after the onset of neurological symptoms, DTI revealed early white matter changes, compared with HC, when standard MRI was normal. On day 68, DTI showed multiple white matter lesions compared with HC, visible at this time also by the MRI images, indicating inflammatory changes in different association and projection white matter pathways.ConclusionWe confirm a limitation in the sensitivity of conventional MRI at the acute setting of post-COVID-19 autoimmune encephalitis. A complementary DTI investigation could be a valuable diagnostic tool in early therapeutic decisions concerning COVID-19-related neurological symptoms.

Investigation of white matter and grey matter alteration in the monkey brain following ischemic stroke by using diffusion tensor imaging.

Investigation of stroke lesion has mostly focused on grey matter (GM) in previous studies and white matter (WM) degeneration during acute stroke is understudied. In the present study, monkeys were utilized to investigate the alterations of GM and WM in the brain following ischemic occlusion using diffusion tensor imaging (DTI). Permanent middle cerebral artery occlusion (pMCAO) was induced in rhesus monkeys (n=6) with an interventional approach. Serial DTI was conducted on a clinical 3T in the hyperacute phase (2-6 hours), 48, and 96 hours post occlusion. Regions of interest in GM and WM of lesion areas were selected for data analysis. Mean diffusivity (MD), radial diffusivity (RD), and axial Diffusivity (AD) in WM decreased substantially during hyperacute stroke, as similar as those seen in GM. No obvious fractional anasotropy (FA) changes were seen in GM and WM during hyper acute phase. until 48 hours post stroke when significant fiber losses were oberved also. Pseudo-normalization of MD, AD, and RD was seen at 96 hours. Pathological changes of WM and GM were observed in ischemic areas at 8, 48, and 96 hours post stroke. Relative changes of MD, AD and RD of WM were correlated negatively with infarction volumes at 6 hours post stroke. The present study revealed the microstructural changes in gray matter and white matter of monkey brains during acute stroke by using DTI. The preliminary results suggest axial and radial diffusivity (AD and RD) may be sensitive surrogate markers to assess specific microstructural changes in white matter during hyper-acute stroke.

Comparison of the prognostic value of cerebrospinal fluid and plasma neurofilament light in predicting longitudinal decline in white matter integrity among older adults

AbstractBackgroundCerebrospinal fluid (CSF) neurofilament light (NFL) is a biomarker of neuroaxonal injury associated with cognitive decline, neurodegeneration, and white matter damage. Recent advances allow for plasma measurement of NFL, increasing accessibility of this biomarker. However, it is unknown if CSF and plasma NFL have similar prognostic value for predicting white matter damage. This study relates baseline CSF and plasma NFL concentrations to longitudinal change in white matter integrity in older adults.MethodVanderbilt Memory &amp; Aging Project participants free of dementia at baseline (n=147, 72±6 years, 32% female) underwent baseline fasting lumbar puncture for CSF sampling and venous blood draw for plasma sampling. Participants completed serial 3T diffusion tensor imaging to assess white matter microstructural integrity at baseline, 18‐months, 3‐years, and 5‐years (follow‐up 4.3±1.3 years). Voxel‐wise linear mixed effects models with follow‐up time interaction terms related baseline CSF and plasma NFL separately to white matter microstructural trajectory, adjusting for baseline demographic and health variables, apolipoprotein E‐ε4 status, diagnosis, and follow‐up time. Follow‐up models tested interactions with diagnosis, amyloid‐β (Aβ), and phosphorylated tau (p‐tau).ResultCSF and plasma NFL were correlated (r=0.50, p&lt;0.001). In the entire sample, CSF NFL related to faster white matter microstructural integrity decline in frontal, parietal, occipital, and subcortical regions (corrected p‐values&lt;0.05). Plasma NFL related to faster white matter microstructural integrity decline in frontal and subcortical regions (corrected p‐values&lt;0.05). CSF (largest β=5.7x10‐9) and plasma (largest β=3.1x10‐7) associations were similar in strength. CSF NFL interacted with diagnosis and Aβ (corrected p‐values&lt;0.04), with associations driven by MCI and Aβ negative participants. Plasma NFL interacted with Aβ and p‐tau (corrected p‐values&lt;0.04), with associations driven by Aβ and p‐tau negative participants.ConclusionAmong older adults, increased baseline CSF and plasma NFL concentrations predicted faster longitudinal decline in white matter integrity. While CSF NFL may relate to more widespread future white matter damage compared to plasma, plasma NFL could be an accessible biomarker for assessing future risk of white matter damage, particularly in individuals without Aβ or p‐tau pathology. CSF NFL may be a better prognostic biomarker in individuals with MCI, whereas plasma NFL has similar prognostic ability across diagnostic groups.

Evaluation of Serial Diffusion Tensor Imaging to Reveal Subclinical Tumor Prior to Detection on Anatomical Imaging in Patients with Glioblastoma

As the majority of patients with glioblastoma (GBM) experience tumor recurrence, early detection of recurrence can facilitate timely adaptation to treatment in order to improve outcomes. We hypothesize that the presence of tumor cells can result in microstructural disruptions in white matter (WM) integrity that can be visualized using DTI prior to tumor detection on conventional, anatomical MR imaging. This retrospective study aimed to evaluate whether changes in serial diffusion tensor imaging (DTI) parameters preceded and localized to the area of GBM tumor recurrence. Under an IRB approved protocol, patients with recurrent GBM following RT who had serial DTI at tumor recurrence and at least 2 prior imaging sessions were included. The serial images, acquired about 1-3 months apart, were gathered from 2014 to 2017. The following images were analyzed: post-contrast T1-weighted (T1w) MRI and DTI at tumor recurrence (t0), the immediate prior scan (t0-1), and the second prior scan (t0-2) to recurrence. Diffusion parameter maps, fractional anisotropy (FA) and mean diffusivity (MD), were extracted. The diffusion maps at recurrence were co-registered with those at t0-1 and t0-2. The T1w images at each time point were aligned with their corresponding diffusion maps. An experienced radiation oncologist manually segmented recurrent gross tumor volume (rGTV) for each patient on T1w images. The rGTV was co-registered to diffusion maps at each time point to form t0-1GTV and t0-2GTV. Mean FA and MD values were calculated for rGTV (t0), t0-1GTV, and t0-2GTV. Qualitative evaluation of abnormal regions on diffusion maps and anatomical images were compared. Pairwise t-tests were used to compare features among the 3 time points to examine WM changes over time. A total of 24 GBM patients (age: 26-77 years; 11 males:13 females) were included in this analysis. The mean FA values of t0-2GTV were statistically lower than those of t0-1GTV and rGTV (t0) (p=0.04 and p=0.02, respectively). The mean FA values of t0-1GTV and rGTV were not statistically different. The mean values of MD across all time points were not statistically different. Qualitatively, structural changes were visible on the FA maps in 70% of cases prior to visible changes on the T1w images. In this retrospective study, FA changes were observed 1-3 months before clinically detected tumor recurrence on anatomical imaging. The FA values were similar between recurrent and immediate pre-recurrent DTI images, suggesting that underlying progressive micro-structure changes may have been present prior to the appearance of enhancing tumor. In our study, FA appeared more sensitive than MD at detecting subclinical tumor presence. Future investigation of a larger cohort and more detailed analysis is planned to evaluate the role of DTI in detection of subclinical GBM in normal appearing brain to potentially refine clinical target volume definition for RT planning and prediction of GBM recurrence.

Tracking white matter degeneration in asymptomatic and symptomatic MAPT mutation carriers

Our aim was to investigate the patterns and trajectories of white matter (WM) diffusion abnormalities in microtubule-associated protein tau (MAPT) mutations carriers. We studied 22 MAPT mutation carriers (12 asymptomatic, 10 symptomatic) and 20 noncarriers from 8 families, who underwent diffusion tensor imaging (DTI) and a subset (10 asymptomatic, 6 symptomatic MAPT mutation carriers, and 10 noncarriers) were followed annually (median = 4 years). Cross-sectional and longitudinal changes in mean diffusivity (MD) and fractional anisotropy were analyzed. Asymptomatic MAPT mutation carriers had higher MD in entorhinal WM, which propagated to the limbic tracts and frontotemporal projections in the symptomatic stage compared with noncarriers. Reduced fractional anisotropy and increased MD in the entorhinal WM were associated with the proximity to estimated and actual age of symptom onset. The annualized change of entorhinal MD on serial DTI was accelerated in MAPT mutation carriers compared with noncarriers. Entorhinal WM diffusion abnormalities precede the symptom onset and track with disease progression in MAPT mutation carriers. Our cross-sectional and longitudinal data showed a potential clinical utility for DTI to track neurodegenerative disease progression for MAPT mutation carriers in clinical trials.

Stereotactic laser ablation for completion corpus callosotomy.

Completion corpus callosotomy can offer further remission from disabling seizures when a prior partial corpus callosotomy has failed and residual callosal tissue is identified on imaging. Traditional microsurgical approaches to section residual fibers carry risks associated with multiple craniotomies and the proximity to the medially oriented motor cortices. Laser interstitial thermal therapy (LITT) represents a minimally invasive approach for the ablation of residual fibers following a prior partial corpus callosotomy. Here, the authors report clinical outcomes of 6 patients undergoing LITT for completion corpus callosotomy and characterize the radiological effects of ablation. A retrospective clinical review was performed on a series of 6 patients who underwent LITT completion corpus callosotomy for medically intractable epilepsy at Stanford University Medical Center and Lucile Packard Children's Hospital at Stanford between January 2015 and January 2018. Detailed structural and diffusion-weighted MR images were obtained prior to and at multiple time points after LITT. In 4 patients who underwent diffusion tensor imaging (DTI), streamline tractography was used to reconstruct and evaluate tract projections crossing the anterior (genu and rostrum) and posterior (splenium) parts of the corpus callosum. Multiple diffusion parameters were evaluated at baseline and at each follow-up. Three pediatric (age 8-18 years) and 3 adult patients (age 30-40 years) who underwent completion corpus callosotomy by LITT were identified. Mean length of follow-up postoperatively was 21.2 (range 12-34) months. Two patients had residual splenium, rostrum, and genu of the corpus callosum, while 4 patients had residual splenium only. Postoperative complications included asymptomatic extension of ablation into the left thalamus and transient disconnection syndrome. Ablation of the targeted area was confirmed on immediate postoperative diffusion-weighted MRI in all patients. Engel class I-II outcomes were achieved in 3 adult patients, whereas all 3 pediatric patients had Engel class III-IV outcomes. Tractography in 2 adult and 2 pediatric patients revealed time-dependent reduction of fractional anisotropy after LITT. LITT is a safe, minimally invasive approach for completion corpus callosotomy. Engel outcomes for completion corpus callosotomy by LITT were similar to reported outcomes of open completion callosotomy, with seizure reduction primarily observed in adult patients. Serial DTI can be used to assess the presence of tract projections over time but does not classify treatment responders or nonresponders.

Longitudinal Analysis of Corpus Callosum Diffusion Tensor Imaging Metrics and Its Association with Neurological Outcome

Traumatic axonal injury (TAI) is the main cause of cognitive and psychological disfunction after a traumatic brain injury (TBI). Diffusion tensor imaging (DTI) is considered a useful technique for indirect assessment of white matter (WM) integrity after a TBI. Scattered WM alterations and its relationship with patient severity have been discovered in normal appearing conventional magnetic resonance imaging (MRI) studies based on DTI sequences. However, there is a lack of large sample studies on the longitudinal changes of DTI metrics to be used to determine the temporal profile after head injury and its association with patient outcome. We performed a prospective observational study in 118 moderate-to-severe TBI patients. The study included clinical outcome assessment based on the Glasgow Outcome Scale Extended (GOSE) and serial DTI studies in the early subacute setting (< 60 days) and 6 and 12 months after injury. Fractional anisotropy (FA) and axial and radial diffusivities (AD and RD, respectively) were measured in the three portions of corpus callosum (genu, body, splenium) at each time-point and compared with normalized values from an age-matched control group. Longitudinal FA analysis and its correlation with patient improvement also was done by non-parametric testing and ordinal regression analysis. Our main results indicated that between all the time-points, dynamic changes in DTI metrics in all three portions of corpus callosum were detected, but TBI patients continued to show significantly lower FA and AD values and higher RD values compared with controls. We also have discovered differences in the change of DTI metrics among different time-points in patient subgroups according with their outcome improvement. In conclusion, even without normalization of DTI metrics in the long-term, knowledge of the temporal profile of change in DTI metrics can provide important information about patients' clinical recovery after TBI.

P13 - Early Evaluation of Radiation-induced White Matter Injury Following High Dose Fractionated Radiation Therapy in Patients with Glioblastoma Using Serial Diffusion Tensor Imaging (DTI)

P13 - Early Evaluation of Radiation-induced White Matter Injury Following High Dose Fractionated Radiation Therapy in Patients with Glioblastoma Using Serial Diffusion Tensor Imaging (DTI)

Dynamics of Water Diffusion Changes in Different Tissue Compartments From Acute to Chronic Stroke-A Serial Diffusion Tensor Imaging Study.

Background and Purpose: The immediate decrease of the apparent diffusion coefficient (ADC) is the main characteristic change of water diffusion in acute ischemic stroke. There is only limited information on the time course of diffusion parameters in different tissue compartments of cerebral ischemia.Materials and Methods: In a longitudinal study, we examined 21 patients with acute ischemic stroke by diffusion tensor imaging within 5 h after symptom onset, 3 h later, 2 days, and 1 month after symptom onset. Acute diffusion lesion and the fluid-attenuated inversion recovery (FLAIR) after 2 days were used as volumes of interest to define persistent core, lesion growth, and reversible acute diffusion lesion. For all diffusion parameters ratios between the stroke lesion VOIs and the mirror VOIs were calculated for each time point. ADC ratio, fractional anisotropy ratios, and eigenvalues ratios were measured in these volumes of interest and in contralateral mirror regions at each time points.Results: In the persistent core, ADC ratio (0.772) and all eigenvalues ratios were reduced on admission up to 1 day after stroke and increased after 1 month (ADC ratio 1.067). Within the region of infarct growth time course of diffusion parameter changes was similar, but delayed. In the brain area with reversible diffusion lesion, a partial normalization of diffusion parameters over the time was observed, while after 1 month diffusion parameters did not show the signature of healthy brain tissue. There were significantly different trends for all parameters over time between the three tissue compartments.Conclusion: Diffusion tensor imaging displays characteristic changes of water diffusion in different tissue compartments over time in acute ischemic stroke. Even regions with reversible diffusion lesion show diffusion signatures of persisting tissue alterations.

Editors' note: Posthemorrhagic ventricular dilatation in preterm infants: When best to intervene?

In reference to “Posthemorrhagic ventricular dilatation in preterm infants: When best to intervene?” Dr. Munakomi supports early intervention after intraventricular bleed and reframes the pertinent question to be how to predict early neuronal damage in these patients. He suggests using diffusion tensor imaging (DTI) to assess for anisotropy in the periventricular tracks and near-infrared spectroscopy (NIRS). Authors de Vries and Leijser agree that while predicting neuronal damage would be advantageous, it is not currently possible. NIRS monitoring, they suggest, may be used in combination with other modalities to inform the timing of neurosurgical intervention. Serial DTIs would be technically challenging in most centers, whereas head ultrasounds are more practical and may provide more useful information. In reference to “Posthemorrhagic ventricular dilatation in preterm infants: When best to intervene?” Dr. Munakomi supports early intervention after intraventricular bleed and reframes the pertinent question to be how to predict early neuronal damage in these patients. He suggests using diffusion tensor imaging (DTI) to assess for anisotropy in the periventricular tracks and near-infrared spectroscopy (NIRS).

Reader response: Nutrients and bioactives in green leafy vegetables and cognitive decline: Prospective study.

In reference to “Posthemorrhagic ventricular dilatation in preterm infants: When best to intervene?” Dr. Munakomi supports early intervention after intraventricular bleed and reframes the pertinent question to be how to predict early neuronal damage in these patients. He suggests using diffusion tensor imaging (DTI) to assess for anisotropy in the periventricular tracks and near-infrared spectroscopy (NIRS). Authors de Vries and Leijser agree that while predicting neuronal damage would be advantageous, it is not currently possible. NIRS monitoring, they suggest, may be used in combination with other modalities to inform the timing of neurosurgical intervention. Serial DTIs would be technically challenging in most centers, whereas head ultrasounds are more practical and may provide more useful information.

PB 1 In vivo assessment of neurodegeneration in the brain by serial longitudinal diffusion tensor imaging – an application to amyotrophic lateral sclerosis

Introduction The potential of magnetic resonance imaging (MRI) as a technical biomarker for cerebral alterations is under investigation in neurodegenerative diseases. In this study, a framework for the longitudinal analysis of diffusion tensor imaging (DTI)-based mapping with a series of follow-up scans was applied to longitudinal microstructure assessment of predefined white matter tracts in the course of amyotrophic lateral sclerosis (ALS), as an example for a rapidly progressive neurodegenerative disease. Methods Fifty-four longitudinal DTI datasets from 6 patients with ALS and 3 controls were recorded each 3 months (with up to 15 follow-up scans), yielding a total of 54 longitudinal DTI data sets. After individual alignment and stereotaxic normalization, an averaged DTI data set was created for fibertracking. Fractional anisotropy (FA) values of the tract structures were used to calculate progression rates based on DTI metrics. Results Patients with ALS showed an FA decline along the corticospinal tract (CST) which has been identified as the first affected tract structure in ALS and as the tract correlating with Braak‘s neuropathological stage 1 ( Kassubek et al., 2014 ). FA of controls remained stable in longitudinal DTI scans, whereas, FA decrease progression in the CST ranged from 0.5% to 6% per year in ALS-patients, i.e. four patients showed low progression rates between 0.5% and 2% per year and two patients showed fast progression rates between 3% and 6% per year. The ALS-FRS-R decline correlated significantly with FA decline over time. Conclusion On the basis of the longitudinal DTI data assessment with multiple follow-up measures, FA values were shown to be an in vivo marker for ALS-associated disease progression. That way, imaging-based progression rates at the individual patient level can be determined from DTI scans.

Impact of Gradient Number and Voxel Size on Diffusion Tensor Imaging Tractography for Resective Brain Surgery.

To explore quantitatively and qualitatively how the number of gradient directions (NGD) and spatial resolution (SR) affect diffusion tensor imaging (DTI) tractography in patients planned for brain tumor surgery, using routine clinical magnetic resonance imaging protocols. Of 67 patients with intracerebral lesions who had 2 different DTI scans, 3 DTI series were reconstructed to compare the effects of NGD and SR. Tractographies for 4 clinically relevant tracts (corticospinal tract, superior longitudinal fasciculus, optic radiation, and inferior fronto-occipital fasciculus) were constructed with a probabilistic tracking algorithm and automated region of interest placement and compared for 3 quantitative measurements: tract volume, median fiber density, and mean fractional anisotropy, using linear mixed-effects models. The mean tractography volume and intersubject reliability were visually compared across scanning protocols, to assess the clinical relevance of the quantitative differences. Both NGD and SR significantly influenced tract volume, median fiber density, and mean fractional anisotropy, but not to the same extent. In particular, higher NGD increased tract volume and median fiber density. More importantly, these effects further increased when tracts were affected by disease. The effects were tract specific, but not dependent on threshold. The superior longitudinal fasciculus and inferior fronto-occipital fasciculus showed the most significant differences. Qualitative assessment showed larger tract volumes given a fixed confidence level, and better intersubject reliability for the higher NGD protocol. SR in the range we considered seemed less relevant than NGD. This study indicates that, under time constraints of clinical imaging, a higher number of diffusion gradients is more important than spatial resolution for superior DTI probabilistic tractography in patients undergoing brain tumor surgery.

Cerebral Microstructural Alterations after Radiation Therapy in High-Grade Glioma: A Diffusion Tensor Imaging-Based Study.

To investigate radiation therapy-induced microstructural damage of white matter in patients with high-grade glioma by diffusion tensor imaging (DTI). DTI was performed in 18 patients with high-grade glioma (WHO grades III and IV) and 13 healthy controls. DTI images were cross-sectionally aligned for the calculation of baseline fractional anisotropy (FA). Interhemispheric FA values in patients with high-grade glioma before or without brain radiation therapy were compared with the interhemispheric FA values in patients after radiation therapy and in healthy controls. In a subgroup without any clinical or diagnostic evidence of tumor progression, serial DTI data (5-11 scans) before and after radiation therapy were collected and longitudinal interhemispheric FA changes were assessed and compared to longitudinal data from the control group.In addition, interhemispheric axial, mean, and radial diffusivity was assessed. Global interhemispheric FA reductions could be detected cross-sectionally in patients after radiation therapy; these were significantly different from global interhemispheric FA differences both in patients without radiation and in healthy controls. Longitudinal scans in patients with radiation therapy confirmed these findings and revealed progressive microstructural white matter damage after partial brain radiotherapy. The additional DTI metrics axial diffusion, mean diffusivity, and radial diffusion confirmed interhemispheric differences in patients without or before radiation therapy, which were lower than the differences in patients after radiation therapy, although not reaching significance. Interhemispheric global FA differences could potentially serve as a biological marker for irradiation-induced microstructural white matter damage.