Diffusion Tensor Imaging Protocol Research Articles

Simultaneous multi-slice technique for reducing acquisition times in diffusion tensor imaging of the knee: a feasibility study.

To explore the feasibility of simultaneous multi-slice (SMS) technique for reducing acquisition times in readout-segmented echo planar imaging (RESOLVE) for diffusion tensor imaging (DTI) of the knee. A total of 30 healthy volunteers and 23 patients with knee acute injury (12 cases with anterior ligament (ACL) tears and 16 cases with patellar cartilage (PC) injury) were enrolled in this prospective study. Three DTI protocols were used: conventional RESOLVE-DTI with 12 directions (protocol 1), SMS-RESOLVE-DTI with 12 directions (protocol 2) and 20 directions (protocol 3). DTI parameters of gastrocnemius, ACL and posterior cruciate ligament (PCL), and PC from three protocols were quantitatively assessed. For volunteers, protocol 2 significantly reduced acquisition time by 38.6% and 34.2% compared to protocols 1 and 3 while maintaining similar high-quality images and similar diffusive parameters, except for the fractional anisotropy (FA) and axial diffusivity (AD) of the PC between protocols 2 and 1 (P < 0.05). For injured ACL and PC, protocols 1 and 2 showed similar accurate diffusive parameters (except for AD, P = 0.025) and similar diagnostic efficacy, which demonstrated significantly lower FA and higher radial diffusivity (RD) in protocols 1 and 2 compared to volunteers (P < 0.05). The 12-direction SMS-RESOLVE-DTI demonstrated a favorable balance between acquisition time and image quality, making it a promising alternative to conventional DTI for evaluating ligament and cartilage injuries. The SMS technique greatly reduces acquisition time while maintaining image quality, which signified the possibility of DTI's clinical application.

Accelerated IVIM-corrected DTI in acute hamstring injury: towards a clinically feasible acquisition time

BackgroundIntravoxel incoherent motion (IVIM)-corrected diffusion tensor imaging (DTI) potentially enhances return-to-play (RTP) prediction after hamstring injuries. However, the long scan times hamper clinical implementation. We assessed accelerated IVIM-corrected DTI approaches in acute hamstring injuries and explore the sensitivity of the perfusion fraction (f) to acute muscle damage.MethodsAthletes with acute hamstring injury received DTI scans of both thighs < 7 days after injury and at RTP. For a subset, DTI scans were repeated with multiband (MB) acceleration. Data from standard and MB-accelerated scans were fitted with standard and accelerated IVIM-corrected DTI approach using high b-values only. Segmentations of the injury and contralateral healthy muscles were contoured. The fitting methods as well as the standard and MB-accelerated scan were compared using linear regression analysis. For sensitivity to injury, Δ(injured minus healthy) DTI parameters between the methods and the differences between injured and healthy muscles were compared (Wilcoxon signed-rank test).ResultsThe baseline dataset consisted of 109 athletes (16 with MB acceleration); 64 of them received an RTP scan (8 with MB acceleration). Linear regression of the standard and high-b DTI fitting showed excellent agreement. With both fitting methods, standard and MB-accelerated scans were comparable. Δ(injured minus healthy) was similar between standard and accelerated methods. For all methods, all IVIM-DTI parameters except f were significantly different between injured and healthy muscles.ConclusionsHigh-b DTI fitting with MB acceleration reduced the scan time from 11:08 to 3:40 min:s while maintaining sensitivity to hamstring injuries; f was not different between healthy and injured muscles.Relevance statementThe accelerated IVIM-corrected DTI protocol, using fewer b-values and MB acceleration, reduced the scan time to under 4 min without affecting the sensitivity of the quantitative outcome parameters to hamstring injuries. This allows for routine clinical monitoring of hamstring injuries, which could directly benefit injury treatment and monitoring.Key points• Combining high-b DTI-fitting and multiband-acceleration dramatically reduced by two thirds the scan time.• The accelerated IVIM-corrected DTI approaches maintained the sensitivity to hamstring injuries.• The IVIM-derived perfusion fraction was not sensitive to hamstring injuries.Graphical

Role of Diffusion Tensor Imaging in Early Diagnosis and Characterization of Movement Disorders.

Symptoms of movement disorders in early stages are similar, which makes definite diagnosis difficult. Hence this study was conducted to explore the role of diffusion tensor imaging (DTI) in enhancing the early diagnosis and characterization of movement disorders. A cross-sectional study was conducted including 60 subjects. All of them were reviewed using conventional magnetic resonance imaging (MRI) and movement disorder DTI protocol. Commercially available software was used to produce fractional anisotropy (FA) maps. Post-processing 3D reconstruction was done to obtain tractograms. Both single and multiple regions of interest (ROIs) were selected for tractography in the pons, midbrain, substantia nigra (SN) and cerebellum. MRIandDTI images were interpretedand correlated with confirmatory diagnosis. According to DTI diagnosis, out of the 30 cases, 28 had movement disorders. Among cases, 36.67% had Parkinson's disease (PD), 23.33% had progressive supranuclear palsy (PSP), 16.67% had essential tremor, 13.33% had multi-system atrophy (MSA) C, and 3.33% had MSA P. DTI correctly classified all cases with PD and PSP. All cases with long disease duration and 88.24% of cases with short disease duration were also correctly classified. A statistically significant difference was observed in the proportion of diagnosis between DTI and conventional MRI. DTI has high sensitivity and specificity for the diagnosis of movement disorders. It is capable of early diagnosis of movement disorders and also differentiating and subcategorizing them.

62 Effect of Blast TBI on Axonal Structure in Networks of Emotional Regulation and Cognitive Control

Objective:Blast-related traumatic brain injury (bTBI) is one of the most common injuries among Veterans who have served in recent wars in Iraq and Afghanistan. Despite representing a distinct mechanism of injury, long-term clinical and functional outcomes of bTBI are generally comparable with non-blast-related traumatic brain injury (TBI). However, controversy remains over whether bTBI etiology differentially impacts emotional regulation and neurocognition - particularly with respect to post-traumatic stress disorder (PTSD) and verbal and visual memory. Through diffusion tensor imaging (DTI), the present study investigates the microstructural pathophysiology of bTBI, compared to non-blast TBI, in neural pathways involved in emotional regulation and cognitive control.Participants and Methods:Participants included 36 Veterans (25% female; age M = 36.33, SD = 10.11; years of education M = 15.67, SD = 2.34). Axial diffusivity (AD) in networks of emotional and cognitive control was acquired using magnetic resonance imaging (MRI) with a DTI protocol. Analyses of variance (ANOVA) were used to compare Veterans with self-reported bTBI (n = 23) to those with non-blast-related TBI (n = 13).Results:In the left hemisphere, Veterans with bTBI exhibited significantly smaller AD in axonal projections from the caudate nucleus (CN) to the orbitofrontal cortex (OFC), as well as in projections from the putamen to the OFC (p &lt; 0.05). In the right hemisphere, Veterans with bTBI also exhibited significantly smaller AD in networks connecting the hippocampus to the amygdala (p &lt; 0.05).Conclusions:Compared to Veterans with non-blast-related TBI, Veterans with bTBI exhibited decreased AD in neural pathways from the CN to the OFC, the putamen to the OFC, and the hippocampus to the amygdala - indicative of increased axonal injury in these areas. Our results suggest that, on a microstructural level, emotional and cognitive networks are susceptible to longitudinal blast-related white matter damage. This is consistent with the literature in post-concussion syndrome (PCS) and provides a potential mechanism underlying results previously reported from this sample, describing subjective cognitive complaints in the absence of objective clinical deficits. As such, therapies that target networks of emotional and cognitive control may be particularly beneficial for Veterans with bTBI.

Diffusion Tensor Imaging in Amyotrophic Lateral Sclerosis: Machine Learning for Biomarker Development.

Diffusion tensor imaging (DTI) allows the in vivo imaging of pathological white matter alterations, either with unbiased voxel-wise or hypothesis-guided tract-based analysis. Alterations of diffusion metrics are indicative of the cerebral status of patients with amyotrophic lateral sclerosis (ALS) at the individual level. Using machine learning (ML) models to analyze complex and high-dimensional neuroimaging data sets, new opportunities for DTI-based biomarkers in ALS arise. This review aims to summarize how different ML models based on DTI parameters can be used for supervised diagnostic classifications and to provide individualized patient stratification with unsupervised approaches in ALS. To capture the whole spectrum of neuropathological signatures, DTI might be combined with additional modalities, such as structural T1w 3-D MRI in ML models. To further improve the power of ML in ALS and enable the application of deep learning models, standardized DTI protocols and multi-center collaborations are needed to validate multimodal DTI biomarkers. The application of ML models to multiparametric MRI/multimodal DTI-based data sets will enable a detailed assessment of neuropathological signatures in patients with ALS and the development of novel neuroimaging biomarkers that could be used in the clinical workup.

Diffusion Tensor MRI of Brain in Healthy Adult Population: Normative Fractional Anisotropy Values at 3 Tesla MRI

Introduction: Diffusion Tensor Imaging (DTI) technique and its clinical application are increasing in clinical routine practice, still very less normative data is available. Awareness regarding regional differences in Fractional Anisotropy (FA) measurements is very important when routinely DTI is used in clinical Magnetic Resonance Imaging (MRI). Aim: To determine the normative FA values data at 3 Tesla (3T) MRI and to determine the degradation of FA values in various regions of brain values with age. Materials and Methods: This cross-sectional study involved a total of 52 participants without any abnormal findings ( presence of tumour, stroke, infarct, degeneration, etc) and whose brain scanning was performed at 3T MRI, in the Department of Radiodiagnosis, Shree Krishna Hospital, and Pramukhswami Medical College, Karamsad, Anand, Gujarat, India. A DTI protocol was set for the healthy patient’s brain scanning. The colour-coded DTI brain images were postprocessed carefully to draw a circular Region of Interest (ROI) in the required areas of white matter and FA values were noted. Descriptive statistics were used to find out the normative data in 11 regions of the brain on right and left side. Pearson correlation was used to check the correlation of FA values with age. Results: There were 52 patients in the present study, with a male to female ratio of 1.7:1 and a mean age of 52 years. The highest FA values were observed in the splenium (0.809), genu (0.767), the body of the corpus callosum (0.627), and the posterior limb of the internal capsule (0.721), rest areas showed moderate to low FA values. Pearson correlation was used to find the variation in the FA values with age in three age groups 18-40, 41-60 and &gt;60 years, where moderate changes in FA values with age were seen in a few regions of the brain such as genu (right side) with p-value=0.003 and foramen magnum at CVJ level (right side) with a p-value of 0.001. Conclusion: Generally, FA values intend to change with the presence of multiple tract areas, field strength, coil sensitivity, and partial volume averaging. FA values were also found to be affected with respect to increasing age.

World Trade Center Site Exposure Duration Is Associated with Hippocampal and Cerebral White Matter Neuroinflammation

Responders to the World Trade Center (WTC) attacks on 9/11/2001 inhaled toxic dust and experienced severe trauma for a prolonged period. Studies report that WTC site exposure duration is associated with peripheral inflammation and risk for developing early-onset dementia (EOD). Free Water Fraction (FWF) can serve as a biomarker for neuroinflammation by measuring in vivo movement of free water across neurons. The present case-controlled study aimed to examine associations between WTC site exposure duration as well as EOD status with increased hippocampal and cerebral neuroinflammation. Ninety-nine WTC responders (mean age of 56) were recruited between 2017 and 2019 (N = 48 with EOD and 51 cognitively unimpaired). Participants were matched on age, sex, occupation, race, education, and post-traumatic stress disorder (PTSD) status. Participants underwent neuroimaging using diffusion tensor imaging protocols for FWF extraction. Region of interest (ROI) analysis and correlational tractography explored topographical distributions of FWF associations. Apolipoprotein-e4 allele (APOEε4) status was available for most responders (N = 91). Hippocampal FWF was significantly associated with WTC site exposure duration (r = 0.30, p = 0.003), as was cerebral white matter FWF (r = 0.20, p = 0.044). ROI analysis and correlational tractography identified regions within the limbic, frontal, and temporal lobes. Hippocampal FWF and its association with WTC exposure duration were highest when the APOEε4 allele was present (r = 0.48, p = 0.039). Our findings demonstrate that prolonged WTC site exposure is associated with increased hippocampal and cerebral white matter neuroinflammation in WTC responders, possibly exacerbated by possession of the APOEε4 allele.

The Topography of the Frontal Terminations of the Uncinate Fasciculus Revisited Through Focused Fiber Dissections: Shedding Light on a Current Controversy and Introducing the Insular Apex as a Key Anatomoclinical Area

Recent studies advocate a connectivity pattern wider than previously believed of the uncinate fasciculus that extends to the ventrolateral and dorsolateral prefrontal cortices. These new percepts on the connectivity of the tract suggest a more expansive role for the uncinate fasciculus. Our aim was to shed light on this controversy through fiber dissections. Twenty normal adult human formalin-fixed cerebral hemispheres were used. Focused dissections on the insular, orbitofrontal, ventromedial, ventrolateral, and dorsolateral prefrontal areas were performed to record the topography of the frontal terminations of the uncinate fasciculus. Three discrete fiber layers were consistently disclosed: the first layer was recorded to terminate at the posterior orbital gyrus and pars orbitalis, the second layer at the posterior two thirds of the gyrus rectus, and the last layer at the posterior one third of the paraolfactory gyrus. The insular apex was documented as a crucial landmark regarding the topographic differentiation of the uncinate and occipitofrontal fasciculi (i.e., fibers that travel ventrally belong to the uncinate fasciculus whereas those traveling dorsally are occipitofrontal fibers). The frontal terminations of the uncinate fasciculus were consistently documented to project to the posterior orbitofrontal area. The area of the insular apex is introduced for the first time as a crucial surface landmark to effectively distinguish the stems of the uncinate and occipitofrontal fasciculi. This finding could refine the spatial resolution of awake subcortical mapping, especially for insular lesions, and improve the accuracy of invivo diffusion tensor imaging protocols.

Brain White Matter Abnormality Induced by Chronic Spinal Cord Injury in the Pediatric Population: A Preliminary Tract-based Spatial Statistic Study.

Objectives: Tract-based spatial statistics (TBSS) is a diffusion tensor imaging (DTI)-based processing technique that aims to improve the objectivity and interpretability of analysis of multisubject diffusion imaging studies. This study used TBSS to measure quantitative changes in brain white matter structures following spinal cord injury (SCI). Methods: Eighteen SCI subjects aged 8-20 years old (mean age, 16.5 years) were scanned using a conventional single-shot EPI DTI protocol using a 3.0T Siemens MR scanner. All participants underwent a complete International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) examination to determine the level and severity of injury. Five participants were classified as American Spinal Injury Association Impairment Scale (AIS) A, nine as AIS B, and four as AIS C/D. Imaging parameters used for data collection were as follows: 20 directions, b = 1000 s/mm2, voxel size = 1.8 mm x 1.8 mm, slice thickness = 5 mm, TE = 95 ms, TR = 4300 ms, slices = 30, TA = 4:45 min. To generate TBSS, nonparametric permutation tests were used for voxel-wise statistical analysis of the fractional anisotropy (FA) skeletons between AIS groups. A two-tailed t test was applied to extract voxels with significant differences at p < .05. Results: Notable significant changes occurred throughout the corticospinal, spinothalamic, and dorsal column/medial lemniscus tracts. Altered regions in the temporal, occipital, and parietal lobes were also identified. Conclusion: These results suggest that white matter structures are altered differently between people with different AIS classifications. TBSS has the potential to serve as a screening tool to identify white matter changes in regions of interest.

Correlation of blunt cervical spinal cord injury magnetic resonance imaging tractography with the American Spinal Injury Association impairment scale motor scores.

BackgroundThe introduction of the Subaxial Cervical Spine Injury Classification system has created the need for a holistic imaging approach that encompasses both functional (neurological) and morphological information.ObjectivesThis study aimed to determine if there was a correlation between the blunt cervical spinal cord injury diffusion tensor imaging (DTI) fraction anisotropy (FA) value and the American Spine Injury Association (ASIA) impairment scale motor score.MethodDiffusion tensor imaging was performed on 26 patients with blunt cervical spine injury (all men with a median age of 46 years) admitted to the Pelonomi Tertiary Hospital spinal unit. Imaging was performed using the 1.5T Siemens Magnetom Aera machine’s built-in spine DTI protocol. Sagittal FA values were acquired at four different cervical spine regions (medulla oblongata, above the injury site, at the injury site and below the injury site).ResultsEight of the 26 patients had complete neurological fallout. Of the participants, 30% had injuries at the C4/C5 level, whilst injuries involving segments below and above C4/C5 affected 15% and 55% of participants, respectively. Injury site FA values (median 0.30) were significantly lower (p < 0.001) than the above injury site FA (median 0.46, p = 0.26) and below injury site FA (median 0.42 and p = 0.019). A significant correlation was noted between the injury site FA values and the ASIA impairment scale motor scores (p = 0.001, r = 0.87).ConclusionFA value showed excellent correlation with the ASIA impairment scale motor scores.

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

This study investigates diffusion tensor imaging (DTI) for providing microstructural insight into changes in arterial tissue by exploring how cell, collagen and elastin content effect fractional anisotropy (FA), mean diffusivity (MD) and tractography. Five ex vivo porcine carotid artery models (n = 6 each) were compared—native, fixed native, collagen degraded, elastin degraded and decellularised. Vessels were imaged at 7 T using a DTI protocol with b = 0 and 800 s/mm2 and 10 isotopically distributed directions. FA and MD were evaluated in the vessel media and compared across models. FA values measured in native (p < 0.0001), fixed native (p < 0.0001) and collagen degraded (p = 0.0018, p = 0.0016, respectively) were significantly higher than those in elastin degraded and decellularised arteries. Native and fixed native had significantly lower MD values than elastin degraded (p < 0.0001) and decellularised tissue (p = 0.0032, p = 0.0003, respectively). Significantly lower MD was measured in collagen degraded compared with the elastin degraded model (p = 0.0001). Tractography yielded helically arranged tracts for native and collagen degraded vessels only. FA, MD and tractography were found to be highly sensitive to changes in the microstructural composition of arterial tissue, specifically pointing to cell, not collagen, content as the dominant source of the measured anisotropy in the vessel wall.

High spatial resolution nerve-specific DTI protocol outperforms whole-brain DTI protocol for imaging the trigeminal nerve in healthy individuals.

Diffusion tensor imaging (DTI) can provide markers of axonal micro-structure of the trigeminal nerve (cranial nerve five [CNV]), which may be affected in trigeminal neuralgia (TN) and other disorders. Previous attempts to image CNV have used low spatial resolution DTI protocols designed for whole-brain acquisition that are susceptible to errors from partial volume effects, particularly with adjacent cerebrospinal fluid (CSF). The purpose of this study was to develop a nerve-specific DTI protocol in healthy subjects that provides more accurate CNV tractography and diffusion quantification than whole-brain protocols. Four DTI protocols were compared in five healthy individuals (age 22-45 years, three males) on a 3 T Siemens Prisma MRI scanner: two newly developed nerve-specific high resolution (1.2 x 1.2 x 1.2 = 1.7 mm3 ) DTI protocols without (3.5 minutes) and with CSF suppression (fluid-attenuated inversion recovery [FLAIR]; 7.5 minutes) with limited slice-coverage, and two typical whole-brain protocols with either isotropic (2 x 2 x 2 = 8 mm3 ) or thicker slice anisotropic (1.9 x 1.9 x 3 = 10.8 mm3 ) voxels. Deterministic tractography was used to identify the CNV and quantify bilateral fractional anisotropy (FA), and mean (MD), axial (AD) and radial diffusivity (RD). CNV volume was determined by manual tracing on T1-weighted images. High spatial resolution nerve-specific protocols yielded better delineation of CNV, with less distortions and blurring, and markedly different diffusion parameters (42% higher FA, 35% lower MD, 27% lower RD and 43% lower AD) compared with the two lower resolution whole-brain protocols. The anisotropic whole-brain protocol showed a positive correlation between CNV FA and volume. The high resolution nerve-specific protocol with FLAIR yielded additional reductions in CNV AD and MD with a value of 1.0 x 10-3 mm2 /s, approaching that expected for healthy young adult white matter. In conclusion, high resolution nerve-specific DTI with FLAIR enhances the identification of CNV and provides more accurate quantification of diffusion compared with lower resolution whole-brain approaches.

A prospective harmonized multicenter DTI study of cerebral white matter degeneration in ALS.

To evaluate progressive white matter (WM) degeneration in amyotrophic lateral sclerosis (ALS). Sixty-six patients with ALS and 43 healthy controls were enrolled in a prospective, longitudinal, multicenter study in the Canadian ALS Neuroimaging Consortium (CALSNIC). Participants underwent a harmonized neuroimaging protocol across 4 centers that included diffusion tensor imaging (DTI) for assessment of WM integrity. Three visits were accompanied by clinical assessments of disability (ALS Functional Rating Scale-Revised [ALSFRS-R]) and upper motor neuron (UMN) function. Voxel-wise whole-brain and quantitative tract-wise DTI assessments were done at baseline and longitudinally. Correction for site variance incorporated data from healthy controls and from healthy volunteers who underwent the DTI protocol at each center. Patients with ALS had a mean progressive decline in fractional anisotropy (FA) of the corticospinal tract (CST) and frontal lobes. Tract-wise analysis revealed reduced FA in the CST, corticopontine/corticorubral tract, and corticostriatal tract. CST FA correlated with UMN function, and frontal lobe FA correlated with the ALSFRS-R score. A progressive decline in CST FA correlated with a decline in the ALSFRS-R score and worsening UMN signs. Patients with fast vs slow progression had a greater reduction in FA of the CST and upper frontal lobe. Progressive WM degeneration in ALS is most prominent in the CST and frontal lobes and, to a lesser degree, in the corticopontine/corticorubral tracts and corticostriatal pathways. With the use of a harmonized imaging protocol and incorporation of analytic methods to address site-related variances, this study is an important milestone toward developing DTI biomarkers for cerebral degeneration in ALS. NCT02405182.

MAPL1: q-space reconstruction using -regularized mean apparent propagator.

To improve the quality of mean apparent propagator (MAP) reconstruction from a limited number of q-space samples. We implement an -regularised MAP (MAPL1) to consider higher order basis functions and to improve the fit without increasing the number of q-space samples. We compare MAPL1 with the least-squares optimization subject to non-negativity (MAP), and the Laplacian-regularized MAP (MAPL). We use simulations of crossing fibers and compute the normalized mean squared error (NMSE) and the Pearson's correlation coefficient to evaluate the reconstruction quality in q-space. We also compare coefficient-based diffusion indices in the simulations and in in vivo data. Results indicate that MAPL1 improves NMSE in 1 to 3% when compared to MAP or MAPL in a high undersampling regime. Additionally, MAPL1 produces more reproducible and accurate results for all sampling rates when there are enough basis functions to meet the sparsity criterion for the regularizer. These improved reconstructions also produce better coefficient-based diffusion indices for in vivo data. Adding an regularizer to MAP allows the use of more basis functions and a better fit without increasing the number of q-space samples. The impact of our research is that a complete diffusion spectrum can be reconstructed from an acquisition time very similar to a diffusion tensor imaging protocol.

Abstract TP75: Normal Appearing White Matter Integrity and Motor Impairment Severity in Acute Ischemic Stroke

Introduction: The effect of white matter hyperintensities (WMH) as measured by fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging on functional impairment and recovery after ischemic stroke has been investigated thoroughly. However, there has been growing interest to investigate normal-appearing white matter (NAWM) microstructural integrity following ischemic stroke onset with techniques such as diffusion tensor imaging (DTI). Methods: 52 patients with acute ischemic stroke and 36 without stroke were evaluated with a DTI and FLAIR imaging protocol and clinically assessed for severity of motor impairment using the Motricity Index within 72 hours of suspected symptom onset. Results: There were widespread decreases in fractional anisotropy (FA) and increases in mean diffusivity (MD) and radial diffusivity (RD) for the acute stroke group compared to the non-stroke group. As shown in the abstract figure with the blue voxels, there was a significant positive association between FA and motor function and a significant negative association between MD/RD and motor function. The NAWM regions of interest that were most sensitive to the Motricity Index were the anterior/posterior limb of the internal capsule in the infarcted hemisphere and the splenium of the corpus callosum, external capsule, posterior limb/retrolenticular part of the internal capsule, superior longitudinal fasciculus, and cingulum (hippocampus) of the intra-/contralateral hemisphere. Conclusion: The microstructural integrity of NAWM is a significant parameter to identify neural differences not only between those individuals with and without acute ischemic stroke, but also correlated with severity of acute motor impairment.

Peripheral Nerve Diffusion Tensor Imaging : Interreader and Test-retest Reliability as Quantified by the Standard Error of Measurement.

Diffusion tensor imaging (DTI) is increasingly being used in magnetic resonance neurography (MRN). The purpose of this study was to determine the interreader and test-retest reliability of peripheral nerve DTI in MRN with focus on the sciatic nerve. In this prospective study 27healthy volunteers each underwent 3 scans of ashort DTI protocol on separate days consisting of aT2-weighted turbo spin-echo and single-shot DTI sequence of the sciatic nerve of the dominant leg. The DTI parameters fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were obtained after manual nerve segmentation by two independent readers. Intraclass correlation coefficients (ICC), standard error of measurement (SEM), and Bland-Altman plots were calculated as measures for both interreader and test-retest agreement for all readout parameters. The mean ± standard deviation was 0.507 ± 0.05 for FA, 1308.5 ± 162.4 × 10-6 mm2/s for MD, 905.6 ± 145.4 ×10-6 mm2/s for RD and 2114.1 ± 219.2 × 10-6 mm2/s for AD. The SEM for FA was 0.02 for interreader and test-retest agreement, the SEM for MD, RD, and AD ranged between 46.2 × 10-6 mm2/s (RD) and 70.1 × 10-6 mm2/s (AD) for interreader reliability and between 45.9 × 10-6 mm2/s (RD) and 70.1 × 10-6 mm2/s (AD) for test-retest reliability. The ICC for interreader reliability of DTI parameters ranged between 0.81 and 0.92 and ICC for test-retest reliability between 0.76 and 0.91. Peripheral nerve DTI of the sciatic nerve is reliable and reproducible. The measures presented here may serve as first orientation values of measurement accuracy when interpreting parameters of sciatic nerve DTI.

The repeatability of bilateral diffusion tensor imaging (DTI) in the upper leg muscles of healthy adults

ObjectivesAssessment of the repeatability of diffusion parameter estimations in the upper leg muscles of healthy adults over the time course of 2 weeks, from a simultaneous bilateral upper leg DTI measurement.MethodsSE-EPI DTI datasets were acquired at 3 T in the upper legs of 15 active adults at a time interval of 2 weeks. ROIs were manually drawn for four quadriceps and three hamstring muscles of both legs. The following DTI parameters were analyzed: 1st, 2nd, and 3rd eigenvalue (λ1, λ2, and λ3), mean diffusivity (MD), and fractional anisotropy (FA). DTI parameters per muscle were calculated with and without intravoxel incoherent motion (IVIM) correction together with SNR levels per muscle. Bland-Altman plots and within-subject coefficient of variation (wsCV) were calculated. Left-right differences between muscles were assessed.ResultsThe Bland-Altman analysis showed good repeatability of all DTI parameters except FA for both the IVIM-corrected and standard data. wsCV values show that MD has the highest repeatability (4.5% IVIM; 5.6% standard), followed by λ2 (4.9% IVIM; 5.5% standard), λ1 (5.3% IVIM; 7.5% standard), and λ3 (5.7% IVIM; 5.7% standard). wsCV values of FA were 15.2% for the IVIM-corrected data and 13.9% for the standard analysis. The SNR (41.8 ± 16.0 right leg, 41.7 ± 17.1 left leg) and wsCV values were similar for the left and right leg and no left-right bias was detected.ConclusionsRepeatability was good for standard DTI data and slightly better for IVIM-corrected DTI data. Our protocol is suitable for DTI of the upper legs with overall good SNR.Key Points• The presented DTI protocol is repeatable and therefore suitable for bilateral DT imaging of the upper legs.• Additional B1+calibrations improve SNR and repeatability.• Correcting for perfusion effects improves repeatability.

The reproducibility of measurements using a standardization phantom for the evaluation of fractional anisotropy (FA) derived from diffusion tensor imaging (DTI).

It is necessary to standardize the examination procedure and diagnostic criteria of diffusion tensor imaging (DTI). Thus, the purpose of this study was to examine the reproducibility of measurements using a standardization phantom composed of different fibre materials with different fibre densities (FDs) for the evaluation of fractional anisotropy (FA) derived from DTI. Two types of fibre materials wrapped in heat-shrinkable tubes were used as fibre phantoms. We designed fibre phantoms with three different FDs of each fibre material. The standardization phantom was examined using DTI protocol six times a day, and each examination session was repeated oncea monthfor7consecutive months. Fibre tracking was performed by setting regions of interest in the FA map, and FA was measured in each fibre phantom. Coefficients of variation (CVs) were used to evaluate the inter-examination reproducibility of FA values. Furthermore, Bland-Altman plots were used to evaluate the intra-operator reproducibility of FA measurements. All CVs for each fibre phantom were within 2% throughout the 7-month study of repeated DTI sessions. The high intra-operator reproducibility of the FA measurement was confirmed. High reproducibility of measurements using a standardization phantom for the evaluation of FA was achieved.

A preliminary analysis of biomechanics and saccadic responses for concussion

Background Concussion is an injury that occurs in non-sporting and sporting environments. To determine improved clinical methods for identifying this injury, it is important to develop and understand how the impact event results in quantifiable differences in brain functioning—functioning that has been quantified in the past using saccadic measures. The purpose of this research was to examine the relationships between oculomotor deficits, specifically antisaccade responses, and the biomechanics of impact for a concussion. Methods Participants underwent a diffusion tensor imaging protocol as well as saccadic testing to determine differences in brain functioning in comparison to controls. The injury event was then reconstructed in laboratory using physical and finite element models to determine the biomechanics of the impact and brain tissue strain. Relationships between the biomechanical variables and antisaccade responses were then examined. Results The diffusion tensor imaging analyses found that there was a decrease in radial diffusivity and axial diffusivity found in the cerebral peduncle (p &lt; 0.05) and cingulum hippocampus (p &lt; 0.05), respectively. There was an increase in the axial diffusivity for the corona radiata (p &lt; 0.05). The saccadic testing found an increase in mean latency for the concussed group (p &lt; 0.05). The results indicated no significant relationship between mean latency, duration, amplitude and peak velocity antisaccade measures and the biomechanical variables. This may have been influenced not only by a lack of sensitivity in biomechanical variable to antisaccade responses, but also to these responses being affected by factors other than injury such as attentiveness and wakefulness. Conclusion While the sample of this research was small, this research suggests that to improve the understanding of the relationship between impact biomechanics and concussion, methods that can quantify the damage to brain structures through imaging, such as diffusion tensor imaging, may be more appropriate.

Optic tract injury after closed head traumatic brain injury in mice: A model of indirect traumatic optic neuropathy.

Adult male C57BL/6J mice have previously been reported to have motor and memory deficits after experimental closed head traumatic brain injury (TBI), without associated gross pathologic damage or neuroimaging changes detectable by magnetic resonance imaging or diffusion tensor imaging protocols. The presence of neurologic deficits, however, suggests neural damage or dysfunction in these animals. Accordingly, we undertook a histologic analysis of mice after TBI. Gross pathology and histologic analysis using Nissl stain and NeuN immunohistochemistry demonstrated no obvious tissue damage or neuron loss. However, Luxol Fast Blue stain revealed myelin injury in the optic tract, while Fluoro Jade B and silver degeneration staining revealed evidence of axonal neurodegeneration in the optic tract as well as the lateral geniculate nucleus of the thalamus and superior colliculus (detectable at 7 days, but not 24 hours, after injury). Fluoro Jade B staining was not detectable in other white matter tracts, brain regions or in cell somata. In addition, there was increased GFAP staining in these optic tract, lateral geniculate, and superior colliculus 7 days post-injury, and morphologic changes in optic tract microglia that were detectable 24 hours after injury but were more prominent 7 days post-injury. Interestingly, there were no findings of degeneration or gliosis in the suprachiasmatic nucleus, which is also heavily innervated by the optic tract. Using micro-computed tomography imaging, we also found that the optic canal appears to decrease in diameter with a dorsal-ventral load on the skull, which suggests that the optic canal may be the site of injury. These results suggest that there is axonal degeneration in the optic tract and a subset of directly innervated areas, with associated neuroinflammation and astrocytosis, which develop within 7 days of injury, and also suggest that this weight drop injury may be a model for studying indirect traumatic optic neuropathy.