PURPOSE: Diffusion tensor imaging (DTI) data must be analyzed by an analyzer after data processing. Hence, the analyzed data of DTI might depend on the analyzer, making it a major limitation. This paper reviewed previous DTI studies reporting the repeatability and reproducibility of data from the corticospinal tract (CST), one of the most actively researched neural tracts on this topic. MATERIALS AND METHODS: Relevant studies published between January 1990 and December 2018 were identified by searching PubMed, Google Scholar, and MEDLINE electronic databases using the following keywords: DTI, diffusion tensor tractography, reliability, repeatability, reproducibility, and CST. As a result, 15 studies were selected. RESULTS: Measurements of the CSTs using region of interest methods on 2-dimensional DTI images generally showed excellent repeatability and reproducibility of more than 0.8 but high variability (0.29 to 1.00) between studies. In contrast, measurements of the CST using the 3-dimensional DTT method not only revealed excellent repeatability and reproducibility of more than 0.9 but also low variability (repeatability, 0.88 to 1.00; reproducibility, 0.82 to 0.99) between studies. CONCLUSION: Both 2-dimensional DTI and 3-dimensional DTT methods appeared to be reliable for measuring the CST but the 3-dimensional DTT method appeared to be more reliable.
Diffusion Tensor Imaging ; Diffusion ; Methods ; Pyramidal Tracts

OBJECTIVE: To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom. MATERIALS AND METHODS: Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman's correlation analysis. RESULTS: The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value. CONCLUSION: A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.
Anisotropy ; Diffusion Magnetic Resonance Imaging/*instrumentation/*methods ; Diffusion Tensor Imaging/*instrumentation/*methods ; Humans ; *Phantoms, Imaging ; Research Design ; Signal-To-Noise Ratio

PURPOSE: To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation. METHODS: Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor. RESULTS: The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy. CONCLUSIONS: An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through in vivo and in situ experiments.
Anisotropy ; Diffusion Tensor Imaging ; Diffusion* ; Electric Conductivity* ; Electric Impedance ; Electric Stimulation* ; Electrodes ; Magnetic Resonance Imaging ; Methods ; Silver ; Water*

OBJECTIVE: To assess the effects of varying the number of diffusion gradient directions (NDGDs) on diffusion tensor fiber tracking (FT) in human brain white matter using tract characteristics. MATERIALS AND METHODS: Twelve normal volunteers underwent diffusion tensor imaging (DTI) scanning with NDGDs of 6, 11, 15, 21, and 31 orientations. Three fiber tract groups, including the splenium of the corpus callosum (CC), the entire CC, and the full brain tract, were reconstructed by deterministic DTI-FT. Tract architecture was first qualitatively evaluated by visual observation. Six quantitative tract characteristics, including the number of fibers (NF), average length (AL), fractional anisotropy (FA), relative anisotropy (RA), mean diffusivity (MD), and volume ratio (VR) were measured for the splenium of the CC at the tract branch level, for the entire CC at tract level, and for the full brain tract at the whole brain level. Visual results and those of NF, AL, FA, RA, MD, and VR were compared among the five different NDGDs. RESULTS: The DTI-FT with NDGD of 11, 15, 21, and 31 orientations gave better tracking results compared with NDGD of 6 after the visual evaluation. NF, FA, RA, MD, and VR values with NDGD of six were significantly greater (smallest p = 0.001 to largest p = 0.042) than those with four other NDGDs (11, 15, 21, or 31 orientations), whereas AL measured with NDGD of six was significantly smaller (smallest p = 0.001 to largest p = 0.041) than with four other NDGDs (11, 15, 21, or 31 orientations). No significant differences were observed in the results among the four NDGD groups of 11, 15, 21, and 31 directions (smallest p = 0.059 to largest p = 1.000). CONCLUSION: The main fiber tracts were detected with NDGD of six orientations; however, the use of larger NDGD (> or = 11 orientations) could provide improved tract characteristics at the expense of longer scanning time.
Adult ; Anisotropy ; Diffusion Tensor Imaging/*methods ; Female ; Humans ; Male ; White Matter/*radiography ; Young Adult

OBJECTIVETo evaluate different degrees of punctate cerebral white matter damage (CWMD) using diffusion tensor imaging (DTI), and to investigate the value of DTI for CWMD in preterm infants.

METHODSThirty-one preterm infants who were hospitalized in the Shengjing Hospital of China Medical University between November 2011 and April 2012 were enrolled and divided into focal CWMD (n=11), widespread CWMD (n=10), and normal groups (n=10). The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were determined in the periventricular regions of patients in three groups, and comparison of the two indices between the three groups was performed using one-way analysis of variance. The correlation between the changes in ADC and FA values was analyzed using the Pearson coefficient, and the color-encoded FA maps in the three groups were evaluated.

RESULTSThe ADC values in the focal CWMD and widespread CWMD groups were both significantly higher than in the normal group, while the FA values in the focal CWMD and widespread CWMD groups were both significantly lower than in the normal group. The FA value in the widespread CWMD group was significantly lower than in the focal CWMD group. The color-encoded FA maps after post-processing indicated that the normal group had the highest FA value in the periventricular white matter regions, followed by the focal CWMD group and the widespread CWMD group.

CONCLUSIONSThe DTI technique can quantitatively evaluate the degree of punctate CWMD. The FA value may be more accurate than the ADC value in the evaluation of CWMD.

Diffusion Tensor Imaging ; methods ; Female ; Humans ; Infant, Newborn ; Infant, Premature ; Male ; White Matter ; pathology

BACKGROUNDMost previous neuroimaging studies have focused on the structural and functional abnormalities of local brain regions in major depressive disorder (MDD). Moreover, the exactly topological organization of networks underlying MDD remains unclear. This study examined the aberrant global and regional topological patterns of the brain white matter networks in MDD patients.

METHODSThe diffusion tensor imaging data were obtained from 27 patients with MDD and 40 healthy controls. The brain fractional anisotropy-weighted structural networks were constructed, and the global network and regional nodal metrics of the networks were explored by the complex network theory.

RESULTSCompared with the healthy controls, the brain structural network of MDD patients showed an intact small-world topology, but significantly abnormal global network topological organization and regional nodal characteristic of the network in MDD were found. Our findings also indicated that the brain structural networks in MDD patients become a less strongly integrated network with a reduced central role of some key brain regions.

CONCLUSIONSAll these resulted in a less optimal topological organization of networks underlying MDD patients, including an impaired capability of local information processing, reduced centrality of some brain regions and limited capacity to integrate information across different regions. Thus, these global network and regional node-level aberrations might contribute to understanding the pathogenesis of MDD from the view of the brain network.

Adult ; Anisotropy ; Brain ; pathology ; Depressive Disorder, Major ; pathology ; Diffusion Tensor Imaging ; methods ; Female ; Humans ; Male

OBJECTIVETo investigate the feasibility of applying diffusion tensor imaging (DTI)-based arcuate fasciculus tractography and intraoperative arcuate fasciculus navigation for neurosurgery.

METHODSTotally 85 patients with interhemispheric tumors who had undergone intra-operative magnetic resonance imaging (MRI) and neuronavigation were divided into sinistrocerebral tumor (SCT) group (n = 55) and sham group (n = 30). All patients accepted routine MRI and DTI preoperatively. The results from both DTI-based arcuate fasciculus tractography and neuronavigation were applied to guide the surgery. All patients were followed up at 2-4 weeks and 3-6 months postoperatively.

RESULTSAll patients smoothly received the pre-operative DTI-based arcuate fasciculus tractography. The three dimensional arcuate fasciculus was successfully integrated with the neuronavigation and achieved microscope heads-up display. Long-term follow-up showed that there were only 4 patients suffered from persistent language dysfunction.

CONCLUSIONSThe combined application of DTI-based arcuate fasciculus tractography and intraoperative arcuate fasciculus navigation is feasible for guiding brain surgery. It can improve the surgical outcomes of intracranial tumor involving language functional area. The technology also maximizes the retention of language function and improves the post-operative quality of life.

Adult ; Aged ; Brain Neoplasms ; surgery ; Diffusion Magnetic Resonance Imaging ; methods ; Diffusion Tensor Imaging ; Female ; Follow-Up Studies ; Humans ; Male ; Middle Aged ; Monitoring, Intraoperative ; methods ; Neuronavigation ; methods ; Young Adult

Because of the long acquisition time and spin-echo planar imaging sequence, diffusion weight magnetic resonance image (DWI) should be denoised effectively to ensure the follow-up applications. The commonly used denoising methods which induced from gray level image lack the use of the specific information from multiple magnitude directions. This paper, therefore, proposes a modified linear minimum mean square error (LMMSE) denosing method used for DWI. The proposed method uses the local information to estimate the parameter of the Rician noise and modifies the LMMSE using the information of multiple magnitude directions synthetically. The simulation and experiment of the synthetic DWI and real human brain DWI dataset demonstrate that the proposed method can more effectively remove the Rician noise compared to the commonly used denoising method and improve the robustness and validity of the diffusion tensor magnetic resonance image (DTI).
Algorithms ; Brain ; anatomy & histology ; Computer Simulation ; Diffusion Magnetic Resonance Imaging ; Diffusion Tensor Imaging ; Humans ; Image Enhancement ; methods ; Image Interpretation, Computer-Assisted ; methods ; Least-Squares Analysis ; Reproducibility of Results

BACKGROUNDDiffusion tensor imaging (DTI) permits quantitative examination within the pyramidal tract (PT) by measuring fractional anisotropy (FA). To the best of our knowledge, the inter-variability measures of FA along the PT remain unexplained. A clear understanding of these reference values would help radiologists and neuroscientists to understand normality as well as to detect early pathophysiologic changes of brain diseases. The aim of our study was to calculate the variability of the FA at eleven anatomical landmarks along the PT and the influences of gender and cerebral hemisphere in these measurements in a sample of young, healthy volunteers.

METHODSA retrospective, cross-sectional study was performed in twenty-three right-handed healthy volunteers who underwent magnetic resonance evaluation of the brain. Mean FA values from eleven anatomical landmarks across the PT (at centrum semiovale, corona radiata, posterior limb of internal capsule (PLIC), mesencephalon, pons, and medulla oblongata) were evaluated using split-plot factorial analysis of variance (ANOVA).

RESULTSWe found a significant interaction effect between anatomical landmark and cerebral hemisphere (F (10, 32) = 4.516, P = 0.001; Wilks' Lambda 0.415, with a large effect size (partial η(2) = 0.585)). The influence of gender and age was non-significant. On average, the midbrain and PLIC FA values were higher than pons and medulla oblongata values; centrum semiovale measurements were higher than those of the corona radiata but lower than PLIC.

CONCLUSIONSThere is a normal variability of FA measurements along PT in healthy individuals, which is influenced by regions of interest location (anatomical landmarks) and cerebral hemisphere. FA measurements should be reported for comparing same-side and same-landmark PT to help avoid comparisons with the contralateral PT; ideally, normative values should exist for a clinically significant age group. A standardized package of selected DTI processing tools would allow DTI processing to be routinely performed in clinical settings.

Adult ; Analysis of Variance ; Anisotropy ; Cerebrum ; metabolism ; Cross-Sectional Studies ; Diffusion Magnetic Resonance Imaging ; methods ; Diffusion Tensor Imaging ; methods ; Female ; Humans ; Male ; Pyramidal Tracts ; metabolism ; Retrospective Studies ; Young Adult

Diffusion-weighted magnetic resonance imaging (dMRI) is widely used to study white and gray matter (GM) micro-organization and structural connectivity in the brain. Super-resolution track-density imaging (TDI) is an image reconstruction method for dMRI data, which is capable of providing spatial resolution beyond the acquired data, as well as novel and meaningful anatomical contrast that cannot be obtained with conventional reconstruction methods. TDI has been used to reveal anatomical features in human and animal brains. In this study, we used short track TDI (stTDI), a variation of TDI with enhanced contrast for GM structures, to reconstruct direction-encoded color maps of fixed tree shrew brain. The results were compared with those obtained with the traditional diffusion tensor imaging (DTI) method. We demonstrated that fine microstructures in the tree shrew brain, such as Baillarger bands in the primary visual cortex and the longitudinal component of the mossy fibers within the hippocampal CA3 subfield, were observable with stTDI, but not with DTI reconstructions from the same dMRI data. The possible mechanisms underlying the enhanced GM contrast are discussed.
Animals ; Brain Mapping ; Diffusion Tensor Imaging ; methods ; Hippocampus ; diagnostic imaging ; Image Processing, Computer-Assisted ; methods ; Male ; Neural Pathways ; diagnostic imaging ; Tupaiidae ; anatomy & histology ; Visual Cortex ; diagnostic imaging