Minimisation of Signal Intensity Differences in Distortion Correction Approaches of Brain Magnetic Resonance Diffusion Tensor Imaging.

OBJECTIVES: To evaluate the effects of signal intensity differences between the b0 image and diffusion tensor imaging (DTI) in the image registration process. METHODS: To correct signal intensity differences between the b0 image and DTI data, a simple image intensity compensation (SIMIC) method, which is a b0 image re-calculation process from DTI data, was applied before the image registration. The re-calculated b0 image (b0ext) from each diffusion direction was registered to the b0 image acquired through the MR scanning (b0nd) with two types of cost functions and their transformation matrices were acquired. These transformation matrices were then used to register the DTI data. For quantifications, the dice similarity coefficient (DSC) values, diffusion scalar matrix, and quantified fibre numbers and lengths were calculated. RESULTS: The combined SIMIC method with two cost functions showed the highest DSC value (0.802 ± 0.007). Regarding diffusion scalar values and numbers and lengths of fibres from the corpus callosum, superior longitudinal fasciculus, and cortico-spinal tract, only using normalised cross correlation (NCC) showed a specific tendency toward lower values in the brain regions. CONCLUSION: Image-based distortion correction with SIMIC for DTI data would help in image analysis by accounting for signal intensity differences as one additional option for DTI analysis. KEY POINTS: • We evaluated the effects of signal intensity differences at DTI registration. • The non-diffusion-weighted image re-calculation process from DTI data was applied. • SIMIC can minimise the signal intensity differences at DTI registration.

Topographic organization of motor fibre tracts in the human brain: findings in multiple locations using magnetic resonance diffusion tensor tractography.

OBJECTIVES: To identify the hand and foot fibre tracts of the corticospinal tract (CST), and to evaluate the relative locations, angles, and distances of two fibre tracts using diffusion tensor tractography (DTT). METHODS: Twelve healthy subjects were enrolled. The regions of interests (ROIs) were drawn in the functional magnetic resonance imaging (fMRI) activation areas and pons in each subject for fibre tracking. We evaluated fibre tract distributions using distances and angles between two fibre tracts starting from the location of a hand fibre tract in multiple brain regions. RESULTS: The measured angles and distances were 96.43-150°/2.69-9.93 mm (upper CR), 91.86-180°/1.63-7.42 mm (lower CR), 54.47-75°/0.75-4.45 mm (PLIC), and 3.65-90°/0.11-2.36 mm (pons), respectively. The distributions between CR and other sections, such as PLIC and pons, were statistically significant (p < 0.05). There were no significant differences between the upper and lower CR\ or between the PLIC and pons. CONCLUSIONS: This study showed that the somatotopic arrangement of the hand fibre tract was located at the anterolateral portion in CR and at the anteromedial portion in PLIC and pons, based on the foot fibre. Our methods and results seem to be helpful in motor control neurological research. KEY POINTS: • We evaluated somatotopic arrangement of CST at multiple anatomical locations. • Somatotopic arrangements and fibre tract distributions were evaluated based on hand fibre location. • Relative angles, locations, and distances between two fibres vary according to their anatomical locations.

Altered small-world property of a dynamic metabolic network in murine left hippocampus after exposure to acute stress.

The acute stress response is a natural and fundamental reaction that balances the physiological conditions of the brain. To maintain homeostasis in the brain, the response is based on changes over time in hormones and neurotransmitters, which are related to resilience and can adapt successfully to acute stress. This increases the need for dynamic analysis over time, and new approaches to examine the relationship between metabolites have emerged. This study investigates whether the constructed metabolic network is a realistic or a random network and is affected by acute stress. While the metabolic network in the control group met the criteria for small-worldness at all time points, the metabolic network in the stress group did not at some time points, and the small-worldness had resilience after the fifth time point. The backbone metabolic network only met the criteria for small-worldness in the control group. Additionally, creatine had lower local efficiency in the stress group than the control group, and for the backbone metabolic network, creatine and glutamate were lower and higher in the stress group than the control group, respectively. These findings provide evidence of metabolic imbalance that may be a pre-stage of alterations to brain structure due to acute stress.

Altered structural brain network resulting from white matter injury in obstructive sleep apnea.

STUDY OBJECTIVES: To assess, using fractional anisotropy (FA) analysis, alterations of brain network connectivity in adults with obstructive sleep apnea (OSA). Abnormal networks could mediate clinical functional deficits and reflect brain tissue injury. METHODS: Structural brain networks were constructed using diffusion tensor imaging (DTI) from 165 healthy (age 57.99 ± 6.02 years, male 27.9%) and 135 OSA participants (age 59.01 ± 5.91 years, male 28.9%) and global network properties (strength, global efficiency, and local efficiency) and regional efficiency were compared between groups. We examined MRI biomarkers of brain tissue injury using FA analysis and its effect on the network properties. RESULTS: Differences between groups of interest were noted in global network properties (p-value < 0.05, corrected), and regional efficiency (p-value < 0.05, corrected) in the left middle cingulate and paracingulate gyri, right posterior cingulate gyrus, and amygdala. In FA analysis, OSA participants showed lower FA values in white matter (WM) of the right transverse temporal, anterior cingulate and paracingulate gyri, and left postcentral, middle frontal and medial frontal gyri, and the putamen. After culling fiber tracts through WM which showed significant differences in FA, we observed no group difference in network properties. CONCLUSIONS: Changes in WM integrity and structural connectivity are present in OSA participants. We found that the integrity of WM affected brain network properties. Brain network analysis may improve understanding of neurocognitive deficits in OSA, enable longitudinal tracking, and provides explanations for specific symptoms and recovery kinetics.

Cortical reorganization demonstrated by diffusion tensor tractography analyzed using functional MRI activation.

The diffusion tensor tractography (DTT) allows the corticospinal tract(CST) to be visualized at the subcortical level and functional MRI (fMRI) is capable of precisely identifying activation sites at the cortex. Therefore, it seems that combined DTT/fMRI would allow more accurate evaluation of the state of the CST. We have attempted to demonstrate cortical reorganization in a patient with cortical hemorrhage using DTT analyzed by fMRI activations. Six normal subjects and a 12-year-old female patient with a hemorrhage in the left fronto-parietal cortex were recruited. fMRI was performed at 1.5-T with timed hand grasp-release movements, and DTT was performed using 1.5-T with a Synergy-L Sensitivity Encoding head coil. Three-dimensional reconstructions of the fiber tracts were obtained using the fMRI activation as the seed region of interest and the CST area of the anterior pons as the target region of interest. The tract of the affected hemisphere originated from the lateral area of the injured precentral knob and descended along the known corticospinal tract pathway. It seems that the motor function of the affected hand was reorganized into the lateral area of the injured precentral knob. Therefore, these combined modalities would be helpful in elucidating the state of the CST.

Recovery of corticospinal tract with diffuse axonal injury: a diffusion tensor image study.

OBJECTIVES: The purpose of this study is to identity the recovery process of the corticospinal tract with diffuse axonal injury (DAI) using diffusion tensor imaging (DTI). DESIGN: A 47-year-old female patient and six age-matched control subjects were evaluated. The patient presented with quadriparesis (more severe in the right extremities than the left ones) due to DAI at the onset of traumatic brain injury. Over the 24-month period following the onset of the injury, motor function of the four extremities slowly recovered to range which was close to normal. Two longitudinal DTIs were acquired from the patient (at 10 weeks and 24 months from onset) and from the control subjects. Fractional anisotropy (FA) and an apparent diffusion coefficient were measured using the region of interest (ROI) method. RESULTS: On the 10-week DTI, FAs of ROIs of the brainstem in both hemispheres of the patient were significantly lower than those of the control subjects. Compared to normal controls, the patient showed significantly increased FA in both sides of the brainstem at 24 months after the onset, which occurred in parallel with the improvement in motor function. CONCLUSIONS: Recovery in this patient could be attributed to the recovery of the corticospinal tract with diffuse axonal injury.

Recovery of a partially damaged corticospinal tract in a patient with intracerebral hemorrhage: a diffusion tensor image study.

PURPOSE: We hypothesized that diffusion tensor imaging (DTI) could be useful for exploring corticospinal tract (CST) regeneration if longitudinal changes of diffusion anisotropy can be detected. In this study, we explored the recovery of a CST partially damaged by intracerebral hematoma in a patient by DTI. METHODS: A 61-year-old female patient and six age-matched control subjects were evaluated. The patient presented with complete paralysis of the left extremities, which occurred at the onset of a spontaneous intracerebral hemorrhage (ICH) in the right corona radiata and internal capsule. Over the five-month period following onset, motor function of the affected extremities slowly recovered to the normal range. Two longitudinal DTIs were acquired from the patient (at 3 weeks and 5 months from onset) and one DTI from the control subjects. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured using a region of interest (ROI) method. RESULTS: On the 3-week DTI, FA values of ROIs in the ICH regions in the affected hemisphere were significantly lower, and ADC values of ROIs in the same areas were significantly higher than those of the control subjects (p<0.002). However, both mean FA and ADC values of the affected hemisphere in the 5-month DTI showed no significant differences versus those of the control.

Focal lesions of the corticospinal tract demonstrated by diffusion tensor imaging in patients with diffuse axonal injury.

OBJECTIVES: Diffusion tensor imaging (DTI) with fiber tractography (FT) could be useful for exploration of the state of the corticospinal tract (CST) at the subcortical white matter level. The purpose of this study was to demonstrate focal lesions of the CST in patients with diffuse axonal injury (DAI), using DTI with FT. DESIGN: Two patients with DAI and six normal control subjects were recruited to this study. DTI was performed using 1.5-T with a synergy-L Sensitivity Encoding (SENSE) head coil. Fractional anisotropy (FA) and apparent diffusion coefficients (ADC) were measured using a region of interest (ROI) method. FTs were obtained with FA <0.3 and an angle change >45 degrees as termination criteria. RESULTS: On the DTI with FT, the focal lesions, which could not observed using routine brain MRI, were detected in the left brainstem of patient 1 and in the right pons and the left and right medulla of patient 2. The patients showed significantly decreased FA values in the focal lesions compared to normal controls. CONCLUSIONS: DTI with FT demonstrated focal lesions at the brainstem that had not been revealed by conventional brain MRI; these focal lesions explained the weaknesses of the patients. We conclude that DTI with FT may be a useful modality for use in investigating the status of CST in patients with DAI.

Symmetrical Location Characteristics of Corticospinal Tract Associated With Hand Movement in the Human Brain: A Probabilistic Diffusion Tensor Tractography.

The purpose of this study is to elucidate the symmetrical characteristics of corticospinal tract (CST) related with hand movement in bilateral hemispheres using probabilistic fiber tracking method. Seventeen subjects were participated in this study. Fiber tracking was performed with 2 regions of interest, hand activated functional magnetic resonance imaging (fMRI) results and pontomedullary junction in each cerebral hemisphere. Each subject's extracted fiber tract was normalized with a brain template. To measure the symmetrical distributions of the CST related with hand movement, the laterality and anteriority indices were defined in upper corona radiata (CR), lower CR, and posterior limb of internal capsule. The measured laterality and anteriority indices between the hemispheres in each different brain location showed no significant differences with P < 0.05. There were significant differences in the measured indices among 3 different brain locations in each cerebral hemisphere with P < 0.001. Our results clearly showed that the hand CST had symmetric structures in bilateral hemispheres. The probabilistic fiber tracking with fMRI approach demonstrated that the hand CST can be successfully extracted regardless of crossing fiber problem. Our analytical approaches and results seem to be helpful for providing the database of CST somatotopy to neurologists and clinical researches.

Possibility Study of Scale Invariant Feature Transform (SIFT) Algorithm Application to Spine Magnetic Resonance Imaging.

The purpose of this study is an application of scale invariant feature transform (SIFT) algorithm to stitch the cervical-thoracic-lumbar (C-T-L) spine magnetic resonance (MR) images to provide a view of the entire spine in a single image. All MR images were acquired with fast spin echo (FSE) pulse sequence using two MR scanners (1.5 T and 3.0 T). The stitching procedures for each part of spine MR image were performed and implemented on a graphic user interface (GUI) configuration. Moreover, the stitching process is performed in two categories; manual point-to-point (mPTP) selection that performed by user specified corresponding matching points, and automated point-to-point (aPTP) selection that performed by SIFT algorithm. The stitched images using SIFT algorithm showed fine registered results and quantitatively acquired values also indicated little errors compared with commercially mounted stitching algorithm in MRI systems. Our study presented a preliminary validation of the SIFT algorithm application to MRI spine images, and the results indicated that the proposed approach can be performed well for the improvement of diagnosis. We believe that our approach can be helpful for the clinical application and extension of other medical imaging modalities for image stitching.

Factors influencing the renal arterial Doppler waveform: a simulation study using an electrical circuit model (secondary publication).

PURPOSE: The goal of this study was to evaluate the effect of vascular compliance, resistance, and pulse rate on the resistive index (RI) by using an electrical circuit model to simulate renal blood flow. METHODS: In order to analyze the renal arterial Doppler waveform, we modeled the renal blood-flow circuit with an equivalent simple electrical circuit containing resistance, inductance, and capacitance. The relationships among the impedance, resistance, and compliance of the circuit were derived from well-known equations, including Kirchhoff's current law for alternating current circuits. Simulated velocity-time profiles for pulsatile flow were generated using Mathematica (Wolfram Research) and the influence of resistance, compliance, and pulse rate on waveforms and the RI was evaluated. RESULTS: Resistance and compliance were found to alter the waveforms independently. The impedance of the circuit increased with increasing proximal compliance, proximal resistance, and distal resistance. The impedance decreased with increasing distal compliance. The RI of the circuit decreased with increasing proximal compliance and resistance. The RI increased with increasing distal compliance and resistance. No positive correlation between impedance and the RI was found. Pulse rate was found to be an extrinsic factor that also influenced the RI. CONCLUSION: This simulation study using an electrical circuit model led to a better understanding of the renal arterial Doppler waveform and the RI, which may be useful for interpreting Doppler findings in various clinical settings.

Brodmann's Area Template Based Region of Interest Setting and Probabilistic Pathway Map Generation in Diffusion Tensor Tractography: Application to the Arcuate Fasciculus Fiber Tract in the Human Brain.

The purpose of this study is to acquire accurate diffusion tensor tractography (DTT) results for arcuate fasciculus (AF) fiber tract using Brodmann's area (BA) template for region of interest (ROI) setting. Thirteen healthy subjects were participated in this study. Fractional anisotropy (FA) map of each subject was calculated using diffusion tensor data, and T1w template was co-registered to FA map. The BA template was also co-registered using the transformation matrix. The ROIs were drawn in the co-registered BA template, and AF fiber tract was extracted. To generate the probabilistic pathway map, a binary mask image was generated based on the fiber tract image and co-registered to T1w template image. We also measured relative location of the AF fiber tract. The location of the probabilistic pathway map of each subject's AF fiber tract was well defined in the brain. By using this probabilistic map, the mediolateral position ratio of AF was measured 18%, and the anteroposterior position ratio of AF was measured 35%, respectively. This study demonstrated that the AF fiber tract can be extracted using BA template for ROI setting and probabilistic pathway of fiber tract. Our results and analytical approaches can helpful for accurate fiber tracking and application of perspective clinical researches.

Impact of sleep restriction on the structural brain network.

Sleep restriction (SR) is defined as the condition of not having enough sleep, and it can cause brain injury. In this study, we examined the impact of SR on the structural brain network. We obtained diffusion MRI (dMRI) data for the SR group of fourteen participants who got less than or equal to 5.5 h of sleep for the last 1 month and normal group of the same number of participants who got 7 h of sleep. We constructed the structural brain networks from the dMRI data and analyzed them using graph theoretical approaches. In comparison with the normal group, the SR group showed higher vulnerability to the targeted node attack and alterations of regional efficiency in the brain regions such as the bilateral orbital part of the frontal gyri, superior occipital gyri, left insula, fusiform, right supplementary motor area, and cingulate gyrus. These findings indicate that SR may cause the reduction of the potential alternative neuronal pathways in the brain and rewiring of neuronal fibers in the structural brain networks, which may result in potential functional impairments, as well as alterations of the structural brain connectivity. Therefore, investigating the structural brain network offers new insight into how SR influences the human brain.

Diffusion anisotrophy in the early stages of stroke can predict motor outcome.

PURPOSE: This study examined whether the degree of impairment of diffusion anisotrophy in the early stages of a stroke can predict the motor function outcome. METHODS: Thirty-one hemiplegic stroke patients were enrolled to this study. Diffusion anisotropy was measured by determining fractional anisotropy (FA) in the two ROIs (region of interests) at corona radiata (CR) and in the posterior limb of internal capsule (IC) during the early stages of stoke (average 7.9 days after stroke onset) and compared with motor outcome of the affected hand 3 months after stroke onset. RESULTS: Both ROIs (CR or IC) and lesion types (hemorrhage or infarction) did not have significant effect on the SBFA (symmetry of bilateral FA) and dMRC (medical research council score improvement), either. Patients with greater initial MRC score had significantly greater SBFA and dMRC. The regression equation between the dMRC (Y axis) and the SBFA (X axis) was semi-linear and significant (P < 0.05); for CR group, Y = 3.296 - 0.1192X + 0.0015X2; for IC group, Y = 2.342 - 0.0533X +0.0007(2). The regression lines had 'threshold points' where a minute SBFA change would make a steep increase in dMRC. CONCLUSION: The degree of impairment in diffusion anisotropy during the early stages of stroke appears to have the potential to predict motor outcome.

Diffusion tensor imaging to determine the potential motor network connectivity between the involved and non-involved hemispheres in stroke.

Hemiparetic stroke is a common motor network disorder that affects a wide range of functional movements due to cortical and subcortical network lesions in stroke patients. Conventional magnetic resonance imaging (MRI) has been used to examine structural brain damage, but the integrity and connectivity of the whole brain are poorly understood. Hence, advanced neuroimaging with diffusion tensor imaging (DTI) has been developed to better localize fiber architecture and connectivity in the motor network or pathways that are responsible for motor impairments in hemiparetic stroke. To ascertain motor network connectivity between the involved and non-involved hemispheres in stroke patients, we analyzed the DTI data from all right hemiparetic stroke patients using fractional anisotropy (FA) and network parameters, including node degree and edge betweenness centrality (EBC). The FA values were substantially lower in the left hemisphere than the right hemisphere. Similarly, the node degree and EBC were significantly lower in the left hemisphere than the right hemisphere. The present brain network analysis may provide a useful neuropathway marker for accurate diagnosis and therapeutic intervention.

The predictive value of cortical activation by passive movement for motor recovery in stroke patients.

PURPOSE: Contralateral primary sensori-motor cortex (SM1) activation by passive movement was investigated by functional MRI (fMRI) at the early stage of stroke, to determine whether SM1 activation can be used to predict the degree of motor recovery of the hemiplegic hand. METHODS: We studied 17 stroke patients who showed complete paralysis of a hemiplegic hand at onset. The motor function of the hemiplegic hand was assessed on 4 separate occasions (at onset, at fMRI evaluation (performed < 4 weeks after onset), and 3 and 6 months after onset). Significant motor recovery was defined as recovery of the affected hand to the extent of it being able to prehend an object against gravity at least at 6 months after onset. RESULTS: The patients having an activated contralateral SM1 showed better motor recovery than those who did not. Only a fourth of the patients with an activated contralateral SM1 experienced a significant motor recovery, whereas none of the patients with an inactivated SM1 showed an improvement 6 months after onset, however, the incidence of significant motor recovery was not significantly difference between the two groups. CONCLUSION: It appears that contralateral SM1 activation by passive movement in the early stage of stroke has a low predictive value for the motor recovery of the hemiplegic hand, because the activation of the contralateral SM1 by passive movement appears to be mediated by somatosensory input to the cortex from the thalamus rather than from the motor pathway.

Ipsilateral motor pathway confirmed by diffusion tensor tractography in a patient with schizencephaly.

We evaluated the hand motor function of a right hemiparetic patient with schizencephaly using a combination of fMRI, transcranial magnetic stimulation, and diffusion tensor tractography (DTT). Only the unaffected (right) primary sensori-motor cortex was found to be activated during either affected (right) or unaffected hand movements. Evoked motor potentials with similar characteristics were obtained from both abductor pollicis brevis muscles simultaneously when stimulating the unaffected motor cortex. Moreover, a tract presumed to be a corticospinal tract was observed in the unaffected hemisphere by DTT, however, no tract was observed in the affected hemisphere. Our results indicate that the ipsilateral corticospinal tract extended from the unaffected (right) motor cortex to both hands. This finding may reflect functional reorganization of motor function in a patient with congenital brain disorder.

Characteristics of geometric distortion correction with increasing field-of-view in open-configuration MRI.

Open-configuration magnetic resonance imaging (MRI) systems are becoming increasingly desirable for musculoskeletal imaging and image-guided radiotherapy because of their non-claustrophobic configuration. However, geometric image distortion in large fields-of-view (FOV) due to field inhomogeneity and gradient nonlinearity hinders the practical applications of open-type MRI. We demonstrated the use of geometric distortion correction for increasing FOV in open MRI. Geometric distortion was modeled and corrected as a global polynomial function. The appropriate polynomial order was identified as the minimum difference between the coordinates of control points in the distorted MR image space and those predicted by polynomial modeling. The sixth order polynomial function was found to give the optimal value for geometric distortion correction. The area of maximum distortion was<1 pixel with an FOV of 285mm. The correction performance error was increased at most 1.2% and 2.9% for FOVs of 340mm and~400mm compared with the FOV of 285mm. In particular, unresolved distortion was generated by local deformation near the gradient coil center.

Diffusion-tensor magnetic resonance imaging for hand and foot fibers location at the corona radiata: comparison with two lesion studies.

The corticospinal tract is the motor pathway in the human brain, and corona radiata (CR) is an important location to diagnose stroke. We detected hand and foot motor fiber tracts in the CR to investigate accurate locations using diffusion-tensor imaging (DTI) and functional imaging. Ten right-handed normal volunteers participated in this study. We used a probabilistic tracking algorithm, a brain normalization method, and functional imaging results to set out region of interests. Moreover, our results were compared to previous results of lesion studies to confirm their accuracy and usefulness. The location measurements were performed in two index types; anteriority index on the basis of the anterior and posterior location of lateral ventricle and laterality index on the basis of the left and right location. The anteriority indices were 56.40/43.2 (hand/foot) at the upper CR and lower CR 40.72/30.90 at the lower CR. The measurements of anteriority and laterality of motor fibers were represented as anteriority index 0.40/0.31 and laterality index 0.60/0.47 (hand/foot). Our results showed that the hand and foot fibers were in good agreements with previous lesion studies. This study and approaches can be used as a standard for DTI combined with lesion location studies in patients who need rehabilitation or follow-up.