Information on longitudinal changes in white matter after stroke is limited. The aim of the present study was to quantitatively investigate longitudinal changes in the microstructural integrity of non-lesioned white matter at 1-3 years following ischemic stroke. In a sample of 80 ischemic stroke patients, we obtained diffusion tensor imaging (DTI) measures of fractional anisotropy (FA), an apparent measure of white matter integrity, in radiologically normal-appearing white matter at baseline and 3 years of follow-up. Mixed model regression analysis results showed a significant improvement in FA from baseline during the first 2 years of follow-up that stabilized by the third year of follow-up. These results demonstrate a long-term improvement in apparent white matter integrity following ischemic stroke that continues, at least, into the second year following the insult.
"Introduction Diffusion tensor imaging (DTI) is a quantitative MRI technique widely used for the in vivo characterization of white matter microstructural organization (Ciccarelli et al., 2008; Mori and Zhang, 2006). DTI can be applied to investigate both normal and pathological conditions, and in longitudinal studies it can measure changes of white matter tissue properties in normal aging (Lebel and Beaulieu, 2011; Sullivan and Pfefferbaum, 2007; Sullivan et al., 2010; Westlye et al., 2010) as well as in brain diseases like for example Alzheimer's Disease (Kantarci et al., 2010; Mielke et al., 2009; Scola et al., 2010; Teipel et al., 2010), Huntington's Disease (Magnotta et al., 2009; Sritharan et al., 2010; Weaver et al., 2009), multiple sclerosis (Calabrese et al., 2011; Harrison et al., 2011; Rashid et al., 2008; Sage et al., 2009), stroke recovery (Wang et al., 2006) and traumatic brain injury (Sidaros et al., 2008). Such longitudinal DTI studies can be used to test and develop DTI-based biomarker models of disease progression/recovery, which may be of great utility in better understanding physiopathology as well as for evaluating therapeutic effects. "
[Show abstract][Hide abstract] ABSTRACT: Large-scale longitudinal neuroimaging studies with diffusion imaging techniques are necessary to test and validate models of white matter neurophysiological processes that change in time, both in healthy and diseased brains. The predictive power of such longitudinal models will always be limited by the reproducibility of repeated measures acquired during different sessions. At present, there is limited quantitative knowledge about the across-session reproducibility of standard diffusion metrics in 3T multi-centric studies on subjects in stable conditions, in particular when using tract based spatial statistics and with elderly people. In this study we implemented a multi-site brain diffusion protocol in 10 clinical 3T MRI sites distributed across 4 countries in Europe (Italy, Germany, France and Greece) using vendor provided sequences from Siemens (Allegra, Trio Tim, Verio, Skyra, Biograph mMR), Philips (Achieva) and GE (HDxt) scanners. We acquired DTI data (2x2x2 mm(3), b=700s/mm(2), 5 b0 and 30 diffusion weighted volumes) of a group of healthy stable elderly subjects (5 subjects per site) in two separate sessions at least a week apart. For each subject and session four scalar diffusion metrics were considered: fractional anisotropy (FA), mean diffusivity (MD), radial (RD) and axial (AD) diffusivity. The diffusion metrics from multiple subjects and sessions at each site were aligned to their common white matter skeleton using tract-based spatial statistics. The reproducibility at each MRI site was examined by looking at group averages of absolute changes relative to the mean (%) on various parameters: i) reproducibility of the signal-to-noise ratio (SNR) of the b0 images in centrum semiovale, ii) full brain test-retest differences of the diffusion metric maps on the white matter skeleton, iii) reproducibility of the diffusion metrics on atlas-based white matter ROIs on the white matter skeleton. Despite the differences of MRI scanner configurations across sites (vendors, models, RF coils and acquisition sequences) we found good and consistent test-retest reproducibility. White matter b0 SNR reproducibility was on average 7±1 % with no significant MRI site effects. Whole brain analysis resulted in no significant test-retest differences at any of the sites with any of the DTI metrics. The atlas-based ROI analysis showed that the mean reproducibility errors largely remained in the range 2-4% for FA and AD and 2-6% for MD and RD, averaged across ROIs. Our results show reproducibility values comparable to those reported in studies using a smaller number of MRI scanners, slightly different DTI protocols and mostly younger populations. We therefore show that the acquisition and analysis protocol used are appropriate for multi-site experimental scenarios.
"Diffusion tensor tractography (DTT), derived from DTI, allows for visualization of the architecture and integrity of the CST in three dimensions and can assess white matter tracts, such as the CST, at the subcortical level. The validity and reliability of DTT for CST have been demonstrated in previous studies [1–5]. In this study, we report three patients who showed hemiparesis due to isolated unilateral medulla infarct. "
[Show abstract][Hide abstract] ABSTRACT: Diffusion tensor imaging (DTI) and tractography (DTT) provide a powerful vehicle for investigating motor recovery mechanisms. However, little is known about these mechanisms in patients with medullary lesions. We used DTI and DTT to evaluate three patients presenting with motor deficits following unilateral medulla infarct. Patients were scanned three times during 1 month (within 7, 14, and 30 days after stroke onset). Fractional anisotropy (FA) values were measured in the medulla, cerebral peduncle, and internal capsule. The three-dimensional corticospinal tract (CST) was reconstructed using DTT. Patients 1 and 2 showed good motor recovery after 14 days, and the FA values of their affected CST were slightly decreased. DTTs demonstrated that the affected CST passed along periinfarct areas and that tract integrity was preserved in the medulla. Patient 3 had the most obvious decrease in FA values along the affected CST, with motor deficits of the right upper extremity after 30 days. The affected CST passed through the infarct and was disrupted in the medulla. In conclusion, DTI can detect the involvement and changes of the CST in patients with medulla infarct during motor recovery. The degree of degeneration and spared periinfarct CST compensation may be an important motor recovery mechanism.
BioMed Research International 05/2014; 2014:524096. DOI:10.1155/2014/524096 · 3.17 Impact Factor
"From these studies it has been established that disruption of the brain tissue microstructure results in a significant reduction in the FA during the subacute and chronic phases of cerebral ischemia. Human studies usually use FA , , ,  and Mean Diffusivity (MD) , ,  to study the recovery of the injured brain over time. Regarding FA values, microstructural integrity of normal-appearing WM improves during 1 and 2 years following ischemic stroke, achieving subsequent stabilization . "
[Show abstract][Hide abstract] ABSTRACT: After stroke, white matter integrity can be affected both locally and distally to the primary lesion location. It has been shown that tract disruption in mirror's regions of the contralateral hemisphere is associated with degree of functional impairment. Fourteen patients suffering right hemispheric focal stroke (S) and eighteen healthy controls (HC) underwent Diffusion Weighted Imaging (DWI) and neuropsychological assessment. The stroke patient group was divided into poor (SP; n = 8) and good (SG; n = 6) cognitive recovery groups according to their cognitive improvement from the acute phase (72 hours after stroke) to the subacute phase (3 months post-stroke). Whole-brain DWI data analysis was performed by computing Diffusion Tensor Imaging (DTI) followed by Tract Based Spatial Statistics (TBSS). Assessment of effects was obtained computing the correlation of the projections on TBSS skeleton of Fractional Anisotropy (FA) and Radial Diffusivity (RD) with cognitive test results. Significant decrease of FA was found only in right brain anatomical areas for the S group when compared to the HC group. Analyzed separately, stroke patients with poor cognitive recovery showed additional significant FA decrease in several left hemisphere regions; whereas SG patients showed significant decrease only in the left genu of corpus callosum when compared to the HC. For the SG group, whole brain analysis revealed significant correlation between the performance in the Semantic Fluency test and the FA in the right hemisphere as well as between the performance in the Grooved Pegboard Test (GPT) and theTrail Making Test-part A and the FA in the left hemisphere. For the SP group, correlation analysis revealed significant correlation between the performance in the GPT and the FA in the right hemisphere.
PLoS ONE 01/2014; 9(1):e86119. DOI:10.1371/journal.pone.0086119 · 3.23 Impact Factor
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