***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Diffusion tensor imaging ( DTI ) fully characterises water molecule mobility in vivo , allowing an exploration of fibre tract integrity and orientation in the human brain . Using DTI this study demonstrates reduced fibre coherence ( anisotropy ) associated with cerebral infa rct ion and in the corticospinal tract remote from the lesion , in five patients 2 to 6 months after ischaemic stroke . The study highlights the potential of DTI to detect and monitor the structural degeneration of fibre pathways , which may provide a better underst and ing of the pattern of clinical evolution after stroke Background and Purpose — The annual risk of ischemic stroke distal to ≥50 % asymptomatic carotid stenoses was ≈2 % to 3 % in early cohort studies and subsequent r and omized trials of endarterectomy . This risk might have fallen in recent years owing to improvements in medical treatment , but there are no published prognostic data from studies initiated within the last 10 years . Methods — In a population -based study of all patients with transient ischemic attack ( TIA ) or stroke in the Oxford Vascular Study , we studied the risk of TIA and stroke in patients with ≥50 % contralateral asymptomatic carotid stenoses recruited consecutively from 2002 to 2009 and given intensive contemporary medical treatment .  Results — Of 1153 consecutively imaged patients presenting with stroke or TIA , 101 ( 8.8 % ) had ≥50 % asymptomatic carotid stenoses ( mean age , 75 years ; 39 % women ; 40 % age ≥80 years ) . During 301 patient-years of follow-up ( mean , 3 years ) , there were 6 ischemic events in the territory of an asymptomatic stenosis , 1 minor stroke ( initially 50 % to 69 % stenosis ) , and 5 TIAs ( 2 initially 50 % to 69 % stenosis ; 3 to 70 % to 99 % stenosis ) , 3 of which led to subsequent endarterectomy . The average annual event rates on medical treatment were 0.34 % ( 95 % CI , 0.01 to 1.87 ) for any ipsilateral ischemic stroke , 0 % ( 95 % CI , 0.00 to 0.99 ) for disabling ipsilateral stroke , and 1.78 % ( 95 % CI , 0.58 to 4.16 ) for ipsilateral TIA . Conclusions — In the first study of the prognosis of ≥50 % asymptomatic carotid stenosis to be initiated in the last 10 years , the risk of stroke on intensive contemporary medical treatment was low . Larger studies are required to determine whether this apparent improvement in prognosis is generalizable Background : Cerebral small vessel disease is a common cause of vascular dementia . Both discrete lacunar infa rcts and more diffuse ischaemic changes , seen as confluent high signal ( leukoaraiosis ) on T2 weighted magnetic resonance imaging ( MRI ) , occur . However , there is a weak correlation between T2 lesion load and cognitive impairment .  Diffusion tensor MRI ( DTI ) is a new technique that may provide a better index of white matter damage . Objectives : To determine whether DTI measures are correlated more strongly with cognitive performance than lesion load on T2 weighted images , and whether these correlations are independent of conventional MRI parameters . Methods : 36 patients with ischaemic leukoaraiosis ( leukoaraiosis plus a previous lacunar stroke ) and 19 healthy volunteers underwent DTI , conventional MRI , and neuropsychological assessment . Results : On DTI , diffusivity was increased both within lesions and in normal appearing white matter . Mean diffusivity of normal appearing white matter correlated with full scale IQ ( r = −0.46 , p = 0.009 ) and tests of executive function . These correlations remained significant after controlling for age , sex , brain volume , and T1/T2 lesion volumes . No significant correlation was identified between T2 lesion load and IQ or neuropsychological scores . Of conventional measures , brain volume correlated best with cognitive function . Conclusions : Diffusion tensor measurements correlate better with cognition than conventional MRI measures . They may be useful in monitoring disease progression and as a surrogate marker for treatment trials . The findings support the role of white matter damage and disruption of white matter connections in the pathogenesis of cognitive impairment in cerebral small vessel disease BACKGROUND AND PURPOSE : Selective white matter ( WM ) damage is a known sequela of mild hypoxic-ischemic ( HI ) injury in the neonatal rat model . The aim of this study was to evaluate longitudinally mild HI-induced WM damage ( represented by the external capsule [ EC ] ) by diffusion tensor MR imaging ( DTI ) and to correlate the findings with histology . MATERIAL S AND METHODS : Seven-day-old Sprague-Dawley rats ( n = 19 ) underwent unilateral ligation of the left common carotid artery followed by hypoxia for 50 minutes to create mild HI injury . DTI was performed longitudinally at 5 time points from day 1 to day 90 postinjury ( n = 19 , 16 , 13 , 11 , 9 , respectively ) , and fractional anisotropy ( FA ) , trace , radial diffusivity ( λ⊥ ) , and axial diffusivity ( λ// ) of the injury and control contralateral ECs were quantified . Rats were r and omly sacrificed ( n = 15 , in total ) , and the corresponding ECs were stained with hematoxylin-eosin , Luxol fast blue ( LFB ) , and neurofilament ( NF ) to evaluate morphologic changes , amount of myelin , and axonal count at every time point . A paired t test was applied to evaluate statistical differences between both ECs , and the Pearson correlation test was used to evaluate the relationships between DTI indices and histologic evaluations . In addition , longitudinal changes in DTI indices and histologic evaluations were analyzed by a linear mixed model and an analysis of variance test , respectively . RESULTS : We demonstrated significantly decreased FA , increased λ⊥ , and similar λ// in the injury compared with the control EC , which was persistent through all time points . Histologic evaluation by LFB and NF staining showed reduced myelin stain intensity in the injury EC and similar axonal counts in both ECs . Longitudinally , there was an increase in FA , a decrease in λ⊥ and trace , and stability in λ// in both ECs . Also , there was progressive reduction in the differences in FA , trace , and λ⊥ between the injury and control EC , especially between day 1 and day 7 postinjury and in t and em with changes in myelin stain . FA was significantly correlated with myelin stain ( r = 0.681 , P < .01 ) and axonal count ( r = 0.673 , P < .01 ) , whereas λ⊥ was significantly correlated with myelin stain only ( r = −0.528 , P < .01 ) , and λ// , with axonal count only ( r = 0.372 , P = .043 ) . CONCLUSIONS : Diffusion indices can reflect dysmyelination in mild HI injury , continual myelination of both injury and control ECs with growth , and the partial recovery of myelin postinjury . We propose that diffusion indices may be used as biomarkers to monitor noninvasively the longitudinal changes of mild HI-induced WM damage Background : Patients with unilateral high- grade carotid stenosis or occlusion have been reported to have more leukoaraiosis and ischemic lesions in ipsilateral than in contralateral cerebral hemisphere . The lesions alter apparent diffusion coefficient ( ADC ) values in diffusion-weighted MRI ( DWI ) . The overall effects of carotid endarterectomy on ADC values have not yet been explored . Objectives : To find out whether 1 ) average ADC ( ADCav ) values differed between hemispheres , 2 ) diffusion changes induced by carotid endarterectomy could be detected in brain tissue with serial DWI , and 3 ) patients with asymptomatic carotid stenosis differed from patients with a symptomatic stenosis . Methods : Forty-five patients ( 22 with asymptomatic carotid stenosis and 23 with symptomatic carotid stenosis ) with unilateral high- grade carotid stenosis underwent DWI before carotid endarterectomy and 3 and 100 days afterward , and 45 age- and sex-matched healthy control subjects were imaged once . We evaluated ADCav values in normal-appearing gray and white matter , watershed regions ( WsR ) , and thalamus . Results : ADCav values of ipsilateral white matter and WsR were higher than those of contralateral white matter and WsR , both being higher than in white matter and WsR of control subjects . After carotid endarterectomy , these differences were diminished , but the levels remained higher than in controls . ADCav values of gray matter and thalamus remained unaffected . Asymptomatic carotid stenosis and symptomatic carotid stenosis patient groups did not differ from each other . Conclusions : Carotid stenosis has an effect on diffusion in the white matter of the ipsilateral hemisphere , and it is partly reversible by carotid endarterectomy . The finding may be associated with leukoaraiotic development ( “ preleukoaraiosis ” ) BACKGROUND Without strong evidence of benefit , the use of carotid endarterectomy for prophylaxis against stroke rose dramatically until the mid-1980s , then declined . Our investigation sought to determine whether carotid endarterectomy reduces the risk of stroke among patients with a recent adverse cerebrovascular event and ipsilateral carotid stenosis . METHODS We conducted a r and omized trial at 50 clinical centers throughout the United States and Canada , in patients in two predetermined strata based on the severity of carotid stenosis--30 to 69 percent and 70 to 99 percent . We report here the results in the 659 patients in the latter stratum , who had had a hemispheric or retinal transient ischemic attack or a nondisabling stroke within the 120 days before entry and had stenosis of 70 to 99 percent in the symptomatic carotid artery . All patients received optimal medical care , including antiplatelet therapy . Those assigned to surgical treatment underwent carotid endarterectomy performed by neurosurgeons or vascular surgeons . All patients were examined by neurologists 1 , 3 , 6 , 9 , and 12 months after entry and then every 4 months . End points were assessed by blinded , independent case review . No patient was lost to follow-up . RESULTS Life-table estimates of the cumulative risk of any ipsilateral stroke at two years were 26 percent in the 331 medical patients and 9 percent in the 328 surgical patients --an absolute risk reduction ( + /- SE ) 17 + /- 3.5 percent ( P less than 0.001 ) . For a major or fatal ipsilateral stroke , the corresponding estimates were 13.1 percent and 2.5 percent -- an absolute risk reduction of 10.6 + /- 2.6 percent ( P less than 0.001 ) . Carotid endarterectomy was still found to be beneficial when all strokes and deaths were included in the analysis ( P less than 0.001 ) . CONCLUSIONS Carotid endarterectomy is highly beneficial to patients with recent hemispheric and retinal transient ischemic attacks or nondisabling strokes and ipsilateral high- grade stenosis ( 70 to 99 percent ) of the internal carotid artery 
    Output:
    
Carotid artery disease is associated with significant ADC and FA value changes , suggesting that carotid disease is associated with quantifiable white matter microstructural damage