***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: Introduction Acute stroke multimodal CT imaging ( MMCT : non-enhanced CT , CT angiography , and CT perfusion ( CTP ) ) may show normal results despite persistent clinical stroke . We prospect ively evaluated the sensitivity/specificity of MMCT infa rct detection and the clinical outcome in patients with normal MMCT findings . Methods From April 2007 to April 2008 , all patients with acute hemispheric stroke within 6 h of symptom onset who underwent complete MMCT and MRI follow-up imaging were included .  MMCT analysis included occlusion type , early infa rct hypodensities ( EIH ) , mean transit time ( MTT ) , and cerebral blood volume ( CBV ) maps according to Alberta Stroke Program Early CT Score ( ASPECTS ) . Clinical assessment included symptom onset to CT scan ( ≤3 h/>3 h ) , the National Institute of Health Stroke Scale score ( admission/discharge ) , and the modified Rankin scale ( mRS ) 90 days after stroke onset . Results One hundred seven were included ( mean age , 68.4 years ; ≤3 h , n = 84 ; > 3 h , n = 23 ; intravenous thrombolysis ( IVT ) , n = 51 ; ≤3 h , n = 40 ; > 3 h , n = 11 ) . In patients with normal MMCT on admission ( n = 54 ) , follow-up MRT detected brain infa rct ions in 23 patients ( lacunar strokes , n = 16 ; infratentorial strokes , n = 4 ; territorial infa rct ion , n = 3 ) . Sensitivity/specificity/positive predictive value/negative predictive value of any infa rct detection was 69.5%/99.8%/99.9%/57.2 % and of a any territorial infa rct detection was 93.9%/99.9%/99.9%/93.6 % , respectively . In univariate regression analysis ( time to CT scan , ≤3 h/>3 h ; IVT : yes/no ; ASPECTS EIH/CBV/MTT , 10/<10 ) , only the evidence of normal CTP ( ASPECTS MTT = 10 ) had a statistically significant impact ( p = 0.02 ) on a good outcome ( mRS 0.1 ) .  Conclusion MMCT sensitivity in acute lacunar or infratentorial stroke was poor . But , we found a high specifity and a fairly good sensitivity in territorial infa rct detection . In acute stroke patients with normal MMCT findings on admission , a good clinical prognosis can be expected Background and Purpose — Different definitions have been proposed to define the ischemic penumbra from perfusion-CT ( PCT ) data , based on parameters and thresholds tested only in small pilot studies . The purpose of this study was to perform a systematic evaluation of all PCT parameters ( cerebral blood flow , volume [ CBV ] , mean transit time [ MTT ] , time-to-peak ) in a large series of acute stroke patients , to determine which ( combination of ) parameters most accurately predicts infa rct and penumbra . Methods — One hundred and thirty patients with symptoms suggesting hemispheric stroke ≤12 hours from onset were enrolled in a prospect i ve multicenter trial . They all underwent admission PCT and follow-up diffusion-weighted imaging/fluid-attenuated inversion recovery ( DWI/FLAIR ) ; 25 patients also underwent admission DWI/FLAIR . PCT maps were assessed for absolute and relative reduced CBV , reduced cerebral blood flow , increased MTT , and increased time-to-peak . Receiver-operating characteristic curve analysis was performed to determine the most accurate PCT parameter , and the optimal threshold for each parameter , using DWI/FLAIR as the gold st and ard . Results — The PCT parameter that most accurately describes the tissue at risk of infa rct ion in case of persistent arterial occlusion is the relative MTT ( area under the curve=0.962 ) , with an optimal threshold of 145 % . The PCT parameter that most accurately describes the infa rct core on admission is the absolute CBV ( area under the curve=0.927 ) , with an optimal threshold at 2.0 ml × 100 g−1 . Conclusion — In a large series of 130 patients , the optimal approach to define the infa rct and the penumbra is a combined approach using 2 PCT parameters : relative MTT and absolute CBV , with dedicated thresholds Background : It is unclear whether octogenarians benefit from intra-arterial thrombolysis ( IAT ) for the treatment of acute ischemic stroke ( AIS ) . The aim of the present study was to compare baseline characteristics , clinical outcome and complications of patients aged ≧80 with those of patients aged < 80 years . Methods : Forty-three octogenarians and 524 younger patients with AIS were treated with IAT .  The modified Rankin scale ( mRS ) score was used to assess 3-month outcome . Results : There was a female preponderance among octogenarians ( 63 vs. 37 % , p = 0.015 ) . Stroke severity , occlusion site , and time from stroke onset to IAT  did not differ between the groups . Good recanalization ( TIMI 2–3 ) was achieved in 65 % of older and in 71 % of younger patients ( p = 0.449 ) . Rates of symptomatic intracranial hemorrhage ( ICH ) were 6 % in patients < 80 years and 2 % in octogenarians ( p = 0.292 ) . Favorable outcome ( mRS 0–2 ) was less frequent among octogenarians ( 28 vs. 46 % , p = 0.019 ) , while mortality was higher ( 40 vs. 22 % , p = 0.008 ) . Octogenarians died more often from extracerebral complications than younger patients ( 59 vs. 27 % , p = 0.008 ) . Conclusions : Compared with younger patients , octogenarians did not have a significantly increased risk of symptomatic ICH  after IAT .  Although favorable outcome was less frequent and mortality rates were higher , IAT appeared to be safe in octogenarians . It seems reasonable to include octogenarians in r and omized clinical trials to assess the balance of risk and benefit of IAT in this patient group To avoid increased radiation exposure and subsequent long-term risk of cancer , iterative reconstruction is a means of lowering the dose on CT studies . Here , the authors compared head CT scans obtained via st and ard dose with low-dose ( 31 % less ) iterative reconstruction .  Signal-to-noise and contrast-to-noise ratios as well as image noise , sharpness , artifacts , and diagnostic acceptability were assessed . Overall these parameters were judged to be better in the st and ard-dose CT , but those obtained with the lower dose and iterative reconstruction were judged acceptable . Thus , iterative reconstruction appears to be useful in adult head CT examinations . ( Editor 's Note : This technique would be ideal in children where radiation dosage is of utmost concern . At my institution we use it for all head and neck studies , but not for temporal bone or paranasal sinus studies as we have found that bone detail may be less than optimal . ) BACKGROUND AND PURPOSE : While CT has found wide use in medical practice , it is also a substantial source of radiation exposure and is associated with an increased lifetime risk of cancer . There is an urgent need for new approaches to reduce the radiation dose in CT . In this regard , ASIR is an alternative method to FBP . We assessed the effect of ASIR on dose reduction in adult head CT . MATERIAL S AND METHODS : We retrospectively evaluated a sample of 149 adult head CT examinations that were divided into 2 groups , STD and LD . We lowered the tube current and used ASIR in the LD group . SNR and CNR were analyzed . Dose parameters were recorded while subjective image noise , sharpness , diagnostic acceptability , and artifacts were grade d. The Student t test , the Mann-Whitney U test , and κ statistics were used for statistical analyses . RESULTS : We achieved a dose reduction of 31 % in the LD group ( STD , 2.3 ± 0.1 mSv ; LD , 1.6 ± 0.1 mSv ; P < .001 ) . There was no significant difference in the noise measured in the air between the 2 comparison groups ( P = .273 ) . Noise in the CSF was higher in the STD group ( P < .001 ) , while the noise in the WM was higher in the LD group ( P < .001 ) . Differences in the CNR between groups were insignificant , but the STD group displayed better SNR values . There was no significant difference in the modal scores of diagnostic acceptability ( P = .062 ) and the artifacts ( P = .148 ) between the 2 groups . Better scores for subjective image noise ( P < .001 ) and sharpness ( P = .04 ) were observed in the STD group . CONCLUSIONS : ASIR appears to be useful in reducing the dose in adult head CT examinations . While the effect of ASIR on noise reduction observed in the present study of head CT is less than that reported previously in abdomen and chest CT , these findings encourage further prospect i ve studies in larger patient sample BACKGROUND Intravenous alteplase is the only approved treatment for acute ischemic stroke . Tenecteplase , a genetically engineered mutant tissue plasminogen activator , is an alternative thrombolytic agent . METHODS In this phase 2B trial , we r and omly assigned 75 patients to receive alteplase ( 0.9 mg per kilogram of body weight ) or tenecteplase ( 0.1 mg per kilogram or 0.25 mg per kilogram ) less than 6 hours after the onset of ischemic stroke . To favor the selection of patients most likely to benefit from thrombolytic therapy , the eligibility criteria were a perfusion lesion at least 20 % greater than the infa rct core on computed tomographic ( CT ) perfusion imaging at baseline and an associated vessel occlusion on CT angiography . The co primary end points were the proportion of the perfusion lesion that was reperfused at 24 hours on perfusion-weighted magnetic resonance imaging and the extent of clinical improvement at 24 hours as assessed on the National Institutes of Health Stroke Scale ( NIHSS , a 42-point scale on which higher scores indicate more severe neurologic deficits ) . RESULTS The three treatment groups each comprised 25 patients . The mean ( ±SD ) NIHSS score at baseline for all patients was 14.4±2.6 , and the time to treatment was 2.9±0.8 hours . Together , the two tenecteplase groups had greater reperfusion ( P=0.004 ) and clinical improvement ( P<0.001 ) at 24 hours than the alteplase group . There were no significant between-group differences in intracranial bleeding or other serious adverse events . The higher dose of tenecteplase ( 0.25 mg per kilogram ) was superior to the lower dose and to alteplase for all efficacy outcomes , including absence of serious disability at 90 days ( in 72 % of patients , vs. 40 % with alteplase ; P=0.02 ) . CONCLUSIONS Tenecteplase was associated with significantly better reperfusion and clinical outcomes than alteplase in patients with stroke who were selected on the basis of CT perfusion imaging . ( Funded by the Australian National Health and Medical Research Council ; Australia New Zeal and Clinical Trials Registry number , ACTRN12608000466347 . ) BACKGROUND Whether intravenous tissue plasminogen activator ( alteplase ) is effective beyond 3 h after onset of acute ischaemic stroke is unclear . We aim ed to test whether alteplase given 3 - 6 h after stroke onset promotes reperfusion and attenuates infa rct growth in patients who have a mismatch in perfusion-weighted MRI ( PWI ) and diffusion-weighted MRI ( DWI ) . METHODS We prospect ively and r and omly assigned 101 patients to receive alteplase or placebo 3 - 6 h after onset of ischaemic stroke . PWI and DWI were done before and 3 - 5 days after therapy , with T2-weighted MRI at around day 90 . The primary endpoint was infa rct growth between baseline DWI and the day 90 T2 lesion in mismatch patients . Major secondary endpoints were reperfusion , good neurological outcome , and good functional outcome . Patients , caregivers , and investigators were unaware of treatment allocations . Primary analysis was per protocol . This study is registered with Clinical Trials.gov , number NCT00238537 . FINDINGS We r and omly assigned 52 patients to alteplase and 49 patients to placebo . Mean age was 71.6 years , and median score on the National Institutes of Health stroke scale was 13 . 85 of 99 ( 86 % ) patients had mismatch of PWI and DWI . The geometric mean infa rct growth ( exponential of the mean log of relative growth ) was 1.24 with alteplase and 1.78 with placebo ( ratio 0.69 , 95 % CI 0.38 - 1.28 ; Student 's t test p=0.239 ) ; the median relative infa rct growth was 1.18 with alteplase and 1.79 with placebo ( ratio 0.66 , 0.36 - 0.92 ; Wilcoxon 's test p=0.054 ) . Reperfusion was more common with alteplase than with placebo and was associated with less infa rct growth ( p=0.001 ) , 
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Conclusions : The current systematic review shows that CTP has a high sensitivity and a very high specificity for detecting infa rcts