Diffusion-weighted Imaging Volume Research Articles

Regional Very Low Cerebral Blood Volume Predicts Hemorrhagic Transformation Better Than Diffusion-Weighted Imaging Volume and Thresholded Apparent Diffusion Coefficient in Acute Ischemic Stroke

Currently, diffusion-weighted imaging (DWI) lesion volume is the most useful magnetic resonance imaging predictor of hemorrhagic transformation (HT). Preliminary studies have suggested that very low cerebral blood volume (VLCBV) predicts HT. We compared HT prediction by VLCBV and DWI using data from the EPITHET study. Normal-percentile CBV values were calculated from the nonstroke hemisphere. Whole-brain masks with CBV thresholds of the <0, 2.5, 5, and 10th percentiles were created. The volume of tissue with VLCBV was calculated within the acute DWI ischemic lesion. HT was graded as per ECASS criteria. HT occurred in 44 of 91 patients. Parenchymal hematoma (PH) occurred in 13 (4 symptomatic) and asymptomatic hemorrhagic infarction (HI) in 31. The median volume of VLCBV was significantly higher in cases with PH. VLCBV predicted HT better than DWI lesion volume and thresholded apparent diffusion coefficient lesion volume in receiver operating characteristic analysis and logistic regression. A cutpoint at 2 mL VLCBV with the <2.5th percentile had 100% sensitivity for PH and, in patients treated with tissue plasminogen activator, defined a population with a 43% risk of PH (95% CI, 23% to 66%, likelihood ratio=16). VLCBV remained an independent predictor of PH in multivariate analysis with traditional clinical risk factors for HT. VLCBV predicted HT after thrombolysis better than did DWI or apparent diffusion coefficient volume in this large patient cohort. The advantage was greatest in patients with smaller DWI volumes. Prediction was better in patients who recanalized. If validated in an independent cohort, the addition of VLCBV to prethrombolysis decision making may reduce the incidence of HT.

Postthrombolysis Blood Pressure Elevation Is Associated With Hemorrhagic Transformation

Reliable predictors of hemorrhagic transformation (HT) after stroke thrombolysis have not been identified. We analyzed hemorrhage in a randomized trial of tissue plasminogen activator (t-PA) vs placebo in ischemic stroke patients. We hypothesized that acute diffusion-weighted imaging (DWI) lesion volumes would be larger and blood pressures would be higher in patients with HT. HT was assessed 2 to 5 days after treatment in 97 patients. Hemorrhage was assessed by using susceptibility-weighted imaging sequences and was classified as petechial hemorrhagic infarction (HI) or parenchymal hematoma (PH). PH was more frequent in t-PA- (11/49) than in placebo- (4/48) treated patients (P=0.049). Patients with PH had larger DWI lesion volumes (63.1+/-56.1 mL) than did those without HT (27.6+/-39.0 mL, P=0.033). There were no differences in baseline systolic blood pressure (SBP) between patients with and without hemorrhage. Weighted average SBP 24 hours after treatment was higher in patients with PH (159.4+/-18.8 mL, P<0.011) relative to those without HT (143.1+/-20.0 mL). Multinomial logistic regression indicated that PH was predicted by DWI lesion volume (odds ratio=1.16 per 10 mL; 95% CI, 1.03 to 1.30), atrial fibrillation (odds ratio=9.33; 95% CI, 2.30 to 37.94), and 24-hour weighted average SBP (odds ratio=1.59 per 10 mm Hg; 95% CI, 1.14 to 2.23). Pretreatment DWI lesion volume and postthrombolysis BP are both predictive of HT. Consideration should be given to excluding patients with very large baseline DWI volumes from t-PA therapy and to more stringent BP control after stroke thrombolysis.

Characteristics of Patients with Target Magnetic Resonance Mismatch Profile: Data from Two Geographically and Racially Distinct Populations

Background: Recently, the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution (DEFUSE) and the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET) trialists suggested that diffusion-perfusion magnetic resonance imaging (MRI) can classify patients into 4 subgroups likely to differentially experience benefit or harm from reperfusion therapies. However, there is a lack of data comparing MR mismatch profiles between different race-ethnic groups. In addition, clinical factors affecting MR mismatch profiles are not well described. Methods: We analyzed clinical and pretreatment MRI data of patients from 2 geographically and ethnically distinct study populations (Seoul, South Korea, and Los Angeles, Calif., USA) who are eligible for recanalization therapy. Diffusion-perfusion mismatch regions were classified among the 4 DEFUSE MR profiles: target mismatch, no mismatch, small lesion and malignant. Results: A total of 147 South Korean and 162 Southern Californian subjects (64.2% Whites) were included. Pretreatment MRIs revealed that the MR mismatch profiles were different in the 2 study populations (p < 0.001). Target mismatch was more prevalent in Southern Californian subjects (67.9%) compared with South Korean subjects (58.5%), whereas the small lesion pattern was more prevalent in the latter (9.9 vs. 23.1%). After adjusting for covariables, 3 features independently decreased the likelihood of presence of target mismatch: history of diabetes (OR 0.369, 95% CI 0.196–0.694), small versus large arterial occlusion (OR 0.052, 95% CI 0.01–0.255) and largest size (highest tertile) of diffusion-weighted imaging (DWI) lesion volume (OR 0.516, 95% CI 0.266–0.999). The one feature independently increasing target mismatch likelihood was intermediate size (middle tertile) DWI volume (OR 2.977, 95% CI 1.431–6.195). Conclusions: Target mismatch profiles are present in 55–70% of patients. Target mismatch is less common in patients with diabetes, small vessel occlusion, Asian ethnicity and extensive DWI lesions, and more common in patients with DWI lesions of intermediate size.

Reproducibility and clinical relevance of quantitative EEG parameters in cerebral ischemia: A basic approach

To investigate reproducibility and clinical relevance of quantitative EEG parameters in ischemic cerebrovascular disease. EEG was recorded in 31 patients suffering from subacute ischemic cerebrovascular disease. Ten age-matched control subjects were included as a reference group. Intra-recording, intrarater and interrater reproducibility was calculated for standard EEG measures and for a pair wise derived Brain Symmetry Index (pdBSI). Correlations between EEG parameters, clinical status and volume of ischemia on diffusion weighted imaging (DWI) were calculated. pdBSI was sensitive to asymmetry in the amplitude and frequency domain in a random white noise model and in a simulated sinusoidal model. Minimal Cronbach alpha for intra-recording, intra- and inter-rater reproducibility ranged between 0.95 and 0.99 for standard spectral parameters and between 0.96 and 0.99 for pdBSI. We found a significant difference in pdBSI between stroke patients and control or TIA (p=0.0003). pdBSI correlated significantly with NIH stroke scale at admission and DWI volume across different levels of stroke probability (Spearman's rho=0.64-0.70 and 0.79-0.84, respectively, p<0.00001 for both). pdBSI displays high multilevel reproducibility and reliably discriminates between stroke and TIA patients or control subjects, and correlates significantly with clinical and radiological status. Based on this methodological analysis, reliable EEG parameters can be evaluated in a general stroke population for clinically relevant state and outcome measures.

Unilateral neglect is more severe and common in older patients with right hemispheric stroke

Unilateral neglect after acute right hemispheric stroke significantly impedes poststroke recovery. We studied patients with right hemispheric stroke to determine whether increasing age was associated with more frequent or more severe neglect. Eight neglect tests within 5 days of symptom onset (and within 24 hours of admission) were administered to 204 subjects with acute right hemispheric stroke. Size of infarct was measured, and neglect tests were scored as percent error. "Any neglect" was defined by an elevated neglect test score, standardized relative to a group of normal controls. When tested for neglect soon after acute stroke admission, 69.6% of subjects older than 65 years had "any neglect" (defined by comparison to a group of normal controls), compared with 49.4% of subjects aged 65 years and younger (p = 0.008). For every additional 10 years of age, patients were 1.83 times as likely to have neglect, even after adjusting for diffusion-weighted imaging (DWI) infarct volume and NIH Stroke Scale (NIHSS) score (95% CI 1.38-2.43). In addition, DWI volume and NIHSS independently predicted neglect. Score on virtually all of the neglect tests worsened as an effect of age. Percentage error on a line cancellation task was 3.8% higher for every additional 10 years of age, after adjustment for DWI volume and NIHSS (p = 0.006). Similar results were found for other neglect tests. Increasing age in patients with acute right hemispheric stroke significantly increases the odds of unilateral neglect as well as severity of neglect, independently of size of the stroke or NIH Stroke Scale score. The reason for this finding in older patients may be because they have more brain atrophy and may be less able to compensate for cerebral infarction, or because they tend to have more cardioembolic strokes, which may be more cortically based.

Acute MRI Changes in Progressive Ischemic Stroke

Background and Purpose: Neurological deterioration following acute stroke is common and associated with increased morbidity and mortality. The underlying pathophysiological mechanisms are not fully understood, and it is difficult to predict which patients are at risk of deterioration. Our study aimed to assess if acute MRI findings could be used for the prediction of stroke in progression (SIP). Methods: Prospectively 41 patients, 13 with lacunar infarcts and 28 with territorial infarcts, were admitted to an acute stroke unit within 24 h of stroke onset (median 11 h, range 3– 22). Diffusion-weighted imaging (DWI), perfusion-weighted imaging and magnetic resonance angiography were performed 3 times, immediately after clinical evaluation, on day 7 and after 3 months. Clinical neurological assessments were performed every 2 h during the first 24 h and once daily from day 2 to 7. SIP was defined as a permanent decrease of ≧3 Scandinavian Stroke Scale (SSS) points for speech or ≧2 SSS points for consciousness or ≧2 SSS points for limb strength, when assessed at baseline compared to the day after admission and daily during the following week. Patients were followed up on day 90 and assessed using the modified Rankin Scale, Barthel Index and SSS score. Patients with and without SIP were compared using both clinical and MRI data obtained on admission, on day 7 and after 3 months. Results: Fifteen patients (37%) developed SIP. Increased DWI lesion volume on day 7 in all strokes was associated with SIP (χ², p = 0.005). All lacunar infarcts with a DWI volume >1.5 cm³ at baseline (4 patients) developed SIP (p < 0.005). Patients with territorial infarcts and SIP had lower baseline SSS scores with severer symptoms than non-SIP patients (p ≤ 0.05). Despite trends in MRI differences at baseline, only the baseline SSS score in patients with territorial infarcts remained an independent predictor of SIP, when using a logistic regression model (p < 0.05). Conclusions: These findings suggest that SIP is due to growth of the lesion volume from baseline to day 7. In patients with lacunar infarcts, there was an association between initial lesion size and risk of developing SIP. However, for territorial infarcts, baseline SSS was found to be the best individual predictor of SIP and clinical outcome.

Statin Use is Independently Associated with Smaller Infarct Volume in Nonlacunar MCA Territory Stroke

Studies have shown an association between HMG-CoA reductase inhibitors (statins) and improved stroke outcomes, possibly secondary to neuroprotective properties. To assess whether patients taking statins prior to ischemic stroke have smaller infarcts on magnetic resonance imaging (MRI), adjusting for other relevant clinical factors. We retrospectively reviewed the Cleveland Clinic Foundation (CCF) Neurology Inpatient Database from June 2002 through June 2004. Demographics, medications, stroke subtype, diffusion-weighted imaging (DWI) infarct volume, admission NIHSS, and hours to MRI were collected. Patients with a nonlacunar middle cerebral artery (MCA) territory infarct and MRI less than 48 hours from symptom onset were included (n= 143). A multivariable linear regression model was constructed to determine independent predictors of smaller infarct volume. A total of 143 patients were studied, including 38 patients taking statins at the time of their stroke. In univariate analysis, patients using statins were significantly more likely to have a history of hyperlipidemia, atrial fibrillation, and coronary artery disease and to be using coumadin, antiplatelet drugs, and angiotensin-converting enzyme inhibitors. Patients on statins had a tendency toward smaller infarcts in univariate analysis (median 25.4 cm(3) vs. 15.5 cm(3), P= 0.054). In multivariable linear regression analysis statin use, patient age, and TIA within the prior 4 weeks were independently associated with smaller DWI volumes; vessel occlusion on vascular imaging, and cardioembolic stroke subtype with larger infarct size. Statin use prior to the onset of nonlacunar MCA infarction was associated with a smaller infarct volume independent of other factors. Further studies utilizing both clinical and radiologic outcomes will be required to confirm these findings.

Conversion of Ischemic Brain Tissue Into Infarction Increases With Age

Brain regions normal on diffusion-weighted imaging (DWI) but abnormal on mean transit time (MTT) maps represent tissue at risk of infarction, yet the fate of these regions is quite variable. The imperfect correlation between tissue outcome and initial imaging parameters suggests that each patient's brain may have different susceptibility to ischemic stress. We hypothesize that age is a marker for tissue susceptibility to ischemia and thus plays a role in determining tissue outcome in human stroke. Sixty patients with acute ischemic stroke and a region of DWI/MTT mismatch that was >20% of the DWI volume were included. All patients were scanned twice, within 12 hours of symptom onset and on day 5 or later. The percentage mismatch lost (PML) was calculated as percentage of initial DWI/MTT mismatch volume that was infarcted on the follow-up MRI. The statistical analysis explored relationships among the covariates age, Trial of Org 10172 in Acute Stroke Treatment (TOAST) subtypes, time-to-MRI, and initial DWI, MTT volume, mean arterial blood pressure and blood glucose level at admission, and previous history of hypertension and diabetes mellitus. Univariate comparisons showed that age (P=0.003), hypertension (P=0.009), and diabetes mellitus (P=0.0002) were significantly associated with PML. Regression analyses showed age to be a significant covariate (P=0.02). The regression model predicted a change in PML of approximately 0.65% per year. The adjusted proportion of variance (R2) in PML that could be explained by age alone was 14%. Age-dependent increase in conversion of ischemic tissue into infarction suggests that age is a biological marker for the variability in tissue outcome in acute human stroke.

The clinical-DWI mismatch: a new diagnostic approach to the brain tissue at risk of infarction.

To evaluate the usefulness of a mismatch between the severity of acute clinical manifestations and the diffusion-weighted imaging (DWI) lesion in predicting early stroke outcome and infarct volume. One hundred sixty-six patients with a hemispheric ischemic stroke of <12 hours' duration were studied. The NIH Stroke Scale (NIHSS) score and the volume of DWI lesion were measured on admission and at 72 +/- 12 hours. Infarct volume was measured on T2-weighted or fluid-attenuated inversion recovery images at day 30. Early neurologic deterioration (END) was defined as an increase of > or =4 points between the two NIHSS evaluations. Thirty-eight patients received IV thrombolysis or abciximab. Clinical-DWI mismatch (CDM) was defined as NIHSS score of > or =8 and ischemic volume on DWI of < or =25 mL on admission. The adjusted influence of CDM on END, DWI lesion enlargement at 72 hours, and infarct growth at day 30 was evaluated by logistic regression analysis and generalized linear models. CDM was found in 87 patients (52.4%). Patients with CDM had a higher risk of END than patients without CDM because NIHSS < 8 (odds ratio [OR], 9.0; 95% CI,1.9 to 42) or DWI lesion > 25 mL (OR, 2.0; 95% CI, 0.8 to 4.9). CDM was associated with an increase of 46 to 68 mL in the mean volume of DWI lesion enlargement and infarct growth in comparison with non-CDM. All the effects were even greater and significant in patients not treated with reperfusion therapies. Acute stroke patients with an NIHSS score of > or =8 and DWI volume of < or =25 mL have a higher probability of infarct growth and early neurologic deterioration. The new concept of CDM may identify patients with tissue at risk of infarction for thrombolytic or neuroprotective drugs.

Acute Basilar Artery Occlusion

Diffusion-perfusion MRI in patients with anterior circulation occlusions has demonstrated salvage of threatened tissue after thrombolytic therapy. Similar studies have not been reported with posterior circulation occlusions. Patients with acute basilar artery occlusion treated with intra-arterial thrombolytics were studied with multimodal MRI before treatment, several hours after treatment, and at day 7. Ten patients were studied (9 men, 1 woman). Mean age was 70 years, and median pretreatment National Institutes of Health Stroke Scale (NIHSS) score was 14. In 6 patients imaged before treatment and at day 7, mean pretreatment diffusion-weighted imaging (DWI) lesion volume was 11 cm(3), and day 7, lesion volume was 2.6 cm(3). Significant mismatch was visualized in all 5 patients with pretreatment perfusion-diffusion imaging (mean, 73%; range, 49% to 99%). Late imaging obtained in 4 of these 5 patients demonstrated that mean posttreatment DWI lesion volume (21 cm(3)) was less than the mean initial perfusion lesion volume (62 cm(3)). Although there was no direct correlation between pretreatment DWI volume and initial NIHSS (r=-0.113), there was good correlation between pretreatment perfusion-weighted imaging volume and initial NIHSS (r=0.72). In this first report of diffusion-perfusion MRI in patients with acute basilar artery occlusions treated with intra-arterial thrombolysis, significant mismatch was visualized on pretreatment studies, suggesting that large volumes of salvageable tissue were present. Final infarct volumes were smaller than pretreatment perfusion volumes, suggesting that substantial volumes of tissue were salvaged by thrombolytic reperfusion.

Comprehensive approach for correction of motion and distortion in diffusion-weighted MRI.

Patient motion and image distortion induced by eddy currents cause artifacts in maps of diffusion parameters computed from diffusion-weighted (DW) images. A novel and comprehensive approach to correct for spatial misalignment of DW imaging (DWI) volumes acquired with different strengths and orientations of the diffusion sensitizing gradients is presented. This approach uses a mutual information-based registration technique and a spatial transformation model containing parameters that correct for eddy current-induced image distortion and rigid body motion in three dimensions. All parameters are optimized simultaneously for an accurate and fast solution to the registration problem. The images can also be registered to a normalized template with a single interpolation step without additional computational cost. Following registration, the signal amplitude of each DWI volume is corrected to account for size variations of the object produced by the distortion correction, and the b-matrices are properly recalculated to account for any rotation applied during registration. Both qualitative and quantitative results show that this approach produces a significant improvement of diffusion tensor imaging (DTI) data acquired in the human brain.

Prediction of early neurological deterioration using diffusion- and perfusion-weighted imaging in hyperacute middle cerebral artery ischemic stroke.

Early neurological deterioration (END) occurs in approximately one third of all ischemic stroke patients and is associated with a poor outcome. Our study sought to assess the value of ultra-early MRI in the prediction of END in stroke patients. Between August 1999 and November 2001, 38 stroke patients with a proven middle cerebral artery (MCA) or intracranial internal carotid artery (ICA) occlusion on MR angiography underwent perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) within 6 hours after onset, and 30 fulfilled all inclusion criteria. Control DWI and MR angiography were performed between days 3 and 5. Cranial CT was performed to rule out hemorrhagic transformation. Vascular risk factors, temperature, blood pressure, glycemia, and blood count were assessed on admission. National Institutes of Health Stroke Scale (NIHSS) scores were obtained at baseline and at 6, 12, 24, and 48 hours. At the same time points, transcranial Doppler (TCD) examinations were conducted to assess arterial recanalization. END was defined as an increase in the NIHSS score >4. A logistic regression model was applied to detect independent predictors of END. The Kruskal-Wallis test was used to evaluate the relationship between infarct growth and duration of vessel occlusion. Initial MR angiography showed an occlusion of intracranial ICA in 7 patients (23.3%), of proximal MCA in 14 (46.6%), and of distal MCA in the remaining 9 (30%). A PWI-DWI mismatch >20% was observed in 28 patients (93.3%). END occurred in 7 patients (23.3%). Baseline NIHSS score (P=0.05), proximal site of occlusion (P=0.002), initial DWI (P=0.002) and PWI (P=0.003) volumes, and reduced PWI-DWI mismatch (P=0.038) were associated with END in the univariate analysis. Only hyperacute DWI volume remained as a predictor of END when a logistic regression model was applied (odds ratio, 11.5; 95% CI, 2.31 to 57.10; P=0.0028). A receiver operator characteristic curve identified a cutoff point of DWI >89 cm(3) (sensitivity, 85.7%; specificity, 95.7%) to predict END. A graded response was seen in DWI lesion expansion in relation to duration of arterial occlusion (P=0.017). Ultra-early DWI is a powerful predictor of END after MCA or intracranial ICA occlusion.

Early evolution of deficits in acute ischemic stroke: Mean transit time, relative blood volume, and relative blood flow

The objective of this prospective pilot study was to determine the evolution of imaging characteristics of perfusion-weighted imaging (PWI), including mean transit time (MTT), relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), diffusion-weighted imaging (DWI), and magnetic resonance (MR) angiography in the first 48 hours after an acute cerebral infarction. In 5 patients with suspected middle cerebral artery (MCA) territory infarction, images were obtained on 4 occasions during the first 48 hours (6-10 hours, 15-18 hours, 22-24 hours, and 48 hours) by an imaging protocol that included echoplanar DWI, PWI, and MR angiography. No patients received thrombolytic or neuroprotective agents. Four of the 5 patients had MCA occlusions on the initial MR angiogram. Presumably, the MCA had recanalized in 1 patient before the first MR angiogram. Recanalization of the MCA was observed by the second scan in 1 patient and by the fourth scan in the remaining 3 patients. The mean MTT volume deficit was greater than the DWI volume (mismatch) until the final MR examination at 48 hours. The mean rCBV and rCBF volumes were larger than the DWI volume (mismatch) on the first MR examination but were smaller on the second and subsequent examinations. Decrease in the size of the MTT volume before recanalization of the MCA was most likely due to opening of collateral channels, but the greatest decrease in the size of the MTT volume occurred with recanalization of the MCA. All patients had progressive enlargement of the abnormal DWI volume. The MR changes following acute cerebral infarction are dynamic, with the volume of the diffusion abnormality nearly doubling between 6 to 10 hours and 48 hours. The volume of the acute MTT abnormality (6-10 hours) is approximately twice the size of the diffusion abnormality at 48 hours. The volume of the rCBV and rCBF between 6 and 10 hours after ictus is a good reflection of the diffusion abnormality at 48 hours. Copyright © 2002 by National Stroke Association

Clinical and Radiological Correlates of Reduced Cerebral Blood Flow Measured Using Magnetic Resonance Imaging

Methods for determining cerebral blood flow (CBF) using bolus-tracking magnetic resonance imaging (MRI) have recently become available. Reduced apparent diffusion coefficient (ADC) values of brain tissue are associated with reductions in regional CBF in animal stroke models. To determine the clinical and radiological features of patients with severe reductions in CBF on MRI and to analyze the relationship between reduced CBF and ADCs in acute ischemic stroke. Case series. Referral center. We studied 17 patients with nonlacunar acute ischemic stroke in whom perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) were performed within 7 hours of symptom onset. A PWI-DWI mismatch of more than 20% was required. We compared patients with ischemic lesions that had CBF of less than 50% relative to the contralateral hemisphere with patients with lesions that had relative CBF greater than 50%. Characteristics analyzed included age, time to MRI, baseline National Institutes of Health Stroke Scale score, mean ADC, DWI and PWI lesion volumes, and 1-month Barthel Index score. Patients with low CBF (n = 5) had lower ADC values (median, 430 x 10 (-6) mm(2)/s vs. 506 x 10 (-6) mm(2)/s; P =.04), larger DWI volumes (median, 41.8 cm(3) vs. 14.5 cm(3); P =.001) and larger PWI lesions as defined by the mean transit time volume (median, 194.6 cm(3) vs. 69.3 cm(3); P =.01), and more severe baseline National Institutes of Health Stroke Scale scores (median, 15 vs. 9; P =.02). Ischemic lesions with severe CBF reductions, measured using bolus-tracking MRI, are associated with lower mean ADCs, larger DWI and PWI volumes, and higher National Institutes of Health Stroke Scale scores.

Time course of lesion development in patients with acute brain stem infarction and correlation with NIHSS score

Background and purpose: diffusion weighted magnetic resonance imaging (MRI) is highly sensitive in detecting acute supratentorial cerebral ischemia and Diffusion Weighted Imaging (DWI) lesion size has been shown to correlate strongly with the neurologic deficit in middle cerebral artery territory stroke. However, data concerning infratentorial strokes are rare. We examined the size and evolution of acute brain stem ischemic lesions and their relationship to neurological outcome. Methods: brain stem infarctions of 11 patients were analyzed. We performed DWI in all patients and in 7/11 patients within 24 h, T2W sequences within the first 2 weeks (10/11 patients) and follow-up MRI (MR2) within 3–9 months (median 4.8 months) later (12/12 patients). Lesion volumes were compared with early and follow-up neurologic deficit as determined by National Institutes of Health Stroke Scale (NIHSS) score. Results: the relative infarct volumes—with MR2 lesion size set to 100%—decreased over the time ( P<0.02) with a mean shrinking factor of 3.3 between DWI (MR0) and the follow-up MRT ( P<0.02), and 1.6 between early T2W (MR1) and MR2 ( P<0.04). The mean DWI volume size (MR0) was larger than the early T2W ( P<0.02). Although neurological outcome was good in all patients (mean NIHSS score of 1.3 at follow-up), early NIHSS and follow-up NIHSS scores were strongly correlated ( r=0.9, P<0.00). NIHSS score at follow-up was highly correlated with lesion size of DWI (MR0; r=0.71, P<0.04) and T2W of MR1 ( r=0.86, P<0.001). Conclusions: in this study, we saw a shrinking of the brain stem infarct volume according to clinical improvement of patients. Great extension of restricted diffusion in the acute stage does not necessarily implicate a large resulting infarction or a bad clinical outcome.

Differential evolution of tissue mean transit time, relative blood volume and flow deficits in acute ischemic stroke

P28 Background and Aim: The presence of a perfusion-weighted imaging (PWI) volume deficit greater than diffusion-weighted imaging (DWI) volume predicts the presence of salvageable tissue. The aim of this prospective study was to determine the evolution of various parameters of perfusion within the ischemic volume using serial MR imaging during the first 48 hours after stroke. Method: Five patients with middle cerebral artery (MCA) territory ischemic stroke were imaged (echoplanar DWI, PWI, MR angiography) within 6–10 hours of stroke onset, then at 15–18 hours, 22–24 hours and 48 hours. No patient received thrombolytic or neuro-protective agents. Results: Four of the 5 patients had a MCA occlusion on the initial MR angiogram. Recanalization of the MCA was observed by the second scan in one patient and by the fourth scan in the remaining 3 patients. Significant DWI and tissue mean transit time (tMTT) volume mismatch (&gt;75%) was observed in 4 patients and moderate mismatch in 1 patient on the initial scan. A significant mismatch between DWI and tMTT volume (&gt;70%) was observed in 2 patients by the second and third scan. By the fourth scan no patient had a significant DWI and tMTT volume mismatch. Significant mismatch (&gt;50%) between DWI and relative blood volume/ relative blood flow (rCBV/rCBF) volume was observed in 3 of the 5 patients on the initial scan. Matched DWI and rCBV was observed by the third scan in all patients. Matched DWI and rCBF was observed by the second scan in all patients. A decrease in the size of the tMTT volume prior to the recanalization of the MCA was likely due to opening of collateral channels but the most dramatic decrease in the size of tMTT volume occurred following recanalization of the MCA. Conclusion: The serial changes in tMTT, rCBV, rCBF progress at different rates following acute ischemic stroke. These results have implications for future studies basing thrombolytic therapy on DWI/PWI. We caution that treatment based only on a tMTT/DWI mismatch may overestimate the size of the salvageable tissue.

CT Perfusion Imaging versus MR Diffusion Weighted Imaging: Prediction of Final Infarct Size in Hyperacute Stroke

10 Background: Both CT perfusion imaging (CTP) and MR diffusion weighted imaging (DWI) have been applied clinically to predict tissue outcome in patients with hyperacute stroke, however these techniques have not been directly compared in the same patient population. In CTP, whole brain CT scanning is performed during the steady state administration of a contrast bolus, creating both perfused blood volume weighted and CT angiographic images. Purpose: To determine the value of CTP imaging, compared to DWI, in predicting final infarct size in hyperacute stroke patients. Materials and Methods: CTP followed by DWI imaging was performed in 23 consecutive patients presenting within 12 hours of stroke onset. Mean time from stroke onset to imaging was 4.6 hours for CTP, 5.4 hours for DWI, and 6.5 days for conventional nonenhanced CT and/or MR follow-up. No patients had secondary events between initial and follow-up scanning. Initial and follow-up ischemic volumes were computed from the CTP, DWI, and follow-up scans using image segmentation software, and compared using linear and multiple regression. Results: CTP and DWI volumes were independent predictors of final infarct size (p=0.02). The regression line for CTP volume vs. final infarct size had slope 1.02 and r 2 = 0.88 (p&lt;0.0001). The regression line for DWI volume vs. final infarct size had slope 1.41 and r 2 = 0.92 (p&lt;0.0001). Overall sensitivity and specificity for parenchymal stroke detection were 83% and 100% for CTP, and 100% and 100% for DWI, respectively. Conclusion: Although DWI is more sensitive than CTP for parenchymal stroke detection, both DWI and CTP are highly accurate predictors of final infarct volume. DWI tends to underestimate final infarct size, whereas CTP more closely approximates final infarct size.

Is early ischemic lesion volume on diffusion-weighted imaging an independent predictor of stroke outcome? A multivariable analysis.

The heterogeneity of stroke makes outcome prediction difficult. Neuroimaging parameters may improve the predictive value of clinical measures such as the National Institutes of Health Stroke Scale (NIHSS). We investigated whether the volume of early ischemic brain lesions assessed with diffusion-weighted imaging (DWI) was an independent predictor of functional outcome. We retrospectively selected patients with nonlacunar ischemic stroke in the anterior circulation from 4 prospective Stanford Stroke Center studies evaluating early MRI. The baseline NIHSS score and ischemic stroke risk factors were assessed. A DWI MRI was performed within 48 hours of symptom onset. Clinical characteristics and early lesion volume on DWI were compared between patients with an independent outcome (Barthel Index score >/=85) and a dependent outcome (Barthel Index score <85) at 1 month. A logistic regression model was performed with factors that were significantly different between the 2 groups in univariate analysis. Sixty-three patients fulfilled the entry criteria. One month after symptom onset, 24 patients had a Barthel Index score <85 and 39 had a Barthel Index score >/=85. In univariate analysis, patients with independent outcome were younger, had lower baseline NIHSS scores, and had smaller lesion volumes on DWI. In a logistic regression model, DWI volume was an independent predictor of outcome, together with age and NIHSS score, after correction for imbalances in the delay between symptom onset and MRI. DWI lesion volume measured within 48 hours of symptom onset is an independent risk factor for functional independence. This finding could have implications for the design of acute stroke trials.