Patients with Diffusion-Perfusion Mismatch on Magnetic Resonance Imaging 48 Hours or More After Stroke Symptom Onset: Clinical and Imaging Features

BACKGROUND: Abnormalities in diffusion-weighted (DWI) and perfusion-weighted (PWI) magnetic resonance imaging (MRI) are thought to reflect the presence of brain tissue at risk for ischemic stroke. Many patients with acute ischemic stroke have a mismatch pattern in which the PWI volume is larger than the DWI lesion. This mismatch typically resolves over 24-48 hours. Little is known about the presence of DWI-PWI mismatch in later stages of stroke. METHODS: This is a retrospective study of 122 patients admitted with a diagnosis of acute ischemic stroke who had DWI and PWI abnormalities on studies performed within 7 days of onset of symptoms. Patients were divided into two groups: those with MRI performed <48 hours and those with MRI performed >or=48 hours from onset of symptoms. RESULTS: Among 42 patients with MRI performed >or=48 hours after onset of stroke symptoms, 15 of 42 (36%) showed a mismatch pattern, compared to 45 of 80 (56%) in the <48 hours group (P < 0.05). Most of the patients in the >or=48 hours group with mismatch had large artery occlusive disease and many had neurological fluctuations. A subset of these patients were treated with induced hypertension and showed clinical improvement. CONCLUSIONS: Some patients have persistent DWI-PWI mismatch up to several days after stroke onset. Further studies are needed to determine if these patients should be candidates for reperfusion therapy.     

Transcranial Doppler Markers of Diffusion-Perfusion Mismatch

BACKGROUND AND PURPOSE: During the evaluation of acute ischemic stroke with diffusion- and perfusion-weighted magnetic resonance imaging (DWI and PWI, respectively), the presence of salvageable brain tissue is suggested by the occurrence of a perfusion-diffusion "mismatch." DWI and PWI, however, are not universally available and have inherent inconveniences, which justify a search for practical diagnostic alternatives. The purpose of this study is to investigate whether there are transcranial Doppler (TCD) markers of mismatch. METHODS: Retrospective analysis of 22 patients with acute ischemic stroke affecting the middle cerebral artery (MCA) territory, who had a TCD performed within 24 hours of magnetic resonance imaging (MRI) with DWI and PWI. RESULTS: MRI and TCD were performed on average 10.8 +/- 9.2 hours apart. Time from symptom onset to MRI and TCD completion were 1.6 +/- 1.6 and 2 +/- 1.9 days, respectively. MCA and intracranial internal carotid artery (ICA) cerebral blood flow velocity (CBFV) asymmetry, together with a large ICA-to-MCA gradient, were associated with the presence of mismatch. The combined use of 2 TCD parameters (MCA CBFV asymmetry of > or = 30% and ICA-to-MCA gradient > or = 20 cm/sec) had a sensitivity of 75%, specificity of 80%, positive predictive value of 82%, and negative predictive value of 73% at detecting mismatch cases. CONCLUSIONS: Diffusion-perfusion mismatch appears to be associated with interhemispheric asymmetry between MCA and ICA CBFVs, and a large CBFV gradient between the ICA and MCA on the affected side. Prospective studies are required to verify these observations and to determine whether TCD can be used to follow patients with mismatch.     

Correlation between diffusion- and perfusion-weighted MRI and neurological deficit measured by the Scandinavian Stroke Scale and Barthel Index in hyperacute subcortical stroke (< or = 6 hours)

OBJECTIVE: We used combined diffusion-weighted (DWI) and perfusion-weighted (PWI) MRI to characterize hyperacute infarctions within 6 h of symptom onset with special reference to subcortical infarctions, and investigated the relation between perfusion-diffusion mismatch volume and functional outcome. MATERIAL AND METHODS: Twenty-two patients presenting with symptoms of acute stroke underwent DWI and PWI within 6 h of symptom onset, and follow-up MRI 30 days later. Twelve of these had a subcortical infarction on acute DWI. Lesion volumes were measured by acute DWI and PWI as well as chronic T(2)-weighted MRI (T2WI). Clinical severity was measured by the Scandinavian Stroke Scale (SSS) and the Barthel Index (BI). RESULTS: In the 12 patients with subcortical infarctions, PWI and especially DWI correlated strongly with acute and chronic neurological SSS score, as well as with final infarct volume. Furthermore, a hyperacute PWI/DWI mismatch in this subgroup predicted lesion growth. There was a weaker correlation between acute DWI/PWI and neurological score among all 22 patients, and patients with a PWI/DWI mismatch larger than 100 ml had a significantly larger lesion growth and a poorer outcome than patients with a smaller mismatch. CONCLUSIONS: Subcortical infarctions may represent a sizeable subgroup of acute stroke patients. Also subcortical infarctions may have a PWI/DWI mismatch and therefore may respond to neuroprotective/thrombolytic therapy. Hyperacute DWI may reflect the acute clinical status and predict the outcome in patients with subcortical infarction.     

Expanding the window for thrombolytic therapy in acute stroke. The potential role of acute MRI for patient selection.

BACKGROUND: Effective therapy was not available for treatment of acute stroke until 1995, when tissue plasminogen activator (tPA) was shown to improve neurological and functional outcome in stroke patients who were treated within 3 hours of symptom onset. SUMMARY OF REVIEW: Currently, many patients do not qualify for tPA therapy because they present for evaluation beyond 3 hours after stroke onset. Attempts to expand the treatment window to 6 hours, using CT to select patients, have failed. Use of early MR imaging may provide significant advantages over CT for identification of patients who are likely to benefit from thrombolytic therapy because (1) the early perfusion-weighted imaging (PWI) lesion estimates the region of acute dysfunctional brain tissue, whereas the acute diffusion-weighted imaging (DWI) lesion appears to correspond to the core of the early infarction; (2) the mismatch between the acute PWI lesion and the smaller DWI lesion represents potentially salvageable brain tissue (an estimate of the ischemic penumbra); and (3) in patients with a PWI/DWI mismatch, early reperfusion is often associated with substantial clinical improvement and reversal or reduction of DWI lesion growth. CONCLUSIONS: Clinical trials that use new MRI techniques to screen patients may be able to identify a subset of acute stroke patients who are ideal candidates for thrombolytic therapy even beyond 3 hours after stroke onset.     

Pretreatment diffusion- and perfusion-MR lesion volumes have a crucial influence on clinical response to stroke thrombolysis

We hypothesized that pretreatment magnetic resonance imaging (MRI) diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) lesion volumes may have influenced clinical response to thrombolysis in the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET). In 98 patients randomized to intravenous (IV) tissue plasminogen activator (tPA) or placebo 3 to 6 h after stroke onset, we examined increasing acute DWI and PWI lesion volumes (Tmax—with 2-sec delay increments), and increasing PWI/DWI mismatch ratios, on the odds of both excellent (modified Rankin Scale (mRS): 0 to 1) and poor (mRS: 5 to 6) clinical outcome. Patients with very large PWI lesions (most had internal carotid artery occlusion) had increased odds ratio (OR) of poor outcome with IV-tPA (58% versus 25% placebo; OR=4.13, P=0.032 for Tmax +2-sec volume >190 mL). Excellent outcome from tPA treatment was substantially increased in patients with DWI lesions <18 mL (77% versus 18% placebo, OR=15.0, P<0.001). Benefit from tPA was also seen with DWI lesions up to 25 mL (69% versus 29% placebo, OR=5.5, P=0.03), but not for DWI lesions >25 mL. In contrast, increasing mismatch ratios did not influence the odds of excellent outcome with tPA. Clinical responsiveness to IV-tPA, and stroke outcome, depends more on baseline DWI and PWI lesion volumes than the extent of perfusion–diffusion mismatch.     

Diffusion- and perfusion-weighted MRI: influence of severe carotid artery stenosis on the DWI/PWI mismatch in acute stroke

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) have been used increasingly in recent years to evaluate acute stroke in the emergency setting. In the present study, we compared DWI and PWI findings in acute stroke patients with and without severe extracranial internal carotid artery (ICA) disease. METHODS: Twenty-seven patients with nonlacunar ischemic stroke were selected for this analysis. DWI, PWI, and conventional MRI were performed in all patients within 24 hours of symptom onset and after 1 week. To exclude patients with partial or complete reperfusion, we included only patients with a PWI deficit larger than the DWI lesion. Severe ICA disease (>70% stenosis) was present unilaterally in 9 and bilaterally in 2 patients. Acute DWI lesion volume, the size of the acute PWI/DWI mismatch, and final infarct size (on T2-weighted images) were determined. RESULTS: The PWI/DWI mismatch was significantly larger in patients with severe ICA disease than in patients without extracranial carotid stenosis, both when time-to-peak and mean transit time maps (P<0.01) were used to calculate the mismatch. Quantitative analysis of the time-to-peak delay in the mismatch indicated that a relatively smaller fraction of the total mismatch was critically ischemic in patients with carotid stenosis than in those without. Average lesion volume increased less in the stenosis group (P=0.14), despite the larger PWI/DWI mismatch, and final infarct size was smaller in the stenosis group (P<0.05). In the 2 patients with bilateral ICA disease, variable hemodynamic involvement of the contralateral hemisphere was found in addition to the ipsilateral PWI deficit. CONCLUSIONS: In most acute stroke patients with severe ICA stenosis, a considerably smaller fraction of the total PWI/DWI mismatch is at risk than in patients without carotid disease.     

Diffusion- and perfusion-weighted MRI. The DWI/PWI mismatch region in acute stroke.

BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) are relatively new MR techniques increasingly used in acute stroke. During the first hours of stroke evolution, the regions with abnormal perfusion are typically larger than the DWI lesions, and this mismatch region has been suggested to be "tissue at risk." The aim of this study was to evaluate the PWI/DWI mismatch region in acute stroke patients and find parameters indicative of both infarct progression and functional impairment. METHODS: Twenty patients with nonlacunar ischemic stroke were imaged with DWI, PWI, and conventional MRI within 24 hours of symptom onset and after 1 week; in addition, the European Stroke Scale (ESS) score was recorded. With PWI, the volumes of regions with "time-to-peak" (TTP) delays of >/=2, 4, 6, 8, and 10 seconds were measured; these volumes were compared with the acute DWI lesion volumes, final infarct size, and ESS score. RESULTS: In 80% of patients the acute DWI lesion was surrounded by regions with abnormal TTP delays (PWI>DWI lesion). A TTP delay of >/=6 s in the mismatch region was found to be associated with lesion enlargement between the initial and follow-up MRI scans. Lesions increased in 9 of 12 patients (75%) in whom the area with TTP delay >/=6 s was larger than the DWI lesion, but they increased in only 1 of 8 (12.5%) of the remaining patients, in whom the area with a TTP delay >/=6 s was smaller than the DWI lesion. The volume of the regions with TTP delays of >/=4 s correlated better with ESS (r=-0.88, P<0.001) than other PWI (or DWI) volumes, which indicated that a TTP delay of approximately 4 s might be the threshold for functional impairment of brain tissue. CONCLUSIONS: Only patients with severe perfusion deficits in the PWI/DWI mismatch (TTP delays of >/=6 s) are at high risk of lesion enlargement. Functionally, more moderate perfusion deficits (TTP delays >/=4 and <6 s) appear to also contribute to the acute clinical deficit.     

Early motor evoked potentials in acute stroke: adjunctive measure to MRI for assessment of prognosis in acute stroke within 6 hours

BACKGROUND: In acute stroke, a magnetic resonance (MR) perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) mismatch (PWI>DWI mismatch) may indicate tissue at risk for infarction and poor prognosis. However, different to early enthusiasm about this surrogate marker, its validity has shown several drawbacks in individual patients. Rather than relying on imaging, we evaluated motor evoked potentials (MEP) as a measure of cerebral function in the acute stroke setting. METHODS: Thirteen patients with acute hemiparetic stroke underwent time to peak PWI and DWI within 6 h after onset as well as recordings of early MEP of first dorsal interosseous muscles. Outcome was assessed by the Unified Neurological Stroke Scale and Barthel Index at day 42. RESULTS: Of 8 patients with PWI>DWI mismatch, 4 patients with normal MEP had a good clinical outcome and 4 patients with absent or pathological MEP had an unfavourable outcome (p < 0.05, Fisher's exact test). In all patients without PWI>DWI mismatch, MEP findings predicted clinical outcome. Normal MEP at day 0--but not PWI/DWI findings--significantly correlated with a good clinical outcome. CONCLUSIONS: Early MEP recordings in acute stroke patients provide valid prognostic information; they may become more useful for specific treatment decisions than presently available MRI surrogate parameters.     

Clinical and radiological correlates of reduced cerebral blood flow measured using magnetic resonance imaging

BACKGROUND: 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. OBJECTIVES: 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. DESIGN: Case series. SETTING: Referral center. METHODS: 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. RESULTS: 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). CONCLUSION: 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.     

Combined diffusion and perfusion MRI with correlation to single-photon emission CT in acute ischemic stroke. Ischemic penumbra predicts infarct growth.

BACKGROUND AND PURPOSE: More effective imaging methods are needed to overcome the limitations of CT in the investigation of treatments for acute ischemic stroke. Diffusion-weighted MRI (DWI) is sensitive in detecting infarcted brain tissue, whereas perfusion-weighted MRI (PWI) can detect brain perfusion in the same imaging session. Combining these methods may help in identifying the ischemic penumbra, which is an important concept in the hemodynamics of acute stroke. The purpose of this study was to determine whether combined DWI and PWI in acute (<24 hours) ischemic stroke can predict infarct growth and final size. METHODS: Forty-six patients with acute ischemic stroke underwent DWI and PWI on days 1, 2, and 8. No patient received thrombolysis. Twenty-three patients underwent single-photon emission CT in the acute phase. Lesion volumes were measured from DWI, SPECT, and maps of relative cerebral blood flow calculated from PWI. RESULTS: The mean volume of infarcted tissue detected by DWI increased from 46.1 to 75.6 cm(3) between days 1 and 2 (P<0.001; n=46) and to 78.5 cm(3) after 1 week (P<0.001; n=42). The perfusion-diffusion mismatch correlated with infarct growth (r=0. 699, P<0.001). The volume of hypoperfusion on the initial PWI correlated with final infarct size (r=0.827, P<0.001). The hypoperfusion volumes detected by PWI and SPECT correlated significantly (r=0.824, P<0.001). CONCLUSIONS: Combined DWI and PWI can predict infarct enlargement in acute stroke. PWI can detect hypoperfused brain tissue in good agreement with SPECT in acute stroke.     

Monitoring intravenous recombinant tissue plasminogen activator thrombolysis for acute ischemic stroke with diffusion and perfusion MRI

BACKGROUND AND PURPOSE: Intravenous recombinant tissue plasminogen activator (rtPA) administration is an effective therapy for ischemic stroke when initiated within 3 hours and possibly up to 6 hours after symptom onset. To improve patient selection, a fast diagnostic tool that allows reliable diagnosis of hemorrhage and ischemia, vessel status, and tissue at risk at an early stage may be useful. We studied the feasibility of stroke MRI for the initial evaluation and follow-up monitoring of patients undergoing intravenous thrombolysis. METHODS: Stroke MRI (diffusion- and perfusion-weighted imaging [DWI and PWI, respectively], magnetic resonance angiography, and T2-weighted imaging) was performed before, during, or after thrombolysis and on days 2 and 5. We assessed clinical scores (National Institutes of Health Stroke Scale [NIHSS], Scandinavian Stroke Scale [SSS], Barthel Index, and Rankin scale) at days 1, 2, 5, 30, and 90. Furthermore, we performed volumetric analysis of infarct volumes on days 1, 2, and 5 as shown in PWI, DWI, and T2-weighted imaging. RESULTS: Twenty-four patients received rtPA within a mean time interval after symptom onset of 3.27 hours and stroke MRI of 3.43 hours. Vessel occlusion was present in 20 of 24 patients; 11 vessels recanalized (group 1), and 9 did not (group 2). The baseline PWI lesion volume was significantly larger (P=0.008) than outcome lesion size in group 1, whereas baseline DWI lesion volume was significantly smaller (P=0.008) than final infarct size in group 2. Intergroup outcome differed significantly for all scores at days 30 and 90 (all P<0.01). Intragroup differences were significant in group 1 for change in SSS and NIHSS between day 1 and day 30 (P=0.003) and for SSS only between day 1 and day 90 (P=0.004). CONCLUSIONS: Stroke MRI provides comprehensive prognostically relevant information regarding the brain in hyperacute stroke. Stroke MRI may be used as a single imaging tool in acute stroke to identify and monitor candidates for thrombolysis. It is proposed that stroke MRI is safe, reliable, and cost effective; however, our data do not prove this assumption. Early recanalization achieved by thrombolysis can save tissue at risk if present and may result in significantly smaller infarcts and a significantly better outcome.     

Association between the perfusion/diffusion and diffusion/FLAIR mismatch: data from the AXIS2 trial

The perfusion-/diffusion-weighted imaging (PWI/DWI) mismatch and the diffusion/fluid attenuated inversion recovery (DWI/FLAIR) mismatch are magnetic resonance imaging (MRI) markers of evolving brain ischemia. We examined whether the DWI/FLAIR mismatch was independently associated with the PWI/DWI mismatch. Furthermore, we determined whether the presence of the DWI/FLAIR mismatch in patients with the PWI/DWI mismatch would provide additional information regarding last seen normal time (LTM). We used data from the ‘AX200 for ischemic stroke'' trial (AXIS 2 study {"type":"clinical-trial","attrs":{"text":"NCT00927836","term_id":"NCT00927836"}}NCT00927836). We studied the association between the presence of the DWI/FLAIR and PWI/DWI mismatch, baseline National Institute of Health Stroke Scale (NIHSS), age, ischemic-core volume, gender, intravenous (IV) tissue plasminogen activator (tPA), and perfusion-mismatch volume in univariate analysis. Significant variables (P<0.05) were added into the final multivariate model. We analyzed 197 patients. Seventy-two (37%) had both the PWI/DWI and the DWI/FLAIR mismatch. Patients with the double mismatch pattern had a shorter LTM than patients with the PWI/DWI mismatch alone (Median difference 90 minutes, P<0.01). Multivariate analysis confirmed the independent association between the two mismatch patterns (odds ratio (OR) 2.6, 95% confidence interval (CI) 1.2 to 5.4). Our study implies that the DWI/FLAIR mismatch and PWI/DWI mismatch are strongly associated, independent from LTM. Furthermore, in the presence of the PWI/DWI mismatch, the DWI/FLAIR pattern indicates a shorter LTM. This could have implications in selecting patients for reperfusion therapy.     

Relationship between severity of MR perfusion deficit and DWI lesion evolution

OBJECTIVE: To assess whether a quantitative analysis of the severity of the early perfusion deficit on MRI in acute ischemic stroke predicts the evolution of the perfusion/diffusion mismatch and to determine thresholds of hypoperfusion that can distinguish between critical and noncritical hypoperfusion. METHODS: Patients with acute ischemic stroke were studied in whom perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI MRI) were performed within 7 hours of symptom onset and again after 4 to 7 days. Patients with early important decreases in points on the NIH Stroke Scale were excluded. Maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) were created. These hemodynamic parameters were correlated with the degree of recruitment of the baseline PWI lesion by the DWI lesion. RESULTS: Twelve patients had an initial PWI > DWI mismatch of >20%. A linear relationship was observed between the initial MTT and the degree of recruitment of the baseline PWI lesion by the DWI lesion at follow-up (R(2) = 0.9, p < 0.001). Higher CBV values were associated with higher degrees of recruitment (rho = 0.732, p < 0.007). The volume of MTT of >4 (R(2) = 0.86, p < 0.001) or >6 seconds (R(2) = 0.85, p < 0.001) predicted final infarct size. CONCLUSION: Among patients who have had an acute stroke with PWI > DWI, who do not have dramatic early clinical improvement, the degree of expansion of the initial DWI lesion correlates with the severity of the initial perfusion deficit as measured by the mean transit time and the cerebral blood volume.     

Cerebral magnetic resonance imaging within 6 hours of stroke onset: inter- and intra-observer reproducibility

BACKGROUND: Magnetic resonance imaging (MRI) provides valuable pathophysiological information during the very first hours of cerebral ischemia. However, the reliability of prime-time MRI in the setting of emergency care remains unknown. AIM: To evaluate the reproducibility between and within observers of the assessment of MRI scans in stroke patients. METHOD: We performed a MRI scan within 6 h of stroke onset, with time-of-flight (TOF), T2* gradient echo, FLAIR, diffusion- (DWI) and perfusion- (PWI) weighted images, in 17 consecutive patients. Four observers, blinded to the clinical history, separately performed a visual assessment of all scans, and repeated the assessment 2-8 days later. Two neuroradiologists made volumetric measures of diffusion and perfusion abnormalities using a semi-automatic technique 2 weeks after the 2nd visual assessment. We evaluated: (i) in the whole set of MRI scans, the quality of scans and their ability to identify primary hemorrhages on T2* gradient echo sequences; (ii) in patients with acute cerebral ischemia only, the inter- and intra-observer agreement for the presence of arterial occlusion and cerebral abnormalities on TOF sequences, and (iii) on DWI and PWI sequences, the relationship between visual and automatic assessments for the presence of a mismatch (defined as the difference between the perfusion and diffusion abnormalities) of >20%. Statistics used the kappa (kappa) method. RESULTS: The median delay between clinical onset and MRI was 285 min. Two patients had primary cerebral hemorrhages, 1 a post-ictal deficit, and 14 cerebral ischemia. The quality of the scans was judged as appropriate for all scans in all sequences except for FLAIR. All observers identified the 2 patients with hemorrhages. The inter- and intra-observer reliability was substantial to excellent (kappa values ranging from 0.63 to 1.00) for all sequences. The agreement between visual and automatic assessments for the presence of a mismatch of >20% was excellent in all observers. CONCLUSION: The visual assessment of T2* gradient echo, TOF, diffusion and perfusion sequences at the acute stage of stroke is reproducible between and within observers. The visual assessment is as good as the volumetric assessment to detect a mismatch of >20%.     

Advances in penumbra imaging with MR

The concept of the ischaemic penumbra as critically hypoperfused and functionally impaired, but potentially viable brain, was introduced over 25 years ago. Recent studies have used a combination of perfusion-weighted magnetic resonance imaging (PWI) and diffusion-weighted imaging (DWI) to delineate the putative penumbra. PWI provides semiquantitative cerebral blood flow imaging and DWI is an index of the largely irreversible ischaemic core. PWI > DWI mismatch is an operational definition of the penumbra that was introduced in the late 1990s. This definition has been modified in recent years with the recognition that the PWI boundary includes a region of benign oligaemia and that a portion of the DWI core is potentially salvageable with rapid reperfusion. An MRI penumbral signature is present in the majority of patients within 6 h of stroke onset, often but not invariably associated with proximal arterial occlusion on magnetic resonance angiography, and is strictly time dependent. It has been postulated that penumbral imaging using MRI can provide a physiological 'tissue clock' and be used to predict benefit from thrombolytic therapy beyond the established 3-hour window. This has been suggested by pilot studies, but confirmation will rely on ongoing, prospective, randomized trials. The presence and extent of the penumbra may also predict the opportunity for tissue salvage with neuroprotection strategies. DWI and PWI parameters are being used in proof-of-principle stroke trials. Such trials can be performed with 100-200 patients randomized between treated and control groups and provide a biological signal of efficacy with only 10% of the sample size required for a Phase III study.     

Longitudinal magnetic resonance imaging study of perfusion and diffusion in stroke: evolution of lesion volume and correlation with clinical outcome.

A prospective longitudinal diffusion-weighted and perfusion-weighted magnetic resonance imaging (DWI/PWI) study of stroke patients (n = 21) at five distinct time points was performed to evaluate lesion evolution and to assess whether DWI and PWI can accurately and objectively demonstrate the degree of ischemia-induced deficits within hours after stroke onset. Patients were scanned first within 7 hours of symptom onset and then subsequently at 3 to 6 hours, 24 to 36 hours, 5 to 7 days, and 30 days after the initial scan. Lesion evolution was dynamic during the first month after stroke. Most patients (18 of 19, 95%) showed increased lesion volume over the first week and then decreased at 1 month relative to 1 week (12 of 14, 86%). Overall, lesion growth appeared to depend on the degree of mismatch between diffusion and perfusion at the initial scan. Abnormal volumes on the acute DWI and PWI (<7 hours) correlated well with initial National Institutes of Health (NIH) stroke scale scores, outcome NIH stroke scale scores, and final lesion volume. DWI and PWI can provide an early measure of metabolic and hemodynamic insufficiency, and thus can improve our understanding of the evolution and outcome after acute ischemic stroke.     

Advantages of adding diffusion-weighted magnetic resonance imaging to conventional magnetic resonance imaging for evaluating acute stroke

BACKGROUND: Accurate localization of acute ischemic lesions in patients with an acute stroke may aid in understanding the etiology of their stroke and may improve the management of these patients. OBJECTIVE: To determine the yield of adding diffusion-weighted magnetic resonance imaging (DWI) to a conventional magnetic resonance imaging (MRI) protocol for acute stroke. DESIGN: A prospective cohort study. SETTING: A referral center. PATIENTS AND METHODS: Fifty-two patients with a clinical diagnosis of acute stroke who presented within 48 hours after symptom onset were included. An MRI scan was obtained within 48 hours after symptom onset. A neuroradiologist (A.M.N.) and a stroke neurologist (G.W.A.) independently identified suspected acute ischemic lesions on MRI sequences in the following order: (1) T2-weighted and proton density-weighted images, (2) fluid-attenuated inversion recovery images, and (3) diffusion-weighted images and apparent diffusion coefficient maps. MAIN OUTCOME MEASURES: Diagnostic yield and interrater reliability for the identification of acute lesions, and confidence and conspicuity ratings of acute lesions for different MRI sequences. RESULTS: Conventional MRI correctly identified at least one acute lesion in 71% (34/48) to 80% (39/49) of patients who had an acute stroke; with the addition of DWI, this percentage increased to 94% (46/49) (P<.001). Conventional MRI showed only moderate sensitivity (50%-60%) and specificity (49%-69%) compared with a "criterion standard." Based on the diffusion-weighted sequence, interrater reliability for identifying acute lesions was moderate for conventional MRI (kappa = 0.5-0.6) and good for DWI (kappa = 0.8). The observers' confidence with which lesions were rated as acute and the lesion conspicuity was significantly (P<.01) higher for DWI than for conventional MRI. CONCLUSION: During the first 48 hours after symptom onset, the addition of DWI to conventional MRI improves the accuracy of identifying acute ischemic brain lesions in patients who experienced a stroke.     

Local mild hypothermia with thrombolysis for acute ischemic stroke within a 6-h window

Objective

To determine the safety and efficacy of combined local mild hypothermia and IV rtPA in treating acute ischemic stroke (AIS) patients with MRI perfusion- and diffusion-weighted imaging (PWI/DWI) mismatch within a 6-h stroke window.

Methods

AIS patients within 6 h of a minimum 20% PWI/DWI MRI mismatch were randomly assigned to 3 groups: local mild hypothermia with IV rtPA (Group A); IV rtPA (Group B); or conventional anti-platelet aggregation (Group C). Mortality and National Institutes of Health Stroke Scale (NIHSS) and the modified Rankin Scale (mRS) score and Barthel Index (BI) were used in evaluation.

Results

There were significant differences in NIHSS 24 h after treatment among the three groups (P < 0.001). Based on mRS and BI, more patients in Groups A and B showed favorable outcomes than patients in Group C (P = 0.017 and P = 0.009, respectively); however, there were no significant efficacy differences between Groups A and B. The incidence of symptomatic ICH and the mortality rates within 90 days in the 3 groups were similar. In addition, there were no significant differences in NIHSS improvement at 24 h and favorable outcomes 90 days after IV rtPA treatment between patients within 3 h and 3–6 h from symptom onset.

Conclusions

There was no benefit of combined local hypothermia/IV rtPA treatment compared to IV rtPA alone. PWI/DWI mismatching on MRI can be a selection criteria for IV rtPA treatment within a 6-h window.     

Prediction of hemorrhagic transformation following acute stroke: role of diffusion- and perfusion-weighted magnetic resonance imaging

BACKGROUND: Acute diffusion-weighted (DWI) and perfusion-weighted (PWI) magnetic resonance imaging (MRI) findings may correlate with secondary hemorrhagic transformation (HT) risk in patients with stroke. This information could be of value, particularly in individuals being considered for thrombolytic therapy. OBJECTIVE: To determine the relationship between DWI and PWI findings and the risk of secondary HT in patients with acute stroke. DESIGN: Retrospective case series. SETTING: Academic medical center. PATIENTS: Twenty-seven patients with acute stroke capable of being evaluated with DWI/PWI 8 hours or less after symptom onset. MAIN OUTCOME MEASURES: Apparent diffusion coefficient values, perfusion delay measurements, and subsequent MRI or computed tomographic scans detected HT. RESULTS: The mean +/- SD apparent diffusion coefficient of ischemic regions that experienced HT was significantly lower than the overall mean +/- SD apparent diffusion coefficient of all ischemic areas analyzed (0.510 +/- 0.140 x 10(-3) mm(2)/s vs 623 +/- 0.113 x 10(-3) mm(2)/s; P =.004). This difference remained significant when comparing the HT-destined ischemic areas with the non-HT-destined areas within the same ischemic lesion (P =.02). Patients receiving recombinant tissue-type plasminogen activator (rt-PA) experienced HT significantly earlier than patients not receiving rt-PA (P =.002). Moreover, a persistent perfusion deficit in the area of subsequent hemorrhage at 3 to 6 hours after the initial MRI scan was identified in significantly more patients who experienced HT than in those who did not (83% vs 30%; P =.03). CONCLUSION: Both DWI and PWI scans detect abnormalities that are associated with HT. These findings support a role for MRI in identifying patients who are at increased risk for secondary HT following acute ischemic stroke.     

弥散加权和灌注加权在缺血性中风的应用

目的　观察缺血性中风早期病灶的部位及程度,评价病灶的微循环状态。方法　ＤＷＩ和ＰＷＩ是一 种新的磁共振成像技术,ＤＷＩ通过测定水分子的布朗运动而获得;ＰＷＩ通过静脉团注造影剂而得到。结果　ＤＷＩ 能明确早期急性缺血性病灶的部位,ＰＷＩ证实病灶区微循环不良的范围。结论　有助于对缺血性中风患者治疗方 法的选择,并提供了一种高度敏感的评价治疗效果的方法。