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.     

Early diagnosis of hemorrhagic transformation: diffusion/perfusion-weighted MRI versus CT scan

Standard magnetic resonance imaging (MRI) techniques failed to image adequately acute hemorrhagic transformation (HT). Therefore, computed tomography (CT) is still needed to exclude intracerebral hemorrhage. New MRI techniques such as diffusion- and perfusion-weighted imaging (DWI and PWI) may improve the early detection of HT. The utility of this approach requires a direct comparison of the sensitivity of CT with these MRI techniques. METHODS: Nine patients experienced an acute carotid artery territory ischemic stroke diagnosed on a first CT performed 3.8 +/- 2 h after the onset of stroke. They underwent a second CT 12 +/- 4 h after the onset of stroke, followed 35 +/- 10 min later by an MRI protocol including: (1) an axial isotropic DWI SE echo-planar imaging (EPI) sequence; (2) time of flight MR angiography (TOF MRA); (3) PWI with an axial T(2)*-weighted gradient echo EPI sequence using 20 ml gadolinium contrast agent (Gd-DTPA); HT was characterized on DWI SE EPI as a heterogeneous area of signal loss within the ischemic area; (4) at day 7, CT was also performed in all patients who had an early suspicion of bleeding according to MRI. RESULTS: An HT was detected exclusively with CT in 1 out of 9 patients, while an MRI pattern of HT was found in 6 out of 9 patients. In 5 of these 6 patients, the CT scan did not show an obvious pattern of HT. Day 7 CT confirmed HT in all patients who had early suspicion of bleeding according to DWI criteria. CONCLUSION: This study suggests that new MRI techniques may allow an early detection of HT, thus improving the management of stroke.     

Etiology of Perfusion-Diffusion Magnetic Resonance Imaging Mismatch Patterns

BACKGROUND AND PURPOSE: Diffusion-and perfusion-weighted magnetic resonance imaging (DWI and PWI) are useful tools for the assessment of brain ischemia. Discrepancies between the extent of DWI and PWI abnormalities are thought to depend pre dominantly on time from symptom onset to magnetic resonance imaging (MRI) examination. However, underlying ischemic stroke etiology can also be important. A mismatch may indicate the presence of tissue at risk for infarction, whereas the relevance of other DWI/PWI patterns is uncertain. The authors therefore investigated the etiology of brain ischemia in patients with different DWI/PWI patterns. METHODS: Retrospective study of 130 patients with acute brain ischemia and detailed stroke workup, including MRI within a week after symptom onset (40 +/- 39 hours). Patients were divided into the following groups: mis-match (PWI > DWI), reverse mismatch (DWI > PWI), and match (<25% difference between PWI and DWI). RESULTS: Mismatch occurred in 49% of patients, whereas 22% had reverse mis-match and 29% matched lesions. Time from symptom onset to MRI examination was similar between the 3 groups. Largeartery atherosclerosis increased by almost 4-fold the odds of mismatch (odds ratio: 3.89, 95% confidence interval: 1.72-8.78; P < .001), whereas patients with reverse mismatch were likely to have cryptogenic stroke. Patients with matched lesions were similarly distributed among different stroke subtypes. CONCLUSIONS: Ischemic stroke etiology appears to influence the development of specific DWI/PWI patterns. Prospective studies are needed to confirm these observations.     

Thrombolysis with reteplase, an unglycosylated plasminogen activator variant, in experimental embolic stroke.

We incorporated diffusion-weighted magnetic resonance imaging (MRI) (DWI) and perfusion-weighted MRI (PWI) to evaluate the efficacy of thrombolysis in experimental embolic stroke using a plasminogen activator, reteplase. Reteplase (rPA) is an unglycosylated plasminogen activator with enhanced fibrinolytic potency. Right internal carotid arteries of 34 rabbits were embolized using aged heterologous thrombi. Baseline DWI and PWI scans 0.5 hours after embolization confirmed successful embolization among 32. Intravenous treatment with rPA (n=11; 1 mg/kg bolus), recombinant tissue plasminogen activator (rt-PA) (n=11; 6 mg/kg bolus over 1 hour), or placebo (n=10) commenced 1 hour after stroke induction. MRIs were performed at 1.75, 3, and 5 hours after embolization. Six hours after embolization, brains were harvested and examined for hemorrhage. Posttreatment areas of diffusion abnormality and perfusion delay were graded using both a semiquantitative scale and percent areas expressed as a ratio of the baseline values. Improved perfusion was seen among the rt-PA, and rPA-treated groups compared with placebo, using a semiquantitative scale (P<.01 rt-PA v controls, P<.05, rPA v controls). DWI scans, however, were not improved with thrombolysis. Cerebral hemorrhage was not increased with thrombolytic treatment, although the incidence of wound site hemorrhage was higher with either rPA or rt-PA. One fatal systemic hemorrhage was observed in each of the thrombolytic-treated groups. Cerebral perfusion was equally improved with either rt-PA or rPA without causing excess cerebral hemorrhage. An advantage of rPA is single-bolus dosing rather than continuous infusion. Use of rPA for stroke treatment should be further explored.     

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.     

Influence of pretreatment MRI parameters on clinical outcome, recanalization and infarct size in 49 stroke patients treated by intravenous tissue plasminogen activator

We hypothesized that pretreatment magnetic resonance imaging (MRI) parameters might predict clinical outcome, recanalization and final infarct size in acute ischemic stroke patients treated by intravenous recombinant tissue plasminogen activator (rt-PA). MRI was performed prior to thrombolysis and at day 1 with the following sequences: magnetic resonance angiography (MRA), T2*-gradient echo (GE) imaging, diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI). Final infarct size was assessed at day 60 by T2-weighted imaging (T2-WI). The National Institutes of Health Stroke Scale (NIHSS) score was assessed prior to rt-PA therapy and the modified Rankin Scale (m-RS) score was assessed at day 60. A poor outcome was defined as a day 60 m-RS score >2. Univariate and multivariate logistic regression analyses were used to identify the predictors of clinical outcome, recanalization and infarct size. Forty-nine patients fulfilled the inclusion criteria. Baseline NIHSS score was the best independent indicator of clinical outcome (p=0.002). A worse clinical outcome was observed in patients with tandem internal carotid artery (ICA)+middle cerebral artery (MCA) occlusion versus other sites of arterial occlusion (p=0.009), and in patients with larger pretreatment PWI (p=0.001) and DWI (p=0.01) lesion volumes. Two factors predict a low rate of recanalization: a proximal site of arterial occlusion (p=0.02) and a delayed time to peak (TTP) on pretreatment PWI (p=0.05). The final infarct size was correlated with pretreatment DWI lesion volume (p=0.025). Recanalization was associated with a lower final infarct size (p=0.003). In conclusion, a severe baseline NIHSS score, a critical level of pretreatment DWI/PWI parameters and a proximal site of occlusion are predictive of a worse outcome after IV rt-PA for acute ischemic stroke.     

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.     

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.     

Evaluation of early reperfusion and i.v. tPA therapy using diffusion- and perfusion-weighted MRI.

OBJECTIVE: To characterize the effects of recombinant tissue plasminogen activator (rt-PA) therapy and early reperfusion on diffusion-weighted (DWI) and perfusion-weighted imaging (PWI) changes observed following acute ischemic injury. METHODS: Twelve patients were evaluated prospectively using echo planar DWI and bolus tracking PWI. Six patients received i.v. rt-PA 0.9 mg/kg and were compared with six patients who did not. Patients receiving rt-PA were initially imaged (T1) 3 to 5 hours postictus (mean, 4 hours 20 minutes) whereas those not treated with tissue plasminogen activator (tPA) were imaged 4 to 7 hours postictus (mean, 5 hours, 25 minutes). Follow-up imaging was performed 3 to 6 hours (T2), 24 to 36 hours (T3), 5 to 7 days (T4), and 30 days (T5) after the first scan in all patients. Lesion volumes were measured on both DWI and time-to-peak maps constructed from PW images. RESULTS: PWI was performed successfully at T1 and T3 in 11 of 12 patients. In the group that received i.v. tPA, initial PWI volumes were less than DWI volumes in five of six patients (83%), whereas only one of five patients (20%) not receiving tPA had PWI < DWI volume (p = 0.08). PWI normalized by 24 to 36 hours (T3) in 6 of 11 patients (early reperfusers), with 5 of 6 of these early reperfusers having received tPA. The aggregate apparent diffusion coefficient (ADC) values for the early reperfusers were consistently higher at T2 (p = 0.04), T3 (p = 0.002), and T4 (p = 0.0005). Five of six patients with early reperfusion demonstrated regions of elevated ADC within the ischemic zone (mean ipsilateral ADC/contralateral ADC, 1.46 +/- 0.19) by 24 to 36 hours, whereas none of the nonearly reperfusers showed these regions of elevated ADC (p = 0.015). CONCLUSION: Early reperfusion is seen more frequently with i.v. tPA therapy. In addition, the study showed that ADC may undergo early increases that are tied closely to reperfusion, and marked ADC heterogeneity may exist within the same lesion. Early reperfusion is seen more frequently with i.v. tPA therapy.     

Seizure at stroke onset: should it be an absolute contraindication to thrombolysis?

BACKGROUND: Current guidelines for the treatment of acute ischemic stroke exclude patients with seizure at stroke onset from consideration for thrombolytic therapy. It may be difficult to differentiate an ischemic stroke from postictal Todd's paralysis by clinical examination and noncontrast CT scan. Magnetic resonance imaging (MRI) with diffusion- (DWI) and perfusion-weighted images (PWI) and angiography (MRA) can be used to confirm the diagnosis of an acute ischemic process in the presence of concurrent seizures. METHODS: A case report of a patient who presented with seizures, in whom the combination of DWI/PWI MRI and MRA confirmed the diagnosis of an embolic ischemic stroke. The patient was treated with intravenous recombinant tissue plasminogen activator with clinical and radiological improvement. CONCLUSIONS: Treatment decisions with regard to thrombolysis in acute stroke patients should be based on parameters of cerebral perfusion, assessment of collateral blood flow and presence of potentially salvageable tissue. Modern neuroimaging techniques that can rapidly assess these variables, such as DWI/PWI MRI and MRA, can improve the current selection of patients who are likely to benefit from thrombolysis and extend its benefit to patients who would otherwise be excluded, such as those with seizures at stroke onset.     

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.     

Diffusion-weighted and perfusion-weighted magnetic resonance imaging to monitor acute intra-arterial thrombolysis

Diffusion-weighted and perfusion-weighted magnetic resonance imaging (DWI, PWI) are useful in detecting early cerebral ischemic lesions. Intra-arterial thrombolysis is an effective treatment for some patients with acute thromboembolic occlusion. We evaluated the efficacy of acute thrombolytic therapy by using DWI and PWI in 3 patients who presented with internal carotid artery or middle cerebral artery occlusion. On the initial magnetic resonance imaging scans, the abnormal areas shown by PWI were bigger than those shown by DWI. All patients received thrombolytic therapy within 6 hours after stroke onset. In 1 patient, the hyperintensity area detected by initial DWI scanning diminished after thrombolysis. DWI and PWI may be useful to monitor the effectiveness of intra-arterial thrombolysis.     

弥散成像和血流灌注成像磁共振诊断急性缺血性脑血管病的意义

目的评价弥散成像（DWI）、血流灌注成像（PWI）磁共振对急性缺血性脑血管病的诊断价值。方法用DWI、PWI诊断急性脑缺血,并与常规MRI结果比较。结果经MRI检查证实的急性缺血性脑血管病患者共22例。其中发病后90分钟至6小时检查者11例,其CT及常规MRI未见异常,3例短暂性脑缺血发作（TIA）患者的DWI、PWI正常;其余8例脑梗死患者经DWI、PWI检查,均发现相对应的病灶,且6例灌注减低体积（PWIv）＞弥散异常体积（DWIv）,2例PWIv＝DWIv。起病在6－12小时5例,4例行PWI检查,3例PWIv＞DWIv,1例PWIv＝DWIv。起病在12－48小时6例,2例行PWI检查,PWIv＝DWIv。8例陈旧病灶在DWI上表现为低信号,所有新病灶在DWI上均为高信号。结论DWI、PWI可超早期诊断脑梗死,并可帮助了解缺血半暗带。T2加权像和DWI结合可以鉴别新旧梗死灶。     

Intra-arterial rtPA treatment of stroke assessed by diffusion- and perfusion-weighted MRI

BACKGROUND: Diffusion-weighted MRI (DWI) and perfusion-weighted MRI (PWI) are new techniques that can be used for the evaluation of acute ischemic stroke. However, their potential role in the management of patients treated with recombinant tissue plasminogen activator (rtPA) has yet to be determined. CASE DESCRIPTION: The authors present the case of a 73-year-old man who was treated with intra-arterial rtPA, and they compare findings on DWI and PWI scans with angiography. PWI revealed decreased cerebral perfusion corresponding to an area that was not successfully recanalized, but revealed no abnormality in regions in which blood flow was restored. DWI was unremarkable in the region that was reperfused early (3 hours) but revealed hyperintensity in an area that was reperfused 3. 5 hours after symptom onset and in the area that was not reperfused. CONCLUSIONS: Findings on PWI correlated well with angiography, and DWI detected injured tissue in the hyperacute stage, whereas conventional MRI findings were negative. This suggests that these techniques may be useful to noninvasively evaluate the success of thrombolytic 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.     

急性缺血性脑卒中rt-PA静脉溶栓后出血性转化的特殊类型

目的溶栓后出血性转化(hemorrhagic transformation,HT)是重组组织型纤维蛋白溶酶原激活剂(rt-PA)治疗急性缺血性脑卒中的一个重要安全指标。HT有不同的亚型,而不同亚型的预后也不尽相同。我们对急性缺血性脑卒中患者rt-PA静脉溶栓后出现的特殊型HT进行分析。方法对发病3zh内的98例缺血性卒中患者用rt-PA(剂量0．6 mg/kg,最大剂量5 0 mg)进行静脉溶栓治疗,溶栓前后行头颅CT、MRI或数字减影血管造影(DSA)检查判断是否有HT,并判定这种HT与责任病灶的关系。结果溶栓后经CT或MRI检查发现4种特殊的远端HT类型,1例发生蛛网膜下腔出血(SAH),1例梗死部位的对侧出现明显占位效应的脑实质出血,1例出现梗死灶对侧的侧脑室出血,1例出现梗死部位对侧的腔隙性出血。这4例患者所引起的4类HT在临床上均为无症状,预后好。结论对急性缺血性脑卒中的溶栓治疗要坚持动态观和平衡观,对症状性出血性转化的诊断要慎重,充分考虑HT的分型和程度,从而正确判断HT对预后的影响。     

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.     

Delayed rt-PA treatment in a rat embolic stroke model: diagnosis and prognosis of ischemic injury and hemorrhagic transformation with magnetic resonance imaging.

The authors characterized effects of late recombinant tissue plasminogen activator (rt-PA) administration in a rat embolic stroke model with magnetic resonance imaging (MRI), to assess potential MRI correlates, or predictors, or both, of rt-PA-induced hemorrhage. Diffusion-, perfusion-, and postcontrast T1-weighted MRI were performed between 4 and 9 hours and at 24 hours after embolic stroke in spontaneously hypertensive rats. Treatment with either rt-PA or saline was started 6 hours after stroke. A spectrophotometric hemoglobin assay quantified hemorrhage severity. Before treatment, relative cerebral blood flow index (rCBFi) and apparent diffusion coefficient (ADC) in the ischemic territory were 30% +/- 23% and 60% +/- 5% (of contralateral), respectively, which increased to 45% +/- 39% and 68% +/- 4% 2 hours after rt-PA. After 24 hours, rCBFi and ADC were 27% +/- 27% and 59 +/- 5%. Hemorrhage volume after 24 hours was significantly greater in rt-PA-treated animals than in controls (8.7 +/- 3.7 microL vs. 5.1 +/- 2.4 microL, P < 0.05). Before rt-PA administration, clear postcontrast T1-weighted signal intensity enhancement was evident in areas of subsequent bleeding. These areas had lower rCBFi levels than regions without hemorrhage (23% +/- 22% vs. 36% +/- 29%, P < 0.05). In conclusion, late thrombolytic therapy does not necessarily lead to successful reperfusion. Hemorrhage emerged in areas with relatively low perfusion levels and early blood-brain barrier damage. Magnetic resonance imaging may be useful for quantifying effects of thrombolytic therapy and predicting risks of hemorrhagic transformation.     

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.     

表观弥散系数对确定急性缺血性卒中缺血半暗带的潜在价值

目的 探讨表观弥散系数（apparent diffusion coefficient,ADC）对确定急性缺血性卒中缺血半暗带的潜在价值。 方法 选择发病9 h内完成多模式磁共振成像（magnetic resonance imaging,MRI）检查的前循环急性缺血性卒中患者49例。应用自制软件进行灌注加权像（perfusion-weighted imaging,PWI）和弥散加权像（diffusion-weighted imaging,DWI）异常区域的体积测量。缺血半暗带以PWI/DWI错配表示。同时采用全自动图像分析系统,以DWI图像计算得到的ADC图作为输入数据,来判断缺血半暗带的存在（以下简称为ADC方法）,然后比较这两种方法在判断缺血半暗带方面的差异。 结果 入选的49例患者中,存在PWI/DWI错配者为43例,符合ADC方法判断缺血半暗带标准者有41例。这两种方法在判断是否存在缺血半暗带的结果中有41例相符,对判断缺血半暗带的差异无统计学意义（P>0.05）。ADC方法判断缺血半暗带的敏感度为88.4%、特异度为50.0%。 结论 由于不需做PWI检查,ADC方法对确定缺血半暗带具有潜在的临床实用价值,有可能成为一种简便易行的确定缺血半暗带的方法。