Sex and Stroke in Thrombolyzed Patients and Controls

Background and Purpose—

We hypothesized that any sex-related difference in outcome poststroke is explained by other prognostic factors and that the response to intravenous recombinant tissue-type plasminogen activator (r-tPA) is equal in males and females after adjustment for such factors.

Methods—

We accessed an independent collection of randomized clinical trials—the VISTA (Virtual International Stroke Trials Archive). Data were preprocessed by selecting complete cases (n=8028) and matching females to males (coarsened exact matching, n=4575, 24.3% r-tPA). Outcome was assessed by the 7-point modified Rankin Scale (mRS) measured at 90 days after ischemic stroke. Relationship among variables was estimated by adjusted regression analysis.

Results—

In nonthrombolyzed patients, ordinal analysis of mRS adjusting for stroke- and sex-related prognostic factors suggested comparable outcomes for females and males (odds ratio, 0.96; 95% confidence interval, 0.85–1.06). Females responded comparably to r-tPA as did males, irrespective of the outcome definition of mRS (ordinal: P Interaction =0.46, relative excess risk because of interaction=0). The number needed to treat was 6.8 and 11.2 for 1 female to achieve mRS score of 0 to 2 and 0 to 1, which was highly congruent with males. Analysis for a nonlinear variation of age-by-sex revealed a good outcome for females <45 years with significant disadvantage thereafter (mRS score of 0–2: P Interaction =0.004). No relationship between sex, r-tPA, and bleeding complications was evident.

Conclusions—

Functional outcome (mRS) without r-tPA was overall similar between the sexes, as was the response to r-tPA. Nonlinear sex-by-age interaction improved estimates of functional independence; this should be considered in sex-related studies in stroke.

β-Blockers, Pneumonia, and Outcome After Ischemic Stroke

Background and Purpose—

Increased sympathetic drive after stroke is involved in the pathophysiology of several complications including poststroke immunudepression. β-Blocker (BB) therapy has been suggested to have neuroprotective properties and to decrease infectious complications after stroke. We aimed to examine the effects of random pre- and on-stroke BB exposure on mortality, functional outcome, and occurrence of pneumonia after ischemic stroke.

Methods—

Data including standard demographic and clinical variables as well as prestroke and on-stroke antihypertensive medication, incidence of pneumonia, functional outcome defined using modified Rankin Scale and mortality at 3 months were extracted from the Virtual International Stroke Trials Archive. For statistical analysis multivariable Poisson regression was used.

Results—

In total, 5212 patients were analyzed. A total of 1155 (22.2%) patients were treated with BB before stroke onset and 244 (4.7%) patients were newly started with BB in the acute phase of stroke. Mortality was 17.5%, favorable outcome (defined as modified Rankin Scale, 0–2) occurred in 58.2% and pneumonia in 8.2% of patients. Prestroke BB showed no association with mortality. On-stroke BB was associated with reduced mortality (adjusted risk ratio, 0.63; 95% confidence interval, 0.42–0.96). Neither prestroke BB nor on-stroke BB showed an association with functional outcome. Both prestroke and on-stroke BB were associated with reduced frequency of pneumonia (adjusted risk ratio, 0.77; 95% confidence interval, 0.6–0.98 and risk ratio, 0.49; 95% confidence interval, 0.25–0.95).

Conclusions—

In this large nonrandomized comparison, on-stroke BB was associated with reduced mortality. Prestroke and on-stroke BB were inversely associated with incidence of nosocomial pneumonia. Randomized trials investigating the potential of β-blockade in acute stroke may be warranted.

Metabolic imaging of ischemic stroke: the present and future

Measures of cerebral metabolism may be useful in the selection of patients for reperfusion therapies and as end points in clinical trials. However, there are currently no clinically routine techniques that provide such data directly. We review how imaging modalities in current clinical use may provide surrogate markers of metabolic activity. Promising techniques for metabolic imaging that are currently in the pipeline are reviewed.

THRIVE Score Predicts Ischemic Stroke Outcomes and Thrombolytic Hemorrhage Risk in VISTA

Background and Purpose—

In previous studies, the Totaled Health Risks in Vascular Events (THRIVE) score has shown broad utility, allowing prediction of clinical outcome, death, and risk of hemorrhage after tissue-type plasminogen activator (tPA) treatment, irrespective of the type of acute stroke therapy applied to the patient.

Methods—

We used data from the Virtual International Stroke Trials Archive to further validate the THRIVE score in a large cohort of patients receiving tPA or no acute treatment, to confirm the relationship between THRIVE and hemorrhage after tPA, and to compare the THRIVE score with several other available outcome prediction scores.

Results—

The THRIVE score strongly predicts clinical outcome (odds ratio, 0.55 for good outcome [95% CI, 0.53–0.57]; P <0.001), mortality (odds ratio, 1.57 [95% confidence interval, 1.50–1.64]; P <0.001), and risk of intracerebral hemorrhage after tPA (odds ratio, 1.34 [95% confidence interval, 1.22–1.46]; P <0.001). The relationship between THRIVE score and outcome is not influenced by the independent relationship of tPA administration and outcome. In receiver operator characteristic curve analysis, the THRIVE score was superior to several other available outcome prediction scores in the prediction of clinical outcome and mortality.

Conclusions—

The THRIVE score is a simple-to-use tool to predict clinical outcome, mortality, and risk of hemorrhage after thrombolysis in patients with ischemic stroke. Despite its simplicity, the THRIVE score performs better than several other outcome prediction tools. A free Web calculator for the THRIVE score is available at http://www.thrivescore.org .

Stroke mismatch volume with the use of ABC/2 is equivalent to planimetric stroke mismatch volume

BACKGROUND AND PURPOSE

In the clinical setting, there is a need to perform mismatch measurements quickly and easily on the MR imaging scanner to determine the specific amount of treatable penumbra. The objective of this study was to quantify the agreement of the ABC/2 method with the established planimetric method.

MATERIALS AND METHODS

Patients (n = 193) were selected from the NINDS Natural History Stroke Registry if they 1) were treated with standard intravenous rtPA, 2) had a pretreatment MR imaging with evaluable DWI and PWI, and 3) had an acute ischemic stroke lesion. A rater placed the linear diameters to measure the largest DWI and MTT lesion areas in 3 perpendicular axes-A, B, and C-and then used the ABC/2 formula to calculate lesion volumes. A separate rater measured the planimetric volumes. Multiple mismatch thresholds were used, including MTT volume - DWI volume ≥50 mL versus ≥60 mL and (MTT volume - DWI volume)/MTT volume ≥20% versus MTT/DWI = 1.8.

RESULTS

Compared with the planimetric method, the ABC/2 method had high sensitivity (0.91), specificity (0.90), accuracy (0.91), PPV (0.90), and NPV (0.91) to quantify mismatch by use of the ≥50 mL definition. The Spearman correlation coefficients were 0.846 and 0.876, respectively, for the DWI and MTT measurements. The inter-rater Bland-Altman plots demonstrated 95%, 95%, and 97% agreement for the DWI, MTT, and mismatch measurements.

CONCLUSIONS

The ABC/2 method is highly reliable and accurate for quantifying the specific amount of MR imaging-determined mismatch and therefore is a potential tool to quickly calculate a treatable mismatch pattern.

Hyperintense vessel sign on fluid-attenuated inversion recovery MR imaging is reduced by gadolinium

The HVS on FLAIR imaging is a useful marker of acute ischemic stroke. We investigated whether prior administration of gadolinium-based contrast hindered detection of this sign on images from subjects with acute nonlacunar ischemic stroke <4.5 hours after onset. Both blinded and comparative unblinded analyses showed significantly reduced HVS detection on postcontrast images. We suggest that assessment for this sign should be performed on images acquired prior to contrast administration.

Blood-brain barrier disruption after cardiac surgery

BACKGROUND AND PURPOSE

CNS complications are often seen after heart surgery, and postsurgical disruption of the BBB may play an etiologic role. The objective of this study was to determine the prevalence of MR imaging-detected BBB disruption (HARM) and DWI lesions after cardiac surgery.

MATERIALS AND METHODS

All patients had an MRI after cardiac surgery. For half the patients (group 1), we administered gadolinium 24 hours after surgery and obtained high-resolution DWI and FLAIR images 24-48 hours later. We administered gadolinium to the other half (group 2) at the time of the postoperative scan, 2-4 days after surgery. Two stroke neurologists evaluated the images.

RESULTS

Of the 19 patients we studied, none had clinical evidence of a stroke or delirium at the time of the gadolinium administration or the scan, but 9 patients (47%) had HARM (67% in group 1; 30% in group 2; P = .18) and 14 patients (74%) had DWI lesions (70% in group 1; 78% in group 2; P = 1.0). Not all patients with DWI lesions had HARM, and not all patients with HARM had DWI lesions (P = .56).

CONCLUSIONS

Almost half the patients undergoing cardiac surgery have evidence of HARM, and three-quarters have acute lesions on DWI after surgery. BBB disruption is more prevalent in the first 24 hours after surgery. These findings suggest that MR imaging can be used as an imaging biomarker to assess therapies that may protect the BBB in patients undergoing heart surgery.

Does the cognitive measure Cog-4 show improvement among patients treated with thrombolysis after acute stroke?

BACKGROUND

Although the established measure of disability post stroke, the modified Rankin Scale emphasizes motor function and may underestimate the importance of cognitive impairment in more disabled patients. A subset of four items from the National Institutes of Health Stroke Scale has been proposed to assess cognitive function after stroke (Cog-4), and to correlate with modified Rankin Scale. Items correspond to orientation, executive function, language, and inattention. We investigated responsiveness of Cog-4 to treatment with thrombolysis and whether it offers information that supplements modified Rankin Scale.

METHODS

We included 6268 patients from the Virtual International Stroke Trials Archive: 2734 received intravenous thrombolysis and 3534 were treated conservatively. We compared day 90 outcomes between treated and untreated groups, by modified Rankin Scale (illustrative) and by Cog-4 (primary measure) adjusting for age, baseline National Institutes of Health stroke scale, hemispheric lateralisation as well as baseline Cog-4 and baseline National Institutes of Health Stroke Scale excluding baseline Cog-4 separately. Analysis of Cog-4 was repeated within strata of 90 day modified Rankin Scale. Statistical analyses included proportional odds logistic regression and Cochran-Mantel-Haenszel test.

RESULTS

Modified Rankin Scale showed a difference between treatment groups of expected magnitude (odds ratio 1·56; 95% confidence interval 1·43-1·72; P < 0·001). After adjustment for imbalance in baseline prognostic factors, the distribution of Cog-4 scores at 90 days was better in thrombolysed patients compared with nonthrombolysed patients (odds ratio 1·31; 95% confidence interval 1·18-1·47; P = 0·006). However, Cog-4 analysis stratified by 90-day modified Rankin Scale was neutral between treatment groups (OR 1·01; 95% CI 0·90-1·14), and Cog-4 was not responsive to treatment group even within modified Rankin Scale categories 4 and 5 despite substantial cognitive deficits in these patients.

CONCLUSION

Although Cog-4 may be responsive to treatment effects, it does not provide additional information beyond modified Rankin Scale assessment.

Hyperacute injury marker (HARM) in primary hemorrhage: a distinct form of CNS barrier disruption

OBJECTIVE

The objective of the study was to characterize a previously unreported form of CNS barrier disruption in intracerebral hemorrhage (ICH): hyperacute injury marker (HARM).

METHODS

In this retrospective cohort analysis of patients presenting with primary ICH, precontrast and postcontrast MRI scans obtained within 5 days of symptom onset were analyzed. The presence of CNS barrier disruption was defined by (1) perihematomal or intrahematomal enhancement visualized on postcontrast T1-weighted MRI or (2) HARM: sulcal or ventricular hyperintensity visualized on postcontrast fluid-attenuated inversion recovery sequences (graded on a 5-point scale).

RESULTS

Forty-six patients were included in the analysis. Mean age was 65 years, median NIH Stroke Scale score was 7, and mean ICH volume was 12.2 mL (range 0.3-46.9 mL). HARM was visualized in 85% of patients, and this was moderate to severe in 50%. In all cases, the sulcal enhancement was noncontiguous with the hematoma. Of those patients with postcontrast T1-weighted imaging, perihematomal or intrahematomal contrast enhancement was visualized in 75% of patients.

CONCLUSIONS

This study demonstrates that HARM occurs in intracerebral hemorrhage and that it likely represents a second type of CNS barrier disruption distinct from parenchymal postcontrast T1-weighted enhancement. Similar to T1 enhancement, this phenomenon may serve as a clinically useful biomarker to test therapies aimed at stabilizing acute ICH and CNS barrier disruption. Future studies are needed to further define the time course and prognostic implications of this finding.

Endothelial progenitor cells correlate with lesion volume and growth in acute stroke

OBJECTIVES

Circulating endothelial progenitor cells (EPC) are markers of vascular injury and their numbers decrease in acute stroke. However, the relation of EPC levels to stroke severity has not been quantified. MRI measurements of lesion volume provide an objective method for stroke severity assessment and outcome prediction. This cross-sectional study aims to determine whether EPC are correlated with lesion volume at baseline, lesion growth, and final lesion volume.

METHODS

Seventeen patients (median age 63 years, NIH Stroke Scale score 7) were selected from 175 patients with imaging-confirmed acute ischemic stroke. EPC were quantified by flow cytometry using CD34, CD133, and VEGFR2 surface markers. Brain MRI was performed at baseline and at days 1 and 5 after the stroke onset. Stroke lesion volumes were quantified.

RESULTS

Larger lesion volumes measured on diffusion-weighted images (DWI) at baseline were associated with low EPC levels, while smaller lesion volumes and less lesion growth were linked with high levels of EPC subsets (CD34+CD133+, CD133+VEGFR2+, and CD34+ CD133+VEGFR2+). Similar results were observed with DWI lesion volumes and EPC (CD34+CD133+) on day 1. Lesion growth volume, represented as a difference between final lesion volume and baseline DWI, was larger in patients with lower day 1 EPC (CD133+VEGFR2+). After adjustments for age and admission glucose (model 1), mean arterial pressure and white blood cells (model 2), INR and hematocrit (model 3), the CD34+CD133+ subset remained predictive of baseline and day 1 lesion volumes, while CD133+VEGFR2+ predicted baseline lesion volume and growth of lesion volume.

CONCLUSIONS

Higher EPC levels were indicative of smaller volumes of acute lesion, final lesion, and lesion growth, and may serve as markers of acute phase stroke severity. However, a larger prospective study is needed to confirm our findings.

Genomic biomarkers and cellular pathways of ischemic stroke by RNA gene expression profiling

OBJECTIVE

The objective of this study was to provide insight into the molecular mechanisms of acute ischemic cerebrovascular syndrome (AICS) through gene expression profiling and pathway analysis.

METHODS

Peripheral whole blood samples were collected from 39 MRI-diagnosed patients with AICS and 25 nonstroke control subjects ≥ 18 years of age. Total RNA was extracted from whole blood stabilized in Paxgene RNA tubes, amplified, and hybridized to Illumina HumanRef-8v2 bead chips. Gene expression was compared in a univariate manner between stroke patients and control subjects using t test in GeneSpring. The significant genes were tested in a logistic regression model controlling for age, hypertension, and dyslipidemia. Inflation of type 1 error was corrected by Bonferroni and Ingenuity Systems Pathway analysis was performed. Validation was performed by QRT-PCR using Taqman gene expression assays.

RESULTS

A 9-gene profile was identified in the whole blood of ischemic stroke patients using gene expression profiling. Five of these 9 genes were identified in a previously published expression profiling study of stroke and are therefore likely biomarkers of stroke. Pathway analysis revealed toll-like receptor signaling as a highly significant canonical pathway present in the peripheral whole blood of patients with AICS.

CONCLUSIONS

Our study highlights the relevance of the innate immune system through toll-like receptor signaling as a mediator of response to ischemic stroke and supports the claim that gene expression profiling can be used to identify biomarkers of ischemic stroke. Further studies are needed to validate and refine these biomarkers for their diagnostic potential.

Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology

OBJECTIVE

To assess the evidence for the use of diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) in the diagnosis of patients with acute ischemic stroke.

METHODS

We systematically analyzed the literature from 1966 to January 2008 to address the diagnostic and prognostic value of DWI and PWI.

RESULTS AND RECOMMENDATIONS

DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset. DWI should be performed for the most accurate diagnosis of acute ischemic stroke (Level A); however, the sensitivity of DWI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. The diagnostic accuracy of DWI in evaluating cerebral hemorrhage is outside the scope of this guideline. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C). Baseline DWI lesion volumes probably predict (final) infarct volumes (Level B) and possibly predict early and late clinical outcome measures (Level C). Baseline PWI volumes predict to a lesser degree the baseline stroke severity compared with DWI (Level C). There is insufficient evidence to support or refute the value of PWI in diagnosing acute ischemic stroke (Level U).

Gradient echo MRI: implementation of a training tutorial for intracranial hemorrhage diagnosis

BACKGROUND

Recent studies have demonstrated that gradient echo (GRE) MRI sequences are as accurate as CT for the detection of intracerebral hemorrhage (ICH) in the context of acute stroke. However, many physicians who currently read acute stroke imaging studies may be unfamiliar with interpretation of GRE images.

METHODS

An NIH Web-based training program was developed including a pretest, tutorial, and posttest. Physicians involved in the care of acute stroke patients were encouraged to participate. The tutorial covered acute, chronic, and mimic hemorrhages as they appear on CT, diffusion-weighted imaging, and GRE sequences. Ability of users to identify ICH presence, type, and age on GRE was compared from the pretest to posttest timepoint.

RESULTS

A total of 104 users completed the tutorial. Specialties represented included general radiology (42%), general neurology (16%), neuroradiology (15%), stroke neurology (14%), emergency medicine (1%), and other (12%). Median overall score improved pretest to posttest from 66.7% to 83.3%, p < 0.001. Improvement by category was as follows: acute ICH, 66.7%-100%, p < 0.001; chronic ICH, 33.3%-66.7%, p < 0.001; ICH negatives/mimics, 100%-100%, p = 0.787. Sensitivity for identification of acute hemorrhage improved from 68.2% to 96.4%.

CONCLUSIONS

Physicians involved in acute stroke care achieved significant improvement in gradient echo (GRE) hemorrhage interpretation after completing the NIH GRE MRI tutorial. This indicates that a Web-based tutorial may be a viable option for the widespread education of physicians to achieve an acceptable level of diagnostic accuracy at reading GRE MRI, thus enabling confident acute stroke treatment decisions.

Distal hyperintense vessels on FLAIR: an MRI marker for collateral circulation in acute stroke?

BACKGROUND

Hyperintense vessels (HV) on fluid-attenuated inversion recovery imaging are frequently observed in acute ischemic stroke patients. However, the exact mechanism and clinical implications of this sign have not yet been clearly defined. The features of HV and its relevance to other imaging factors are presented here.

METHODS

Prominence and location of HV were documented in 52 consecutive patients with middle cerebral artery (MCA) territory infarction, before treatment with IV recombinant tissue plasminogen activator. Pretreatment ischemic lesion volume, perfusion lesion volume, and vessel occlusion were determined in addition to recanalization status and ischemic lesion volume on follow-up imaging. NIH Stroke Scale (NIHSS) was used as a measure of clinical severity.

RESULTS

HV distal to arterial occlusion was observed in 73% of patients; more frequent in proximal than distal MCA occlusion patients. Among the 38 patients with proximal MCA occlusion, initial perfusion lesion volume was comparable among patients with different grade distal HV. However, patients with more prominent distal HV had smaller initial, 24-hour, and subacute ischemic lesion volumes and lower initial NIHSS scores.

CONCLUSIONS

The presence of distal hyperintense vessels before thrombolytic treatment is associated with large diffusion-perfusion mismatch and smaller subacute ischemic lesion volumes in patients with proximal middle cerebral artery occlusion. DWI = diffusion-weighted imaging; FLAIR = fluid-attenuated inversion recovery; GRE = gradient recalled echo; HV = hyperintense vessels; MCA = middle cerebral artery; MRA = magnetic resonance angiography; MTT = mean transit time; NIHSS = NIH Stroke Scale; PWI = perfusion-weighted imaging; rt-PA = recombinant tissue plasminogen activator; TE = echo time; TI = inversion time; TIMI = thrombolysis in myocardial infarction; TR = repetition time.

Racial differences in microbleed prevalence in primary intracerebral hemorrhage

BACKGROUND

Primary intracerebral hemorrhage is two to three times more common in many racial populations, including black patients. Previous studies have shown that microbleeds, identified on gradient echo MRI (GRE), are present in 50-80% of patients with primary ICH. The objective of this study was to compare, by race, the rates, risk factors, and topography of microbleeds in patients hospitalized for primary ICH.

METHODS

Patients diagnosed with primary ICH at two metropolitan stroke centers were included. Clinical and neuroimaging data were recorded for each patient. Analyses were performed to compare baseline characteristics as well as imaging findings by race.

RESULTS

A total of 87 patients met inclusion criteria (42 black subjects, 45 white subjects). The black cohort was younger (p < 0.001), and had a greater rate of hypertension (p = 0.001), but not other vascular risk factors. Microbleeds were more prevalent in the black population, with 74% of blacks having one or more microbleeds compared to 42% of whites (p = 0.005). The black population also tended to have a greater frequency of microbleeds in multiple territories than the white population (38% vs 22%, p = 0.106). When adjusting for age, hypertension, and alcohol use, race was an independent predictor of microbleeds (OR 3.308, 95% CI 1.144-9.571, p = 0.027).

CONCLUSIONS

These pilot data suggest that significant racial differences exist in the frequency and topography of microbleeds in patients with primary ICH. Microbleeds may be an important emerging imaging biomarker with the potential to provide insights into ICH pathophysiology, prognosis, and disease progression, as well as possible therapeutic strategies, particularly in medically underserved populations.

Reliability of MR perfusion-weighted and diffusion-weighted imaging mismatch measurement methods

BACKGROUND AND PURPOSE

We investigated 2 methods of measuring MR imaging perfusion-diffusion mismatch to determine whether reliability is improved by direct measurement on a single, blended map.

MATERIALS AND METHODS

Image software was used for measurement of lesion volumes from diffusion-weighted images (DWI) and mean transit time (MTT) calculated from perfusion-weighted (PWI) images on 64 patients with acute stroke. For the first method, the DWI and MTT lesions were measured separately. For the second method, the mismatch volume was measured directly on the blended images created from the registered DWI and MTT images.

RESULTS

Test-retest agreement was 100% and 97% for the separate and blended methods using mismatch cutoffs of 20% or more versus less than 20%. There were no significant differences in the mismatch statistics between the methods.

CONCLUSIONS

Mismatch volumes by a single reader can provide highly reliable and consistent results even when separately measuring DWI and MTT lesions. Propagation of measurement error was not demonstrated, and the methods were statistically comparable.

Higher prevalence of cortical lesions observed in patients with acute stroke using high-resolution diffusion-weighted imaging

Ischemic lesion conspicuity on routine diffusion-weighted imaging (DWI, 30 seconds) was compared with an improved sequence (high-resolution DWI [DWI-HR], 256 seconds) having increased spatial resolution and signal to noise and decreased eddy current artifact in 42 patients with acute ischemic stroke. Total lesion volumes were similar; however, twice as many lesions were identified on DWI-HR, predominately in cortical gray matter. Modest improvements to imaging resulted in increased conspicuity, potentially affecting diagnosis, suspected pathogenic mechanism, and therapeutic decision.

Cooling for Acute Ischemic Brain Damage (COOL AID): a feasibility trial of endovascular cooling

OBJECTIVE

To report results of a randomized pilot clinical feasibility trial of endovascular cooling in patients with ischemic stroke.

METHODS

Forty patients with ischemic stroke presenting within 12 hours of symptom onset were enrolled in the study. An endovascular cooling device was inserted into the inferior vena cava of those randomized to hypothermia. A core body temperature of 33 degrees C was targeted for 24 hours. All patients underwent clinical assessment and MRI initially, at days 3 to 5 and days 30 to 37.

RESULTS

Eighteen patients were randomized to hypothermia and 22 to receive standard medical management. Thirteen patients reached target temperature in a mean of 77 +/- 44 minutes. Most tolerated hypothermia well. Clinical outcomes were similar in both groups. Mean diffusion-weighted imaging (DWI) lesion growth in the hypothermia group (n = 12) was 90.0 +/- 83.5% compared with 108.4 +/- 142.4% in the control group (n = 11) (NS). Mean DWI lesion growth in patients who cooled well (n = 8) was 72.9 +/- 95.2% (NS).

CONCLUSIONS

Induced moderate hypothermia is feasible using an endovascular cooling device in most patients with acute ischemic stroke. Further studies are needed to determine if hypothermia improves outcome.

Early and late recurrence of ischemic lesion on MRI: Evidence for a prolonged stroke-prone state?

BACKGROUND

Based on previous observations of a high rate of ischemic lesion recurrence on diffusion-weighted imaging (DWI) within 1 week after an acute ischemic stroke, the authors hypothesized that silent new ischemic lesions are common between 1 week and 90 days after index stroke and that early lesion recurrence may be associated with late lesion recurrence.

METHODS

The authors studied 80 acute ischemic stroke patients who had initial MRI performed within 48 hours, and follow-up scans at 5 days and at 30 or 90 days after onset. Early lesion recurrences were defined as new ischemic lesions on 5-day DWI, and late lesion recurrences were defined as those on 30- or 90-day DWI or fluid attenuation inversion recovery image. Early lesion recurrence occurring outside the initial perfusion deficit was termed distant lesion recurrence.

RESULTS

Late lesion recurrence occurred in 26%, more frequently observed on 30-day MRI than 90-day MRI (p = 0.016). Early lesion recurrence (OR 4.0; 95% CI 1.3 to 11.7) and distant early lesion recurrence (OR 6.9; 95% CI 1.5 to 32.2) were independently associated with late lesion recurrence by multiple logistic regression analyses.

CONCLUSIONS

There may be a continued risk for recurrent ischemic lesions in the weeks following the clinically symptomatic stroke. Future studies are needed to investigate whether MRI-defined ischemic lesion recurrences predict subsequent clinical recurrence and thus may be a potential surrogate endpoint in stroke secondary prevention trials.

Magnetic resonance imaging criteria for thrombolysis in acute cerebral infarct

BACKGROUND AND PURPOSE

Magnetic resonance imaging (MRI) selection of stroke patients eligible for thrombolytic therapy is an emerging application. Although the efficacy of therapy within 3 hours after onset of symptoms with intravenous (IV) tissue plasminogen activator (tPA) has been proven for patients selected with computed tomography (CT), no randomized, double-blinded MRI trial has been published yet.

SUMMARY OF REVIEW

MRI screening of acute stroke patients before thrombolytic therapy is performed in some cerebrovascular centers. In contrast to the CT trials, MRI pilot studies demonstrate benefit of therapy up to 6 hours after onset of symptoms. This article reviews the literature that has lead to current controlled MRI-based thrombolysis trials. We examined the MRI criteria applied in 5 stroke centers. Along with the personal views of clinicians at these centers, the survey reveals a variety of clinical and MRI technical aspects that must be further investigated: the therapeutic consequence of microbleeds, the use of magnetic resonance angiography, dynamic time windows, and others.

CONCLUSION

MRI is an established application in acute evaluation of stroke patients and may suit as a brain clock, replacing the currently used epidemiological time clock when deciding whether to initiate thrombolytic therapy. MRI criteria for thrombolytic therapy are applied in some cerebrovascular centers, but the results of ongoing clinical trials must be awaited before it is possible to reach consensus.

Elevated pro-inflammatory CD4+CD28- lymphocytes and stroke recurrence and death

OBJECTIVE

To determine if the CD4+CD28- T-cell subset is expanded in patients with recurrent stroke or death after acute ischemic stroke. This subset of the peripheral blood T-cell lymphocyte population has a strong pro-inflammatory and tissue-damaging potential.

METHODS

Consecutive patients within the first 48 hours of ischemic stroke were prospectively studied. Peripheral blood CD4+CD28- cells were quantified by flow cytometry. The study endpoint was recurrent stroke or death from any cause during 1 year of follow-up.

RESULTS

One hundred six patients (mean age 75.0 +/- 13.5 years; 50 women) were studied. The median CD4+CD28- cell count was 4.5% (range 0.2 to 72.2%). Twenty-seven endpoints (10 recurrent strokes and 17 deaths) occurred during follow-up. Stroke recurrence/death rates were significantly associated with increasing CD4+CD28- counts, rising from 14.2% in patients with CD4+CD28- levels of <1.0 to 48.1% for those with CD4+CD28- counts of >8.0% (p = 0.003, Cochran linear test of trend). Higher CD4+CD28- counts were also present in patients with a history of prior stroke (p = 0.03). After adjustment for age, admission NIH Stroke Scale score, prior stroke, and atrial fibrillation, CD4+CD28- counts of >8.0% were associated with a cumulative hazard ratio of 5.81 (95% CI: 1.58 to 21.32) for stroke recurrence or death.

CONCLUSIONS

Rising counts of circulating CD4+CD28- cells are associated with an increasing risk of stroke recurrence and death, in addition to an observed association with prior stroke. Expansion of this T-cell subset presumably represents a biomarker and possibly a contributory pathogenic mechanism of recurrent stroke and death after ischemic stroke.

Diffusion-perfusion MR evaluation of perihematomal injury in hyperacute intracerebral hemorrhage

BACKGROUND

It has been suggested that a zone of perihematomal ischemia analogous to an ischemic penumbra exists in patients with primary intracerebral hemorrhage (ICH). Diffusion-perfusion MRI provides a novel means of assessing injury in perihematomal regions in patients with ICH.

OBJECTIVE

To characterize diffusion-perfusion MRI changes in the perihematomal region in patients with hyperacute intracerebral hemorrhage.

METHOD

Twelve patients presenting with hyperacute, primary ICH undergoing CT scanning and diffusion-perfusion MRI within 6 hours of symptom onset were reviewed. An automated thresholding technique was used to identify decreased apparent diffusion coefficient (ADC) values in the perihematomal regions. Perfusion maps were examined for regions of relative hypo- or hyperperfusion.

RESULTS

Median baseline NIH Stroke Scale score was 17 (range, 6 to 28). Median hematoma volume was 13.3 mL (range, 3.0 to 74.8 mL). MRI detected the hematoma in all patients on echo-planar susceptibility-weighted imaging and in all seven patients imaged with gradient echo sequences. In six patients who underwent perfusion imaging, no focal defects were visualized on perfusion maps in tissues adjacent to the hematoma; however, five of six patients demonstrated diffuse ipsilateral hemispheric hypoperfusion. On diffusion imaging, perihematomal regions of decreased ADC values were identified in three of 12 patients. All three subsequently showed clinical and radiologic deterioration.

CONCLUSIONS

A rim of perihematomal decreased ADC values was visualized in the hyperacute period in a subset of patients with ICH. The presence of a rim of decreased ADC outside the hematoma correlated with poor clinical outcome. Although perfusion maps did not demonstrate a focal zone of perihematomal decreased blood flow in any patient, most patients had ipsilateral hemispheric hypoperfusion.

New imaging strategies for patient selection for thrombolytic and neuroprotective therapies

Ischemic stroke trials have traditionally sought to limit the range of disease studied according to several dimensions based on clinical examination and CT scan results. It has been proposed that the optimal sample for stroke trials would include a positive imaging diagnosis of a pathology rationally linked to the drug's mechanisms of action and that this would improve the likelihood of positive results. This principle has been supported by the results of the Prolyse in Acute Cerebral Thromoembolism II (PROACT II) study. Whereas trials of iv thrombolysis between 3 and 6 hours after symptom onset in a general sample of patients were not positive, selection of a subgroup by angiography was an effective strategy in this time period for PROACT II. This study contradicted the hypothesis that treatment of stroke beyond 3 hours would not be successful. MRI with diffusion and perfusion has been an appealing imaging modality because it provides pretreatment angiography, perfusion, and lesion volume information during a brief, non-invasive assessment. Current literature supports the validity of MRI as a marker for clinical severity and clinical improvement. The diffusion-perfusion mismatch, the MRI marker for the ischemic penumbra, is a very strong predictor of lesion volume growth. Several acute trials in progress use a positive imaging diagnosis for the basis of selection. As the field of stroke clinical trials examines opportunities for improving trial design, positive imaging diagnoses in patient selection are likely to assume an increasingly useful role.

Relationship between magnetic resonance arterial patency and perfusion-diffusion mismatch in acute ischemic stroke and its potential clinical use

BACKGROUND

In patients with acute ischemic stroke the magnetic resonance (MR) perfusion-diffusion mismatch pattern (perfusion lesion at least 20% larger than the lesion on diffusion-weighted imaging) may indicate ischemically threatened but viable tissue. To our knowledge, the relationship of this MR pattern to serial changes in MR angiography (MRA) has not been reported.

OBJECTIVES

To investigate the relationship between MRA changes and patterns of diffusion-weighted imaging and perfusion abnormalities and to determine if the information obtained could be used in clinical management.

METHODS

The MR studies of 35 patients who had undergone sequential multimodality MR imaging studies within the first 4 days of stroke were reviewed. All lesions were in the internal carotid artery territory distribution. Magnetic resonance angiographies were read by 2 observers blinded to the clinical data.

RESULTS

During the first 24 hours a perfusion-diffusion mismatch was present in 22 (92%) of the 24 patients with an MRA arterial occlusive lesion. (At this time 5 [46%] of the 11 patients with a normal MRA [P =.006] also had a mismatch.) Two to 4 days after stroke, of these 22 patients resolution of the mismatch occurred in 8 (87%) of 9 patients with recanalization on MRA compared with 5 (39%) of 13 patients without arterial recanalization (P =.03). Resolution of mismatch occurred in 3 (60%) of 5 patients with a normal MRA and a mismatch at the first time point.

CONCLUSIONS

Concordance between MRA and the MR perfusion-diffusion mismatch pattern provides supportive evidence for an arterial vascular basis for this MR signature in acute stroke. Discordance between MRA lesions and mismatch may result from arterial branch occlusions undetected by MRA or from an alternate mechanism for the mismatch. The MR imaging patterns identified extend our understanding of the pathophysiology of stroke and may contribute to the improvement of stroke management in the future.

A three-item scale for the early prediction of stroke recovery

BACKGROUND

Accurate assessment of prognosis in the first hours of stroke is desirable for best patient management. We aimed to assess whether the extent of ischaemic brain injury on magnetic reasonance diffusion-weighted imaging (MR DWI) could provide additional prognostic information to clinical factors.

METHODS

In a three-phase study we studied 66 patients from a North American teaching hospital who had: MR DWI within 36 h of stroke onset; the National Institutes of Health Stroke Scale (NIHSS) score measured at the time of scanning; and the Barthel Index measured no later than 3 months after stroke. We used logistic regression to derive a predictive model for good recovery. This logistic regression model was applied to an independent series of 63 patients from an Australian teaching hospital, and we then developed a three-item scale for the early prediction of stroke recovery.

FINDINGS

Combined measurements of the NIHSS score (p=0.01), time in hours from stroke onset to MR DWI (p=0.02), and the volume of ischaemic brain tissue on MR DWI (p=0.04) gave the best prediction of stroke recovery. The model was externally validated on the Australian sample with 0.77 sensitivity and 0.88 specificity. Three likelihood levels for stroke recovery-low (0-2), medium (3-4), and high (5-7)-were identified on the three-item scale.

INTERPRETATION

The combination of clinical and MR DWI factors provided better prediction of stroke recovery than any factor alone, shortly after admission to hospital. This information was incorporated into a three-item scale for clinical use.

Diffusion-weighted imaging and National Institutes of Health Stroke Scale in the acute phase of posterior-circulation stroke

BACKGROUND

Occlusive disease of the posterior circulation represents a heterogeneous group of strokes that differ in etiology, clinical presentation, and prognosis. Computed tomography provides suboptimal visualization of posterior-circulation infarcts. Anatomic definition of traditional magnetic resonance imaging sequences has been used for clinicoradiologic correlation in patients with posterior-circulation disease. These studies focused on the subacute rather than the acute phase of ischemia. Lesion volumes on diffusion-weighted imaging (DWI) and perfusion imaging were found to have a good correlation with 24-hour National Institutes of Health stroke scale (NIHSS) score in ischemia of the anterior circulation. Correlation between NIHSS score and lesion volume in posterior-circulation infarcts is unknown.

OBJECTIVES

To investigate whether DWI is useful for clinicoradiologic correlation of posterior-circulation ischemia within 24 hours after symptom onset and whether NIHSS score correlates with lesion volumes in patients with posterior-circulation stroke.

PATIENTS AND METHODS

In a database analysis of 631 patients with stroke from June 26, 1996, to July 30, 1999, 115 patients (18%) had symptoms of posterior-circulation ischemia by imaging and clinical criteria. Among these 115, we included all patients (n = 40) who underwent DWI within 24 hours from symptom onset (mean, 9.7 +/- 7.1 hours). All 40 patients also underwent magnetic resonance angiography and T2-weighted imaging. Seventy-five did not meet inclusion criteria: in 45, magnetic resonance imaging was performed more than 24 hours after symptom onset; 12 did not have DWI; in 11 patients, symptoms resolved within 24 hours; 6 had hemorrhages; and 1 had a border zone infarct.

RESULTS

An acute lesion on DWI corresponding to the patient's symptoms was detected in all 40 patients, 16 (40%) of whom had detectable acute lesions on T2-weighted images. The lesions on DWI were larger in 11 of the 16 patients with positive T2-weighted images. Acute lesion volume did not correlate with NIHSS score (n = 40; rho = 0.30; P =.06, Spearman rank) also when DWI lesion volumes were divided by cause and territory.

CONCLUSIONS

Diffusion-weighted imaging is more effective than T2-weighted imaging in patients with acute posterior-circulation strokes. The DWI lesion volume did not significantly correlate with NIHSS score, suggesting that NIHSS is more weighted toward anterior-circulation stroke symptoms.

Effect of citicoline on ischemic lesions as measured by diffusion-weighted magnetic resonance imaging. Citicoline 010 Investigators

We examined the effect of the neuroprotective and neuroreparative agent citicoline on the growth of cerebral ischemic lesions in a double-blind placebo-controlled study involving patients with acute ischemic stroke using diffusion-weighted magnetic resonance imaging (DWI). Patients with acute ischemic stroke symptom onset 24 hours or less before the start of treatment, National Institutes of Health Stroke Scale (NIHSS) scores of 5 or higher, and lesions of 1 to 120 cc in cerebral gray matter by DWI were enrolled. DWI, T2-weighted magnetic resonance imaging (MRI), perfusion-weighted MRI, and magnetic resonance angiography were obtained at baseline, week 1, and week 12. Citicoline (500 mg/day) was administered orally for 6 weeks, and patients were followed for 12 weeks. The primary assessment was progression of ischemic lesion volume from baseline to 12 weeks as measured by MRI. A total of 100 patients entered the study. The primary MRI analysis included 40 placebo-treated patients and 41 citicoline-treated patients with both baseline and week 12 MRI data and failed to demonstrate a significant difference in lesion volume change from baseline to week 12. From baseline to week 12, ischemic lesion volume [all values mean (SE)] expanded by 180% (107) among placebo-treated patients compared with 34% (19) among citicoline-treated patients. In a secondary analysis, lesion volume decreased from week 1 to week 12 by 6.9 cc (2.8) on placebo versus 17.2 cc (2.6) on citicoline. Baseline variables that were predictors of change in lesion size over 12 weeks were the volume of hypoperfusion (strongest association), baseline NIHSS score, lesion volume on DWI, arterial lesion by magnetic resonance angiography, and categorized elapsed time (< or =12 or >12 hours) from stroke onset to first dose. A marked association between lesion volume reduction and improvement of NIHSS score by seven or more points was observed. Significant correlations between lesion volumes and clinical measures were found, replicating values reported in the literature for smaller case series. We observed a reduction in lesion volume growth from baseline to week 12 with citicoline treatment, with a significantly greater reduction in volume from week 1 to week 12 with citicoline. We found a significant inverse relationship between lesion volume change over 12 weeks as measured by MRI and clinical outcome for ischemic stroke. This relationship supports the role of DWI as a surrogate marker of clinically meaningful lesion progression in stroke clinical trials. The hypothesis that citicoline reduces lesion growth and improves clinical outcome will be tested further.

Clinical correlations of diffusion and perfusion lesion volumes in acute ischemic stroke

The aim of this study was to describe the clinico-radiological correlations of magnetic resonance (MR) perfusion and diffusion-weighted imaging (DWI) abnormalities in ischemic stroke. Eighteen patients had undergone MR imaging and clinical evaluation within 24 h of symptom onset and at or after 7 days. During the first 24 h the volume of perfusion abnormality (measured on the relative mean transit time map) was larger than the DWI lesion in 12/18 patients. In 6/18 patients the DWI lesion volume was larger. Acutely (<24 h) all lesion volumes showed a significant correlation with acute clinical severity measured by the National Institutes of Health Stroke Scale score. The correlations of the hypoperfusion volume (rho = 0.86, p = 0.0001) and the volume 'tissue at risk' (larger than the DWI and perfusion lesion volumes, rho = 0.86, p = 0. 0001) with acute clinical severity were slightly higher than for the DWI lesion volume (rho = 0.76, p = 0.0001). The difference between the volume of tissue at risk (acutely) and the infarct on follow-up T(2)-weighted imaging correlated significantly with change in clinical severity from acute to chronic time points (rho = 0.72, p = 0.001). Such clinico-radiological relationships may support the use of DWI and perfusion MR in decisions concerning the administration and evaluation of stroke therapies.

Diffusion- and perfusion-weighted MRI patterns in borderzone infarcts

BACKGROUND AND PURPOSE

The pathophysiology of borderzone infarcts is not well understood. We investigated whether combined diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) could identify pathophysiologically meaningful categories of borderzone infarcts.

METHODS

Seventeen patients with borderzone infarcts were identified from the Beth Israel Deaconess Medical Center Stroke Database. All patients had DWI and PWI, the majority of them within the first 24 hours of symptom onset.

RESULTS

Three patterns of perfusion abnormalities were associated with the diffusion lesions: 1, normal perfusion (5 patients); 2, localized perfusion deficits matching the area of restricted diffusion (5 patients); and 3, extensive perfusion deficits involving 1 or more vascular territories (7 patients). All but 1 patient with pattern 1 had transient peri-infarct hypotension as the presumed stroke mechanism. Two patients with pattern 2 had cardiac or aortic embolic sources; none had large-artery disease or arterial hypotension. Reperfusion was detected in all patients with this pattern who submitted to a follow-up study. All patients with pattern 3 had severe stenosis or occlusion of a large artery: the internal carotid, anterior cerebral, or middle cerebral.

CONCLUSIONS

We postulate that the perfusion abnormality varies according to the mechanism of the borderzone infarction. Transient perfusion deficits occurring with hypotension in the absence of significant large-artery disease may not be revealed by PWI. Embolism may cause some cases of small borderzone perfusion deficits. Critical large-artery disease may cause large territorial perfusion deficits and predispose to borderzone infarction.

Multiple acute stroke syndrome: marker of embolic disease?

OBJECTIVE

To determine the frequency and etiologic significance of multiple acute ischemic lesions in stroke.

BACKGROUND

Although patients may have more than one stroke during the course of their lives, acute ischemic stroke is usually thought of as a single event. Using diffusion-weighted imaging (DWI), an MRI technique that detects ischemic injury within minutes after onset, we have often observed multiple acute ischemic lesions.

METHODS

The MRI scans of 59 consecutively studied patients were reviewed to determine the frequency and etiologic significance of multiple acute ischemic lesions on DWI.

RESULTS

Multiple acute ischemic lesions were present in 10 (17%) of 59 patients. The lesions usually occurred within one major circulation (anterior or posterior), but in two patients (3%), lesions occurred in both cerebral hemispheres or in the anterior and the posterior circulations. The lesions often were small and resulted from presumed multiple emboli or the break-up of an embolus. Two patients had internal carotid artery occlusive disease and four had a cardiac or aortic source. In the other four patients the source was not determined. Lesions larger than 1 cm in diameter progressed to infarction, but some smaller lesions were not seen on follow-up T2-weighted imaging.

CONCLUSIONS

Multiple acute stroke lesions on DWI are common and could be caused by multiple emboli or the breakup of an embolus. In some cases it might become possible to make early inferences concerning the stroke mechanism that could be of use for immediately directing the clinical work-up and treatment of the patient.

Silent functional magnetic resonance imaging demonstrates focal activation in rapid eye movement sleep

Functional imaging of human sleep has been performed with nuclear medicine methods, but MRI has been difficult to implement, in part because of the noise associated with echo-planar imaging as well as the difficulty in reading physiologic signals in the MRI environment. We describe a silent MR sequence that can record brain activation over many hours with simultaneous acquisition of an EEG. This shows activation of occipital cortex and deactivation of frontal cortex during REM sleep, in agreement with previous studies using other techniques. MRI-Sleep-REM sleep.

MRI features of intracerebral hemorrhage within 2 hours from symptom onset

BACKGROUND AND PURPOSE

MRI has been increasingly used in the evaluation of acute stroke patients. However, MRI must be able to detect early hemorrhage to be the only imaging screen used before treatment such as thrombolysis. Susceptibility-weighted imaging, an echo-planar T2* sequence, can show intracerebral hemorrhage (ICH) in patients imaged between 2.5 and 5 hours from symptom onset. It is unknown whether MRI can detect ICH earlier than 2.5 hours. We describe 5 patients with ICH who had MRI between 23 and 120 minutes from symptom onset and propose diagnostic patterns of evolution of hyperacute ICH on MRI.

METHODS

As part of our acute imaging protocol, all patients with acute stroke within 24 hours from symptom onset were imaged with a set of sequences that included susceptibility-weighted imaging, diffusion- and perfusion-weighted imaging, T1- and T2-weighted imaging, fluid-attenuated inversion recovery (FLAIR), and MR angiography using echo-planar techniques. Five patients with ICH had MRI between 23 and 120 minutes from the onset of symptoms.

RESULTS

ICH was identified in all patients. Distinctive patterns of hyperacute ICH and absence of signs of ischemic stroke were the hallmark features of this diagnosis. The hyperacute hematoma appears to be composed of 3 distinct areas: (1) center: isointense to hyperintense heterogeneous signal on susceptibility-weighted and T2-weighted imaging; (2) periphery: hypointense (susceptibility effect) on susceptibility-weighted and T2-weighted imaging; and (3) rim: hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, representing vasogenic edema encasing the hematoma.

CONCLUSIONS

MRI is able to detect hyperacute ICH and show a pattern of evolution of the hematoma within 2 hours from the onset of symptoms.

The ischemic penumbra: operationally defined by diffusion and perfusion MRI

BACKGROUND

Identifying tissue at risk for infarction is important in deciding which patients would benefit most from potentially harmful therapies and provides a way to evaluate newer therapies with regard to the amount of ischemic tissue salvaged.

OBJECTIVE

To operationally define and characterize cerebral tissue at risk for stroke progression.

METHODS

We retrospectively selected 25 patients with an acute onset of a hemispheric stroke from our database who had undergone a combination of two diffusion-weighted MRI studies and a perfusion-weighted MRI study. We applied a logistic regression model using maps of the relative mean transit time and relative cerebral blood flow (rCBF) as well as three different maps of the relative cerebral blood volume (rCBV) to predict an operationally defined penumbra (region of mismatch between the diffusion lesion on day 1 and its extension 24 to 72 hours later).

RESULTS

Maps of the rCBF and initial rCBV were significant predictors for identifying penumbral tissue. Our operationally defined penumbral region was characterized by a reduction in the initial rCBV (47% of contralateral control region [CCR]), an increase (163% of CCR) in the total rCBV, and a reduction (37% of CCR) in the rCBF, whereas the operationally defined ischemic core showed a more severe reduction in the rCBF (12% of CCR) and in the initial rCBV (19% of CCR).

CONCLUSION

These MR indexes may allow the identification and quantification of viable but ischemically threatened cerebral tissue amenable to therapeutic interventions in the hyperacute care of stroke patients.

Echoplanar MR imaging for ultrafast detection of brain lesions

OBJECTIVE

We retrospectively evaluated the use of echo-planar imaging for ultrafast detection of brain lesions.

MATERIALS AND METHODS

In our retrospective study, 61 patients were imaged with the following echo-planar sequences: single-shot proton density-weighted, single-shot T2-weighted, single-shot T2-weighted high-resolution, multishot proton density-weighted, and multishot T2-weighted. Lesions revealed in these patients ranged from 0.5 to 12.0 cm (mean, 3.7 cm) and were the result of tumor (n = 16), stroke (n = 21), demyelination (n = 18), and toxoplasmosis (n = 2). Four patients had scans with normal findings. Two neuroradiologists who were unaware of pertinent clinical data reviewed the images. The images were retrospectively compared with conventional spin-echo images for diagnosis, sensitivity of lesion detection, and qualitative criteria: subjective image quality, gray and white matter differentiation, lesion conspicuity, delineation of lesion borders, and artifacts. (Artifacts included those caused by motion, susceptibility, pulsation, and ghosting.) Quantitative criteria, including signal-to-noise and signal difference-to-noise measurements, were also evaluated in 40 lesions.

RESULTS

Sensitivity for lesion detection was 97% for single-shot echo-planar T2-weighted MR images and 100% for multishot echo-planar T2-weighted MR images. Single-shot echo-planar proton density-weighted MR images had the highest signal-to-noise ratio (91.2+/-19.3). Echo-planar T2-weighted MR images had the highest signal difference-to-noise (33.8+/-22.9). Echo-planar sequences were superior to spin-echo sequences regarding motion and pulsation artifacts. Spin-echo sequences lacked susceptibility and ghosting artifacts, and were superior in lesion conspicuity and delineation of lesion borders.

CONCLUSION

In this study, echo-planar sequences were as sensitive as conventional spin-echo imaging for the diagnostic assessment of lesions. Echo-planar sequences had a strikingly shorter acquisition time and substantially reduced motion and pulsation artifacts. Echo-planar sequences may be a useful diagnostic tool for use in claustrophobic and unstable patients.

Neuroprotection by the NMDA receptor-associated open-channel blocker memantine in a photothrombotic model of cerebral focal ischemia in neonatal rat

Excessive accumulation of glutamate or other excitatory amino acids and the subsequent overactivity of NMDA receptors is currently thought to lead to neuronal injury in cerebral ischemia. Therefore, antagonists of the NMDA receptor may offer an approach for the treatment of ischemic brain injury. Dizocilpine (MK-801), an NMDA receptor-associated channel blocker, protects neurons in several rodent stroke models. However, this drug has numerous side effects and causes apoptosis of neonatal neurons. Recently, another NMDA receptor-associated channel blocker, memantine, has been shown to ameliorate NMDA-receptor mediated neurotoxicity in neuronal cell cultures and in focal cerebral ischemia models in adult rats without substantial side effects. Memantine has been used clinically in the treatment of Parkinson's disease and spasticity for a number of years. Here we tested the effects of memantine on focal stroke caused by photochemical thrombosis in neonatal rats and demonstrated a neuroprotective effect of memantine in this model. We also found excellent correlation between infarct size determined by magnetic resonance imaging (MRI) and histopathological analysis in the same animals. A single pre-ischemic dose of memantine (20 mg/kg) given 15 min prior to induction of stroke reduced the infarct size by 36.3% when compared to control animals treated with normal saline (P < 0.0001). At this dosage, memantine manifests few, if any, neurobehavioral side effects. Thus memantine appears to be both safe and effective in neonatal as well as adult animal models of stroke.

Schizophrenic subjects activate dorsolateral prefrontal cortex during a working memory task, as measured by fMRI

BACKGROUND

Neuroimaging studies of schizophrenic subjects performing working memory (WM) tasks have demonstrated a relative hypoactivity of prefrontal cortex compared with normal subjects.

METHODS

Using functional magnetic resonance imaging (fMRI), we compared dorsolateral prefrontal cortex (DLPFC) activation in 12 schizophrenic and 10 normal subjects during rewarded performance of a WM task. Subjects performed a modified version of the Sternberg Item Recognition Paradigm (SIRP), a continuous performance, choice reaction time (RT) task that requires WM. We compared a high WM load condition with a nonWM choice RT condition and with a low WM load condition.

RESULTS

Schizophrenic subjects performed the tasks better than chance but worse than normal subjects. They showed greater activation than normal subjects in the left DLPFC but did not differ in the right DLPFC or in the control region. In the schizophrenic group, left DLPFC activation was inversely correlated with task performance, as measured by errors.

CONCLUSIONS

These findings contrast with previous studies that demonstrated task-related hypofrontality in schizophrenia. Task parameters that may contribute to this difference are discussed. We hypothesize that the performance and activation differences we observed are also manifestations of prefrontal dysfunction in schizophrenia. They reflect inefficient functioning of the neural circuitry involved in WM.

Diffusion-weighted magnetic resonance imaging in Alzheimer's disease

Diffusion-weighted imaging (DWI) is a powerful new magnetic resonance imaging technique for evaluating tissue pathophysiology in vivo. We performed DWI in three orthogonal spatial directions in 10 patients with mild to moderate Alzheimer's disease (AD) and 11 control subjects. Average apparent diffusion coefficients (ADCavg) were calculated for gray matter regions, and anisotropy indexes were calculated for white matter regions. Global measures of atrophy and white matter hyperintensities (WMH) were obtained on T2-weighted images to control for their potential confounding effects on ADCavg and anisotropy. The measures of atrophy and WMH differed between the groups and were used as covariates in the subsequent statistical analyses. Patients with AD demonstrated diminished anisotropy in the posterior white matter (p < 0.0001) and increased ADCavg in the hippocampus (p < 0.05) when compared to the control group. Diffusion measures did not correlate with the severity of dementia. DWI provides a unique, quantitative parameter that may be sensitive to the pathophysiological and/or microstructural abnormalities that occur in AD.

Imaging developing brain infarction

Continued advances in neuroimaging technology have made it practical to image multiple aspects of evolving brain infarction during the potential window period of therapeutic opportunity in stroke. Recent methodologic developments include computed tomography angiography and perfusion, and the description of quantitative parameters for magnetic resonance blood oxygen level-dependent perfusion imaging. In pathophysiologic studies, metabolism and function in the ischemic focus and the peri-infarct tissue have been further characterized. Clinical studies have focused on the applications of computed tomography and magnetic resonance imaging for prethrombolysis patient selection. These methods have an important role in the evaluation and development of new pharmaceutical agents and will be increasingly used in clinical practice as new therapies become available.

A phantom for diffusion-weighted imaging of acute stroke

A tissue phantom for diffusion-weighted imaging was developed, basing its contrast between two compartments on different apparent diffusion coefficients, without contrast due to T2 relaxation and proton density. These contrast properties of the phantom simulate the situation found in normal gray matter and areas of acute ischemia. A possible application of the phantom was demonstrated for the investigation of the accuracy of volume measurements based on diffusion-weighted images.