Perfusion-weighted MRI as a marker of response to treatment in acute and subacute stroke

Cerebral Ischemic Reperfusion Injury: Preventative and Therapeutic Strategies

Acute ischemic stroke is a leading cause of morbidity and mortality in the United States. Treatment goals remain focused on restoring blood flow to compromised areas. However, a major concern arises after reperfusion occurs. Cerebral ischemic reperfusion injury is defined as damage to otherwise salvageable brain tissue occurring with the reestablishment of the vascular supply to that region. The pool of eligible patients for revascularization continues to grow, especially with the recently expanded endovascular therapeutic window. Neurointensivists should understand and manage complications of successful recanalization. In this review, we examine the pathophysiology, diagnosis, and potential management strategies in cerebral ischemic reperfusion injury.

Persistent perfusion abnormalities at day 1 correspond to different clinical trajectories after stroke

BACKGROUND

Perfusion abnormalities after thrombolysis are frequent within and surrounding ischemic lesions, but their relative frequency is not well known.

OBJECTIVE

To describe the different patterns of perfusion abnormalities observed at 24 hours and compare the characteristics of the patients according to their perfusion pattern.

METHODS

From our thrombolysis registry, we included 226 consecutive patients with an available arterial spin labeling (ASL) perfusion sequence at day 1. We performed a blinded assessment of the perfusion status (hypoperfusion-h, hyperperfusion-H, or normal-N) in the ischemic lesion and in the surrounding tissue. We compared the time course of clinical recovery, the rate of arterial recanalization, and hemorrhagic transformations in the different perfusion profiles.

RESULTS

We identified seven different perfusion profiles at day 1. Four of these (h/h, h/H, H/H, and H/N) represented the majority of the population (84.1%). The H/H profile was the most frequent (34.5%) and associated with 3-month good outcome (modified Rankin Scale (mRS): 63.5%). Patients with persistent hypoperfusion within and outside the lesion (h/h, 12.4%) exhibited worse outcomes after treatment (mRS score 0-2: 23.8%) than other patients, were less frequently recanalized (40.7%), and had more parenchymal hematoma (17.8%). The h/H profile had an intermediate clinical trajectory between the h/h profile and the hyperperfused profiles.

CONCLUSION

ASL hypoperfusion within the infarct and the surrounding tissue was associated with poor outcome. A more comprehensive view of the mechanisms in the hypoperfused surrounding tissue could help to design new therapeutic approaches during and after reperfusion therapies.

Hyperintense vessels on imaging account for neurological function independent of lesion volume in acute ischemic stroke

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Studies have revealed variable significance of FLAIR hyperintense vessels (FHV).

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We found number and location of FHV are associated with functional deficits.

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Functional measures correlated with FHV independently of lesion volume.

In acute ischemic stroke, reported relationships between lesion metrics and behavior have largely focused on lesion volume and location. However, hypoperfusion has been shown to correlate with deficits in the acute stage. Hypoperfusion is typically identified using perfusion imaging in clinical settings, which requires contrast. Unfortunately, contrast is contraindicated for some individuals. An alternative method has been proposed to identify hypoperfusion using hyperintense vessels on fluid-attenuated inversion recovery (FLAIR) imaging. This study aimed to validate the clinical importance of considering hypoperfusion when accounting for behavior in acute stroke and demonstrate the clinical utility of scoring the presence of hyperintense vessels to quantify it.

One hundred and fifty-three participants with acute ischemic stroke completed a battery of commonly-used neurological and behavioral measures. Clinical MRIs were used to determine lesion volume and to score the presence of hyperintense vessels seen on FLAIR images to estimate severity of hypoperfusion in six different vascular regions. National Institutes of Health Stroke Scale (NIHSS) scores, naming accuracy (left hemisphere strokes), and language content produced during picture description were examined in relation to lesion volume, hypoperfusion, and demographic variables using correlational analyses and multivariable linear regression.

Results showed that lesion volume and hypoperfusion, in addition to demographic variables, were independently associated with performance on NIHSS, naming, and content production. Specifically, hypoperfusion in the frontal lobe independently correlated with NIHSS scores, while hypoperfusion in parietal areas independently correlated with naming accuracy and content production.

These results correspond to previous reports associating hypoperfusion with function, confirming that hypoperfusion is an important consideration—beyond lesion volume—when accounting for behavior in acute ischemic stroke. Quantifying hypoperfusion using FLAIR hyperintense vessels can be an essential clinical tool when other methods of identifying hypoperfusion are unavailable or time prohibitive.

Pressor therapy in acute ischaemic stroke: an updated systematic review

Background

Low blood pressure (BP) in acute ischaemic stroke (AIS) is associated with poor functional outcome, death, or severe disability. Increasing BP might benefit patients with post-stroke hypotension including those with potentially salvageable ischaemic penumbra. This updated systematic review considers the present evidence regarding the use of vasopressors in AIS.

Methods

We searched the Cochrane Database of Systematic Reviews, MEDLINE, EMBASE and trial databases using a structured search strategy. We examined reference lists of relevant publications for additional studies examining BP elevation in AIS.

Results

We included 27 studies involving 1886 patients. Nine studies assessed increasing BP during acute reperfusion therapy (intravenous thrombolysis, mechanical thrombectomy, intra-arterial thrombolysis or combined). Eighteen studies tested BP elevation alone. Phenylephrine was the most commonly used agent to increase BP (n = 16 studies), followed by norepinephrine (n = 6), epinephrine (n = 3) and dopamine (n = 2). Because of small patient numbers and study heterogeneity, a meta-analysis was not possible. Overall, BP elevation was feasible in patients with fluctuating or worsening neurological symptoms, large vessel occlusion with labile BP, sustained post-stroke hypotension and ineligible for intravenous thrombolysis or after acute reperfusion therapy. The effects on functional outcomes were largely unknown and close monitoring is advised if such intervention is undertaken.

Conclusion

Although theoretical arguments support increasing BP to improve cerebral blood flow and sustain the ischaemic penumbra in selected AIS patients, the data are limited and results largely inconclusive. Large, randomised controlled trials are needed to identify the optimal BP target, agent, duration of treatment and effects on clinical outcomes.

Blood Pressure Management Before, During, and After Endovascular Thrombectomy for Acute Ischemic Stroke

There is an absence of specific evidence or guideline recommendations on blood pressure management for large vessel occlusion stroke patients. Until randomized data are available, the periprocedural blood pressure management of patients undergoing endovascular thrombectomy can be viewed in two phases relative to the achievement of recanalization. In the hyperacute phase, prior to recanalization, hypotension should be avoided to maintain adequate penumbral perfusion. The American Heart Association guidelines should be followed for the upper end of prethrombectomy blood pressure: ≤185/110 mm Hg, unless post-tissue plasminogen activator administration when the goal is <180/105 mm Hg. After successful recanalization (thrombolysis in cerebral infarction [TICI]: 2b-3), we recommend a target of a maximum systolic blood pressure of < 160 mm Hg, while the persistently occluded patients (TICI < 2b) may require more permissive goals up to <180/105 mm Hg. Future research should focus on generating randomized data on optimal blood pressure management both before and after endovascular thrombectomy, to optimize patient outcomes for these divergent clinical scenarios.

Association of Blood Pressure During Thrombectomy for Acute Ischemic Stroke With Functional Outcome: A Systematic Review

Background and Purpose- Optimal blood pressure (BP) targets during mechanical thrombectomy (MT) for acute ischemic stroke (AIS) are unknown, and randomized controlled trials addressing this issue are lacking. We aimed to perform a systematic review of studies evaluating the influence of periprocedural BP on functional outcome after MT. Methods- Studies assessing periprocedural BP effect on functional outcome published after January 1st, 2012 were included in the systematic review. The PRISMA checklist and flow diagram were followed for the design and reporting of this work. Results- Nine studies were included, for a total of 1037 patients. The heterogeneity in findings with respect to BP monitoring and studied parameters precluded a meta-analysis. Mean arterial pressure was the most frequently reported parameter to describe BP variability during MT, and systolic BP was the main parameter used to define periprocedural BP targets. Five studies suggested an association between 3 types of BP drops as predictors of poor functional outcome at 3 months: >40% drop in mean arterial pressure compared with baseline (odds ratio=2.8; [1.09-7.19]; P=0.032), lowest mean arterial pressure before recanalization (odds ratio=1.28; [1.01-1.62] per 10 mm Hg drop below 100 mm Hg; P=0.04), and MAP drops (odds ratio=4.38; [1.53-12.6] for drops >10%). Four studies did not show an association between BP during MT and functional outcome, including 3 studies with strict periprocedural systolic BP targets (within a 140-180 mm Hg). Conclusions- BP drops during MT may be associated with a worse functional outcome. When strict systolic BP targets are achieved, no association between BP and functional outcome was also noted. Both conclusions require further evaluation in randomized studies.

Cerebral Blood Flow Response During Bolus Normal Saline Infusion After Ischemic Stroke

GOALS

We quantified cerebral blood flow response to a 500 cc bolus of 0.9%% normal saline (NS) within 96 hours of acute ischemic stroke (AIS) using diffuse correlation spectroscopy (DCS).

MATERIALS AND METHODS

Subjects with AIS in the anterior, middle, or posterior cerebral artery territory were enrolled within 96 hours of symptom onset. DCS measured relative cerebral blood flow (rCBF) in the bilateral frontal lobes for 15 minutes at rest (baseline), during a 30-minute infusion of 500 cc NS (bolus), and for 15 minutes after completion (post-bolus). Mean rCBF for each time period was calculated for individual subjects and median rCBF for the population was compared between time periods. Linear regression was used to evaluate for associations between rCBF and clinical features.

RESULTS

Among 57 subjects, median rCBF (IQR) increased relative to baseline in the ipsilesional hemisphere by 17% (-2.0%, 43.1%), P< 0.001, and in the contralesional hemisphere by 13.3% (-4.3%, 36.0%), P < .004. No significant associations were found between ipsilesional changes in rCBF and age, race, infarct size, infarct location, presence of large vessel stenosis, NIH stroke scale, or symptom duration.

CONCLUSION

A 500 cc bolus of .9% NS produced a measurable increase in rCBF in both the affected and nonaffected hemispheres. Clinical features did not predict rCBF response.

Sphenopalatine Ganglion Stimulation to Augment Cerebral Blood Flow

Background and Purpose—

Many patients with acute ischemic stroke are not eligible for thrombolysis or mechanical reperfusion therapies due to contraindications, inaccessible vascular occlusions, late presentation, or large infarct core. Sphenopalatine ganglion (SPG) stimulation to enhance collateral flow and stabilize the blood-brain barrier offers an alternative, potentially more widely deliverable, therapy.

Methods—

In a randomized, sham-controlled, double-masked trial at 41 centers in 7 countries, patients with anterior circulation ischemic stroke not treated with reperfusion therapies within 24 hours of onset were randomly allocated to active SPG stimulation or sham control. The primary efficacy outcome was improvement beyond expectations on the modified Rankin Scale of global disability at 90 days (sliding dichotomy), assessed in the modified intention-to-treat population. The initial planned sample size was 660 patients, but the trial was stopped early when technical improvements in device placement occurred, so that analysis of accumulated experience could be conducted to inform a successor trial.

Results—

Among 303 enrolled patients, 253 received at least one active SPG or sham stimulation, constituting the modified intention-to-treat population (153 SPG stimulation and 100 sham control). Age was median 73 years (interquartile range, 64–79), 52.6% were female, deficit severity on the National Institutes of Health Stroke Scale was median 11 (interquartile range, 9–15), and time from last known well median 18.6 hours (interquartile range, 14.5–22.5). For the primary outcome, improved 3-month disability beyond expectations, rates in the SPG versus sham treatment groups were 49.7% versus 40.0%; odds ratio, 1.48 (95% CI, 0.89–2.47); P =0.13. A significant treatment interaction with stroke location (cortical versus noncortical) was noted, P =0.04. In the 87 patients with confirmed cortical involvement, rates of improvement beyond expectations were 50.0% versus 27.0%; odds ratio, 2.70 (95% CI, 1.08–6.73); P =0.03. Similar response patterns were observed for all prespecified secondary efficacy outcomes. No differences in mortality or serious adverse event safety end points were observed.

Conclusions—

SPG stimulation within 24 hours of onset is safe in acute ischemic stroke. SPG stimulation was not shown to statistically significantly improve 3-month disability above expectations, though favorable outcomes were nominally higher with SPG stimulation. Beneficial effects may distinctively be conferred in patients with confirmed cortical involvement. The results of this study need to be confirmed in a larger pivotal study.

Clinical Trial Registration—

URL: https://www.clinicaltrials.gov . Unique identifier: NCT03767192.

Language recovery following stroke

Objective: To review the research literature pertaining to post-stroke language recovery, and to discuss neurocognitive assessment in patients in the context of aphasia, time course of language recovery, factors associated with language recovery, and therapeutic techniques designed to facilitate language recovery. Method: Articles were identified through PubMed, MEDLINE, PsychINFO, and Google Scholar searches. Examples of utilized keywords include "post-stroke aphasia," "post-stroke language recovery," "post-stroke neurocognitive assessment," and "neuropsychology and aphasia." Results: Most language recovery occurs in the first few weeks following stroke, but residual recovery may occur for many years. Although initial aphasia severity is the single largest determinant of post-stroke language recovery, a number of other variables also contribute. Several techniques have been developed to aid in the recovery process including speech-language therapy and noninvasive brain stimulation, although the effectiveness of acute and subacute treatment remains unclear. Some degree of valid neurocognitive assessment is possible in patients with aphasia, and the information gained from such an evaluation can aid the rehabilitative process Conclusions: Significant recovery of language function is possible following a stroke, but prediction of level of recovery in an individual patient is difficult. Information about initial aphasia severity and the integrity of cognitive domains other than language can help guide the rehabilitation team, as well as manage expectations for recovery.

Cerebral Ischemic Reperfusion Injury Following Recanalization of Large Vessel Occlusions

Although stroke has recently dropped to become the nation's fifth leading cause of mortality, it remains the top leading cause of morbidity and disability in the US. Recent advances in stroke treatment, including intravenous fibrinolysis and mechanical thromboembolectomy, allow treatment of a greater proportion of stroke patients than ever before. While intra-arterial fibrinolysis with recombinant tissue plasminogen is an effective for treatment of a broad range of acute ischemic strokes, endovascular mechanical thromboembolectomy procedures treat severe strokes due to large artery occlusions, often resistant to intravenous drug. Together, these procedures result in a greater proportion of revascularized stroke patients than ever before, up to 88% in 1 recent trial (EXTEND-IA). Subsequently, there is a growing need for neurointensivists to develop more effective strategies to manage stroke patients following successful reperfusion. Cerebral ischemic reperfusion injury (CIRI) is defined as deterioration of brain tissue suffered from ischemia that concomitantly reverses the benefits of re-establishing cerebral blood flow following mechanical or chemical therapies for acute ischemic stroke. Herein, we examine the pathophysiology of CIRI, imaging modalities, and potential neuroprotective strategies. Additionally, we sought to lay down a potential treatment approach for patients with CIRI following emergent endovascular recanalization for acute ischemic stroke.

Blood Pressure and Penumbral Sustenance in Stroke from Large Vessel Occlusion

The global burden of stroke remains high, and of the various subtypes of stroke, large vessel occlusions (LVOs) account for the largest proportion of stroke-related death and disability. Several randomized controlled trials in 2015 changed the landscape of stroke care worldwide, with endovascular thrombectomy (ET) now the standard of care for all eligible patients. With the proven success of this therapy, there is a renewed focus on penumbral sustenance. In this review, we describe the ischemic penumbra, collateral circulation, autoregulation, and imaging assessment of the penumbra. Blood pressure goals in acute stroke remain controversial, and we review the current data and suggest an approach for induced hypertension in the acute treatment of patients with LVOs. Finally, in addition to reperfusion and enhanced perfusion, efforts focused on developing therapeutic targets that afford neuroprotection and augment neural repair will gain increasing importance. ET has revolutionized stroke care, and future emphasis will be placed on promoting penumbral sustenance, which will increase patient eligibility for this highly effective therapy and reduce overall stroke-related death and disability.

The value of resting-state functional MRI in subacute ischemic stroke: comparison with dynamic susceptibility contrast-enhanced perfusion MRI

To evaluate the potential clinical value of the time-shift analysis (TSA) approach for resting-state fMRI (rs-fMRI) blood oxygenation level-dependent (BOLD) data in detecting hypoperfusion of subacute stroke patients through comparison with dynamic susceptibility contrast perfusion weighted imaging (DSC-PWI). Forty patients with subacute stroke (3–14 days after neurological symptom onset) underwent MRI examination. Cohort A: 31 patients had MRA, DSC-PWI and BOLD data. Cohort B: 9 patients had BOLD and MRA data. The time delay between the BOLD time course in each voxel and the mean signal of global and contralateral hemisphere was calculated using TSA. Time to peak (TTP) was employed to detect hypoperfusion. Among cohort A, 14 patients who had intracranial large-vessel occlusion/stenosis with sparse collaterals showed hypoperfusion by both of the two approaches, one with abundant collaterals showed neither TTP nor TSA time delay. The remaining 16 patients without obvious MRA lesions showed neither TTP nor TSA time delay. Among cohort B, eight patients showed time delay areas. The TSA approach was a promising alternative to DSC-PWI for detecting hypoperfusion in subacute stroke patients who had obvious MRA lesions with sparse collaterals, those with abundant collaterals would keep intact local perfusion.

Identifying Dysfunctional Cortex: Dissociable Effects of Stroke and Aging on Resting State Dynamics in MEG and fMRI

Spontaneous signals in neuroimaging data may provide information on cortical health in disease and aging, but the relative sensitivity of different approaches is unknown. In the present study, we compared different but complementary indicators of neural dynamics in resting-state MEG and BOLD fMRI, and their relationship with blood flow. Participants included patients with post-stroke aphasia, age-matched controls, and young adults. The complexity of brain activity at rest was quantified in MEG using spectral analysis and multiscale entropy (MSE) measures, whereas BOLD variability was quantified as the standard deviation (SDBOLD), mean squared successive difference (MSSD), and sample entropy of the BOLD time series. We sought to assess the utility of signal variability and complexity measures as markers of age-related changes in healthy adults and perilesional dysfunction in chronic stroke. The results indicate that reduced BOLD variability is a robust finding in aging, whereas MEG measures are more sensitive to the cortical abnormalities associated with stroke. Furthermore, reduced complexity of MEG signals in perilesional tissue were correlated with hypoperfusion as assessed with arterial spin labeling (ASL), while no such relationship was apparent with BOLD variability. These findings suggest that MEG signal complexity offers a sensitive index of neural dysfunction in perilesional tissue in chronic stroke, and that these effects are clearly distinguishable from those associated with healthy aging.

What is the nature of poststroke language recovery and reorganization?

This review focuses on three main topics related to the nature of poststroke language recovery and reorganization. The first topic pertains to the nature of anatomical and physiological substrates in the infarcted hemisphere in poststroke aphasia, including the nature of the hemodynamic response in patients with poststroke aphasia, the nature of the peri-infarct tissue, and the neuronal plasticity potential in the infarcted hemisphere. The second section of the paper reviews the current neuroimaging evidence for language recovery in the acute, subacute, and chronic stages of recovery. The third and final section examines changes in connectivity as a function of recovery in poststroke aphasia, specifically in terms of changes in white matter connectivity, changes in functional effective connectivity, and changes in resting state connectivity after stroke. While much progress has been made in our understanding of language recovery, more work needs to be done. Future studies will need to examine whether reorganization of language in poststroke aphasia corresponds to a tighter, more coherent, and efficient network of residual and new regions in the brain. Answering these questions will go a long way towards being able to predict which patients are likely to recover and may benefit from future rehabilitation.

A Randomized Placebo Controlled Trial of Early Treatment of Acute Ischemic Stroke with Atorvastatin and Irbesartan

Background

Cholesterol and blood pressure lowering therapies are effective in the secondary prevention of ischemic stroke.

Aim

To determine whether 30 days of treatment with atorvastatin, or irbesartan, initiated within 96 h of symptom onset improves recovery from acute ischemic stroke.

Methods

Eighty-one patients with acute ischemic stroke participated in this double-blind, placebo-controlled, randomized trial of atorvastatin (80 mg) vs. placebo, and/or irbesartan (150 mg) vs. placebo. Fifty-two patients (randomized 53 ± 22 h after onset of symptoms) completed the 30-day primary outcome follow-up.

Results

The primary outcome, maximal brain infarct size at days 3 and 30 measured by perfusion computed tomography, was not significantly altered by random assignment to irbesartan (1088 (IQR 216, 2594) mm2 at day 3, compared with 398 (144, 2053) mm2 among the placebo group, P=0·79 controlling for baseline values; and 822 (159, 1717) mm2 at day 30, cf 280 (76, 1330) mm2; P=0·63); or atorvastatin (454 (107, 1765) mm2 cf 825 (265, 2509) mm2 at day 3; P=0·33; and 462 (43, 1399) mm2 cf 280 (128, 1559) mm2 at day 30, P=0·79). There were no other significant differences among the treatment groups with the exception of: • high sensitivity C-reactive protein concentrations, which were lower in the irbesartan treatment group at day 30 (mean difference 12·6 mg/L; 95% CI: −25·1, −0·1; P=0·048); and • the mean cerebral blood flow in the affected cerebral hemisphere at 30 days after stroke, which was significantly reduced by random assignment to irbesartan compared with placebo in both the affected cerebral hemisphere (−7·5 mL/100 mL/min (95% CI: −1·7 to −13·4, P=0·01)) and in the unaffected hemisphere (−7·3 mL/100 mL/min (95% CI: −1·3, −13·4; P=0·02)). Atorvastatin therapy was well tolerated, but irbesartan therapy was associated with an increased rate of withdrawal from therapy ( n=10 (29%), compared with n=3 (9%) who withdrew from placebo, P=0·04).

Conclusions

Treatment with atorvastatin and irbesartan, initiated on day 3 after acute ischemic stroke, did not appear to substantially modify infarct growth.

Case of “Slow” Stroke from Carotid Artery Occlusion Treated by Delayed but Cautious Endovascular Intervention

In a challenging case of carotid occlusion with slowly evolving stroke, we used brain imaging to facilitate endovascular revascularization resulting in the relief of the patient's symptoms. Patients with carotid occlusion and continued neurological worsening or fluctuations present enormous treatment challenges. These patients may present “slow” strokes with subacute infarcts that present significant challenges and risks during attempts at revascularization of the occluded artery. We present such a case in which we used multimodal imaging techniques, including MR-perfusion, to facilitate endovascular revascularization. Our approach of delayed but cautious intra-arterial thrombolytic therapy, guided by brain imaging, and followed by stent placement across the residual stenosis, enabled revascularization of the occluded artery without overt in-hospital complications.

Effects of hypoperfusion in Alzheimer's disease

The role of hypoperfusion in Alzheimer's disease (AD) is a vital component to understanding the pathogenesis of this disease. Disrupted perfusion is not only evident throughout disease manifestation, it is also demonstrated during the pre-clinical phase of AD (i.e., mild cognitive impairment) as well as in cognitively healthy persons at high-risk for developing AD due to family history or genetic factors. Studies have used a variety of imaging modalities (e.g., SPECT, MRI, PET) to investigate AD, but with its recent technological advancements and non-invasive use of blood water as an endogenous tracer, arterial spin labeling (ASL) MRI has become an imaging technique of growing popularity. Through numerous ASL studies, it is now known that AD is associated with both global and regional cerebral hypoperfusion and that there is considerable overlap between the regions implicated in the disease state (consistently reported in precuneus/posterior cingulate and lateral parietal cortex) and those implicated in disease risk. Debate exists as to whether decreased blood flow in AD is a cause or consequence of the disease. Nonetheless, hypoperfusion in AD is associated with both structural and functional changes in the brain and offers a promising putative biomarker that could potentially identify AD in its pre-clinical state and be used to explore treatments to prevent, or at least slow, the progression of the disease. Finally, given that perfusion is a vascular phenomenon, we provide insights from a vascular lesion model (i.e., stroke) and illustrate the influence of disrupted perfusion on brain structure and function and, ultimately, cognition in AD.

Neglect is more common and severe at extreme hemoglobin levels in right hemispheric stroke

BACKGROUND AND PURPOSE

Anemia is 1 potential mechanism by which the brain receives inadequate oxygenation. The purpose of this study was to determine in acute stroke patients whether lower hemoglobin values were associated with worse hemispatial neglect.

METHODS

In 203 subjects, neglect testing batteries were administered within 24 hours of admission for acute right hemispheric stroke. We analyzed the error rate on each test as well as "any neglect" (z score >or=2 on any of 3 selected tests compared with normal controls), as predicted by hemoglobin level, with adjustment for infarct size, National Institutes of Health Stroke Scale score, age, and sex.

RESULTS

The association between hemoglobin and neglect varied on the basis of hemoglobin level. At lower hemoglobin levels (<12 g/dL), each 1-point higher hemoglobin value was protective (adjusted odds ratio=0.56; 95% CI, 0.35 to 0.89) from having "any neglect." However, for a hemoglobin value >14 g/dL, each 1-point higher hemoglobin value was associated with higher odds of having neglect (adjusted odds ratio=1.67; 95% CI, 1.09 to 2.57). Similar relations were found for predicted error rate on the horizontal line bisection, line cancellation, and copy Ogden scene neglect tests. These relations seemed to be more pronounced in individuals who had a diffusion/perfusion mismatch.

CONCLUSIONS

Lower and higher hemoglobin levels were each associated with increased odds of neglect and with worse severity of neglect, independent of stroke size and severity. Higher hemoglobin values may represent dehydration or hyperviscosity. The importance of the extremes of hemoglobin in identifying individuals at risk for worse functional consequences of stroke warrants further study.

Role of vasopressor administration in patients with acute neurologic injury

INTRODUCTION

Pharmacologic blood pressure elevation is often utilized to prevent or treat ischemia in patients with acute neurologic injury, and routinely requires administration of vasopressor agents. Depending on the indication, vasopressor agents may be administered to treat hypotension or to induce hypertension.

METHODS

Although numerous guideline statements exist regarding the management of blood pressure in these patients, most recommendations are based largely on Class III evidence. Further, there are few randomized controlled trials comparing vasopressor agents in these patients and selection is often guided by expert consensus.

RESULTS

We discuss the clinical evidence regarding vasopressor administration for blood pressure management in patients with acute neurologic injury. The effect of various vasopressors on cerebral hemodynamics is also discussed.

CONCLUSION

Although high-quality clinical data are scarce, the available evidence suggests that norepinephrine should be considered as the vasopressor of choice when blood pressure elevation is indicated in patients with acute neurologic injury.

Blood pressure management in acute stroke

The optimal management of arterial blood pressure in the setting of an acute stroke has not been defined. Many articles have been published on this topic in the past few years, but definitive evidence from clinical trials continues to be lacking. This situation is complicated further because stroke is a heterogeneous disease. The best management of arterial blood pressure may differ, depending on the type of stroke (ischemic or hemorrhagic) and the subtype of ischemic or hemorrhagic stroke. This article reviews the relationship between arterial blood pressure and the pathophysiology specific to ischemic stroke, primary intracerebral hemorrhage, and aneurysmal subarachnoid hemorrhage, elaborating on the concept of ischemic penumbra and the role of cerebral autoregulation. The article also examines the impact of blood pressure and its management on outcome. Finally, an agenda for research in this field is outlined.

Supratentorial regions of acute ischemia associated with clinically important swallowing disorders: a pilot study

BACKGROUND AND PURPOSE

Dysphagia is a common problem after stroke associated with significant morbidity and mortality. Except for patients with brain stem strokes, particularly lateral medullary strokes, it is difficult to predict which cases are likely to develop swallowing dysfunction based on their neuroimaging. Clear models of swallowing control and integration of cortico-bulbar input have not been defined and the role of subcortical structures is unclear. The purpose of this study was to identify supratentorial regions of interest (ROIs) that might be related to clinically important dysphagia in acute stroke patients, focusing on subcortical structures.

METHODS

We studied 29 acute supratentorial ischemic stroke cases admitted to our institution between 2001 and 2005 diagnoses with first ischemic stroke and without history of swallowing dysfunction. Subjects had MRI within 24 hours. Cases were defined as those subjects who were diagnosed as dysphagic after clinical evaluation by a speech language pathologist (SLP) and whose dysphagia was considered clinically significant, ie, requiring treatment by diet modification. Controls were defined as those patients who: (1) passed the stroke unit's dysphagia screening, (2) had a clinical evaluation by SLP that did not result in a diagnosis of dysphagia or diet modifications, or (3) had no documented evidence of dysphagia evaluation or treatment during hospitalization and were discharged on a regular diet. A trained technician, blinded to case-control status, examined 12 ROIs for dysfunctional tissue in diffusion and perfusion-weighted images. The odds ratio (OR) of dysphagia was calculated for each ROI. Logistic regression models were used to adjust for stroke severity (NIHSS) and volume.

RESULTS

Analysis of data on 14 cases and 15 controls demonstrated significant differences in the unadjusted odds of dysphagia for the following ROIs: (1) primary somatosensory, motor, and motor supplementary areas (PSSM; OR=10, P=0.009); (2) orbitofrontal cortex (OFC; OR=6.5, P=0.04); (3) putamen, caudate, basal ganglia (PCBG; OR=5.33, P=0.047); and (4) internal capsule (IC; OR=26; P=0.005). Nonsignificant differences were found in the insula and temporopolar cortex. Adjusted OR of dysphagia for subjects with strokes affecting the IC was 17.8 (P=0.03). Adjusted odds ratios for the PSSM, OFC, and PCBG were not statistically significant.

CONCLUSIONS

Significantly increased odds of dysphagia were found in subjects with IC involvement. Other supratentorial areas that may be associated with dysphagia include the PSSM, OFC, and PCBG. Analysis of additional areas was limited by the number of subjects in our sample. Future studies with larger sample size are feasible and will contribute to the development of a full swallowing control model.

Systematic review of CT and MR perfusion imaging for assessment of acute cerebrovascular disease

BACKGROUND AND PURPOSE

Perfusion imaging sequences are an important part of imaging studies designed to provide information to guide therapy for treatment of cerebrovascular disease. The purpose of this study was to perform a meta-analysis of the medical literature on perfusion imaging to determine its role in clinical decision making for patients with acute cerebral ischemia.

MATERIALS AND METHODS

We searched MEDLINE by using a strategy that combined terms related to perfusion imaging with terms related to acute cerebral ischemia and brain tumors. We identified 658 perfusion imaging articles and classified them according to the clinical usefulness criteria of Thornbury and Fryback. We found 59 articles with promise of indicating usefulness in clinical decision making. We devised and implemented a clinical decision making scoring scale more appropriate to the topic of acute cerebral ischemia.

RESULTS

Several articles provided important insights into the physiologic processes underlying acute cerebral ischemia by correlation of initial perfusion imaging deficits with clinical outcome or ultimate size of the infarct. However, most articles showed relatively low relevance to influencing decisions in implementing treatment.

CONCLUSION

Most perfusion imaging articles are oriented toward important topics such as optimization of imaging parameters, determination of ischemia penumbra, and prediction of outcome. However, information as to the role of perfusion imaging in clinical decision making is lacking. Studies are needed to demonstrate that use of perfusion imaging changes outcome of patients with acute cerebral ischemia.

Mild induced hypertension improves blood flow and oxygen metabolism in transient focal cerebral ischemia

BACKGROUND AND PURPOSE

In focal ischemic cortex, cerebral blood flow autoregulation is impaired, and perfusion passively follows blood pressure variations. Although it is generally agreed that profound hypotension is harmful in acute stroke, the hemodynamic and metabolic impact of increased blood pressure on the ischemic core and penumbra are less well understood. We, therefore, tested whether pharmacologically induced hypertension improves cerebral blood flow and metabolism and tissue outcome in acute stroke using optical imaging with high spatiotemporal resolution.

METHODS

Cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen were measured noninvasively using simultaneous multispectral reflectance imaging and laser speckle flowmetry during distal middle cerebral artery occlusion in mice. Hypertension was induced by phenylephrine infusion starting 10 or 60 minutes after ischemia to raise blood pressure by 30% for the duration of ischemia; control groups received saline infusion.

RESULTS

Mild induced hypertension rapidly increased cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen in both the core and penumbra and prevented the expansion of cerebral blood flow deficit during 1 hour distal middle cerebral artery occlusion. Induced hypertension also diminished the deleterious effects of periinfarct depolarizations on cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen without altering their frequency. Consistent with this, mild induced hypertension reduced infarct volume by 48% without exacerbating tissue swelling when measured 2 days after 1 hour transient distal middle cerebral artery occlusion.

CONCLUSIONS

Our data suggest that mild induced hypertension increases collateral cerebral blood flow and oxygenation and improves cerebral metabolic rate of oxygen in the core and penumbra, supporting its use as bridging therapy in acute ischemic stroke until arterial recanalization is achieved.

Quantitative measurement of spinal cord blood volume in humans using vascular-space-occupancy MRI

Although perfusion is of major interest for many spinal cord disorders, there is no established, reproducible technique for evaluating blood flow or blood volume of the spinal cord in humans. Here the first report of in vivo measurement of human spinal cord blood volume (scBV) is presented. An FDA-approved contrast agent, Gd-DTPA, was used as an intravascular agent for the cord parenchyma, and pre-/post-contrast vascular-space-occupancy (VASO) MRI experiments were performed to obtain a quantitative estimation of scBV in mL blood/100 mL tissue. VASO MRI was used because it does not rely on knowledge of an arterial input function, it avoids the imaging artifacts of single-shot echo planar imaging approaches, and it requires only relatively simple and direct calculations for scBV quantification. Preliminary tests at 1.5 T and 3 T gave mean +/- SD scBV values of 4.3 +/- 0.7 ml/100 mL tissue (n = 6) and 4.4 +/- 0.7 ml/100 mL tissue (n = 4), respectively, consistent with the expectation that the scBV values would not be field-dependent.

Blood pressure augmentation in acute ischemic stroke

Although control of hypertension is established as an important factor in the primary and secondary prevention of stroke, management of blood pressure in the setting of acute ischemic stroke remains controversial. Given limited data, the general consensus is that there is no proven benefit to lowering blood pressure in the first hours to days after acute ischemic stroke. Instead, there is concern that relative hypotension may lead to worsening of cerebral ischemia. For many years, the use of blood pressure augmentation ("induced hypertension") has been studied in animal models and in humans as a means of maintaining or improving perfusion to ischemic brain tissue. This approach is now widely used in neurocritical care units to treat delayed neurological deficits after subarachnoid hemorrhage, but its use in ischemic stroke patients remains anecdotal. This article reviews the cerebral physiology, animal models and human studies of induced hypertension as a treatment for acute ischemic stroke. Although there has not been a large, randomized clinical trial of this treatment, the available clinical data suggests that induced hypertension can result in at least short-term neurological improvement, with an acceptable degree of safety.

Reversible brain ischemia: lessons from transient ischemic attack

PURPOSE OF REVIEW

In recent years, there has been considerable scientific inquiry regarding transient ischemic attack. In an effort to synthesize at times conflicting data, this paper will review the recent evidence and provide a critical overview of reversible brain ischemia.

RECENT FINDINGS

Transient ischemic attack is now understood to indicate a higher risk of recurrence than completed ischemic stroke. Efforts to unravel the mechanisms of this instability following transient ischemic attack using imaging studies have led to new concepts and definitions, and sparked further debate. While imaging has increased diagnostic certainty, it has yet to provide reliable prognostic markers. The evidence suggests that risk of clinical recurrence is most closely linked to the degree to which the initial deficit reverses. From a tissue level, however, there are also data to support the notion of a 'stroke-prone state' following both transient ischemic attack and completed stroke, suggesting that mechanistically they may be less distinct than previously thought. Transient ischemic attack may simply highlight the dynamic nature of all acute ischemic cerebrovascular syndromes.

SUMMARY

Reversible brain ischemia is a harbinger for subsequent ischemic stroke. Although recent advances have focused on imaging markers, the most important predictor of risk following brain ischemia is degree of early clinical reversibility.

Endovascular thrombolysis and stenting of a middle cerebral artery occlusion beyond 6 hours post-attack: special reference to the usefulness of diffusion-perfusion MRI

Intra-arterial thrombolysis and percutaneous angioplasty is feasible in patients with acute middle cerebral artery (MCA) occlusion limited to 6 hours post-ictus, but there are some limitations such as reocclusion or hemorrhagic complications. In this report, we describe a stent placement in the treatment of a refractory artherothrombotic MCA occlusion beyond 6 hours of symptom onset. A 57-year-old man presented with a progressive left-sided weakness and verbal disturbance resulting from an acute thrombotic occlusion of the right MCA superimposed on severe proximal atheromatous stenosis. Diffusion-perfusion magnetic resonance imaging (MRI) demonstrated the significant diffusion-perfusion mismatch. After chemical and mechanical thrombolysis of the clot, balloon angioplasty of the underlying MCA stenosis was performed 2 days post-attack, without significant angiographic improvement. Percutaneous endovascular deployment of a stent (Driver 2.5 x 12 mm, MTI, Irvine, CA) was subsequently performed, with excellent angiographic results. Follow-up diffusion-perfusion MRI showed improved perfusion in the hypoperfused area. The patient's National Institutes of Health Stroke Scale (NIHSS) score was increased from 12 to 3. Clot thrombolysis and subsequent stenting in patients with refractory proximal MCA occlusion is feasible and allows for a significant reduction in the amount of thrombolytic drug required. In selective patients with acute MCA occlusion, the therapeutic window for recanalization procedures can be safely and effectively extended beyond the 'traditional 6 hours'. Diffusion-perfusion MRI in acute MCA occlusion is important for indication of therapy.

Effects of balloon angioplasty on perfusion- and diffusion-weighted magnetic resonance imaging results and outcome in patients with cerebral vasospasm

OBJECT

The aim of this study was to analyze the effects and outcome of transluminal balloon angioplasty (TBA) on brain tissue perfusion by using combined perfusion- and diffusion-weighted (PW/DW) magnetic resonance (MR) imaging in patients with cerebral vasospasm after subarachnoid hemorrhage.

METHODS

Ten consecutive patients with cerebral vasospasm treated using TBA were included in this prospective study. Hemodynamically relevant vasospasm was diagnosed using a standardized PW/DW MR imaging protocol. Digital subtraction angiography was used to confirm vasospasm, and TBA was performed to dilate vasospastic arteries. The PW/DW imaging protocol was repeated after TBA. The evaluation of the passage of contrast medium after standardized application using the bolus tracking method allowed for the calculation of the time to peak (TTP) before and after TBA. Tissue at risk was defined based on perfusion delays in individual vessel territories compared with those in reference territories. In cases with proximal focal vasospasm, TBA could dilate spastic arteries. Follow-up PW/DW MR imaging showed the disappearance of, or a decrease in, the mismatch. A TBA-induced reduction in the perfusion delay of 6.2 +/- 1 seconds (mean +/- standard error of the mean) to 1.5 +/- 0.45 seconds resulted in the complete prevention of infarction; a reduction in the delay of 6.2 +/- 2.7 to 4.1 +/- 1.9 seconds resulted in the preservation of those brain tissue parts having only small infarcts in the vessel territories. Without TBA, however, the perfusion delay remained or even increased (11.1 +/- 3.7 seconds), and the complete infarction of a territory occurred.

CONCLUSIONS

Angioplasty of vasospastic arteries leads to hemodynamic effects that can be quantified using PW/DW MR imaging. In cases of a severe PW/DW imaging mismatch successful TBA improved tissue perfusion and prevented cerebral infarction. The clinical significance of PW/DW MR imaging and the concept of tissue at risk is shown by cerebral infarction in vessels not accessible by TBA.

Reperfusion injury following cerebral ischemia: pathophysiology, MR imaging, and potential therapies

Introduction

Restoration of blood flow following ischemic stroke can be achieved by means of thrombolysis or mechanical recanalization. However, for some patients, reperfusion may exacerbate the injury initially caused by ischemia, producing a so-called “cerebral reperfusion injury”. Multiple pathological processes are involved in this injury, including leukocyte infiltration, platelet and complement activation, postischemic hyperperfusion, and breakdown of the blood–brain barrier.

Methods/results and conclusions

Magnetic resonance imaging (MRI) can provide extensive information on this process of injury, and may have a role in the future in stratifying patients’ risk for reperfusion injury following recanalization. Moreover, different MRI modalities can be used to investigate the various mechanisms of reperfusion injury. Antileukocyte antibodies, brain cooling and conditioned blood reperfusion are potential therapeutic strategies for lessening or eliminating reperfusion injury, and interventionalists may play a role in the future in using some of these therapies in combination with thrombolysis or embolectomy. The present review summarizes the mechanisms of reperfusion injury and focuses on the way each of those mechanisms can be evaluated by different MRI modalities. The potential therapeutic strategies are also discussed.

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.

Blood Pressure Management in Acute Stroke

The optimal management of arterial blood pressure in the setting of acute stroke has not been firmly defined. The different types of stroke--ischemic, intracerebral hemorrhage, and subarachnoid hemorrhage--have different pathophysiologies and require different approaches in terms of blood pressure management in the acute setting. This article reviews the current literature and experience at the authors' institution.

Pressor Therapy in Acute Ischemic Stroke

Background and Purpose— Systolic blood pressure (SBP) levels below 140 mm Hg after acute stroke occur in 18% to 25% of patients, and may be associated with adverse outcome, in terms of death and disability. It has thus been proposed that BP elevation in acute ischemic stroke may be beneficial by increasing perfusion to the peri-infarct penumbra, though not only in those with low BP levels.

Methods— All articles studying BP elevation in the context of acute stroke were identified using a structured search strategy.

Results— Two reviewers independently searched the databases, and 12 relevant publications were identified. All identified publications related to acute ischemic stroke and no articles on pressor therapy in primary hemorrhagic stroke were found. The review included 319 subjects (age: 42 to 88 years, 46% male), with phenylephrine being the most commonly used pressor agent, though 8 studies incorporated volume expansion. Because of small numbers, and varying entry/outcome criteria, no meta-analysis of outcome measures was possible. Overall, in these few studies undertaken, pressor therapy in acute stroke appears feasible and well-tolerated. The benefit and risks in terms of clinical outcomes remains unknown, but intensive monitoring is advised if such therapy is undertaken.

Conclusions— Theoretical arguments exist for inducing BP elevation in acute ischemic stroke to increase blood flow to the ischemic penumbra across patients with a broad BP range. To date, there have only been a few small trials with inconclusive results. Many questions are still unanswered about the safety and potential benefits of pressor therapy in acute stroke. Hopefully, ongoing trials will answer some of these important questions.

Advances in stroke neuroprotection: hyperoxia and beyond

Refinements in patient selection, improved methods of drug delivery, use of more clinically relevant animal stroke models, and the use of combination therapies that target the entire neurovascular unit make stroke neuroprotection an achievable goal. This article provides an overview of the major mechanisms of neuronal injury and the status of neuroprotective drug trials and reviews emerging strategies for treatment of acute ischemic stroke. Advances in the fields of stem cell transplantation, stroke recovery, molecular neuroimaging, genomics, and proteomics will provide new therapeutic avenues in the near future. These and other developments over the past decade raise expectations that successful stroke neuroprotection is imminent.

Pediatric Perfusion MR Imaging Using Arterial Spin Labeling

Cerebral blood flow (CBF, cerebral perfusion) mirrors cerebral metabolic demand and neuronal function, and therefore, is a vital parameter in the evaluation of pediatric brain injury and recovery. Until recently, measurement of CBF involved intravenous bolus injection of contrast agents or nuclear medicine methods that were technically difficult or ethically problematic in pediatrics. The development of arterial spin label (ASL) perfusion MR imaging as a noninvasive method for measuring CBF allows for the increased ability to measure this vital physiologic parameter in any age group. This article presents the technical aspects of performing ASL perfusion MR imaging in pediatrics, and discusses its current use in clinical studies and its potential for influencing important management strategies in specific disease entities.

Neuroimaging of ischemia and infarction

Since the introduction of thrombolytic therapy as the foundation of acute stroke treatment, neuroimaging has rapidly advanced to empower therapeutic decision making. Diffusion-weighted imaging is the most sensitive and accurate method for stroke detection, and, allied with perfusion-weighted imaging, provides information on the functional status of the ischemic brain. It can also help to identify a response to thrombolytic and neuroprotective therapies. Additionally, multimodal magnetic resonance imaging, including magnetic resonance angiography, offers information on stroke mechanism and pathophysiology that can guide long-term medical management. Multimodal computed tomography is a comprehensive, cost-effective, and safe stroke imaging modality that can be easily implemented in the emergency ward and that offers fast and reliable information with respect to the arterial and functional status of the ischemic brain. Accessibility, contraindications, cost, speed, and individual patient-determined features influence which is the best imaging modality to guide acute stroke management.

Three-dimensional Dynamic Susceptibility-weighted Perfusion MR Imaging at 3.0 T: Feasibility and Contrast Agent Dose

PURPOSE

To prospectively investigate if T2*-weighted dynamic susceptibility-weighted first-pass perfusion magnetic resonance (MR) imaging is feasible at 3.0 T and which dose of contrast agent is suitable for high-field-strength imaging.

MATERIALS AND METHODS

Informed consent was obtained from all participants; study protocol was approved by the institutional review board. Study included three volunteers (two men, one woman aged 35, 39, and 52 years) and 26 patients (mean age, 49 years +/- 12.8 [standard deviation]; range, 19-76 years). Volunteers underwent 3.0-T perfusion MR imaging with 0.20, 0.10, and 0.05 mmol per kilogram body weight of gadopentetate dimeglumine; patients underwent imaging with 0.10- and 0.05-mmol doses. Perfusion MR imaging was performed with three-dimensional echo-shifted echo-planar imaging (repetition time msec/echo time msec, 14/21; isotropic 4 mm3 voxels; 50 dynamic volumes with 30 sections each, covering entire brain at temporal resolution of 1.5 seconds per MR image). Quality of source echo-planar images and perfusion maps was assessed; perfusion maps obtained at studies with different contrast media doses were compared. Quantitative perfusion values and diagnostic sensitivity of perfusion studies with 0.10-mmol dose were compared with results with 0.05-mmol dose. Image quality scores were compared with marginal homogeneity test for multinomial variables (Mantel-Haenszel statistics for ordered categorized values). Signal-to-noise ratio and baseline signal intensity in perfusion studies were tested (Student t test for paired samples). Mean transit time (MTT), negative integral (NI), and maximum T2* effect from region-of-interest analysis were compared (one-tailed Student t test for paired samples). Quantitative data on number of gamma-fitted pixels were compared (t test for paired samples). Difference with P=.05 (t test for paired samples) was considered significant.

RESULTS

Perfusion image quality was satisfactory even in areas close to skull base (47 of 52 images, minor distortions; remaining images, marked distortions). Perfusion imaging with 0.20-mmol dose caused almost complete signal cancellation during first pass, particularly in cortical gray matter, since mean maximum T2* effect of 98%, 99%, and 98% for gray matter was reached such that the accurate calculation of perfusion maps was impossible. With 0.10-mmol dose, the NI and maximum T2* effect were comparable to published data for 1.5-T perfusion imaging with 0.20- and 0.05-mmol doses; perfusion maps of sufficient diagnostic quality were obtained. For gray matter, mean maximum T2* effect was 25.4% +/- 9.8 with 0.10-mmol dose and 17.5% +/- 9.0 with 0.05-mmol dose. For white matter, mean maximum T2* effect was 15.2% +/- 4.5 with 0.10-mmol dose and 7.7% +/- 2.9 with 0.05-mmol dose. Difference in maximum signal intensity decrease was significant (P <.01). For NI, the difference between 0.10- and 0.05-mmol doses was significant: For gray matter, mean NI was 3.1 +/- 1.60 for 0.10-mmol dose and 1.56 +/- 1.16 for 0.05-mmol dose. For white matter, mean NI was 1.35 +/- 0.59 with 0.1-mmol dose and 0.59 +/- 0.30 with 0.05-mmol dose.

CONCLUSION

With echo-shifted multishot echo-planar imaging, dynamic susceptibility-weighted perfusion MR imaging at high field strength is feasible without relevant image distortions. Compared with contrast agent dose for 1.5 T imaging, the dose for 3.0 T can be reduced to 0.10 mmol.

The roles of the “visual word form area” in reading

Activation of the left midfusiform gyrus in response to reading words and pseudowords is such a reliable finding in functional imaging that this region has been called "the visual word form area" (VWFA). However, this label has recently been challenged, because activation in VWFA is also observed in other lexical tasks. We evaluated whether VWFA is necessary, sufficient, or specialized for reading by examining how frequently acute lesions in VWFA disrupt tasks that require access to written word forms versus other lexical tasks. We administered lexical tasks with spoken and written input and output, and identified damage or dysfunction of VWFA and other regions of interest (ROI) on diffusion- and perfusion-weighted imaging (DWI and PWI) in 80 patients within 24 h of onset of acute left ischemic stroke. Associations between abnormalities in each region of interest and impairment on lexical tasks were evaluated with chi-squared tests. Damage or dysfunction of VWFA was not significantly associated with impairment of written word comprehension or lexical decision, but was significantly associated with impairment on all tasks requiring lexical output: oral reading and oral naming (visual or tactile input), and written naming. We account for these results and results from functional imaging by proposing that the left midfusiform gyrus normally has two roles in reading: (1) computation of location- and modality-independent grapheme sequences from written word stimuli, and (2) a modality-independent stage of lexical processing that links modality-specific input and output representations. VWFA is not necessary for the former because the right homologue of VWFA can immediately assume this role.