Early Functional Recovery and the Fate of the Diffusion/Perfusion Mismatch in Patients with Proximal Middle Cerebral Artery Occlusion

Imaging Acute Stroke: From One-Size-Fit-All to Biomarkers

In acute stroke management, time window has been rigidly used as a guide for decades and the reperfusion treatment is only available in the first few limited hours. Recently, imaging-based selection of patients has successfully expanded the treatment window out to 16 and even 24 h in the DEFUSE 3 and DAWN trials, respectively. Recent guidelines recommend the use of imaging techniques to guide therapeutic decision-making and expanded eligibility in acute ischemic stroke. A tissue window is proposed to replace the time window and serve as the surrogate marker for potentially salvageable tissue. This article reviews the evolution of time window, addresses the advantage of a tissue window in precision medicine for ischemic stroke, and discusses both the established and emerging techniques of neuroimaging and their roles in defining a tissue window. We also emphasize the metabolic imaging and molecular imaging of brain pathophysiology, and highlight its potential in patient selection and treatment response prediction in ischemic stroke.

Development and validation of a penumbra-based predictive model for thrombolysis outcome in acute ischemic stroke patients

The use of thrombolysis in acute ischemic stroke is restricted to a small proportion of patients because of the rigid 4·5-h window. With advanced imaging-based patient selection strategy, rescuing penumbra is critical to improving clinical outcomes. In this study, we included 155 acute ischemic stroke patients (84 patients in training dataset, age from 43 to 80, 59 males; 71 patients in validation dataset, age from 36 to 80, 45 males) who underwent MR scan within the first 9-h after onset, from 7 independent centers. Based on the mismatch concept, penumbra and core area were identified and quantitatively analyzed. Moreover, predictive models were developed and validated to provide an approach for identifying patients who may benefit from thrombolytic therapy. Predictive models were constructed, and corresponding areas under the curve (AUC) were calculated to explore their performances in predicting clinical outcomes. Additionally, the models were validated using an independent dataset both on Day-7 and Day-90. Significant correlations were detected between the mismatch ratio and clinical assessments in both the training and validation datasets. Treatment option, baseline systolic blood pressure, National Institutes of Health Stroke Scale score, mismatch ratio, and three regional radiological parameters were selected as biomarkers in the combined model to predict clinical outcomes of acute ischemic stroke patients. With the external validation, this predictive model reached AUCs of 0·863 as short-term validation and 0·778 as long-term validation. This model has the potential to provide quantitative biomarkers that aid patient selection for thrombolysis either within or beyond the current time window.

Motor Recovery as Assessed with Isometric Finger Movements and Perfusion Magnetic Resonance Imaging after Acute Ischemic Stroke

Objective. Recovery from hemiparetic stroke is variable. An important goal for clinicians and clinical researchers is to identify predictors of recovery. The initial phase after acute ischemic stroke is considered to be of major importance for neurological outcome. The authors sought to determine in patients with acute ischemic stroke whether early motor recovery, as measured by repetitive isometric index-thumb oppositions, is correlated with ischemic lesion volume. Methods. Thirty-six acute hemiparetic stroke patients with residual hand function were investigated. The European Stroke Scale (ESS) score was determined on admission and at discharge. Performance of repetitive index finger-thumb pinch movements was measured daily during the 1st 8 days after stroke onset. Brain ischemia volume was determined digitally in time-to-peak magnetic resonance images of per-fusion. Results. The recovery of patients with ( P = 0.002) and without ( P < 0.001) thrombolysis as assessed with the ESS was paralleled by an increase in isometric grip force and movement rate ( P < 0.05). Recovery was predicted by the area of moderately impaired perfusion indicated by the per-fusion mismatch volume ( r = 0.578, P < 0.001). Conclusions. In acute stroke, recovery of hand function is predicted by the volume of salvageable ischemic tissue, as determined by the perfusion mismatch.

Does preinterventional flat-panel computer tomography pooled blood volume mapping predict final infarct volume after mechanical thrombectomy in acute cerebral artery occlusion?

PURPOSE

Decreased cerebral blood volume is known to be a predictor for final infarct volume in acute cerebral artery occlusion. To evaluate the predictability of final infarct volume in patients with acute occlusion of the middle cerebral artery (MCA) or the distal internal carotid artery (ICA) and successful endovascular recanalization, pooled blood volume (PBV) was measured using flat-panel detector computed tomography (FPD CT).

MATERIALS AND METHODS

Twenty patients with acute unilateral occlusion of the MCA or distal ACI without demarcated infarction, as proven by CT at admission, and successful Thrombolysis in cerebral infarction score (TICI 2b or 3) endovascular thrombectomy were included. Cerebral PBV maps were acquired from each patient immediately before endovascular thrombectomy. Twenty-four hours after recanalization, each patient underwent multislice CT to visualize final infarct volume. Extent of the areas of decreased PBV was compared with the final infarct volume proven by follow-up CT the next day.

RESULTS

In 15 of 20 patients, areas of distinct PBV decrease corresponded to final infarct volume. In 5 patients, areas of decreased PBV overestimated final extension of ischemia probably due to inappropriate timing of data acquisition and misery perfusion.

CONCLUSION

PBV mapping using FPD CT is a promising tool to predict areas of irrecoverable brain parenchyma in acute thromboembolic stroke. Further validation is necessary before routine use for decision making for interventional thrombectomy.

Therapeutic results of intra-arterial thrombolysis after full-dose intravenous tissue plasminogen activator administration

BACKGROUND AND PURPOSE

IV administration of tPA is accepted as a standard treatment for acute cerebral ischemia, but the clinical outcomes cannot be guaranteed in patients who are not recanalized after IV-tPA and in those who are not eligible for IV-tPA. In this study, outcomes from groups of patients treated with additional IA thrombolytic therapy with the use or omission of IV-tPA administration were compared.

MATERIALS AND METHODS

IA thrombolytic therapy (thrombolytic agents combined with mechanical intervention) was attempted in those patients who were not eligible for IV-tPA and who showed continuous major vessel occlusion after IV-tPA. Sixty-three patients were divided into 2 groups: a tPA group (n = 29, IA thrombolysis after IV-tPA) and a non-tPA group (n = 34, IA thrombolysis without IV-tPA). These groups were subdivided according to match or mismatch DWI/PWI after MR imaging. Treatment results were compared by recanalization rate, clinical outcome, mortality, and ICH rate.

RESULTS

The recanalization rate was 79.3% in the tPA group and 55.9% in the non-tPA group (χ(2) test, P < .05). Subgroup analysis between DWI/PWI mismatch in the tPA group and DWI/PWI mismatch in the non-tPA group also showed no statistical difference in recanalization rate, favorable clinical outcome, and mortality (χ(2) test, P > .05), but the significant ICH rate was high in the tPA group (χ(2) test, P < .05).

CONCLUSIONS

Additional IA thrombolytic treatment after full-dose IV-tPA administration might be an acceptable treatment option for patients with DWI/PWI mismatch.

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.

Clinical review: Imaging in ischaemic stroke--implications for acute management

Imaging has become a cornerstone of stroke management, translating pathophysiological knowledge to everyday decision-making. Plain computed tomography is widely available and remains the standard for initial assessment: the technique rules out haemorrhage, visualizes the occluding thrombus and identifies early tissue hypodensity and swelling, which have different implications for thrombolysis. Based on evidence from positron emission tomography (PET), however, multimodal imaging is increasingly advocated. Computed tomography perfusion and angiography provide information on the occlusion site, on recanalization and on the extent of salvageable tissue. Magnetic resonance-based diffusion-weighted imaging (DWI) has exquisite sensitivity for acute ischaemia, however, and there is increasingly robust evidence that DWI combined with perfusion-weighted magnetic resonance imaging (PWI) and angiography improves functional outcome by selecting appropriate patients for thrombolysis (small DWI lesion but large PWI defect) and by ruling out those who would receive no benefit or might be harmed (very large DWI lesion, no PWI defect), especially beyond the 3-hour time window. Combined DWI–PWI also helps predict malignant oedema formation and therefore helps guide selection for early brain decompression. Finally, DWI–PWI is increasingly used for patient selection in therapeutic trials. Although further methodological developments are awaited, implementing the individual pathophysiologic diagnosis based on multimodal imaging is already refining indications for thrombolysis and offers new opportunities for management of acute stroke patients.

Pathophysiology of ischaemic stroke: insights from imaging, and implications for therapy and drug discovery

Preventing death and limiting handicap from ischaemic stroke are major goals that can be achieved only if the pathophysiology of infarct expansion is properly understood. Primate studies showed that following occlusion of the middle cerebral artery (MCA)--the most frequent and prototypical stroke, local tissue fate depends on the severity of hypoperfusion and duration of occlusion, with a fraction of the MCA territory being initially in a 'penumbral' state. Physiological quantitative PET imaging has translated this knowledge in man and revealed the presence of considerable pathophysiological heterogeneity from patient to patient, largely unpredictable from elapsed time since onset or clinical deficit. While these observations underpinned key trials of thrombolysis, they also indicate that only patients who are likely to benefit should be exposed to its risks. Accordingly, imaging-based diagnosis is rapidly becoming an essential component of stroke assessment, replacing the clock by individually customized management. Diffusion- and perfusion-weighted MR (DWI-PWI) and CT-based perfusion imaging are increasingly being used to implement this, and are undergoing formal validation against PET. Beyond thrombolysis per se, knowledge of the individual pathophysiology also guides management of variables like blood pressure, blood glucose and oxygen saturation, which can otherwise precipitate the penumbra into the core, and the oligaemic tissue into the penumbra. We propose that future therapeutic trials use physiological imaging to select the patient category that best matches the drug's presumed mode of action, rather than lumping together patients with entirely different pathophysiological patterns in so-called 'large trials', which have all failed so far.

Pattern of cortex and white matter involvement in severe middle cerebral artery ischemia

BACKGROUND AND PURPOSE

In middle cerebral artery (MCA) stroke, ischemia usually is unevenly distributed within the MCA territory. We sought to investigate which brain structures are critical for the acute neurological deficit in severe MCA stroke.

METHODS

We used magnetic resonance (MR) imaging and statistical parametric mapping in 64 consecutive stroke patients (64 +/-13 years) to study the pattern of the initial perfusion abnormality.

RESULTS

Patients with lesion progression had more severe time-to-peak (TTP) abnormalities (P < .0001) in the inferior frontal gyrus, superior temporal gyrus, insula, and underlying hemispheric white matter than those with lesion regression. Also, patients with lesion progression had more severe T2 abnormalities on day 8 than those with lesion regression. In contrast, the changes of water diffusion were similar among the two groups resulting in a perfusion-diffusion mismatch in lesion progression. TTP-lesions were related to the neurological deficit score (r(s)=-0.563, P < .0001), T2-lesions (r= 0.686, P < .0001), and cerebral artery abnormalities assessed on MR-angiography (r(s)= 0.399, P < .01).

CONCLUSIONS

In major MCA, stroke ischemia was most severe in the central portion of the MCA territory. It is suggested that involvement of hemispheric white matter accentuated the neurological deficit probably by affecting cortico-cortical and cortico-subcortical fibers.

Significance of the perfusion-diffusion mismatch in chronic cerebral ischemia

PURPOSE

To determine whether the perfusion deficit could predict brain infarction in patients with chronic cerebral ischemia who experienced recurring episodes of neurological symptoms and showed a perfusion-diffusion mismatch on magnetic resonance (MR) images.

MATERIALS AND METHODS

In 53 consecutive patients (38 males and 15 females, 62+/-13 years old) with ischemia in the middle cerebral artery (MCA) territory, lesion volumetry was performed on parametric maps of the time-to-peak, the cerebral blood volume, and diffusion-weighted (DW) images. The infarct lesions were assessed on follow-up T2-weighted (T2W) MR images after eight days. Cerebrovascular changes were determined by time-of-flight (TOF) MR angiography (MRA). Inferential and correlation statistics were used.

RESULTS

Patients with chronic ischemic brain disease (N=39) who presented with a severe perfusion-diffusion mismatch in the presence of a normal cerebral blood volume had no or small brain infarctions as found on follow-up T2W images. MRA revealed widespread abnormalities of the basal cerebral arteries compatible with brain perfusion abnormalities. In contrast, in acute stroke patients (N=14) the deficit of cerebral perfusion predicted the infarct lesion in the T2W images.

CONCLUSION

Our results suggest that in chronic cerebral ischemia the normal blood volume was maintained despite the depression of cerebral perfusion and recurring minor insults.

Imaging the penumbra in acute stroke

Imaging continues to have a huge impact on the understanding of the ischemic penumbra and the management of acute stroke. Determinants of penumbral tissue fate, such as age, hyperglycemia, hematocrit, and oxygen concentration, are increasingly being recognized using neuroimaging. The significance of the penumbra in the white matter and in posterior circulation stroke is also becoming clearer. Neuroimaging is also making invaluable contributions to clinical decision making in acute stroke, especially in relation to reperfusion therapies in the 3- to 6-hour time window. Despite ongoing questions over the choice of parameters to identify the penumbra and their respective clinical usefulness, imaging is gaining widespread use in acute stroke management. However, definitive evidence of its benefit is still lacking. This review explores the recent progress and controversies relating to imaging of the penumbra.

Imaging of acute stroke

Thrombolytic therapy has led to a higher proportion of patients presenting to hospital early, and this, with parallel developments in imaging technology, has greatly improved the understanding of acute stroke pathophysiology. Additionally, MRI, including diffusion-weighted imaging (DWI) and gradient echo, or T2*, imaging is important in understanding basic structural information--such as distinguishing acute ischaemia from haemorrhage. It has also greatly increased sensitivity in the diagnosis of acute cerebral ischaemia. The pathophysiology of the ischaemic penumbra can now be assessed with CT or MRI-based perfusion imaging techniques, which are widely available and clinically applicable. Pathophysiological information from CT or MRI increasingly helps clinical trial design, may allow targeted therapy in individual patients, and may extend the time scale for reperfusion therapy.

Ischemic Thresholds for Gray and White Matter

Background and Purpose— Although gray matter (GM) and white matter (WM) have differing neurochemical responses to ischemia in animal models, it is unclear whether this translates into differing thresholds for infarction. We studied this issue in ischemic stroke patients using magnetic resonance (MR) techniques.

Methods— MR studies were performed in patients with acute hemispheric ischemic stroke occurring within 24 hours and at 3 months. Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and apparent diffusion coefficient (ADC) were calculated. After segmentation based on a probabilistic map of GM and WM, tissue-specific diffusion and perfusion thresholds for infarction were established.

Results— Twenty-one patients were studied. Infarction thresholds for CBF were significantly higher in GM (median 34.6 mL/100 g per minute, interquartile range 26.0 to 38.8) than in WM (20.8 mL/100 g per minute; interquartile range 18.0 to 25.9; P <0.0001). Thresholds were also significantly higher in GM than WM for CBV (GM: 1.67 mL/100 g; interquartile range 1.39 to 2.17; WM: 1.19 mL/100 g; interquartile range 0.94 to 1.53; P <0.0001), ADC (GM: 918×10 −6 mm 2 /s; 868 to 975×10 −6 ; WM: 805×10 −6 ; 747 to 870×10 −6 ; P <0.001), and there was a trend toward a shorter MTT in GM (GM 4.94 s, 4.44 to 5.38; WM 5.15, 4.11 to 5.68; P =0.11).

Conclusions— GM has a higher infarction threshold for CBF, CBV, and ADC than WM in patients within 24 hours of ischemic stroke onset. Hence, when assessing patients for potential therapies, tissue-specific rather than whole-brain thresholds may be a more precise measure of predicting the likelihood of infarction.

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.

Initial Ischemic Event: Perfusion-weighted MR Imaging and Apparent Diffusion Coefficient for Stroke Evolution

PURPOSE

To prospectively determine if the degree of acute perfusion or diffusion abnormalities measured prior to treatment onset help predict the evolution of brain infarction on magnetic resonance (MR) images.

MATERIALS AND METHODS

Local ethics committee approval and informed consent were obtained. On parametric maps obtained in 64 patients (mean age, 64 years +/- 13 [standard deviation]; 37 men and 27 women) with acute middle cerebral artery infarction, lesion volumetry was performed to determine time to peak, mean transit time, cerebral blood volume, and apparent diffusion coefficient obtained within 3 hours of symptom onset. The infarct lesions were assessed on T2-weighted MR images obtained at follow-up on day 8. Cerebrovascular changes were determined on MR angiograms. Inferential and correlation statistics were used.

RESULTS

A perfusion delay of more than 6 seconds relative to the nonaffected hemisphere on time-to-peak maps helped to predict the lesion volume on T2-weighted images (r = 0.686, P < .001). In contrast, neither the volume nor the degree of the diffusion abnormality helped to predict the infarct volume (r < 0.46). This was because in one subgroup of patients there was an increase and in one subgroup there was a decrease in infarct volume on the T2-weighted images (P < .001). There was a greater prevalence (P < .02) of cerebral artery abnormalities in the patients with larger infarcts. Clinically, the neurologic impairment was more severe (P < .01) and the mean arterial pressure higher (P < .04) in these patients.

CONCLUSION

The results suggest that in acute stroke the severity of the initial ischemic event as determined on time-to-peak maps indicates hemodynamic compromise in addition to internal carotid artery or middle cerebral artery occlusion, because of abnormalities in other cerebral arteries.

Comparative analysis of the CD19+ and CD138+ cell antibody repertoires in the cerebrospinal fluid of patients with multiple sclerosis

Increased amounts of intrathecally synthesized IgG and oligoclonal bands have long been recognized as a hallmark of multiple sclerosis (MS). B cells and plasma cells are components of the inflammatory infiltrates in both active and chronic MS lesions, and increased numbers of these cells are present in MS cerebrospinal fluid (CSF). Single-cell RT-PCR was used to analyze both the CD19+ B cell and CD138+ plasma cell populations in CSF of two patients with clinically definite MS and of one MS patient whose CSF was obtained after a clinically isolated syndrome, but before the second episode. Sequence analysis of amplified IgG V region sequences identified the rearranged germline segments, extent of somatic mutation, and clonal relationships within and between the two cell populations in the three MS patients. Expanded B cell and plasma cell clones were detected in each MS CSF and in all three patients the CD138+ IgG repertoire was more restricted. However, little if any significant sequence overlap was observed between the CD19+ and CD138+ repertoires of each donor. Detection of plasma cell clones by single-cell PCR will facilitate the in vitro production of recombinant Abs useful in identifying disease-relevant Ags.

Antigen discovery in chronic human inflammatory central nervous system disease: panning phage-displayed antigen libraries identifies the targets of central nervous system-derived IgG in subacute sclerosing panencephalitis

The presence of increased IgG in the brains of humans with infectious and inflammatory CNS diseases of unknown etiology such as multiple sclerosis may be a clue to the cause of disease. For example, the intrathecally synthesized oligoclonal bands in diseases such as subacute sclerosing panencephalitis (SSPE) or cryptococcal meningitis have been shown to represent Ab directed against the causative agents, measles virus (MV), or Cryptococcus neoformans, respectively. Using SSPE as a model system, we developed a strategy to identify the antigenic targets of the intrathecal disease-relevant IgG in chronic human inflammatory and demyelinating diseases of the CNS. Libraries of cDNA Ags were displayed on the surface of T7Select bacteriophage and biopanned on IgG extracted from the brain of an SSPE patient, or on a monospecific recombinant Fab identified from SSPE brain. After three or six rounds of biopanning on either Ab, positive phage-displayed Ags reacting with IgG were enriched to 35-77% of all panned clones. Sequence analysis of the positive clones identified fragments of the nucleocapsid protein of MV, the cause of SSPE. The sensitivity of the system was determined by diluting the positive clones from this SSPE phage-displayed library at a ratio of 10(-6) into another phage-displayed library that did not contain any detectable MV Ags; after six rounds of panning, the positive clones comprised 34% of all phage and were also shown to be MV nucleocapsid specific. This strategy will be useful to identify potentially rare Ags in diseases of unknown cause.

Oligoclonal IgA response in the vascular wall in acute Kawasaki disease

Kawasaki Disease (KD) is a potentially fatal acute vasculitis of childhood. Although KD is the leading cause of acquired heart disease in children in developed nations, its pathogenesis remains unknown. We previously reported the novel observation that IgA plasma cells infiltrate the vascular wall in acute KD. We have now examined the clonality of this IgA response in vascular tissue from three fatal cases of KD to determine whether it is oligoclonal, suggesting an Ag-driven process, or polyclonal, suggesting nonspecific B cell activation or a response to a superantigen. We first sequenced VDJ junctions of 44 alpha genes isolated from a primary, unamplified KD vascular cDNA library. Five sets of clonally related alpha sequences were identified, comprising 34% (15 of 44) of the isolated alpha sequences. Furthermore, point mutations consistent with somatic mutation were detected in the related sequences. Next, using formalin-fixed coronary arteries from two additional fatal KD cases, we sequenced VDJ junctions of alpha genes isolated by RT-PCR, and a restricted pattern of CDR3 usage was observed in both. We conclude that the vascular IgA response in acute KD is oligoclonal. The identification of an oligoclonal IgA response in KD strongly suggests that the immune response to this important childhood illness is Ag-driven.