Comparison of admission perfusion computed tomography and qualitative diffusion- and perfusion-weighted magnetic resonance imaging in acute stroke patients

Interventional neuroradiology of stroke, still not dead

Since the National Institute of Neurological Disorders and Stroke trial, intravenous thrombolysis has been gaining wide acceptance as the modality of treatment for acute embolic stroke, with a current therapeutic window of up to 4.5 h. Both imaging [with either magnetic resonance imaging (MRI) or computed tomography (CT)] and interventional techniques (thrombolysis and/or thrombectomy) have since improved and provided us with additional imaging of the penumbra using CT or MRI and more advanced thrombolysis or thrombectomy strategies that have been embraced in many centers dealing with patients with acute cerebral ischemia. These techniques, however, have come under scrutiny due to their accrued healthcare costs and have been questioned following major recent studies. These studies basically showed that interventional techniques were not superior to the traditional intravenous thrombolysis techniques and that penumbra imaging could not determine what patients would benefit from more aggressive (i.e., interventional) treatment. We discuss this in the light of the latest developments in both diagnostic and interventional neuroradiology and point out why further studies are needed in order to define the right choices for patients with acute stroke. Indeed, these studies were in part conducted with suboptimal patient recruitment strategies and did not always use the latest interventional techniques available today. So, while these studies may have raised some relevant questions, at the same time, definitive answers have not been given, in our opinion.

Clinical application of perfusion computed tomography in neurosurgery

OBJECT

Currently, perfusion CT (PCT) is a valuable imaging technique that has been successfully applied to the clinical management of patients with ischemic stroke and aneurysmal subarachnoid hemorrhage (SAH). However, recent literature and the authors' experience have shown that PCT has many more important clinical applications in a variety of neurosurgical conditions. Therefore, the authors share their experiences of its application in various diseases of the cerebrovascular, neurotraumatology, and neurooncology fields and review the pertinent literature regarding expanding PCT applications for neurosurgical conditions, including pitfalls and future developments.

METHODS

A pertinent literature search was conducted of English-language articles describing original research, case series, and case reports from 1990 to 2011 involving PCT and with relevance and applicability to neurosurgical disorders.

RESULTS

In the cerebrovascular field, PCT is already in use as a diagnostic tool for patients suspected of having an ischemic stroke. Perfusion CT can be used to identify and define the extent of the infarct core and ischemic penumbra core, and thus aid patient selection for acute reperfusion therapy. For patients with aneurysmal SAH, PCT provides assessment of early brain injury, cerebral ischemia, and infarction, in addition to vasospasm. It may also be used to aid case selection for aggressive treatment of patients with poor SAH grade. In terms of oncological applications, PCT can be used as an imaging biomarker to assess angiogenesis and response to antiangiogenetic treatments, differentiate between glioma grades, and distinguish recurrent tumor from radiation necrosis. In the setting of traumatic brain injury, PCT can detect and delineate contusions at an early stage. In patients with mild head injury, PCT results have been shown to correlate with the severity and duration of postconcussion syndrome. In patients with moderate or severe head injury, PCT results have been shown to correlate with patients' functional outcome.

CONCLUSIONS

Perfusion CT provides quantitative and qualitative data that can add diagnostic and prognostic value in a number of neurosurgical disorders, and also help with clinical decision making. With emerging new technical developments in PCT, such as characterization of blood-brain barrier permeability and whole-brain PCT, this technique is expected to provide more and more insight into the pathophysiology of many neurosurgical conditions.

Recent advances in endoluminal revascularization for intracranial atherosclerotic disease

More than 750,000 strokes occur annually in the United States. Of these, 8-10% are due to intracranial atherosclerosis. Less than 50% of patients with strokes from intracranial atherosclerosis will have a transient ischemic attack. For those patients with symptomatic intracranial atherosclerosis, the prognosis is poor; and the recent Warfarin-Aspirin Symptomatic Intracranial Stenosis (WASID) trial results have demonstrated the high risk of warfarin without clear benefit. Intracranial angioplasty and stenting is emerging as a viable and effective treatment alternative for patients with symptomatic intracranial stenosis. Advances in stent design, endovascular wires, and catheters and balloons are allowing endovascular surgeons to safely treat intracranial atherosclerosis. Wider clinical experience has led to refinement of patient selection and endoluminal techniques. Drug eluting-stents have the promise of decreasing the risk of restenosis. In this review, the most recent clinical, laboratory, and technical details for the treatment of intracranial angioplasty and stenting are discussed.

A rat's whiskers point the way toward a novel stimulus-dependent, protective stroke therapy

Stroke is the fourth leading cause of death in the United States and the leading cause of long-term disability. Ischemic stroke, due to an interruption in blood supply, is particularly prevalent; 87% of all strokes are ischemic. Unfortunately, current options for acute treatment are extremely limited and there is a great need for new treatment strategies. This review will discuss evidence that mild sensory stimulation can completely protect the jeopardized brain from an impending stroke in a rodent model. When delivered within the first 2 hours following ischemic onset, this stimulation results in complete protection, including a full reestablishment of cortical function, sensorimotor capabilities, and blood flow. Identical stimulation, however, initiated 3 hours following ischemic onset, results in an increase in damage compared with untreated animals. The protective effect is not specific to a single sensory modality, anesthesia, or age, and increasing evoked cortical activity by increasing stimulation accelerates recovery. Taken together, these findings demonstrate that cortical activity is a critical factor for protection and suggest a new, exciting potential avenue for the development of acute stroke treatment strategies that may produce a noninvasive, drug-free, equipment-free, and side effect-free means of protecting from ischemic stroke.

64-Slice spiral CT perfusion combined with vascular imaging of acute ischemic stroke for assessment of infarct core and penumbra

The aim of this study was to determine the value of computed tomography perfusion (CTP) parameters, including cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time-to-peak (TP), in a clinical study of patients with stroke. Additionally, we determined which parameter or combination of parameters are reliable in detecting the presence of an infarct and penumbra. CTP was performed within 24 h of the onset of symptoms in 20 patients with possible stroke. Magnetic resonance imaging (MRI) was performed 3-7 days later and the threshold of the CTP was adjusted according to the results to provide CT images that correlated with the MRI; the MRI results were taken as the gold standard. CBV, CBF and TP contrast agent enhancement were calculated using the CT results. The CTP results were compared with the MRI findings. All CTP parameters were reliable in detecting the penumbra (P<0.001). In these parameters, changes of MTT were the most useful. CTP revealed various changes in CBF, CBV, MTT and TP in ischemic areas. CTP parameters were also reliable in detecting the infarct core (P<0.001). We determined that when detecting the penumbra, all CTP parameters are reliable, and when detecting cerebral ischemia, a combination of parameters should be used.

A phantom approach to interscanner comparability of computed tomographic brain perfusion parameters

OBJECTIVE

This study aimed to create a phantom, which allows reproducible computed tomography perfusion experiments, and to identify the influence of contrast bolus configuration, scan parameters, and scanner hardware on the calculation of perfusion parameters.

METHODS

A discoid perfusion phantom with centrifugally directed flow was constructed. Brain parenchyma was simulated by inert polyoxymethylene spheres. Repeated measurements were performed with variations of the above-mentioned factors, and their effects on perfusion results were analyzed.

RESULTS

Calculated flow values measured during experiments were reproducible and showed good correlation with the true flow (R = 0.995, P < 0.01). Tube voltage, injection rate of the contrast agent, the mathematical perfusion algorithm, and the hardware of the scanner hardware had a reproducible influence on calculated perfusion results.

CONCLUSIONS

In the long term, perfusion phantoms might be helpful in identifying hardware-specific and protocol-related factors of different computed tomography scanners to improve comparability of different scanners and scanning protocols.

Admission hyperglycaemia and cerebral perfusion deficits in acute ischaemic stroke

INTRODUCTION

Hyperglycaemia (HG) occurs in 30-40% of the patients with acute ischaemic stroke and is associated with larger infarct size and poor functional outcome. It is unknown whether HG is also associated with larger perfusion deficits in the acute stage of ischaemic stroke. As perfusion computed tomography (CT) is a reliable technique to determine the infarct core and ischaemic penumbra, we aimed to determine if patients with acute ischaemic stroke and HG have larger perfusion deficits or infarct cores on admission perfusion CT than patients with normoglycaemia (NG).

METHODS

We identified 80 consecutive patients (mean age 69 ± 11 years, 58% men) with acute supratentorial non-lacunar ischaemic stroke in whom CT showed a perfusion deficit within 24 h after stroke onset. The size of the total perfusion deficit area (mean transit time of >145% compared to the contralateral hemisphere) and the infarct core area (cerebral blood volume of <2.0 ml/100 g) at the level of the basal ganglia (level 1) and at the level of the corona radiata (level 2) were compared between patients with HG (admission glucose ≥7.0 mM) and patients with NG with a MANOVA. Clinical outcome [modified Rankin Scale (mRS) score] after 6 months was correlated to glucose levels at admission.

RESULTS

Admission HG was present in 33 of the 80 patients (41%). A perfusion deficit was present in 79 (40% HG) patients at level 1 and 75 (43% HG) at level 2. The total area with a perfusion deficit (level 1 HG 22.1 ± 11.3 and NG 23.3 ± 12.3 cm(2); level 2 HG 27.1 ± 12.3 and NG 25.4 ± 12.0 cm(2)) and the proportion of the infarct core (level 1 HG 31 ± 30% and NG 25 ± 22%; level 2 HG 33 ± 27% and NG 26 ± 23%) did not differ significantly between the groups. HG was associated with worse outcome (mRS ≥3) at 6 months (OR 2.6, 95% CI 0.72-9.1).

CONCLUSIONS

As compared to patients with NG, patients with HG did not have larger perfusion deficits in the acute stage of ischaemic stroke. Nevertheless, functional outcome was worse in patients with HG, which means that poor clinical outcome in stroke patients with HG could not be explained by a larger perfusion deficit in the acute stage. Therefore, our study suggests that there might be a window of opportunity for glucose-lowering therapy in the future.

Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

The authors present an overview of the current evidence and management recommendations for evaluation and treatment of adults with acute ischemic stroke. The intended audiences are prehospital care providers, physicians, allied health professionals, and hospital administrators responsible for the care of acute ischemic stroke patients within the first 48 hours from stroke onset. These guidelines supersede the prior 2007 guidelines and 2009 updates.

METHODS

Members of the writing committee were appointed by the American Stroke Association Stroke Council's Scientific Statement Oversight Committee, representing various areas of medical expertise. Strict adherence to the American Heart Association conflict of interest policy was maintained throughout the consensus process. Panel members were assigned topics relevant to their areas of expertise, reviewed the stroke literature with emphasis on publications since the prior guidelines, and drafted recommendations in accordance with the American Heart Association Stroke Council's Level of Evidence grading algorithm.

RESULTS

The goal of these guidelines is to limit the morbidity and mortality associated with stroke. The guidelines support the overarching concept of stroke systems of care and detail aspects of stroke care from patient recognition; emergency medical services activation, transport, and triage; through the initial hours in the emergency department and stroke unit. The guideline discusses early stroke evaluation and general medical care, as well as ischemic stroke, specific interventions such as reperfusion strategies, and general physiological optimization for cerebral resuscitation.

CONCLUSIONS

Because many of the recommendations are based on limited data, additional research on treatment of acute ischemic stroke remains urgently needed.

Accuracy of CT cerebral perfusion in predicting infarct in the emergency department: lesion characterization on CT perfusion based on commercially available software

This study aims to assess the diagnostic accuracy of a single vendor commercially available CT perfusion (CTP) software in predicting stroke. A retrospective analysis on patients presenting with stroke-like symptoms within 6 h with CTP and diffusion-weighted imaging (DWI) was performed. Lesion maps, which overlays areas of computer-detected abnormally elevated mean transit time (MTT) and decreased cerebral blood volume (CBV), were assessed from a commercially available software package and compared to qualitative interpretation of color maps. Using DWI as the gold standard, parameters of diagnostic accuracy were calculated. Point biserial correlation was performed to assess for relationship of lesion size to a true positive result. Sixty-five patients (41 females and 24 males, age range 22-92 years, mean 57) were included in the study. Twenty-two (34 %) had infarcts on DWI. Sensitivity (83 vs. 70 %), specificity (21 vs. 69 %), negative predictive value (77 vs. 84 %), and positive predictive value (29 vs. 50 %) for lesion maps were contrasted to qualitative interpretation of perfusion color maps, respectively. By using the lesion maps to exclude lesions detected qualitatively on color maps, specificity improved (80 %). Point biserial correlation for computer-generated lesions (R pb = 0.46, p < 0.0001) and lesions detected qualitatively (R pb = 0.32, p = 0.0016) demonstrated positive correlation between size and infarction. Seventy-three percent (p = 0.018) of lesions which demonstrated an increasing size from CBV, cerebral blood flow, to MTT/time to peak were true positive. Used in isolation, computer-generated lesion maps in CTP provide limited diagnostic utility in predicting infarct, due to their inherently low specificity. However, when used in conjunction with qualitative perfusion color map assessment, the lesion maps can help improve specificity.

Mild sensory stimulation protects the aged rodent from cortical ischemic stroke after permanent middle cerebral artery occlusion

BACKGROUND

Accumulated research has shown that the older adult brain is significantly more vulnerable to stroke than the young adult brain. Although recent evidence in young adult rats demonstrates that single-whisker stimulation can result in complete protection from ischemic damage after permanent middle cerebral artery occlusion (pMCAO), it remains unclear whether the same treatment would be effective in older animals.

METHODS AND RESULTS

Aged rats (21 to 24 months of age) underwent pMCAO and subsequently were divided into "treated" and "untreated" groups. Treated aged rats received intermittent single-whisker stimulation during a 120-minute period immediately after pMCAO, whereas untreated aged rats did not. These animals were assessed using a battery of behavioral tests 1 week before and 1 week after pMCAO, after which their brains were stained for infarct. An additional treated aged group and a treated young adult group also were imaged with functional imaging. Results demonstrated that the recovery of treated aged animals was indistinguishable from that of the treated young adult animals. Treated aged rats had fully intact sensorimotor behavior and no infarct, whereas untreated aged rats were impaired and sustained cortical infarct.

CONCLUSIONS

Taken together, our results confirm that single-whisker stimulation is protective in an aged rodent pMCAO model, despite age-associated stroke vulnerability. These findings further suggest potential for translation to the more clinically relevant older adult human population. (J Am Heart Assoc. 2012;1:e001255 doi: 10.1161/JAHA.112.001255.).

Reliability of cerebral blood volume maps as a substitute for diffusion-weighted imaging in acute ischemic stroke

PURPOSE

To assess the reliability of cerebral blood volume (CBV) maps as a substitute for diffusion-weighted MRI (DWI) in acute ischemic stroke. In acute stroke, DWI is often used to identify irreversibly injured "core" tissue. Some propose using perfusion imaging, specifically CBV maps, in place of DWI. We examined whether CBV maps can reliably subsitute for DWI, and assessed the effect of scan duration on calculated CBV.

MATERIALS AND METHODS

We retrospectively identified 58 patients who underwent DWI and MR perfusion imaging within 12 h of stroke onset. CBV in each DWI lesion's center was divided by CBV in the normal-appearing contralateral hemisphere to yield relative regional CBV (rrCBV). The proportion of lesions with decreased rrCBV was calculated. After using the full scan duration (110 s after contrast injection), rrCBV was recalculated using simulated shorter scans. The effect of scan duration on rrCBV was tested with linear regression.

RESULTS

Using the full scan duration (110 s), rrCBV was increased in most DWI lesions (62%; 95% confidence interval, 48-74%). rrCBV increased with increasing scan duration (P < 0.001). Even with the shortest duration (39.5 s) rrCBV was increased in 33% of lesions.

CONCLUSION

Because DWI lesions may have elevated or decreased CBV, CBV maps cannot reliably substitute for DWI in identifying the infarct core.

The evolution of the cerebral blood volume abnormality in patients with ischemic stroke: a CT perfusion study

BACKGROUND

Accurate identification of the acute infarct core abnormality is important for guiding acute stroke treatment. Abnormality volumes from diffusion-weighted MRI (DWI) and CT perfusion (CTP)-cerebral blood volume (CBV) are highly correlated. DWI lesions have been shown to be reversible at 24 h.

PURPOSE

To examine the temporal profile of the CT perfusion (CTP)-derived CBV abnormality out to 7 days post ischemic stroke.

MATERIAL AND METHODS

Twenty-six patients were included. Group A (n = 13) underwent a non-contrast CT (NCCT), CTP/CT angiography (CTA) within 6 h of stroke onset, CTP/CTA at 24 h, and CTP/NCCT at 5-7 days post stroke. Group B (n = 13) underwent a NCCT, CTP/CTA within 6 h of stroke onset, and NCCT at 5-7 days. Recanalization status was established in all patients. For both groups, infarct volumes were traced on 5-7 day NCCT images and superimposed onto all CTP-CBV functional maps to determine CBV. Group B (n = 13) admission images were used to define CBV infarct thresholds for gray and white matter. CBV-lesion over-estimation was determined for Group A using the thresholds from Group B.

RESULTS

CBV (mL·100g(- 1); mean ± stdev) for gray/white matter, within confirmed infarcted regions (CBV(I)) at admission, 24 h, and 5-7 days were 1.82 ± 0.56, 1.56 ± 0.42, 1.75 ± 0.31, and 1.38 ± 0.65, 1.13 ± 0.31, 1.32 ± 0.44, respectively, when averaged over all patients (P > 0.05). Four patients had tissue time-density curves from ischemic lesions (TDC(i)) with an incomplete contrast medium wash-out phase (truncation) at admission and/or 24 h. Compared to admission, gray matter CBV(I) was higher at 5-7 days for patients with TDC(i) truncation (P < 0.05). There were no significant CBV(I) increases for the eight patients without truncation (P > 0.05). Over-estimation of acute CBV lesion was present in 3/4 (75%) and 1/9 (11%) of patients with/without TDC(i) truncation, respectively.

CONCLUSION

CTP-derived CBV lesion reversal is associated with TDC(i) truncation during the acute stroke phase.

Perfusion/Diffusion mismatch is valid and should be used for selecting delayed interventions

The mismatch between a larger perfusion lesion and smaller diffusion lesion on magnetic resonance imaging is a validated signal of the ischemic penumbra, namely the region at risk in acute ischemic stroke that is critically hypoperfused and the target of reperfusion therapies. Clinical trials have shown strong correlations between reperfusion in mismatch patients and improved clinical outcomes. Attenuation of infarct growth is associated with reperfusion and corresponding clinical gains. Using computed tomography perfusion, the mismatch between relative cerebral blood flow or cerebral blood volume and perfusion delay is a comparable penumbral marker. Automated techniques allow rapid quantitative assessment of mismatch with thresholding to exclude benign oligemia. The penumbra is often present beyond the current 4.5-h time window, defined for the use of intravenous tPA. Treatment beyond this time point remains investigational. Although the efficacy of thrombolysis in mismatch patients requires further validation in randomized trials, there is now sufficient evidence to recommend that advanced neuroimaging of mismatch should be used for selection of delayed therapies in phase 3 trials.

CT perfusion imaging in acute stroke

Computed tomographic perfusion (CTP) imaging is an advanced modality that provides important information about capillary-level hemodynamics of the brain parenchyma. CTP can aid in diagnosis, management, and prognosis of acute stroke patients by clarifying acute cerebral physiology and hemodynamic status, including distinguishing severely hypoperfused but potentially salvageable tissue from both tissue likely to be irreversibly infarcted ("core") and hypoperfused but metabolically stable tissue ("benign oligemia"). A qualitative estimate of the presence and degree of ischemia is typically required for guiding clinical management. Radiation dose issues with CTP imaging, a topic of much current concern, are also addressed in this review.

Selection of arterial input function for postprocessing of cerebral ct perfusion in chronic unilateral high-grade stenosis or occlusion of the carotid or middle cerebral artery

RATIONALE AND OBJECTIVES

We evaluated the effect of the arterial input function (AIF) on computed tomography perfusion (CTP) in patients with unilateral high-grade stenosis or occlusion in the carotid artery or middle cerebral artery without acute stroke.

MATERIALS AND METHODS

CTP datasets were retrospectively postprocessed using the same venous output function and different AIF selections: the second segment of the anterior cerebral artery (A2 AIF), the second segment of the middle cerebral artery (MCA) on the lesion side (affected M2 AIF), and M2 on the contralateral side (nonaffected M2 AIF). We measured CTP values in the region of interest (ROI) in the bilateral MCA territory and evaluated the lesion-to-contralateral ratios.

RESULTS

The mean and standard deviations of cerebral blood flow (CBF) on the normal side were similar to previously reported data only when using "non-affected M2 AIF." Selecting an "affected M2 AIF" overestimated the CBF and shortened the mean transit time (MTT) in normal and lesion areas. Selecting an "A2 AIF" may cause overestimation of CBF in the normal side in patients with nonaffected-side A1 hypoplasia or occlusion. The sensitivity of the CBF ratio or MTT ratio to detect these unilateral cerebrovascular diseases was 100% using "nonaffected M2 AIF for bilateral MCA ROIs" and 70% (CBF ratio) and 90% (MTT ratio) using "respective AIF."

CONCLUSION

The use of "nonaffected AIF for the bilateral MCA ROIs" was found to be the best of these AIF-ROI combinations in patients with chronic unilateral carotid or M1 severe stenosis or occlusion.

The role of imaging studies for evaluation of stroke in children

Stroke is a major cause of morbidity and mortality in children and long-term neurological deficits. Although cerebrovascular disorders occur less often in children than in adults, recognition of stroke in children has probably increased because of the widespread application of noninvasive diagnostic studies such as magnetic resonance imaging and computed tomography.Computed tomography (CT) should be the first imaging choice in the emergency setting when stroke is suspected. It will show the presence of hemorrhage (eg, bleeding from arteriovenous malformation). It is often normal within the first hours in arterial ischemic stroke. As in adults, magnetic resonance imaging is the neuroimaging modality to confirm the clinical diagnosis of ischemic stroke. In children, however, magnetic resonance imaging requires sedation and may not be as readily available as CT. Perfusion imaging demonstrates flow within the brain and can detect areas that are at risk of ischemia; however, further studies in the pediatric population need to be validated for this technique in children. Angiography detects arterial disease (eg, aneurysm); however, its use has been largely superseded by better magnetic resonance angiography, which is sensitive enough to visualize lesions in the proximal anterior cerebral artery, middle cerebral artery, and distal internal carotid artery (ICA). Magnetic resonance imaging using diffusion- weighted imaging is the most versatile and sensitive imaging technique for identifying ischemic lesions. In the future, we need to identify the pediatric patient presenting to the emergency department with an acute stroke and develop a pathway for the use of particular imaging techniques (eg, CT vs magnetic resonance imaging).

Perfusion-CT guided intravenous thrombolysis in patients with unknown-onset stroke: a randomized, double-blind, placebo-controlled, pilot feasibility trial

INTRODUCTION

Patients with unknown stroke onset are generally excluded from acute recanalisation treatments. We designed a pilot study to assess feasibility of a trial of perfusion computed tomography (PCT)-guided thrombolysis in patients with ischemic tissue at risk of infarction and unknown stroke onset.

METHODS

Patients with a supratentorial stroke of unknown onset in the middle cerebral artery territory and significant volume of at-risk tissue on PCT were randomized to intravenous thrombolysis with alteplase (0.9 mg/kg) or placebo. Feasibility endpoints were randomization and blinded treatment of patients within 2 h after hospital arrival, and the correct application (estimation) of the perfusion imaging criteria.

RESULTS

At baseline, there was a trend towards older age [69.5 (57-78) vs. 49 (44-78) years] in the thrombolysis group (n = 6) compared to placebo (n = 6). Regarding feasibility, hospital arrival to treatment delay was above the allowed 2 h in three patients (25%). There were two protocol violations (17%) regarding PCT, both underestimating the predicted infarct in patients randomized in the placebo group. No symptomatic hemorrhage or death occurred during the first 7 days. Three of the four (75%) and one of the five (20%) patients were recanalized in the thrombolysis and placebo group respectively. The volume of non-infarcted at-risk tissue was 84 (44-206) cm(3) in the treatment arm and 29 (8-105) cm(3) in the placebo arm.

CONCLUSIONS

This pilot study shows that a randomized PCT-guided thrombolysis trial in patients with stroke of unknown onset may be feasible if issues such as treatment delays and reliable identification of tissue at risk of infarction tissue are resolved. Safety and efficiency of such an approach need to be established.

Comprehensive CT Evaluation in Acute Ischemic Stroke: Impact on Diagnosis and Treatment Decisions

Background. With modern CT imaging a comprehensive overview of cerebral macro- and microcirculation can be obtained within minutes in acute ischemic stroke. This opens for patient stratification and individualized treatment. Methods. Four patients with acute ischemic stroke of different aetiologies and/or treatments were chosen for illustration of the comprehensive CT protocol and its value in subsequent treatment decisions. The patients were clinically evaluated according to the NIHSS-scale, examined with the comprehensive CT protocol including both CT angiography and CT perfusion, and followed up by MRI. Results. The comprehensive CT examination protocol increased the examination time but did not delay treatment initiation. In some cases CT angiography revealed the cause of stroke while CT perfusion located and graded the perfusion defect with reasonable accuracy, confirmed by follow-up MR-diffusion. In the presented cases findings of the comprehensive CT examination influenced the treatment strategy. Conclusions. The comprehensive CT examination is a fast and safe method allowing accurate diagnosis and making way for individualized treatment in acute ischemic stroke.

Imaging of acute ischemic stroke

In this article the individual components of multimodal computed tomography and multimodal magnetic resonance imaging are discussed, the current status of neuroimaging for the evaluation of the acute ischemic stroke is presented, and the potential role of a combined multimodal stroke protocol is addressed.

Real-time diffusion-perfusion mismatch analysis in acute stroke

Diffusion-perfusion mismatch can be used to identify acute stroke patients that could benefit from reperfusion therapies. Early assessment of the mismatch facilitates necessary diagnosis and treatment decisions in acute stroke. We developed the RApid processing of PerfusIon and Diffusion (RAPID) for unsupervised, fully automated processing of perfusion and diffusion data for the purpose of expedited routine clinical assessment. The RAPID system computes quantitative perfusion maps (cerebral blood volume, CBV; cerebral blood flow, CBF; mean transit time, MTT; and the time until the residue function reaches its peak, T(max)) using deconvolution of tissue and arterial signals. Diffusion-weighted imaging/perfusion-weighted imaging (DWI/PWI) mismatch is automatically determined using infarct core segmentation of ADC maps and perfusion deficits segmented from T(max) maps. The performance of RAPID was evaluated on 63 acute stroke cases, in which diffusion and perfusion lesion volumes were outlined by both a human reader and the RAPID system. The correlation of outlined lesion volumes obtained from both methods was r(2) = 0.99 for DWI and r(2) = 0.96 for PWI. For mismatch identification, RAPID showed 100% sensitivity and 91% specificity. The mismatch information is made available on the hospital's PACS within 5-7 min. Results indicate that the automated system is sufficiently accurate and fast enough to be used for routine care as well as in clinical trials.

Quantitative Evaluation of the Penumbra and Ischemic Core in Acute Cerebral Infarction Using Whole-Brain CT Perfusion

The objectives of the study were to quantitatively assess whole-brain CT Perfusion (CTP) data using an automatic region of interest (ROI) analysis program in order to distinguish between the degree of ischemia in the ischemic core and that in the penumbra and to assess the relationship between expansion of the area of infarction. The subjects were 20 patients with acute cerebral infarction. Whole-brain CTP was performed for all subjects using a 320-row area detector CT scanner. The penumbra* is defined as the region in which the CBV value is 2 mL/100 g or more and the ischemic core* is defined as the region in which the CBV value is less than 2 mL/100 g. The quantitative values of CTP parameters were automatically measured using the automatic ROIs analysis program. The Mann-Whitney U test was applied to differentiate between the ischemic core* and the penumbra*. The reduction in perfusion pressure in the penumbra* was smaller in the group with expansion of the area of infarction than in the group without expansion of the area of infarction. The difference in the median values between the penumbra* and the ischemic core* was larger in the group with expansion of the area of infarction than the group without expansion of the area of infarction. It is considered that the quantitative analysis method using whole-brain CTP may be useful for more accurately distinguishing between the ischemic core and the penumbra and for evaluating the risk of expansion of the ischemic core into the penumbra.

Neuroimaging of cerebral ischemia and infarction

The imaging workup for patients with suspected acute ischemic stroke has advanced significantly over the past few years. Evaluation is no longer limited to noncontrast computed tomography, but now frequently also includes vascular and perfusion imaging. Although acute stroke imaging has made significant progress in the last few decades with the development of multimodal approaches, there are still many unanswered questions regarding their appropriate use in the setting of daily patient care. It is important for all physicians taking care of stroke patients to be familiar with current multimodal computed tomography and magnetic resonance imaging techniques, including their strengths, limitations, and their role in guiding therapy.

Low Cerebral Blood Volume Is Predictive of Diffusion Restriction Only in Hyperacute Stroke

Background and Purpose— Diffusion-weighted MRI (DWI) demonstrates ischemic tissue with high sensitivity. Although low cerebral blood volume (CBV) is also used as a marker for infarction, the quantitative relationship between diffusion abnormalities and CBV is unknown. We tested the hypothesis that CBV would decrease proportionally to the apparent diffusion coefficient in patients with acute stroke and thus could be used as a surrogate parameter for diffusion restriction.

Methods— Perfusion-weighted imaging and DWI was performed in 54 patients within 28 hours of symptom onset. Mean apparent diffusion coefficient, cerebral blood flow, and CBV were measured within DWI lesions and contralateral regions.

Results— Within DWI lesions, CBV (3.3±1.9 mL/100 g) was significantly decreased relative to contralateral regions (4.1±2.1 mL/100 g, P <0.001). Relative CBV was not decreased in patients with evidence of early reperfusion (1.2±0.5) or mild stroke (National Institutes of Health Stroke Scale <4, 1.1±0.6). Linear regression indicated that relative CBV was predictive of relative apparent diffusion coefficient only in patients imaged within 9 hours of symptom onset ( R =0.50, P =0.02). Ischemic tissue volumes generated using a CBV threshold of the 50th percentile of normal tissue were correlated with DWI lesion volumes ( R =0.73, P <0.001). The mean difference between the CBV threshold of the 50th percentile of normal tissue and DWI lesion volumes was 6.3 mL (95% limits of agreement, 0.1 to 12.6 mL).

Conclusions— Decreases in relative CBV are predictive of diffusion abnormalities in ischemic stroke. The pattern of CBV changes varies with clinical severity and symptom duration. Ischemic tissue volumes comparable to DWI lesions can be generated using CBV thresholds, but the use of this method is limited in patients with minor stroke.

Advantages of extended brain perfusion computed tomography: 9.6 cm coverage with time resolved computed tomography-angiography in comparison to standard stroke-computed tomography

OBJECTIVE

Recent technical developments have led to an extension of perfusion computed tomography (PCT) scan range to cover nearly the entire brain and to reconstruct time resolved (4d) CT-angiography (CTA) datasets from the PCT data. The purpose of this study was to compare the results of simulated standard PCT and extended PCT with 4d-CTA.

MATERIALS AND METHODS

Extended multimodal stroke CT (unenhanced cranial CT, CTA, and PCT) was acquired in 72 patients. PCT images with a scan coverage of 9.6 cm in the z-axis, simulated 2 cm PCT images at the level of the basal ganglia comparable to standard PCT, standard supra-aortic CTA, and 4d-CTA images were reconstructed. Two readers assessed the PCT image quality as well as pathologic findings in extended and simulated PCT, CTA, and 4d-CTA. The brain was divided into 4 axial segments. The independent samples t test was applied to test differences between data for significance.

RESULTS

In 75.0% of all patient exams, pathologic findings were observed in the PCT; these were located in 138 brain segments. In 24.1% of all 54 exams with pathologic PCT findings, the pathology would have been missed on standard PCT. The longer scan coverage resulted in a different final diagnosis in 34.7% of all exams. Quality of the PCT parameter maps was on average very good both for the supratentoric and the infratentoric brain areas (4.28 and 4.18, respectively, on a 5-point scale). In 90% of all exams with pathologic changes in the CTA, these abnormalities were also noted on 4d-CTA. In only 2.8% of all cases, the additional time resolution of the 4d-CTA provided additional information.

CONCLUSION

Extending the scan coverage of PCT from 2 cm to 9.6 cm led to an augmentation of clinically important information in the imaging of acute stroke.

Perfusion CT in acute ischemic stroke: a qualitative and quantitative comparison of deconvolution and maximum slope approach

BACKGROUND AND PURPOSE

PCT postprocessing commonly uses either the MS or a variant of the DC approach for modeling of voxel-based time-attenuation curves. There is an ongoing discussion about the respective merits and limitations of both methods, frequently on the basis of theoretic reasoning or simulated data. We performed a qualitative and quantitative comparison of DC and MS by using identical source datasets and preprocessing parameters.

MATERIALS AND METHODS

From the PCT data of 50 patients with acute ischemic stroke, color maps of CBF, CBV, and various temporal parameters were calculated with software implementing both DC and MS algorithms. Color maps were qualitatively categorized. Quantitative region-of-interest-based measurements were made in nonischemic GM and WM, suspected penumbra, and suspected infarction core. Qualitative results, quantitative results, and PCT lesion sizes from DC and MS were statistically compared.

RESULTS

CBF and CBV color maps based on DC and MS were of comparably high quality. Quantitative CBF and CBV values calculated by DC and MS were within the same range in nonischemic regions. In suspected penumbra regions, average CBF(DC) was lower than CBF(MS). In suspected infarction core regions, average CBV(DC) was similar to CBV(MS). Using adapted tissue-at-risk/nonviable-tissue thresholds, we found excellent correlation of DC and MS lesion sizes.

CONCLUSIONS

DC and MS yielded comparable qualitative and quantitative results. Lesion sizes indicated by DC and MS showed excellent agreement when using adapted thresholds. In all cases, the same therapy decision would have been made.

A Comparison of Computed Tomography Perfusion-Guided and Time-Guided Endovascular Treatments for Patients With Acute Ischemic Stroke

Background and Purpose— The role of CT perfusion (CT-P) imaging for the selection of patients with acute ischemic stroke who may benefit from endovascular treatment is not defined. The objective of this study was to determine whether CT-P-guided endovascular treatment improves clinical outcomes compared with standard endovascular treatment based on the time interval between symptom onset and presentation and noncontrast cranial CT imaging.

Methods— A retrospective study was performed comparing the clinical characteristics, complications, and clinical outcomes of patients with acute ischemic stroke who were treated using endovascular modalities based on either CT-P imaging (CT-P-guided) or time interval between symptom onset and presentation and absence of intracerebral hemorrhage or extensive ischemic changes on noncontrast cranial CT scan (time-guided).

Results— The rates of partial and complete recanalization were similar between the CT-P- and time-guided treatment groups (n=61 [88%] versus n=103 [81%]; P =0.52) regardless of whether they received intravenous recombinant tissue plasminogen activator before endovascular treatment. Comparing the CT-P-guided with the time-guided patients, favorable discharge outcome (modified Rankin Scale 0 to 2) was observed in 23 (32%) versus 41 (33%) of the patients, respectively ( P =0.9). In-hospital mortality was observed in 15 (21%) of CT-P- and 29 (23%) of time-guided patients ( P =0.74).

Conclusion— CT-P-guided endovascular treatment did not increase the rate of short-term favorable outcomes among patients with acute ischemic stroke. Prospective studies are required to validate the CT-P criteria and protocols currently in use before incorporating CT-P as a routine modality for patient selection for endovascular treatment.

The role of CT and MRI in the emergency evaluation of persons with suspected stroke

As a growing number of therapeutic treatment options for acute stroke are being introduced, multimodal acute neuroimaging is assuming a growing role in the initial evaluation and management of patients. Multimodal neuroimaging, using either a CT or MRI approach, can identify the type, location, and severity of the lesion (ischemia or hemorrhage); the status of the cerebral vasculature; the status of cerebral perfusion; and the existence and extent of the ischemic penumbra. Both acute and long-term treatment decisions for stroke patients can then be optimally guided by this information.

Assessment of collateral flow with multi-phasic CT: correlation with diffusion weighted MRI in MCA occlusion

PURPOSE

To correlate collateral flow on multiphasic contrast enhancement computed tomography (CT) and graded ischemic changes on diffusion weighted MR in patients with acute middle cerebral artery (MCA) infarction.

MATERIALS AND METHODS

A retrospective evaluation of diffusion weighted images (DWIs) and three phasic contrast enhanced CT (CECT) was performed on 11 patients with MCA occlusions. The area of ischemic change on DWIs was graded according to the Alberta Stroke Program Early CT Score (ASPECTS) criteria. To evaluate collateral flow on three phasic CECT, we counted the number of contrast enhancing MCA branches distal to the occlusion site at the sylvian fissure from predetermined axial images. The collateral ratios of counted numbers to those at the normal side were calculated at each phase (CR1, CR2, CR3). We then compared collateral ratios from the three phasic CECT with ASPECTS data from DWIs.

RESULTS

Collateral ratios from the three phasic CECT were determined to be CR1 .48 ± .27, CR2 .73 ± .36 and CR3 .72 ± .30. We discovered a correlation between both the CR2 and ASPECTS (r= .675, P= .023) and the CR3 and ASPECTS (r= .664, P= .026).

CONCLUSION

The number of contrast enhancing branches distal to the MCA occlusion, as counted in the sylvian fissure on later phase images of multiphasic CECT, reflects the status of collateral flow, and correlates with ASPECTS on DWIs.

Certainty of stroke diagnosis: incremental benefit with CT perfusion over noncontrast CT and CT angiography

PURPOSE

To systematically evaluate the diagnostic benefits and inter- and intraobserver reliability of an incremental computed tomographic (CT) protocol in the confirmation of clinically suspected stroke, with combined imaging and clinical data as the reference standard.

MATERIALS AND METHODS

Institutional review board approval was obtained, and participants gave informed consent. A total of 191 patients (mean age, 67 years +/- 16 [standard deviation]; 105 men) with strokelike symptoms of no more than 3 hours duration were recruited. Blinded review was performed by four readers with limited stroke imaging experience. Diagnostic confidence was recorded on a five-point scale. Logistic regression analysis was used to calculate the difference between the real and observed diagnoses, adjusting for confidence. Predictive effects of observed diagnostic performance and confidence score were quantified with the entropy r(2) value. Sensitivity, specificity, and confidence intervals were calculated while accounting for multiple reader assessments. Receiver operating characteristic (ROC) analyses, including area under the ROC curve, were conducted for three modalities in combination with confidence score. Inter- and intraobserver agreement was established with the Cohen kappa statistic.

RESULTS

The final diagnosis was infarct in 64% of the patients, transient ischemic attack in 18%, and stroke mimic in 17%. Large-vessel occlusion occurred in 70% of the patients with an infarct. Sensitivity for stroke determination with noncontrast CT, CT angiography, and CT perfusion increased by 12.4% over that with noncontrast CT and CT angiography and by 18.2% over that with only noncontrast CT for a confidence level of 4 or higher. The incremental protocol was more likely to enable confirmation of clinical stroke diagnosis (odds ratio, 13.3) than was noncontrast CT and CT angiography (odds ratio, 6.4) or noncontrast CT alone (odds ratio, 3.3), The area under the ROC curve was 0.67 for the combination of noncontrast CT and confidence score, 0.72 for the combination of CT angiography and confidence score, and 0.81 for the combination of CT perfusion and confidence score. Inter- and intraobserver agreement increased with progressive sequence use.

CONCLUSION

An incremental stroke protocol that includes CT perfusion increases diagnostic performance for stroke diagnosis and inter- and intraobserver agreement.

Evaluation of CT perfusion in the setting of cerebral ischemia: patterns and pitfalls

CTP has a growing role in evaluating stroke. It can be performed immediately following NCCT and has advantages of accessibility and speed. Differentiation of salvageable ischemic penumbra from unsalvageable core infarct may help identify patients most likely to benefit from thrombectomy or thrombolysis. Still, CTP interpretation can be complex. We review normal and ischemic perfusion patterns followed by an illustrative series of technical/diagnostic challenges of CTP interpretation in the setting of acute stroke syndromes.