Improvement of Sensitivity and Interrater Reliability to Detect Acute Stroke by Dynamic Perfusion Computed Tomography and Computed Tomography Angiography

Diagnostic performance of single-phase CT angiography in detecting large vessel occlusion in ischemic stroke: A systematic review

PURPOSE

To systematically review the diagnostic performance of single-phase CT angiography (CTA) in detecting intracranial large vessel occlusion (LVO).

METHOD

MEDLINE and Embase were searched for studies investigating the diagnostic performance of single-phase CTA in detecting LVO. Study quality was assessed. Sensitivity and specificity were calculated and meta-analyzed with a bivariate random-effects model. Heterogeneity was assessed with a chi-squared test.

RESULTS

Eleven studies were included. High risk of bias with regard to "patient selection", "reference standard", and "flow and timing" was present in 4, 1, and 2 studies, respectively. In 7 studies, it was unclear whether reference tests were interpreted blinded to CTA readings. There was variability in types of vessel segments analyzed, resulting in heterogeneous sensitivity and specificity (P < 0.05). Two studies provided data for the proximal anterior circulation (distal intracranial carotid artery, A1-, A2-, M1- and M2-segments), with pooled sensitivity of 88.4 % (95 % CI: 62.2-97.2 %) and pooled specificity of 98.5 % (95 % CI: 33.2-100 %). One study suggested that multiphase CTA improved agreement between nonexperts and an expert in detecting A1-, A2-, M1-, M2-, and M3-segment occlusions compared to single-phase CTA (ĸ = 0.72-0.76 vs. ĸ = 0.32-0.45). No other included study reported added value of advanced CTA (CT perfusion, 4D-CTA, or multiphase CTA) compared to single-phase CTA in detecting proximal anterior circulation LVO.

CONCLUSION

There is lack of high-quality studies on the diagnostic performance of single-phase CTA for LVO detection in the proximal anterior circulation. The added value of advanced CTA techniques in detecting proximal anterior circulation LVO is not completely clear yet.

Variability in the decision-making process of acute ischemic stroke in difficult clinical and radiological constellations: analysis based on a cross-sectional interview-administered stroke questionnaire

BACKGROUND AND PURPOSE

Notwithstanding guidelines, indications for mechanical thrombectomy (MT) in acute ischemic stroke are multifactorial and can be complex. Our aim was to exploratively evaluate decision-making on the advisability of performing MT in cases presented as an interview-administered questionnaire.

METHODS

Fifty international raters assessed 12 cases and decided to recommend or exclude MT. Each case contained a brief summary of clinical information and eight representative images of the initial multimodal CT. The demographic characteristics and stroke protocols were recorded for raters. For each case, the reasons for excluding MT were recorded. Uni- and multivariate logistic regression analysis were performed for the different demographic and case characteristics to identify factors that might influence decision-making.

RESULTS

All raters performed MT (median MTs/hospital/year [IQR], 100 [50-141]) with a median of 7 years of experience as first operator (IQR, 4-12). Per case, diversity in decision-making ranged between 1 (case 6, 100% yes MT) and 0.50 (case 12, 54.2% yes MT and 45.8% no MT). The most common reasons for excluding MT were small CBV/CBF mismatch (17%, 102/600), size of infarct core on the CBV map (15.2%, 91/600), and low NIHSS score (National Institute of Health Stroke Scale, 8.3%, 50/600). All clinical and radiological characteristics significantly affected the decision regarding MT, but the general characteristics of the raters were not a factor.

CONCLUSIONS

Clinical and imaging characteristics influenced the decision regarding MT in stroke. Nevertheless, a consensus was reached in only a minority of cases, revealing the current divergence of opinion regarding therapeutic decisions in difficult cases.

KEY POINTS

• This is the first study to explore differences in decision-making in respect of mechanical thrombectomy in ischemic stroke with complex clinical and radiological constellations. • Fifty experienced international neurointerventionalists answered this interview-administered stroke questionnaire and made decisions as to whether to recommend or disadvise thrombectomy in 12 selected cases. • Diversity in decision-making for thrombectomy ranged from 1 (100% of raters offered the same answer) to 0.5 (50% indicated mechanical thrombectomy). There was a consensus in only a minority of cases, revealing the current disparity of opinion regarding therapeutic decisions in difficult cases.

A useful diagnostic method to reduce the in-hospital time delay for mechanical thrombectomy: volume perfusion computed tomography with added vessel reconstruction

OBJECTIVE

Volume perfusion CT (VPCT) with added CT angiography (CTA)-like reconstruction from VPCT source data (VPCTA) can reveal multiple intracranial parameters. The authors examined the usefulness of VPCTA in terms of reducing the in-hospital time delay for mechanical thrombectomy.

METHODS

A total of 180 patients who underwent mechanical thrombectomy at the authors' institution between January 2014 and March 2017 were divided into 2 groups: a CTA-based thrombectomy decision group (group 1: CTA) and a VPCTA-based decision group (group 2: VPCTA). Multiple time interval categories (from symptom onset to groin puncture, from hospital arrival to groin puncture, procedure time, from symptom onset to reperfusion, and from hospital arrival to reperfusion) were reviewed. All patients underwent clinical assessment with the National Institutes of Health Stroke Scale score and the modified Rankin Scale, and radiological results were evaluated by the Thrombolysis in Cerebral Infarction score.

RESULTS

In all of the time interval categories except for procedure time, the VPCTA group showed a significantly shorter in-hospital time delay during the prethrombectomy period than did the CTA group. The 3-month modified Rankin Scale score was significantly lower in the VPCTA group (2.8) compared with the CTA group (3.5) (p = 0.003). However, there were no statistically significant differences between the 2 groups in the other clinical and radiological outcomes.

CONCLUSIONS

Compared with CTA, VPCTA significantly reduced the in-hospital time delay during the prethrombectomy period.

Optimized Flat-Detector CT in Stroke Imaging: Ready for First-Line Use?

Background: Using flat-detector CT (FD-CT) for stroke imaging has the advantage that both diagnostic imaging and endovascular therapy can be performed directly within the Angio Suite without any patient transfer and time delay. Thus, stroke management could be speeded up significantly, and patient outcome might be improved. But as precondition for using FD-CT as primary imaging modality, a reliable exclusion of intracranial hemorrhage (ICH) has to be possible. This study aimed to investigate whether optimized native FD-CT, using a newly implemented reconstruction algorithm, may reliably detect ICH in stroke patients. Additionally, the potential to identify ischemic changes was evaluated. Methods: Cranial FD-CT scans were obtained in 102 patients presenting with acute ischemic stroke (n = 32), ICH (n = 45) or transient ischemic attack (n = 25). All scans were reconstructed with a newly implemented half-scan cone-beam algorithm. Two experienced neuroradiologists, unaware of clinical findings, evaluated independently the FD-CTs screening for hemorrhage or ischemic signs. The findings were correlated to CT, and rater and inter-rater agreement was assessed. Results: FD-CT demonstrated high sensitivity (95-100%) and specificity (100%) in detecting intracerebral and intraventricular hemorrhage (IVH). Overall, interobserver agreement (κ = 0.92) was almost perfect and rater agreement to CT highly significant (r = 0.81). One infratentorial ICH and 10 or 11 of 22 subarachnoid hemorrhages (SAHs) were missed of whom 7 were perimesencephalic. The sensitivity for detecting acute ischemic signs was poor in blinded readings (0 or 25%, respectively). Conclusions: Optimized FD-CT, using a newly implemented reconstruction algorithm, turned out as a reliable tool for detecting supratentorial ICH and IVH. However, detection of infratentorial ICH and perimesencephalic SAH is limited. The potential of FD-CT in detecting ischemic changes is poor in blinded readings. Thus, plain FD-CT seems insufficient as a standalone modality in acute stroke, but within a multimodal imaging approach primarily using the FD technology, native FD-CT seems capable to exclude reliably supratentorial hemorrhage. Currently, FD-CT imaging seems not yet ready for wide adoption, replacing regular CT, and should be reserved for selected patients. Furthermore, prospective evaluations are necessary to validate this approach in the clinical setting.

Multidetector computed tomography angiography in clinically suspected hyperacute ischemic stroke in the anterior circulation: an etiological workup in a cohort of Brazilian patients

OBJECTIVE

The potential of computed tomography angiography (CTA) was assessed for early determination of stroke subtypes in a Brazilian cohort of patients with stroke.

METHOD

From July 2011 to July 2013, we selected patients with suspected hyperacute stroke (< 6 hours). Intracranial and cervical arteries were scrutinized on CTA and their imaging features were correlated with concurrent subtype of stroke.

RESULTS

Stroke was documented in 50/106 selected patients (47.2%) based on both clinical grounds and imaging follow-up (stroke group), with statistically significant arterial stenosis and vulnerable plaques on CTA. Intracranial large artery disease was demonstrated in 34% of patients in the stroke group. Partial territorial infarct prevailed (86%) while artery-to-artery embolization was the most common stroke mechanism (52%).

CONCLUSION

Multidetector CTA was useful for the etiologic work-up of hyperacute ischemic stroke and facilitated the knowledge about the topographic pattern of brain infarct in accordance with its causative mechanism.

Identification of acute stroke using quantified brain electrical activity

OBJECTIVES

Acute stroke is a leading cause of brain injury and death and requires rapid and accurate diagnosis. Noncontrast head computed tomography (CT) is the first line for diagnosis in the emergency department (ED). Complicating rapid triage are presenting conditions that clinically mimic stroke. There is an extensive literature reporting clinical utility of brain electrical activity in early diagnosis and management of acute stroke. However, existing technologies do not lend themselves to easily acquired rapid evaluation. This investigation used an independently derived classifier algorithm for the identification of traumatic structural brain injury based on brain electrical activity recorded from a reduced frontal montage to explore the potential clinical utility of such an approach in acute stroke assessment.

METHODS

Adult patients (age 18 to 95 years) presenting with stroke-like and/or altered mental status symptoms were recruited from urban academic EDs as part of a large research study evaluating the clinical utility of quantitative brain electrical activity in acutely brain-injured patients. All patients from the parent study who had confirmed strokes, and a control group of stroke mimics (those with final ED diagnoses of migraine or syncope), were selected for this study. All stroke patients underwent head CT scans. Some patients with negative CTs had further imaging with magnetic resonance imaging (MRI). Ten minutes of electroencephalographic data were acquired on a hand-held device in development, from five frontal electrodes. Data analyses were done offline. A Structural Brain Injury Index (SBII) was derived using an independently developed binary discriminant classification algorithm whose input was specified features of brain electrical activity. The SBII was previously found to have high accuracy in the identification of traumatic brain-injured patients who were found to have brain injury on CT (CT+). This algorithm was applied to patients in this study and used to classify patients as CT+ or not CT+. Performance was assessed using sensitivity, specificity, and negative and positive predictive values (NPV, PPV).

RESULTS

Forty-eight stroke patients (31 ischemic and 17 hemorrhagic) and 135 stroke mimic controls were included. Within the ischemic population, approximately half were CT- but later confirmed for stroke with MRI (CT-/MRI+). Sensitivity to stroke was 91.7%, specificity 50.4% (to stroke mimic), NPV 94.4%, and PPV 39.6%. Eighty percent of the CT-/MRI+ ischemic strokes were correctly identified at the time of the CT- scan.

CONCLUSIONS

Despite a small population and the use of a classifier without the benefit of training on a stroke population, these data suggest that a rapidly acquired, easy-to-use system to assess brain electrical activity at the time of evaluation of acute stroke could be a valuable adjunct to current clinical practice.

Radiation dose associated with cerebral CT angiography and CT perfusion: an experimental phantom study

A study on the radiation dose associated with cerebral CT angiography (CTA) and CT perfusion (CTP) was conducted on an anthropomorphic phantom with the aim of estimating the effective dose (E) and entrance skin dose (ESD) in the eyes and thyroid gland during different CTA and CTP protocols. The E was calculated to be 0.61 and 0.28 mSv in CTA with 100 and 80 kV(p), respectively. In contrast, CTP resulted in an estimated E of 2.74 and 2.07 mSv corresponding to 40 and 30 s protocols, respectively. The eyes received a higher ESD than the thyroid gland in all of these protocols. The results of this study indicate that combining both CTA and CTP procedures are not recommended in the stroke evaluation due to high radiation dose. Application of modified techniques in CTA (80 kV(p)) and CTP (30 s) is highly recommended in clinical practice for further radiation dose reduction.

Cerebral CT angiography and CT perfusion in acute stroke detection: a systematic review of diagnostic value

The purpose of this study was to analyse the diagnostic value of cerebral CT angiography (CTA) and CT perfusion (CTP) examinations in the detection of acute stroke based on a systematic review of the current literature. The review was conducted based on searching of seven databases for articles published between 1993 and 2013. Diagnostic value in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy was analysed from 21 articles which were found to meet selection criteria. The mean sensitivity, specificity, PPV, NPV and accuracy for CTA were significantly higher than those for CTP with 83.2% (95% CI: 57.9-100.0%), 95.0% (95% CI: 74.4-100%), 84.1% (95% CI: 50.0-100%), 97.1 (95% CI: 94.0-100%) and 94.0% (95% CI: 83.0-99.0) versus 69.9% (95% CI: 20.0-97.0%), 87.4 (95% CI: 61.0-100.0%), 76.4% (95% CI: 48.0-95.4%), 78.2% (95% CI: 55.8-93.9%) and 89.8% (95% CI: 75.7-97.1%), respectively. This analysis shows that CTA has high diagnostic value in detecting high degree of cerebral arterial stenosis (>70%) whereas CTP provides high specificity in the detection of ischemia and infarct tissue of brain.

Imaging recommendations for acute stroke and transient ischemic attack patients: A joint statement by the American Society of Neuroradiology, the American College of Radiology, and the Society of NeuroInterventional Surgery

SUMMARY

Stroke is a leading cause of death and disability worldwide. Imaging plays a critical role in evaluating patients suspected of acute stroke and transient ischemic attack, especially before initiating treatment. Over the past few decades, major advances have occurred in stroke imaging and treatment, including Food and Drug Administration approval of recanalization therapies for the treatment of acute ischemic stroke. A wide variety of imaging techniques has become available to assess vascular lesions and brain tissue status in acute stroke patients. However, the practical challenge for physicians is to understand the multiple facets of these imaging techniques, including which imaging techniques to implement and how to optimally use them, given available resources at their local institution. Important considerations include constraints of time, cost, access to imaging modalities, preferences of treating physicians, availability of expertise, and availability of endovascular therapy. The choice of which imaging techniques to employ is impacted by both the time urgency for evaluation of patients and the complexity of the literature on acute stroke imaging. Ideally, imaging algorithms should incorporate techniques that provide optimal benefit for improved patient outcomes without delaying treatment.

Advanced neuroimaging to guide acute stroke therapy

Traditionally non-contrast CT has been considered the first choice imaging modality for acute stroke. Acute ischemic stroke patients presenting to the hospital within 3-hours from symptom onset and without any visible hemorrhages or large lesions on CT images are considered optimum reperfusion therapy candidates. However, non-contrast CT alone has been unable to identify best reperfusion therapy candidates outside this window. New advanced imaging techniques are now being used successfully for this purpose. Non-invasive CT or MR angiography images can be obtained during initial imaging evaluation for identification and characterization of vascular lesions, including occlusions, aneurysms, and malformations. Either CT-based perfusion imaging or MRI-based diffusion and perfusion imaging performed immediately upon arrival of a patient to the hospital helps estimate the extent of fixed core and penumbra in ischemic lesions. Patients having occlusive lesions with small fixed cores and large penumbra are preferred reperfusion therapy candidates.

Anatomical variations in the posterior part of the circle of willis and vascular pathology in bilateral thalamic infarction

BACKGROUND AND PURPOSE

Bilateral paramedian thalamic infarction is a rare subtype of stroke the etiology of which still remains undetermined in many patients.

METHODS

From a computed tomography (CT)/magnetic resonance imaging report database, we identified and analyzed 48 patients with bilateral paramedian thalamic infarction on diffusion-weighted imaging. Vascular pathologies were noted on CT angiography (CTA)/magnetic resonance angiography (MRA) and the P1 segments of the posterior cerebral artery (PCA) described as normal, hypoplastic, or absent.

RESULTS

Vascular imaging revealed top of the basilar artery (BA) occlusion in 6 (12.5%), BA occlusion in 4 (8.3%), BA stenosis in 1 (2.1%), and BA hypoplasia in 3 (6.3%), PCA occlusion in 4 (8.3%), and PCA stenosis in 4 (8.3%) patients. In 18 (37.5%) patients, one or both P1 segments of the PCA were hypoplastic or absent. Patients with hypoplastic/absent P1 segments were more likely to have exclusively bilateral paramedian thalamic lesions (P < .001). An embolic source could be identified in 25 (55.6%) patients; there were no significant differences between both groups.

CONCLUSIONS

Vascular imaging is useful to determine underlying vascular pathologies and may support the diagnosis of small vessel disease in those patients with isolated bilateral paramedian thalamic infarction, hypoplastic/absent P1 segment of the PCA, and lack of vascular pathology.

Assessing diagnostic tests: how to correct for the combined effects of interpretation and reference standard

We describe a general solution to the problem of determining diagnostic accuracy without the use of a perfect reference standard and in the presence of interpreter variability. The accuracy of a diagnostic test is typically determined by comparing its outcomes with those of an established reference standard. But the accuracy of the standard itself and those of the interpreters strongly influence such assessments. We use our solution to examine the effects of the properties of the standard, the reliability of the interpreters, and the prevalence of abnormality on the measured sensitivity and specificity. Our results provide a method of systematically adjusting the measured sensitivity and specificity in order to estimate their true values. The results are validated by simulations and their detailed application to specific cases are described.

A smartphone client-server teleradiology system for primary diagnosis of acute stroke

Background

Recent advances in the treatment of acute ischemic stroke have made rapid acquisition, visualization, and interpretation of images a key factor for positive patient outcomes. We have developed a new teleradiology system based on a client-server architecture that enables rapid access to interactive advanced 2-D and 3-D visualization on a current generation smartphone device (Apple iPhone or iPod Touch, or an Android phone) without requiring patient image data to be stored on the device. Instead, a server loads and renders the patient images, then transmits a rendered frame to the remote device.

Objective

Our objective was to determine if a new smartphone client-server teleradiology system is capable of providing accuracies and interpretation times sufficient for diagnosis of acute stroke.

Methods

This was a retrospective study. We obtained 120 recent consecutive noncontrast computed tomography (NCCT) brain scans and 70 computed tomography angiogram (CTA) head scans from the Calgary Stroke Program database. Scans were read by two neuroradiologists, one on a medical diagnostic workstation and an iPod or iPhone (hereafter referred to as an iOS device) and the other only on an iOS device. NCCT brain scans were evaluated for early signs of infarction, which includes early parenchymal ischemic changes and dense vessel sign, and to exclude acute intraparenchymal hemorrhage and stroke mimics. CTA brain scans were evaluated for any intracranial vessel occlusion. The interpretations made on an iOS device were compared with those made at a workstation. The total interpretation times were recorded for both platforms. Interrater agreement was assessed. True positives, true negatives, false positives, and false negatives were obtained, and sensitivity, specificity, and accuracy of detecting the abnormalities on the iOS device were computed.

Results

The sensitivity, specificity, and accuracy of detecting intraparenchymal hemorrhage were 100% using the iOS device with a perfect interrater agreement (kappa = 1). The sensitivity, specificity, and accuracy of detecting acute parenchymal ischemic change were 94.1%, 100%, and 98.09% respectively for reader 1 and 97.05%, 100%, and 99.04% for reader 2 with nearly perfect interrater agreement (kappa = .8). The sensitivity, specificity, and accuracy of detecting dense vessel sign were 100%, 95.4%, and 96.19% respectively for reader 1 and 72.2%, 100%, and 95.23% for reader 2 using the iOS device with a good interrater agreement (kappa = .69). The sensitivity, specificity, and accuracy of detecting vessel occlusion on CT angiography scans were 94.4%, 100%, and 98.46% respectively for both readers using the iOS device, with perfect interrater agreement (kappa = 1). No significant difference (P < .05) was noted in the interpretation time between the workstation and iOS device.

Conclusion

The smartphone client-server teleradiology system appears promising and may have the potential to allow urgent management decisions in acute stroke. However, this study was retrospective, involved relatively few patient studies, and only two readers. Generalizing conclusions about its clinical utility, especially in other diagnostic use cases, should not be made until additional studies are performed.

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.

Increasing sampling interval in cerebral perfusion CT: limitation for the maximum slope model

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate increased sampling intervals on cerebral dynamic perfusion computed tomographic (PCT) imaging calculated using software relying on the maximum slope model.

MATERIALS AND METHODS

PCT data sets from 32 patients with suspected acute stroke were acquired with a sampling interval of 1 image/s. The PCT data sets were modified to simulate sampling intervals of 2, 3, and 4 seconds. Maps of cerebral blood flow (CBF), cerebral blood volume, and time to peak (TTP) were calculated using software relying on the maximum slope model. Parenchymal and vascular peak enhancement; absolute values of CBF, cerebral blood volume, and TTP in the nonischemic hemisphere; and ischemic area in the different perfusion maps were measured.

RESULTS

Parenchymal peak enhancement of the nonischemic hemisphere was statistically significantly decreased in all simulated data sets with >1-second sampling intervals (P < .001). Absolute CBF and TTP values in the nonischemic hemisphere were increased in all simulated data sets with >1-second sampling intervals (P = .044-.001 and P = .008-.001, respectively). The ischemic area was significantly underestimated for CBF and TTP in all simulated data sets with >1-second sampling intervals (P = .022-.005 and P = .019-.005, respectively).

CONCLUSIONS

Sampling intervals of >1 second on PCT imaging calculated using software relying on the maximum slope model significantly alter absolute CBF and TTP values and the size of ischemia in CBF and TTP. Thus, increasing the sampling interval on dynamic PCT imaging cannot be recommended in combination with this algorithm.

Dynamic CT angiography and CT perfusion employing a 320-detector row CT: protocol and current clinical applications

The aim of this study is to report the authors' initial clinical experience of a 320-detector row computed tomography (CT) scanner in cerebrovascular disorders. Volumetric CT using the full 160-mm width of the 320 detector rows enables full brain coverage in a single rotation that allows for combined time-resolved whole-brain perfusion and four-dimensional CT angiography (CTA). The protocol for the combined dynamic CTA and CT perfusion (CTP) is presented, and its potential applications in stroke, stenoocclusive disease, arteriovenous malformations and dural shunts are reviewed based on clinical examples. The combined CTA/CTP data can provide visualization of dynamic flow and perfusion as well as motion of an entire volume at very short time intervals which is of importance in a variety of pathologies with altered cerebral hemodynamics. The broad coverage enabled by 320 detector rows offers z-axis coverage allowing for whole-brain perfusion and subtracted dynamic angiography of the entire intracranial circulation.

Imaging after brain injury

Head injury remains an important cause of death and disability in young adults. This review will discuss the role of structural imaging using computed tomography (CT) and magnetic resonance imaging (MRI) and physiological imaging using CT perfusion, 131Xe CT, MRI and spectroscopy (MRS), single photon emission computed tomography, and positron emission tomography (PET) in the assessment, management, and prediction of outcome after head injury. CT allows rapid assessment of brain pathology which ensures patients who require urgent surgical intervention receive appropriate care. Although MRI provides greater spatial resolution, particularly within the posterior fossa and deep white matter, a complete assessment of the burden of injury requires imaging of cerebral physiology. Physiological imaging techniques can only provide 'snap shots' of physiology within the injured brain, but they can be repeated, and such data can be used to assess the impact of therapeutic interventions. Perfusion imaging based on CT techniques (xenon CT and CT perfusion) can be implemented easily in most hospital centres, and provide quantitative perfusion data in addition to structural images. PET imaging provides unparalleled insights into cerebral physiology and pathophysiology, but is not widely available and is primarily a research tool. MR technology continues to develop and is becoming generally available. Using a complex variety of sequences, MR can provide data concerning both structural and physiological derangements. Future developments with such imaging techniques should improve understanding of the pathophysiology of brain injury and provide data that should improve management and prediction of functional outcome.

Perfusion CT in acute stroke: prediction of vessel recanalization and clinical outcome in intravenous thrombolytic therapy

This study evaluated perfusion computed tomography (PCT) for the prediction of vessel recanalization and clinical outcome in patients undergoing intravenous thrombolysis. Thirty-nine patients with acute ischemic stroke of the middle cerebral artery territory underwent intravenous thrombolysis within 3 h of symptom onset. They all had non-enhanced CT (NECT), PCT, and CT angiography (CTA) before treatment. The Alberta Stroke Program Early Computed Tomography (ASPECT) score was applied to NECT and PCT maps to assess the extent of ischemia. CTA was assessed for the site of vessel occlusion. The National Institute of Health Stroke Scale (NIHSS) score was used for initial clinical assessment. Three-month clinical outcome was assessed using the modified Rankin scale. Vessel recanalization was determined by follow-up ultrasound. Of the PCT maps, a cerebral blood volume (CBV) ASPECT score of >6 versus < or =6 was the best predictor for clinical outcome (odds ratio, 31.43; 95% confidence interval, 3.41-289.58; P < 0.002), and was superior to NIHSS, NECT and CTA. No significant differences in ASPECT scores were found for the prediction of vessel recanalization. ASPECT score applied to PCT maps in acute stroke patients predicts the clinical outcome of intravenous thrombolysis and is superior to both early NECT and clinical parameters.

Imaging of cerebral blood flow and metabolism

PURPOSE OF REVIEW

To review the techniques for imaging cerebral blood flow and metabolism following injury to the brain.

RECENT FINDINGS

Xenon enhanced computerized tomography (Xenon CT), CT perfusion and single photon emission CT provide measurements of cerebral perfusion, while positron emission tomography (PET), and magnetic resonance imaging and spectroscopy (MRI and MRS) are able to assess both perfusion and cerebral metabolism. Xenon CT and CT perfusion are readily available and have proved useful in a variety of causes of brain injury. PET is an extremely useful research tool for defining cerebral physiology, but is limited in its availability. Despite the continuing development of MRI and MRS imaging, the scanning environment remains hostile for critically ill patients, and further research is required before the techniques become generally available.

SUMMARY

Imaging of cerebral blood flow and metabolism has been shown to be useful following a variety of causes of brain injury, as it can help to define the cause and extent of injury, identify appropriate treatments and predict outcome. Imaging based on CT techniques (Xenon CT and CT perfusion) can be implemented easily in most hospital centres, and are able to provide quantitative perfusion data in addition to structural images.