Second harmonic imaging In acute middle cerebral artery infarction. Preliminary results

Ultrasound Perfusion Imaging for the Detection of Cerebral Hypoperfusion After Aneurysmal Subarachnoid Hemorrhage

Background

Delayed cerebral ischemia increases mortality and morbidity after aneurysmal subarachnoid hemorrhage (aSAH). Various techniques are applied to detect cerebral vasospasm and hypoperfusion. Contrast-enhanced ultrasound perfusion imaging (UPI) is able to detect cerebral hypoperfusion in acute ischemic stroke. This prospective study aimed to evaluate the use of UPI to enable detection of cerebral hypoperfusion after aSAH.

Methods

We prospectively enrolled patients with aSAH and performed UPI examinations every second day after aneurysm closure. Perfusion of the basal ganglia was outlined to normalize the perfusion records of the anterior and posterior middle cerebral artery territory. We applied various models to characterize longitudinal perfusion alterations in patients with delayed ischemic neurologic deficit (DIND) across the cohort and predict DIND by using a multilayer classification model.

Results

Between August 2013 and December 2015, we included 30 patients into this prospective study. The left–right difference of time to peak (TTP) values showed a significant increase at day 10–12. Patients with DIND demonstrated a significant, 4.86 times increase of the left–right TTP ratio compared with a mean fold change in patients without DIND of 0.9 times (p = 0.032).

Conclusions

UPI is feasible to enable detection of cerebral tissue hypoperfusion after aSAH, and the left–right difference of TTP values is the most indicative result of this finding.

Twenty Years of Cerebral Ultrasound Perfusion Imaging-Is the Best yet to Come?

Over the past 20 years, ultrasonic cerebral perfusion imaging (UPI) has been introduced and validated applying different data acquisition and processing approaches. Clinical data were collected mainly in acute stroke patients. Some efforts were undertaken in order to compare different technical settings and validate results to gold standard perfusion imaging. This review illustrates the evolution of the method, explicating different technical aspects and milestones achieved over time. Up to date, advancements of ultrasound technology as well as data processing approaches enable semi-quantitative, gold standard proven identification of critically hypo-perfused tissue in acute stroke patients. The rapid distribution of CT perfusion over the past 10 years has limited the clinical need for UPI. However, the unexcelled advantage of mobile application raises reasonable expectations for future applications. Since the identification of intracerebral hematoma and large vessel occlusion can also be revealed by ultrasound exams, UPI is a supplementary multi-modal imaging technique with the potential of pre-hospital application. Some further applications are outlined to highlight the future potential of this underrated bedside method of microcirculatory perfusion assessment.

Microvascular imaging in acute ischemic stroke

BACKGROUND

Microvascular imaging (MVI), a new ultrasound technology, is used to analyze brain perfusion at the patient's bedside. This study aims to evaluate the diagnostic and prognostic value of MVI in patients with acute ischemic stroke (AIS).

METHODS

Nineteen patients suffering from AIS (mean age, 70.9 ± 12.2 years; 47% female; mean NIHSS-score, 12 ± 8) were investigated within the first 12 hours after symptom onset. We used the iU22 (Philips) system (S5-1 probe; low-mechanical index; depth, 13 cm), and 2 bolus injections of an ultrasound contrast agent (2.4 mL SonoVue per injection). The area of maximal perfusion deficit (AMPD) was compared with infarction on follow-up cranial computed tomography (CT) and NIHSS score 24 hours after stroke onset.

RESULTS

Of 19 patients, 15 patients (79%) had sufficient insonation conditions. Of these patients, 12 had infarctions. The sensitivity and specificity of detecting infarctions with ultrasound perfusion imaging were 91% and 67%, respectively. A significant correlation existed between the AMPD and NIHSS score at 24 hours after symptom onset (P= .023), and with occlusion of the internal carotid artery (P= .005).

CONCLUSION

Performing bedside MVI in the early phase of AIS provides information on brain parenchyma perfusion and prognosis of AIS.

Transcranial contrast imaging of cerebral perfusion in patients with space-occupying intracranial lesions

OBJECTIVE

The aim of this study was to evaluate a deficit in cerebral perfusion after administration of the contrast agent SonoVue (Bracco Altana Pharma, Konstanz, Germany) in patients with intracranial space-occupying lesions.

METHODS

We used transcranial duplex sonography to examine 10 healthy volunteers and 4 patients. Of the patients, one 55-year-old woman had an intracranial glioblastoma; one 54-year-old woman had an intracranial hemorrhage; and one 49-year-old woman and one 69-year-old man had a malignant middle cerebral artery infarction. A decompressive craniectomy was performed in the 2 patients with malignant middle cerebral artery infarction. Triggered images with pulsing intervals of 1000 milliseconds were used for the evaluation of time-intensity curves in several regions of interest. The mechanical index was set at 1.6; in patients with a craniectomy, the mechanical index was set at 1.1.

RESULTS

In all patients, the perfusion deficit could be recognized in the ipsilateral hemisphere. The superimposition of the sonographic images with those from computed tomography or magnetic resonance imaging showed a good correspondence in shape and size in patients with a craniectomy. In patients without a craniectomy, a rough correspondence with findings from magnetic resonance imaging or computed tomography could be recognized.

CONCLUSIONS

By using contrast-enhanced transcranial duplex sonography, it is possible to image the perfusion deficit in cerebral microcirculation in patients with intracranial space-occupying lesions. These results should be confirmed by more pathologic cases and correlated with magnetic resonance imaging and other neuroimaging techniques. Additionally, further technical development in sonographic systems is necessary to improve the diagnostics of cerebral perfusion deficit.

Hemodynamics of the posterior cerebral arteries in neonates with periventricular leukomalacia

PURPOSE

The purpose of this study was to evaluate the cerebral blood flow of the posterior cerebral arteries (PCAs) in neonates in relation to the onset of periventricular leukomalacia (PVL).

METHODS

Among 57 low-birth-weight neonates studied, 7 were diagnosed with PVL with cyst formation on sonography and MRI. The mean cerebral blood flow velocity (CBFV) was measured in all the neonates by Doppler sonography through the posterior fontanel separately in the right and left PCA at days 0, 1, 2, 3, 4, 5, 7, 10, 14, 21, 28, 42, 56, and 70 following birth.

RESULTS

In the 7 neonates with PVL the mean CBFV in the right PCA was significantly lower than that in neonates without PVL at days 10, 14, 21, 28, 42, 56, and 70; the mean CBFV in the left PCA of neonates with PVL was significantly lower than that in those without PVL at days 7, 10, 14, 21, 28, 42, 56, and 70. CBFV measured in neonates without PVL exhibited a gradual increase postnatally. In contrast, CBFV values for neonates with PVL plateaued after day 5 or 7.

CONCLUSIONS

The serial measurement of PCA CBFV postnatally may prove useful as a predictor of the development of PVL.

Ultrasonic evaluation with second harmonic imaging and SonoVue in the assessment of cerebral perfusion in diabetic patients: a case-control study

The purpose was to compare human brain tissue perfusion in diabetic patients and healthy subjects with second harmonic imaging ultrasound and SonoVue to test the hypothesis that brain tissue perfusion differences are present in these two groups of patients. In a prospective case-control study, second harmonic examinations performed in 20 patients with type II diabetes mellitus and in 20 matched control patients were compared. After administration of 2.5 ml of SonoVue, 60 time-triggered images were recorded. Time-intensity curves, including peak intensity and positive gradient normalized to the middle cerebral artery, were calculated to quantify ultrasound intensity in a region of interest. The Mann-Whitney U-test was used to reveal any differences between healthy and diabetic subjects. Mean peak intensity was 0.64+/-0.1 Au in healthy subjects and 0.53+/-0.09 Au in diabetic patients. Mean positive gradient was 0.04+/-0.007 Au/s in healthy subjects and 0.04+/-0.008 Au/s in diabetic patients. Peak intensity and positive gradient were significantly lower in diabetic patients than in healthy subjects (P<0.05). Ultrasound examination with second harmonic imaging and SonoVue administration is able to detect clinically silent, reduced cerebral perfusion in type II diabetic patients. Diabetic patients have reduced cerebral perfusion in comparison to healthy subjects.

Validation of the depletion kinetic in semiquantitative ultrasonographic cerebral perfusion imaging using 2 different techniques of data acquisition

OBJECTIVE

To validate the potential of ultrasonographic depletion imaging for semiquantitatively visualizing cerebral parenchymal perfusion with contrast burst depletion imaging (CODIM) in comparison with phase inversion harmonic depletion imaging (PIDIM) in healthy volunteers.

METHODS

Thirteen healthy adults were examined with both CODIM and PIDIM in accordance with previously described criteria. In addition to the perfusion coefficient, the time to decrease image intensity to 10% above equilibrium intensity from the initial value and the relative error (deviation of measured data from the fitted model) were evaluated to compare the reliability of both techniques in 3 different regions of interest.

RESULTS

Perfusion coefficient values did not show significantly differing values in both groups (1.57-1.64 * 10(-2) s(-1) for CODIM and 1.42-1.58 * 10(-2) s(-1) for PIDIM). The relative error was significantly smaller in the PIDIM group (0.38-0.53 for CODIM and 0.18-0.25 for PIDIM; P < .002).

CONCLUSIONS

Phase inversion harmonic depletion imaging proved to be more reliable than CODIM because values of the relative error were significantly lower in PIDIM even in this relatively small cohort. This is of interest because the underlying technique, phase inversion harmonic imaging, is more widely available than contrast burst imaging.

Ultrasound evaluation of normal and abnormal fetuses: comparison of conventional, tissue harmonic, and pulse-inversion harmonic imaging techniques

OBJECTIVE

To determine the usefulness of tissue harmonic imaging (THI) and pulse-inversion harmonic imaging (PIHI) in the evaluation of normal and abnormal fetuses.

MATERIALS AND METHODS

Forty-one pregnant women who bore a total of 31 normal and ten abnormal fetuses underwent conventional ultrasonography (CUS), and then THI and PIHI. US images of six organ systems, namely the brain, spine, heart, abdomen, extremities and face were compared between the three techniques in terms of overall conspicuity and the definition of borders and internal structures.

RESULTS

For the brain, heart, abdomen and face, overall conspicuity at THI and PIHI was significantly better than at CUS (p < 0.05). There was, though, no significant difference between THI and PIHI. Affected organs in abnormal fetuses were more clearly depicted at THI and PIHI than at CUS.

CONCLUSION

Both THI and PIHI appear to be superior to CUS for the evaluation of normal or abnormal structures, particularly the brain, heart, abdomen and face.

Perfusion harmonic imaging in acute middle cerebral artery infarction

Initial reports indicate that cerebral perfusion deficits in acute ischemic stroke might be detectable by means of transcranial harmonic imaging after an ultrasound contrast agent (UCA) bolus injection. Twenty-four patients with acute middle cerebral artery (MCA) infarction were investigated twice with perfusion harmonic imaging (PHI) after Levovist (Schering, Berlin, Germany) bolus injection no longer than 12 h after symptom onset. The findings were compared with those of cranial computed tomography (CCT). All 24 patients suffered from acute ischemic stroke of the MCA territory (median National Institutes of Health Stroke Scale score: 15 points). Corresponding to the area of infarction in follow-up CCT, a marked contrast deficit was visualized in 19 of 24 patients by initial PHI, which had a sensitivity and specificity of 86.4% and 96.2%, respectively, for predicting the occurrence and localization of a definite infarction in the midthalamic plane. The area of hypoperfusion in the initial PHI investigation correlated with the definite area of infarction in follow-up CCT (r=0.66, p<0.01). When time-intensity curves of both hemispheres were compared, the areas under the curve were significantly less in the symptomatic brain regions (p=0.01). With PHI and UCA bolus injection, it is possible to assess cerebral perfusion deficits that correlate with the definite area of infarction in acute ischemic stroke patients.

Acetazolamide vasoreactivity evaluated by transcranial harmonic perfusion imaging: relationship with transcranial Doppler sonography and dynamic CT

To establish the reliability and clinical significance of transcranial ultrasonic harmonic perfusion imaging (HPI), we evaluated HPI's relationships with transcranial Doppler (TCD) and with dynamic CT (DCT), during acetazolamide (ACZ) vasoreactivity tests.

METHODS

The subjects were 12 neurological patients. Time-averaged maximum velocity (TAVMX) in the middle (MCA) and posterior cerebral arteries was measured by TCD. Time-intensity (-density) curves of HPI (DCT) after bolus intravenous contrast injections were created in 3 regions of interest (ROI) on the axial plane involving the temporal lobe, basal ganglia, and thalamus on both sides. Assessments of vasoreactivity were based on comparisons conducted before and after ACZ administration in terms of: a) relative changes (%delta) of the TCD TAVMX, b) HPI contrast area enlargement, c) %delta of calculated cerebral blood volume and flow of the HPI and DCT.

RESULTS

1) TCD vasoreactivity decrease in the left MCA tended to correlate with lower frequency of HPI contrast area enlargement on the left side. 2) HPI and DCT vasoreactivity tended to be disturbed in the same side ROIs.

CONCLUSIONS

Transcranial HPI achieves repeatable non-invasive bedside evaluation of cerebrovascular reserve capacity through qualitative and quantitative measurements of brain tissue perfusion, and will have clinical value in pathophysiological follow-up and therapeutic effectiveness determination of neurointensive care patients.

Brain perfusion and ultrasonic imaging techniques

Advances in neurosonology have generated several techniques of ultrasonic perfusion imaging employing ultrasound echo contrast agents (ECAs). Doppler imaging techniques cannot measure the low flow velocities that are associated with parenchymal perfusion. Ultrasonic perfusion imaging, therefore, is a combination of a contrast agent-specific ultrasound imaging technique (CAI) mode and a data acquisition and processing (DAP) technique that is suited to observe and evaluate the perfusion kinetics. The intensity in CAI images is a measure of ECA concentration but also depends on various other parameters, e.g. depth of examination. Moreover, ECAs can be destroyed by ultrasound, which is an artifact but can also be a feature. Thus, many different DAPs have been developed for certain CAI techniques, ECAs and target organs. Although substantial progress in ECA and CAI technology can be foreseen, ultrasound contrast imaging has yet to reliably differentiate between normal and pathological perfusion conditions. Destructive imaging techniques, such as contrast burst imaging (CBI) or time variance imaging (TVI), in combination with new DAP techniques provide sufficient signal-to-noise ratio (SNR) for transcranial applications, and consider contrast agent kinetics and destruction to eliminate depth dependency and to calculate semi-quantitative parameters. Since ultrasound machines are widely accessible and cost-effective, ultrasonic perfusion imaging techniques should become supplementary standard perfusion imaging techniques in acute stroke diagnosis and monitoring. This paper gives an overview on different CAI and DAP techniques with special focus on recent innovations and their clinical potential.

Transcranial contrast diminution imaging of the human brain: a pilot study in healthy volunteers

Analysis of contrast diminution kinetics after bubble destruction is a new aspect in harmonic imaging. The purpose of this study was to investigate this approach to human cerebral perfusion. A total of 12 healthy volunteers were investigated transtemporally (Philips SONOS 5500, S4-probe, 1.8 to 3.6 MHz, 10 cm) at two ultrasound (US) contrast agent (UCA) infusion rates (0.5 and 1.0 mL/min of Optison). After achieving a steady-state, a set of 12 US pulses (6.67 Hz, MI 1.6) was applied. Time-intensity plots of three regions-of-interest (ROIs) (thalamus, white matter and cortex) were analyzed, using an exponential curve fit (I((t)) = I(0)e(-betat) + B). A total of 20 of 20 successful investigations showed a signal decrease after pulsed US application. In all cases, it was possible to generate exponential time-intensity curves. Half-life (T(1/2) = ln2/beta) and baseline intensity (B) showed a significant dependence on infusion rate (p = 0.01). At 1.0 mL/min, T(1/2) also depended on investigation depth (p = 0.01). It is possible to assess contrast diminution kinetics in human cerebral microcirculation. This new approach may provide additional information on cerebral perfusion within a short investigation time.

Perspectives of B-mode transcranial ultrasound

Transcranial color coded sonography has proved valuable in the diagnostic work-up of cerebrovascular disorders in adults. More recently, evidences have converged that transcranial sonography is also useful in the diagnosis of brain parenchymal disorders. Here, a new field of application is the visualization of signal intensity shift in specific brain areas in some neurodegenerative disorders (Parkinson's disease, idiopathic dystonia, and depression). Findings obtained by transcranial ultrasound complement information from other neuroimaging data in these disorders and have led to the generation of new pathophysiological concepts. In this review we summarize the application fields of transcranial sonography with special emphasis on recent findings in neurodegenerative disorders and their implications for future research. As new application and processing techniques are being developed transcranial color coded sonography will gain increasing impact on both diagnosis and research of neurological disorders.

Human cerebral perfusion analysis with ultrasound contrast agent constant infusion: a pilot study on healthy volunteers

With ultrasound (US) contrast agent (UCA) continuous infusion providing a steady state, mean tissue microbubble velocity can be assessed by analyzing the reappearance rate after microbubble destruction with US energy (refill kinetics). In this study, we investigated this new approach for the assessment of human cerebral perfusion. A total of 12 healthy volunteers were investigated transtemporally with increasing pulsing intervals (250, 500, 750, 1000, 1250, 1500, 2000, 3000 and 4000 ms) and two UCA infusion rates (0.5 and 1.0 mL/min of Optison). Intensity vs. pulsing interval curves were analyzed using an exponential curve fit and parameters of the curve (plateau echo enhancement, A, representing the microbubble concentration within the interrogated tissue; rate constant, beta, which is related to blood flow and their product, F = Abeta) were compared. For 20/20 investigations being available for further analysis, it was possible to generate a typical exponential intensity vs. pulsing interval curve from the ipsilateral thalamus. The plateau echo enhancement A showed a significant (p = 0.02), and the beta as well as the F values displayed a nonsignificant (p = 0.06, both), increase with infusion rate. The qualitative analysis of beta and F parameter images displayed the most homogeneous visualisation of perfusion in the ipsilateral thalamus and main territory of the middle cerebral artery. In conclusion, it is possible to display the UCA refill kinetics in human cerebral microcirculation after microbubble destruction by transcranial US. Grey-scale harmonic imaging allows a quantitative approach to cerebral perfusion with a large interindividual variation of the parameters.

Harmonic imaging--a new method for the sonographic assessment of cerebral perfusion

In this review, methodological aspects of cerebral perfusion imaging with ultrasound signal enhancing agents are described. The various experimental bases, contributing to the understanding of the phenomena are summarised and the resulting human investigation techniques are illustrated. By means of harmonic imaging technology, human cerebral perfusion can be depicted as a two-dimensional scan. The two major principles of contrast measurement are analysis of the bolus kinetics and analysis of the refill kinetics. Using the bolus method, hypoperfused areas in stroke patients can be visualised and parameter images of wash-in and wash-out curves can be generated off-line. The recently developed theory on the refill kinetics of UCA enables us to calculate quantitative parameters for the description of the cerebral microcirculation, being less affected by the depth dependence of the contrast effect. These parameters, too, can be visualised as parameter images. The ultrasound methods described in this article represent new minimal-invasive bedside techniques for analysing brain perfusion. Although their development is still in an early state, the potential of these ultrasound technologies to compete with perfusion-CT, perfusion-MRI or single-photon emission computed tomography in the diagnostic arsenal of brain imaging techniques is becoming evident.

Evaluation of blood flow in the cerebral microcirculation: analysis of the refill kinetics during ultrasound contrast agent infusion

By means of harmonic imaging, it is possible to display brain perfusion qualitatively using ultrasound (US) contrast agent (UCA) bolus injection. With UCA continuous infusion reaching a steady state, mean microbubble velocity can be measured, analyzing the reappearance rate after microbubble destruction by US (refill kinetics). We performed an animal pilot study to investigate this new method for the assessment of brain perfusion. Using harmonic grey-scale imaging, five sedated male beagle dogs were investigated through the intact skull with increasing pulsing intervals (250 to 8000 ms) and three UCA infusion rates (0.5, 1.0 and 1.5 mL/min of Optison). Cerebral blood flow was increased by acetazolamide (30 mg/kg BW). Intensity vs. pulsing interval curves were analyzed using an exponential curve fit [I(t) = A(1-e(-beta t))] and parameters of the curve were compared. We found that increasing the pulsing interval above 4000 ms led to no further increase of echo enhancement for infusion rates. Mean beta values were not influenced by infusion rate (p = 0.25 and p = 0.55). Mean F values increased nonsignificantly with rising infusion rate (p = 0.25 and p = 0.86). Acetazolamide led to an increase of mean beta and F values (p = 0.18 and p = 0.025, respectively). It is possible to evaluate changes in brain perfusion through the intact skull by analyzing the UCA refill kinetics after US-induced microbubble destruction.

Contrast agent specific imaging modes for the ultrasonic assessment of parenchymal cerebral echo contrast enhancement

Previous work has demonstrated that cerebral echo contrast enhancement can be assessed by means of transcranial ultrasound using transient response second harmonic imaging (HI). The current study was designed to explore possible advantages of two new contrast agent specific imaging modes, contrast burst imaging (CBI) and time variance imaging (TVI), that are based on the detection of destruction or splitting of microbubbles caused by ultrasound in comparison with contrast harmonic imaging (CHI), which is a broadband phase-inversion-based implementation of HI. Nine healthy individuals with adequate acoustic temporal bone windows were included in the study. Contrast harmonic imaging, CBI, and TVI examinations were performed in an axial diencephalic plane of section after an intravenous bolus injection of 4 g galactose-based microbubble suspension in a concentration of 400 mg/mL. Using time-intensity curves, peak intensities and times-to peak-intensity (TPIs) were calculated off-line in anterior and posterior parts of the thalamus, in the region of the lentiform nucleus, and in the white matter. The potential of the different techniques to visualize cerebral contrast enhancement in different brain areas was compared. All techniques produced accurate cerebral contrast enhancement in the majority of investigated brain areas. Contrast harmonic imaging visualized signal increase in 28 of 36 regions of interest (ROIs). In comparison, TVI and CBI examinations were successful in 32 and 35 investigations, respectively. In CHI examinations, contrast enhancement was most difficult to visualize in posterior parts of the thalamus (6 of 9) and the lentiform nucleus (6 of 9). In TVI examinations, anterior parts of the thalamus showed signal increase in only 6 of 9 examinations. For all investigated imaging modes, PIs and TPIs in different ROIs did not differ significantly, except that TVI demonstrated significantly higher PIs in the lentiform nucleus as compared with the thalamus and the white matter (P < 0.05). The current study demonstrates for the first time that CBI and TVI represent new ultrasonic tools that allow noninvasive assessment of focal cerebral contrast enhancement and that CBI and TVI improve diagnostic sensitivity as compared with CHI.

Ultrasonic evaluation of pathological brain perfusion in acute stroke using second harmonic imaging

OBJECTIVE

To evaluate the use of transient response second harmonic imaging (HI) by means of ultrasound to assess abnormalities of cerebral echo contrast agent enhancement in patients with acute stroke.

METHODS

The study comprised 25 patients with acute onset of hemispheric stroke (<24 h) with sufficient insonation conditions and 14 control subjects without cerebrovascular disease. All stroke patients had HI, extracranial and transcranial colour coded duplex examinations of the arteries supplying the brain, and clinical examinations (European stroke scale) performed in the acute phase, on day 2, and within 1 week. Acute CT was repeated within 1 week and facultatively accompanied by angiography. Examinations using HI were performed in an axial diencephalic plane of section using the transtemporal acoustic bone window. After bolus application of galactose based microbubbles, 61 ultrasound images with a cardiac cycling triggering frequency of once every 2 seconds were recorded and evaluated off line. Focal perfusion deficit was identified if no contrast enhancement was visualised in a circumscribed region of interest and insufficient temporal bone window was excluded. In cases of reappearance of contrast enhancement reperfusion was assessed.

RESULTS

Adequate cerebral contrast enhancement could be seen in 21 subjects. In seven, a large hemispheric deficit of contrast enhancement affecting the entire middle cerebral artery (MCA) territory was detectable; the lentiform nucleus was affected in three subjects. Assessment of cerebral contrast abnormalities was possible in two patients with superficial MCA infarctions but in none of the patients with lacunar ischaemias. None of the control persons had focal deficits of cerebral echo contrast enhancement. In all patients with complete MCA infarction and striatocapsular infarction, presumed ischaemic areas in HI examinations correlated with final CT findings. Overall sensitivity and specifity of HI examinations for predicting size and localisation of the infarction were 75 and 100%, respectively. During follow up, reappearance of contrast enhancement was determined in three patients, in two patients circulatory arrest due to malignant brain oedema with missing contrast enhancement in the entire cerebral hemisphere could be seen. Extent of contrast enhancement deficits significantly correlated with the clinical status on admission and after 1 week (p<0.01).

CONCLUSIONS

Second harmonic imaging is the first ultrasonic technique that enables visualisation of pathological cerebral echo contrast enhancement. Because this method identifies deficits of focal contrast enhancement in patients with acute stroke and allows estimation of the final infarct size and clinical prognosis, it may help to select and monitor patients for invasive therapies.