Diffusion and perfusion magnetic resonance imaging for the evaluation of acute stroke: potential use in guiding thrombolytic therapy

Diffusion-weighted magnetic resonance imaging and magnetic resonance spectroscopy for non-invasive characterization of azoospermia: A prospective comparative single-center study

BACKGROUND

Azoospermia affects about 15% of childless males. The differential diagnosis between subtypes of azoospermia is the initial step in its management.

OBJECTIVES

To investigate the role of diffusion-weighted magnetic resonance imaging and proton magnetic resonance spectroscopy in distinguishing obstructive azoospermia from non-obstructive azoospermia and predicting sperm retrieval together with histological alterations in men with non-obstructive azoospermia.

MATERIALS AND METHODS

This prospective comparative study involved 60 men with obstructive azoospermia (group A) and 60 men with non-obstructive azoospermia (group B). Scrotal proton magnetic resonance spectroscopy and diffusion-weighted magnetic resonance imaging were conducted for all participants to respectively evaluate testicular metabolites and normalized apparent diffusion coefficient 1 week before sperm retrieval.

RESULTS

Apparent diffusion coefficient was significantly higher in group B as compared to group A (0.47 ± 0.11 vs. 0.29 ± 0.05; and 0.46 ± 0.14 vs. 0.28 ± 0.02) for the right and left testis, respectively. Conversely, testicular choline and lipids were significantly higher in group A as compared to group B. Normalized apparent diffusion coefficient, choline, and lipids at cut-off levels of 0.353, 0.31, and 0.725 could differentiate between obstructive azoospermia and non-obstructive azoospermia (area under the curve = 0.963; confidence interval = 0.939-0.986, area under the curve = 0.985; confidence interval = 0.974-0.997, and area under the curve = 0.970; confidence interval = 0.940-0.999, respectively). Regarding the prediction of sperm retrieval in the non-obstructive azoospermia group, choline levels had the highest area under the curve (0.923), and its cut-off level was 0.195. The normalized apparent diffusion coefficient was significantly lower in men with positive sperm retrieval as compared to men with unsuccessful retrieval. Finally, it was revealed that all magnetic resonance imaging parameters except creatine could independently predict testicular histology in men with non-obstructive azoospermia. The highest prediction was 95% in normal spermatogenesis, and the least prediction was 40% in spermatid arrest. Regression analysis was used to detect final predictors and extrapolate an equation that could be used to predict testicular pathology CONCLUSIONS: Normalized apparent diffusion coefficient and proton magnetic resonance spectroscopy are helpful in differentiating obstructive azoospermia from non-obstructive azoospermia and predicting sperm retrieval and related histological alterations in men with non-obstructive azoospermia.

Experimental model of brainstem stroke in rabbits via endovascular occlusion of the basilar artery

BACKGROUND

Basilar artery thrombosis remains a significant clinical problem, and no reproducible animal model has been established to study the stroke within the vertebrobasilar distribution. We report a study designed to pilot test a novel model of brainstem stroke in rabbits, created by selective endovascular occlusion of the basilar artery.

METHODS

Basilar artery occlusion was induced in 8 New Zealand white rabbits by injection of the autologous clot through the microcatheter positioned within the distal vertebral artery. Animals were divided into subgroups (I and II) based on the length of produced ischemia (3 and 6 hours, respectively). Magnetic resonance (MR) imaging of the brain and MR angiography of the intracranial vessels were performed before the procedure, and at 3 hours after induced ischemia for groups I and II, with continued imaging up to 6 hours for group II, with diffusion-weighted images acquired approximately every 30 minutes. Animals were killed at the end of the 3-hour (group I) or 6-hour (group II) ischemia time.

RESULTS

Brainstem stroke was successfully induced in all animals, with pathological changes documented in all cases. The earliest changes of ischemia on MR diffusion-weighted images were identified at only 4.5 hours of basilar artery occlusion.

CONCLUSION

These results suggest that a reproducible model of brainstem stroke can be induced in rabbits using selective endovascular occlusion of the basilar artery. The availability of such a model, integrated with state-of-the-art imaging techniques, holds promise for preclinical investigations of emergent therapeutic approaches in stroke.

Very brief focal ischemia simulating transient ischemic attacks (TIAs) can injure brain and induce Hsp70 protein

This study examined very brief focal ischemia that simulates transient ischemic attacks (TIAs) that occur in humans. Adult rats were subjected to sham operations or 5 min, 10 min, or 2 h of middle cerebral artery (MCA) ischemia using the suture (thread) model. Hsp70 protein was induced 24 h, 48 h and 72 h later in neurons throughout the entire MCA territory in many but not all animals. Following 5- and 10-minute MCA occlusions, 9 of 32 animals (28%) had microinfarcts mostly in dorsal lateral striatum. Uncommon Hsp70 stained intracellular cytoplasmic inclusions, some of which co-localized with activated caspase-3, were detected in microglia, macrophages, astrocytes and oligodendrocytes. Hsp70 stained neurons were TUNEL negative at 24 h and 48 h whereas some Hsp70 stained neurons were TUNEL positive at 72 h after reperfusion. Hsp70 positive, activated "bushy" microglia and Hsp70 negative, activated "polarized" or rod-shaped microglia were located outside of the microinfarcts. Thus, experimental focal ischemia simulating TIAs can: induce Hsp70 protein throughout the ischemic vessel territory; produce Hsp70 protein positive glial inclusions; activate Hsp70 positive and negative microglia; and cause microinfarcts in some animals.

Comparison of combined venous and arterial thrombolysis with primary arterial therapy using recombinant tissue plasminogen activator in acute ischemic stroke

OBJECTIVE

We sought to compare the safety and efficacy of combined intravenous (IV) and intra-arterial (IA) thrombolysis with primary IA therapy using tissue plasminogen activator for acute ischemic stroke presenting within 6 hours of symptom onset.

METHODS

We performed quasirandomization of a single institution's prospectively collected stroke database, comparing IV/IA (0.6 mg/kg IV < or = 60 mg, followed by 0.3 mg/kg IA < or = 30 mg) versus primary IA. Outcome measures include 90-day modified Rankin scale score, mortality, symptomatic intracerebral hemorrhage, and recanalization rates. Statistical analysis was performed using bivariate and propensity score methods.

RESULTS

Of 1057 patients, 41 patients were treated with IV/IA, and 55 with IA. There was significant difference in time to treatment (mean of 151 minutes for the combined group and 261 minutes for the IA, P < .0001) and arterial tissue plasminogen activator dose (17.5 mg for IV/IA v 22.8 mg for IA only, P = .05). Propensity score matching yielded 25 patients in each group. Symptomatic intracerebral hemorrhage rate was 12% in each group. Mortality was 20% in the IV/IA group versus 16% in the IA group (relative risk 1.3 [0.4-4.1], P = .7). More patients in IV/IA group had modified Rankin scale score less than or equal to 2 (odds ratio 1.6 [0.5-5.8], P = .3). Recanalization was 64% with IV/IA versus 48% with IA (odds ratio 1.9 [0.5-7.0], P = .3).

CONCLUSION

This study demonstrates that both combined IV/IA and primary IA recombinant tissue plasminogen activator therapy is feasible and safe in the treatment of acute ischemic stroke. Combined IV/IA therapy may be associated with an improvement in clinical outcome without a significant increase in the risk of symptomatic intracerebral hemorrhage and mortality compared with IA therapy.

Diffusion-weighted magnetic resonance imaging versus computed tomography in the diagnosis of acute ischemic stroke

Current treatment protocols using reperfusion therapy for acute ischemic stroke rely on non-contrast computed tomography (NCCT), with most indications including the absence of acute hemorrhage or large volume of infarction in the presence of clinical signs and symptoms. This predictably results in a significant incidence of the administration of reperfusion therapy to patients with "stroke mimics," such as migraine headache or Todd's paralysis after a seizure. Diffusion-weighted imaging (DWI) is a technique based on magnetic resonance imaging (MRI) that may be more sensitive and specific for acute cerebral ischemia than NCCT. In addition, data for techniques such as perfusion-weighted imaging can be acquired with minimal additional time required. This may allow better risk assessment of a clinical response to reperfusion therapy vs. the possibility of hemorrhagic complications. This article describes a methodical review of studies comparing the sensitivity, specificity, positive predictive value, and negative predictive value of DWI vs. NCCT in the evaluation of acute ischemic stroke. Data from studies meeting our screening criteria are combined to produce overall values for each.

A supervised method for calculating perfusion/diffusion mismatch volume in acute ischemic stroke

Diffusion and perfusion (MR) imaging modalities identify overlapping but not identical areas of tissue as lesion following a stroke. It is thought that the 'mismatch' between modalities may represent tissue that could be recovered with proper (thrombolytic) treatment. We have designed a tool for semi-automated segmentation of the images and calculation of the mismatch volume. We present results from software phantoms and clinical data. Phantom results show our mismatch volume calculations are unbiased at realistic noise levels. Clinical data show that raters using our tool are consistent, fast (15min per subject) and indistinguishable from an expert using manual segmentation.

Acute studies of a new primate model of reversible middle cerebral artery occlusion

The recent failure of many clinical trials of neuroprotective compounds may be due in part to poor animal models of human stroke. We have developed an endovascular stroke model in nonhuman primates that is compatible with serial magnetic resonance imaging (MRI) monitoring. Using cynomologous macaques (n = 4), a microcatheter was navigated transarterially (under fluoroscopic guidance) from the femoral artery to the middle cerebral artery (MCA). The microcatheter was wedged in a branch of the MCA for 3 hours to cause focal cerebral ischemia, as verified angiographically. During occlusion and/or reperfusion, animals were scanned with MRI, and imaging findings were compared with the stained brain sections. All animals demonstrated small stroke lesions in the expected vascular territory, as seen on diffusion-weighted MRI and confirmed by postmortem examination. Reperfusion after 3 hours was confirmed angiographically (n = 2) and also by MRI (n = 4). The mean initial lesion volume, measured on the postreperfusion MRI scans, was 2.3 +/- 1.3 mL (n = 4). There was good agreement between anatomic location of the lesion on MRI and postmortem histological staining (n = 3). A "minimally invasive" primate model of focal cerebral ischemia was developed that is ideally suited to MRI studies of both acute and chronic stroke. By using serial MRI scans to measure changes in lesion size over time, we will be able to control for variability in lesion size/location. This model should prove useful as a test bed for new stroke therapies, in which noninvasive imaging findings are readily comparable to human stroke.

The Janus face of inflammation in ischemic brain injury

Brain ischemia elicits an intense inflammatory reaction as evidenced by endogenous activation of microglia and infiltration of leukocytes from the systemic circulation into the brain. A key issue regarding the well-described inflammation in brain injury is whether this reaction is of salutary or detrimental nature in the short and longterm post ischemia. In this brief review, evidence in support for the possible beneficial as well as detrimental role of inflammatory cells and mediators in ischemic brain injury is highlighted. We offer the opinion that both benefits and adverse effects of the inflammatory reaction at large depent on the levels of a specific mediator, the temporal relationships to the injury, the context in which the mediator operates and the spatial relationships to the injury.

Rapid perfusion abnormality estimation in acute stroke with temporal correlation analysis

BACKGROUND AND PURPOSE

Determination of the presence or absence of ischemic penumbra through diffusion-perfusion mismatch requires rapid delineation of both abnormalities. Although singular value decomposition-based perfusion parameter estimation has offered valuable insights into the underlying cerebral hemodynamics, the associated postprocessing procedures have limited its widespread use. We explored the utility of a simple technique to define perfusion abnormality in acute stroke patients.

METHODS

Twenty acute stroke patients were studied. The MR dynamic contrast approach was used to obtain cerebral blood flow, cerebral blood volume, and mean transit time (MTT). Temporal correlation was used to correlate 4 reference functions-an arterial input function (AIF), a normal tissue function, a lesion function, and a venous output function-with dynamic contrast MR images, and correlation coefficients (CCs) were calculated pixel by pixel. In addition, chronic-state T2-weighted images were coregistered onto the images acquired acutely for assessing the sensitivity and specificity of CC-defined lesion.

RESULTS

Statistically significant differences in cerebral blood flow and MTT were found between CC-defined normal and abnormal tissues with all 4 reference functions used. When the final infarct volume was used as the gold standard, a similar sensitivity between MTT (78%) and AIF (76%) CC-defined lesion was obtained, whereas the specificity was higher for AIF (61%) than that obtained with MTT-defined lesion (52%).

CONCLUSIONS

We explored CC maps as a simpler alternative of estimating perfusion abnormality, and results demonstrated the potential clinical utility of a correlation-based technique for estimating brain perfusion status.

Functional neuroimaging in acute stroke

To the present day, the first and most widespread diagnostic approach in the assessment of acute stroke remains CT scan. Its sensitivity is very high (nearly 100%) in detecting intracerebral hemorrhage in the acute period, but its capability of revealing ischemic injury in the very first hours from symptom onset is relatively poor. Since the efficacy of thrombolytic treatment in acute stroke has been suggested by the ECASS and NINDS rt-PA trials, functional neuroimaging able to distinguish potentially salvageable tissue from irreversibly injured areas has acquired primary importance. The possibility to correctly identify the tissue of the ischemic penumbra within the first hours from symptom onset is essential for correct patient selection for thrombolitic treatment. Different imaging strategies are available for the definition of perfusion deficits within the acute time window; among these are positron emission tomography (PET), single photon emission computed tomography (SPECT), Xenon CT (XeCT), dynamic CT perfusion imaging (CTP), diffusion weighted magnetic resonance imaging (DW-MRI), and perfusion weighted magnetic resonance imaging (PW-MRI). Though each technique has its advantages and limitations to present day functional MRI remains the most widespread imaging technique in the assessment of acute stroke being more accessible than both SPECT and PET, and capable of giving information on both perfusion and tissue functional status in a single imaging session. In this paper we discuss the role of functional neuroimaging in acute stroke.

Ischaemic penumbra: highlights

The ischaemic penumbra was described for the first time in the late 1970s as a ring of hypoperfused zone surrounding the region of complete infarction. The penumbral zone is a functionally silent tissue which is able to regain its function if promptly reperfused. This implies that the ischaemic penumbra is not a static but a "dynamic" and "time-dependent" concept. In this paper we describe the role of neuroimmaging tecniques such as single photon emission tomography (SPET), positron emission tomography (PET), and diffusion-weighted and perfusion-weighted magnetic resonance imaging (DWI and PWI) in the study of ischaemic penumbra. These functional imaging techniques have the advantage of giving "in vivo" quantitative estimate of cerebral blood flow (CBF) as well as information on how the ischaemic tissue metabolic changes develop. It follows that, as therapeutic options for treating acute stroke evolve, neuroimaging strategies are assuming an increasingly important role in the initial evaluation and management of the acute ischaemic patient. In this regard, a wide range of therapeutic approaches have been investigated for either ameliorating the perfusion, or interfering with the pathobiochemical cascade leading to ischaemic neuronal damage, or improving endogenous neuroprotection pathways. The "time windows" required for these treatments to be effective varies being rather short for reperfusion and longer for neuroprotection. Salvaging more penumbra would enhance recovery and thereby allow the most appropriate candidate for therapeutic trials to be selected.

The very acute stroke treatment: fibrinolysis and after

Thrombolytic therapy with rt-PA given within 3 h after stroke onset to patients with ischemic stroke significantly improves outcome after stroke. There are some evidences that thrombolysis may also work up to 6 h after stroke onset in carefully identified patients, but the three most important trials, which used 0-6 h time-windows, combined with CT-scans to define the ischemic areas, failed individually to produce statistical benefits for the rt-PA-treated patients. In order to enlarge the time-window there is a need for additional information about the functionality of the affected brain area. There is a growing interest in the use of Diffusion Weighted (magnetic resonance) imaging (DWI) and Perfusion Weighted (magnetic resonance) imaging (PWI) in the assessment of patients with acute ischemic stroke. These magnetic resonance techniques are powerful methods for identifying the extent and location of early cerebral ischemia.

Use of diffusion weighted MRI to predict the occurrence and severity of hemorrhagic transformation in a rabbit model of embolic stroke

Severe hemorrhagic transformation (HT) is an important complication of thrombolytic therapy. A method to identify stroke victims destined to severe HT could improve the patient selection and thus the safety of such treatment. In this study, we investigated whether very early serial diffusion weighted magnetic resonance imaging (DWI) could predict the occurrence of HT in an embolic model of experimental stroke. We tested the hypothesis that the ischemic brains with very low initial apparent diffusion coefficients (ADC) are destined to severe early (<or=5.5 h) HT. We retrospectively analyzed DWI scans of 45 New Zealand white rabbits subjected to thromboembolic stroke and treated with thrombolysis. DWI was obtained 0.5, 2, 3 and 5 h after embolization. Various thrombolytics were administered 1 h post embolization. The percentage of pixels within the ischemic hemisphere with ADC values below 550 x 10(-6) mm(2)/s was calculated and then compared to the severity of HT observed on gross brain sections at 5.5 h. As early as 30 min after embolization, ischemic brains destined to severe HT exhibited a significantly greater percentage of pixels below the cut-off value compared to those without HT: severe HT: 25%, 18.75-37.25% vs. no HT: 12%, 5.00-16.00% (median, 25th-75th %, P<0.001). Petechial HT when percentages were in the intermediate range. Quantitative analysis of initial ADC value might identify individual stroke patients at risk of severe HT.

Response to intra-arterial and combined intravenous and intra-arterial thrombolytic therapy in patients with distal internal carotid artery occlusion

BACKGROUND AND PURPOSE

The objective of this study was to determine the clinical features, angiographic findings, and response to treatment with thrombolytic therapy in patients with ischemic stroke caused by acute occlusion of the distal internal carotid artery.

METHODS

This is a retrospective case series from a prospectively collected stroke database for patients with acute internal carotid occlusion presenting within 6 hours of stroke onset to evaluate safety, feasibility, and response to thrombolytic therapy. The University Hospital-based brain attack database was reviewed over a 5-year period. Demographics, clinical features, stroke mechanisms, severity, imaging findings, type of thrombolysis, treatment responses, mortality, and long-term outcome using modified Rankin Scale and Barthel Index were determined. The short-term outcome was assessed using the National Institutes of Health Stroke Scale (NIHSS). Acute thrombolytic therapy was administered using recombinant tissue plasminogen activator or urokinase given intra-arterially or in combination with intravenous (IV) routes.

RESULTS

Two hundred seven patients treated with thrombolysis between 1995 and 2000 were reviewed, and of these, 101 were studied with cerebral angiography. Eighteen patients were identified with acute ischemic stroke and ipsilateral occlusion of the distal internal carotid artery. Time to treatment was the most powerful predictor of response to thrombolytic therapy (P<0.001). The response to therapy also correlated well with the severity of the initial clinical deficit as judged by the NIHSS (P<0.001). There was no difference in recanalization rate, symptomatic hemorrhage, and NIHSS for IV/intra-arterial (IA) versus IA alone (P=NS). Complete angiographic recanalization was accomplished in 80% of those who received combined IV/IA thrombolysis and in 62% of those who received IA therapy (P=NS). Those with distal occlusions extending to the middle and anterior cerebral arteries were the least likely to respond to thrombolysis. Symptomatic intracerebral hemorrhage occurred in 20% of the patients receiving IV/IA therapy, and in 15% of the IA only (P=NS). At 24 hours, the NIHSS dropped by 3 points in the IA group and 4 points in the IV/IA group (P=NS). Mild disability with independence was found in 77% of the survivors at 3-month follow-up. The mortality rate was 50% in this group despite thrombolysis.

CONCLUSIONS

Thrombolytic therapy using a combination of IV and IA routes and using the IA-only route may be effective in improving outcome for the patients suffering from occlusion of the distal internal carotid artery. Shorter intervals between onset and treatment seem to be correlated with higher rate of recanalization and improved outcome.

Intravenous rt-PA for stroke

Thrombolytic therapy remains the most potent known treatment for acute ischaemic stroke. Treatment can significantly improve neurological outcome with only a mild increase in haemorrhage risk. Previous concerns over the importance of subtle CT detect early infarct signs appears unwarranted. Most patients with a significant neurological deficit and without evidence of haemorrhage on initial head imaging in the < 3 h window should be considered for treatment. Subgroup analysis suggests that even patients with severe strokes and early signs of cerebral ischaemia on CT may benefit from treatment, albeit to a lesser degree. Community based studies indicate that a similar degree of efficacy can be achieved in routine clinical practice, especially at centres experienced at thrombolytic administration. Treatment beyond 3 h may also be efficacious in selected cases, but further clinical trials are necessary before routine use in this time period can be advocated.

Treatment of acute basilar artery thrombosis with a combination of systemic alteplase and tirofiban, a nonpeptide platelet glycoprotein IIb/IIIa inhibitor: report of four cases

In four patients with acute basilar artery thrombosis, complete arterial recanalization and good neurologic outcome were achieved with a treatment combining alteplase with tirofiban. In no cases were cerebral or extracerebral hemorrhagic complications observed. Combined fibrinolytic agents and glycoprotein IIb/IIIa inhibitors may have high potential in the treatment of acute cerebrovascular thrombosis.

Perfusion magnetic resonance imaging maps in hyperacute stroke: relative cerebral blood flow most accurately identifies tissue destined to infarct

BACKGROUND AND PURPOSE

In ischemic stroke, perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) provide important pathophysiological information. A PWI>DWI mismatch pattern suggests the presence of salvageable tissue. However, improved methods for distinguishing PWI>DWI mismatch tissue that is critically hypoperfused from benign oligemia are required.

METHODS

We investigated the usefulness of maps of relative cerebral blood flow (rCBF), volume (rCBV), and mean transit time (rMTT) to predict transition to infarction in hyperacute (<6 hours) stroke patients with PWI>DWI mismatch patterns. Semiquantitative color-thresholded analysis was used to measure hypoperfusion volumes, including increasing color signal intensity thresholds of rMTT delay, which were compared with infarct expansion, outcome infarct size, and clinical status.

RESULTS

Acute rCBF lesion volume had the strongest correlation with final infarct size (r=0.91, P<0.001) and clinical outcome (r=0.67, P<0.01). There was a trend for acute rCBF>DWI mismatch volume to overestimate infarct expansion between the acute and outcome study (P=0.06). Infarct expansion was underestimated by acute rCBV>DWI mismatch (P<0.001). When rMTT lesions included tissue with moderately prolonged transit times (mean delay 4.3 seconds, signal intensity values 50% to 70%), infarct expansion was overestimated. In contrast, when rMTT lesions were restricted to more severely prolonged transit times (mean delay 6.1 seconds, signal intensity >70%), these regions progressed to infarction in all except 1 patient, but infarct expansion was underestimated (P<0.001).

CONCLUSIONS

The acute rCBF lesion most accurately identified tissue in the PWI>DWI mismatch region at risk of infarction. Color-thresholded PWI maps show potential for use in an acute clinical setting to prospectively predict tissue outcome.

A survey of neuroimaging research in European neurological departments

In the international neurological literature, neuroimaging research plays an important role. Neuroimaging techniques are also of steadily increasing importance for clinical diagnosis and treatment monitoring. Therefore, neuroimaging research activities were surveyed by a questionnaire, which was completed by 100 neurological centres across Europe. It showed that most groups use magnetic resonance imaging (MRI), fMRI, computerized tomography (CT) and single photon emission computerized tomography (SPECT). Positron emission tomography (PET) and ultrasound are also employed by nearly half of the centres. Neuroimaging research involves co-operation amongst typically five to 10 disciplines. Cerebrovascular disease, dementia, cognitive disorders, epilepsy, movement disorders, brain tumours and multiple sclerosis are frequently being studied. Many groups rely on small budgets, have few full-time scientists and limited access to expensive resources. There is little exchange of scientists amongst laboratories. It was felt that funding and co-operation needed improvement in order to maintain a high standard in neuroimaging research.

Recent advances in the diagnosis and treatment of stroke

Stroke is defined as an abnormality in brain function resulting from disruption of cerebral circulation. It is the third leading cause of death in the United States and the primary cause of long-term disability. The economic burden of stroke will only increase as the population ages, making prevention and treatment of stroke one of the most important public health issues of the upcoming millennium. New therapies for the treatment of acute stroke, especially thrombolysis, have turned what was once considered an inevitable deficit into a potentially treatable illness. It is increasingly important for all physicians to be able to identify symptoms of cerebral ischemia. Neurons have a very limited tolerance for ischemia, making the rapid evaluation and diagnosis of stroke critical. This is particularly relevant for the ophthalmologist, who may be the first physician to see individuals presenting with visual deficits. Trials are underway to look specifically at central retinal artery and basilar artery ischemia and their response to thrombolytic therapy. This review will focus on description of recent advances in treatment and diagnosis of stroke, including thrombolytic trials and the expanding role of neuroimaging.