Value of single-photon emission-computed tomography in acute stroke therapeutic trials

Radiological predictors of hemorrhagic transformation after acute ischemic stroke: An evidence-based analysis

Hemorrhagic transformation (HT) is one of the most common adverse events related to acute ischemic stroke (AIS) that affects the treatment plan and clinical outcome. Identification of a sensitive radiological marker may influence the controversial thrombolytic decision in the setting of AIS and may at a minimum indicate more intensive monitoring or further prophylactic interventions. In this article we summarize possible radiological biomarkers and the role of different radiological modalities including computed tomography (CT), magnetic resonance imaging, angiography, and ultrasound in predicting HT. Different radiological indices of early ischemic changes, large ischemic lesion volume, severe blood flow restriction, blood-brain barrier disruption, poor collaterals and high blood flow velocities have been reported to be associated with higher risk of HT. The current levels of evidence of the available studies highlight the role of the different CT perfusion parameters in predicting HT. Further large standardized studies are recommended to compare the sensitivity and specificity of the different radiological markers combined and delineate the most reliable predictor.

Single photon emission computed tomography imaging of cerebral blood flow, blood–brain barrier disruption, and apoptosis time course after focal cerebral ischemia in rats

Background

Cerebral ischemia is a leading cause of disability worldwide and no other effective therapy has been validated to date than intravenous thrombolysis. In this context, many preclinical models have been developed and recent advances in preclinical imaging represent promising tools. Thus, we proposed here to characterize in vivo time profiles of cerebral blood flow, blood–brain barrier disruption and apoptosis following a transient middle cerebral artery occlusion in rats using SPECT/CT imaging.

Methods

Rats underwent a 1-h middle cerebral artery occlusion followed by reperfusion. Cerebral blood flow, blood–brain barrier disruption and apoptosis were evaluated by SPECT/CT imaging using respectively 99mTc-HMPAO, 99mTc-DTPA and the experimental 99mTc-Annexin V-128, up to 14 days after middle cerebral artery occlusion. Histological evaluation of apoptosis has been performed using TUNEL method to validate the 99mTc-Annexin V-128 uptake.

Results

99mTc-HMPAO cerebral blood flow evaluation showed hypoperfusion during occlusion, partially restored on days 4 and 7 and sustained up to 14 days after middle cerebral artery occlusion. 99mTc-DTPA SPECT/CT showed a blood–brain barrier disruption starting on day 1 post-middle cerebral artery occlusion, peaking on day 2, with barrier integrity totally restored on day 7. 99mTc-Annexin V-128 SPECT/CT imaging showed significant positive correlation with TUNEL immunohistochemistry and allowed ischemic-induced apoptosis to be detected from day 2 to day 7, peaking on day 3 after middle cerebral artery occlusion.

Conclusions

Using SPECT/CT imaging, we showed that after transient middle cerebral artery occlusion in rat there was a sustained decrease in cerebral blood flow followed by blood–brain barrier disruption preceding meanwhile apoptosis. Rodent SPECT/CT imaging of cerebral blood flow, blood–brain barrier disruption and apoptosis appears to be an efficient tool for evaluating neuroprotective drugs and regenerative therapies against cerebral ischemia and time-windows for therapeutic intervention.

New Regression Equation for 123I-IMP Non-invasive Cerebral Blood Flow Measurement Using the Graph Plot Method

PURPOSE

A graph plot (GP) method using 123I-N-isopropyl-p-iodoamphetamine (123I-IMP) has been proposed as a simple and non-invasive estimation of quantitative cerebral bloodflow (CBF). A regression equation for the GP method was estimated by the data of resting state. Therefore, the accuracy of CBF values in high flow range may be an underestimated possibility in this method.The aim of this study was to formulate a new regression equation for the GP method by the data of resting state and acetazolamide (ACZ) challenge, and to clarify the accuracy of it.

METHODS

The images of 26 consecutive patients who underwent both 123I-IMP chest radioisotope-angiography (RIA) and single photon emission computed tomography (SPECT) examinations were used to construct the new regression equation. Examinations of the resting state and ACZ challenge were performed in different days. All patients were analyzed by both the GP method and autoradiography (ARG) method which is the conventional examination with the one-point arterial blood sampling. A linear regression equation between the index of the input function was obtained by the GP method and CBF value of ARG. The linear regression equation based on the resting data was compared with the equation based on the resting and ACZ challenge (rest+stress) data.

RESULTS

Goodliner correlation was obtained between the index of the input function obtained by the GP method and CBF value of the ARG method in the rest+stress state (y=2.75x+15.1, r=0.78). In contrast, correlation results between the index of the input function obtained by the GP method and CBF value of the ARG method in the resting state was expressed as y=2.28x+18.4, r=0.54 rCBF values based on the resting data was 20% underestimated in the high flow range compared with values based on the rest+stress data.

CONCLUSION

The new linear regression equation for the GP method is useful for clinical study. Key words: non-invasive cerebral blood flow measurement method, graph plot (GP), autoradiography (ARG), 123I-N-isopropyl-p-iodoamphetamine (123I-IMP).

Elevated blood pressure management in acute ischemic stroke remains controversial: could this issue be resolved?

A transient elevated arterial blood pressure is common in acute ischemic stroke and is often associated with a poor prognosis. The underlying mechanisms of blood pressure elevation are not well understood and its management is still unresolved. This article focuses on pathophysiology and management of elevated blood pressure in acute ischemic stroke. There is evidence that the main causes of a transient blood pressure elevation in acute ischemic stroke are the focal cerebral hypoperfusion and the stress responses with neuroendocrine systems activation. Clinical trials have reported that blood pressure lowering in acute ischemic stroke may have detrimental effect, probably because of impaired cerebral autoregulation. However, quantitative assessment of cerebral perfusion has not been performed during emergency blood pressure reduction in acute ischemic stroke. We suggest that ultrasound carotid artery disease evaluation and cerebral hemodynamics monitoring using bilateral transcranial ultrasonography, during blood pressure management in acute ischemic stroke might contribute to maintaining of an adequate penumbral perfusion and prevent infarct enlargement. Such an approach could individualize the antihypertensive treatment in acute ischemic stroke and improve functional outcome. Prospective studies are needed to confirm such a treatment strategy.

Xenon-enhanced computed tomography cerebral blood flow measurements in acute cerebral ischemia: Review of 56 cases

OBJECTIVE

Ischemic stroke must be diagnosed promptly if patients are to be treated with thrombolytic therapy. The diagnosis of acute cerebral ischemia, however, is usually based on clinical and computed tomography (CT) scan findings. CT scans are often normal in the first few hours after stroke. The purpose of this study was to determine whether Xenon-enhanced CT (XeCT) cerebral blood flow (CBF) studies could increase the sensitivity of stroke detection in the acute stage.

METHODS

CBF studies performed within 8 hours of symptom onset were evaluated in 56 patients who presented with hemispheric stroke symptoms. Mean CBF in the symptomatic vascular territory was calculated and compared with the corresponding contralateral area. CBF values below 18 mL/100g/min on 2 adjacent regions of interest were considered ischemic lesions. CT scans and angiograms were compared with the XeCt findings. Neurological condition on admission and discharge was evaluated by using National Institutes of Health Stroke Scale (NIHSS) scores.

RESULTS

The mean NIHSS score on admission was 12+/-5. Early CT scans were abnormal in 28 (50%) patients. There were 9 (16%) patients who had normal XeCT scans because of spontaneous reperfusion of the ischemic area. XeCT studies showed an ischemic lesion in 47 (84%) patients. In these patients, the mean CBF in the affected vascular territory was 16+/-8 mL/100g/min compared with 35+/-13 mL/100g/min in the contralateral specular territory (P<0.001). There were no false positive or negative XeCT studies, and the location of the perfusion defect corresponded with the CT and/or angiographic findings in all cases. Eight patients died (14%), and the 48 survivors (86%) had a mean NIHSS score of 9+/-6 on discharge.

CONCLUSIONS

CBF measurements were correlated with the CT and angiographic results and greatly assisted in the diagnosis of acute ischemic stroke. XeCT studies used for estimating the location and extent of cerebral ischemia may be important in the triage of patients for acute stroke therapy.

Crossed cerebellar hypoperfusion in hyperacute ischemic stroke

OBJECTIVE

In chronic stage of cerebral hemispheric infarction, contralateral cerebellar blood flow and metabolism are depressed, which is known as crossed cerebellar diaschisis (CCD). The present study was performed to elucidate (1) whether the diaschisis occurs in hyperacute stage of ischemic stroke when computed tomography (CT) scans is not able to identify infarction, and (2) which site of lesion in the cerebrum is responsible for the depression in contralateral cerebellar blood flow.

METHODS

Single photon emission computed tomography was performed in 21 patients with middle cerebral artery (MCA) embolic infarction within 6 h of the onset (3.2+/-1.1 h, mean+/-S.D.). Regions of interest (ROIs) were symmetrically located in the cerebral hemispheres including cerebral cortex and subcortex, and in the cerebellar hemispheres.

RESULTS

The side-to-side ratio of cerebellar blood flow ipsilateral to that contralateral to cerebral infarct was significantly increased compared with that in normal control (P<0.001), indicating that contralateral cerebellar blood flow was significantly depressed. In hyperacute stage, the ratio of cerebellar blood flow appeared to be associated with the ratio of cerebral blood flow in whole hemispheres (r=0.44, P<0.05), in anterior frontal lobe (r=0.44, P<0.05) and in anterior temporal lobe (r=0.58, P<0.01), but not in infarct areas (r=0.26, P=0.3). Stepwise regression analysis revealed that the ratios in cerebellar hemispheres were associated with those in anterior temporal lobe (multiple regression analysis, r=0.58, P<0.01).

CONCLUSIONS

Crossed cerebellar diaschisis occurs at hyperacute stage of stroke of the MCA infarction. It may be related to the hypoperfusion in the anterior frontal and anterior temporal lobes of the cerebrum where regional blood flow is decreased by ischemic infarction per se or by ipsilateral hemispheric depression from infarct area (diaschisis mechanism).

Hypointense transcerebral veins at T2*-weighted MRI: a marker of hemorrhagic transformation risk in patients treated with intravenous tissue plasminogen activator

Prediction of hemorrhagic transformation (HT) in patients treated by intravenous recombinant tissue-type plasminogen activator (rt-PA) is a challenging issue in acute stroke management. HT may be correlated with severe hypoperfusion. Signal changes may be observed at susceptibility-weighted magnetic resonance imaging (MRI) within large perfusion defects. A signal drop within cerebral veins at T2*-weighted gradient-echo MRI may be expected in severe ischemia, and may indicate subsequent risk of HT. The authors prospectively searched for an abnormal visibility of transcerebral veins (AVV) within the ischemic area in patients with hemispheric ischemic stroke, before they were treated with intravenous rt-PA therapy. Any correlation between AVV and baseline clinical or MRI findings, or further HT, was noted. An AVV was present in 23 of 49 patients (obvious, n = 8; moderate, n = 15), and was supported by severe hemodynamic changes at baseline MRI. The AVV was correlated with the occurrence of parenchymal hematoma type 2 at computed tomography during the first week (r = 0.44, P = 0.002). Five of six type 2 parenchymal hematomas occurred in association with obvious AVV. At multiple regression analysis, two baseline MRI factors had an independent predictive value for HT risk during the first week: the AVV and the cerebral blood volume ratio (Nagelkerke R2 = 0.48).

[Brain perfusion SPECT in the prognostic assessment of stroke]

PURPOSE

To compare the diagnostic yield of CT scan and perfusion SPECT on admission and its prognostic value in clinical outcome.

METHODS

25 ischemic stroke cases were studied on admission (<24 h) and at 30-60 days by CT scan, 99mTc-HMPAO-SPECT and neurological scales. Infarct size and severity on SPECT were assessed: visually "Total Weighted Score," added value in 22 areas, and by several semiquantitative count-based indices.

RESULTS

Sensitivity: the first CT scan was positive in 24% patients, initial SPECT in 75% (73% of pure subcortical infarcts and 91% of those with cortical involvement). Localization: kappa: 0.725 between SPECT findings on admission and those in control-CT at 5 days. Extent and severity: correlations between count-based and visual indices (r: >0.719), the latter correlated slightly better with clinical scales. Both predicted similarly (Rho>0.739) infarct size in CT diagnostic scan. Early Outcome: There were statistical differences between deceased and survivors in SPECT (<24h) indices and CT-infarct size (mean 5 days), but not in neurological scores on admission. Long term Outcome: Correlation of initial SPECT indices with follow-up functional scores (SNSLP, Barthel index; mean 37 days) was only significant for visual SPECT indices (Rho:0.560 to 0.620). Nevertheless the best predictor of functional status on discharge was the Barthel Index on admission.

CONCLUSIONS

1) Early SPECT has good sensitivity and accurate infarct size prediction so it can be a useful tool for deciding thrombolytic therapy; 2) Visual scores perform as well as more complex indices; 3) Infarct volume seems to be a critical determinant in vital outcome; other factors (strategic localization, etc.) might influence long term functional status.

Comparative evaluation of cerebral blood volume and cerebral blood flow in acute ischemic stroke by using perfusion-weighted MR imaging and SPECT

PURPOSE

To investigate the relationship between relative cerebral blood volume (CBV) measured with perfusion-weighted (PW) MR imaging and relative cerebral blood flow (CBF) measured with SPECT in acute ischemic stroke.

MATERIAL AND METHODS

Fifteen patients who had acute unilateral middle cerebral artery occlusion underwent both PW MR imaging and 99mTc-HMPAO SPECT with an interval less than 20 min between the two examinations within 6 h after stroke onset. Lesion-to-contralateral relative CBV and CBF ratios measured in multiple regions of interest were compared to evaluate the relationship of the two parameters.

RESULTS

An overall linear relationship was found between relative CBV and relative CBF ratios (R2 = 0.54, p < 0.0001). The two parameters correlated linearly to each other in regions with evolving infarction (R2 = 0.43, p<0.0001), but not in regions without evolving infarction (R2 = 0.001, p>0.05). Regions with evolving infarction had more severe hypoperfusion (mean relative CBF ratio, 0.38 +/- 0.22) than regions without (mean relative CBF ratio, 0.70+/-0.13) (p<0.0001).

CONCLUSION

A significant linear relationship existed between relative CBV and relative CBF in acute ischemic stroke, although relative CBV did not change linearly to relative CBF in mild hypoperfusion. Relative CBV can be used as an alternative to relative CBF within 6 h after stroke onset, particularly in regions with severe hypoperfusion proceeding to infarction.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Evaluation of crossed cerebellar diaschisis in 30 patients with major cerebral artery occlusion by means of quantitative I-123 IMP SPECT

Quantitative crossed cerebellar diaschisis (CCD) and the correlation with a reduction in supratentorial regional cerebral blood flow (rCBF) and cerebrovascular reserve capacity (CVR) were investigated in clinically stable patients with major cerebral artery occlusion by the iodine-123-N-isopropyl-p-iodoamphetamine (I-123 IMP) single photon emission computed tomography (SPECT) method. Thirty patients with major cerebral artery occlusion underwent SPECT by the I-123 IMP autoradiographic method. Regional CBF was measured in the cerebral hemisphere, frontal and parietal lobes, temporo-parietal lobe, and cerebellum both at rest and after administration of acetazolamide. Eighteen of 30 patients (60%) had CCD. CCD was significantly related to magnetic resonance imaging evidence of infarction. Quantitative CCD was 17% and the CVR in the cerebellum was preserved in patients with CCD. There was a significant difference in CBF and CVR between the affected and normal sides in all regions of interest in the patients without CCD [CBF (ml/100 g/min): hemisphere (H), normal side (N): 31.4 +/- 6.8, affected side (A): 27.5 +/- 7.4; p < 0.05. CVR: H, N: 0.56 +/- 0.38, A: 0.42 +/- 0.18; p < 0.01]. CCD is common in patients with major cerebral artery occlusion, and quantitative I-123 IMP SPECT is helpful in detecting CCD in clinically stable patients with occlusion of major cerebral arteries.

Prediction of acute embolic stroke outcome after local intraarterial thrombolysis: value of pretreatment and posttreatment 99mTc-ethyl cysteinate dimer single photon emission computed tomography

The aim of this study was to investigate the efficacy of pre- and posttreatment 99mTc-ethyl cysteinate dimer (99mTc-ECD) single photon emission computed tomography (SPECT) for predicting the ischemic outcome of embolic middle cerebral artery occlusion after treatment with local intraarterial thrombolysis. The authors examined 28 patients with a moderately ischemic area (ratio of affected regional activity to cerebellar activity (A/C ratio) of 0.4 to 0.7) determined using pretreatment SPECT, and with complete recanalization within 6 hours. Posttreatment dynamic and static SPECT studies were performed immediately after thrombolysis. The extent of the affected area outlined on pretreatment SPECT was used for the posttreatment SPECT images, and A/C ratios were calculated. The relative retention ratio of 99mTc-ECD in the affected area was also analyzed using posttreatment dynamic SPECT. Fourteen patients either without infarction or with small subcortical and basal ganglial infarction, 11 patients with medium or large cortical infarction, and 3 patients with hemorrhage were identified by follow-up computed tomography. Ischemic outcome correlated with the relative retention ratio of 99mTc-ECD more closely than either the pre- or posttreatment A/C ratios. In particular, a threshold value for the development of hemorrhage was distinct only in the relative retention ratio of 99mTc-ECD. Pretreatment 99mTc-ECD SPECT did not always predict the occurrence of hemorrhagic transformation, whereas dynamic 99mTc-ECD SPECT performed immediately after thrombolysis allowed clear identification of patients at risk for hemorrhagic transformation.

Potential of rheopheresis for the treatment of acute ischemic stroke when initiated between 6 and 12 hours

Improvement of hemorheology is one of the most important approaches in the treatment of acute ischemic stroke. We investigated the influence of extracorporal rheopheresis (ER) on cerebral blood flow in patients with acute ischemic stroke and evaluated its therapeutic effect. Thirty-three patients (rheopheresis group, 17; control group, 16; mean age 64 +/- 10 years) with acute ischemic stroke were included in our prospective randomized trial. The first treatment was started within 12 h after onset of symptoms, and treatment was repeated 3 times at an interval of 24 h. Hemorheological parameters were measured before and after each session. The cerebral blood flow was analyzed using 99mTc-ECD-SPECT. The functional and neurological outcomes were determined by follow-up investigations after 3 months. The hemorheological parameters were significantly different between the rheopheresis group (18% decrease of plasma viscosity, 55% decrease of red blood cell aggregation) and the control group (no decrease of both parameters). The single photon emission computed tomography (SPECT) analysis showed early reperfusion in 35% of the patients treated with rheopheresis and in 37% of the control group (NS). There were no differences in the neurological outcomes between the 2 groups. Extracorporal rheopheresis is practicable and safe. It rapidly and consistently improved the hemorheological parameters. Although this did not impact on cerebral perfusion or clinical outcome in patients with acute ischemic stroke in this report, we propose that ER deserves to be further evaluated by initiating the first treatment within 6 h post-insult.

Quantitative measurement of cerebral blood flow by (99m)Tc-HMPAO SPECT in acute ischaemic stroke: usefulness in determining therapeutic options

OBJECTIVE

Early recanalisation by thrombolysis is a conclusive therapy for acute ischaemic stroke. But this therapy may increase the risk of intracerebral haemorrhage or severe brain oedema. The purpose was to evaluate usefulness of quantitative measurement of cerebral blood flow by single photon emission computed tomography (SPECT) in predicting the risk of haemorrhage or oedema, and determining the therapeutic options in acute hemispheric ischaemic stroke.

METHODS

The relation was studied retrospectively between initial regional cerebral blood flow (rCBF) quantitatively measured by technetium-99m-labelled hexamethylpropyleneamine oxime ((99m)Tc-HMPAO) SPECT and final clinical and radiological outcome in 20 patients who presented hemispheric ischaemic stroke and were treated conservatively or received early recanalisation by local intra-arterial thrombolysis. The non-invasive Patlak plot method was used for quantitative measurement of rCBF by SPECT.

RESULTS

Regions where residual rCBF was preserved over 35 ml/100 g/min had a low possibility of infarction without recanalisation and regions where residual rCBF was preserved over 25 ml/100 g/min could be recovered by early recanalisation. However, regions where residual rCBF was severely decreased (< 20 ml/100 g/min) had a risk of intracerebral haemorrhage and severe oedema.

CONCLUSIONS

A quantitative assessment of residual rCBF by (99m)Tc-HMPAO SPECT is useful in predicting the risk of haemorrhage or severe oedema in acute ischaemic stroke. Therapeutic options should be determined based on the results of rCBF measurement.

Ischemic penumbra: evidence from functional imaging in man

The ischemic penumbra is defined as tissue with flow within the thresholds for maintenance of function and of morphologic integrity. Penumbra tissue has the potential for recovery and therefore is the target for interventional therapy in acute ischemic stroke. The identification of the penumbra necessitates measuring flow reduced less than the functional threshold and differentiating between morphologic integrity and damage. This can be achieved by multitracer positron emission tomography (PET) and perfusion-weighted (PW) and diffusion-weighted magnetic resonance imaging (DW-MRI) in experimental models, in which the recovery of critically perfused tissue or its conversion to infarction was documented in repeat studies. Neuroimaging modalities applied in patients with acute ischemic stroke--multitracer PET, PW- and DW-MRI, single photon emission computed tomography (SPECT), perfusion, and Xe-enhanced computed tomography (CT)-- often cannot reliably identify penumbra tissue: multitracer studies for the assessment of flow and irreversible metabolic damage usually cannot be performed in the clinical setting; CT and MRI do not reliably detect irreversible damage in the first hours after stroke, and even DW-MRI may be misleading in some cases: determinations of perfusion alone yield a poor estimate of the state of the tissue as long as the time course of changes is not known in individual cases. Therefore, the range of flow values in ischemic tissue found later, either within or outside the infarct, was rather broad. New tracers--for example, receptor ligands or hypoxia markers--might improve the identification of penumbra tissue in the future. Despite these methodologic limitations, the validity of the concept of the penumbra was proven in several therapeutic studies in which thrombolytic treatment reversed critical ischemia and decreased the volume of final infarcts. Such neuroimaging findings might serve as surrogate targets in the selection of other therapeutic strategies for large clinical trials.

Early serial SPET in acute middle cerebral artery infarction

The size and severity of perfusion defects in acute cerebral ischaemia on single photon emission tomographic (SPET) images may provide useful information regarding long-term (> 3 month) stroke outcome. A decreased predictive value has been reported with delayed SPET more than 24 h after stroke onset. We examined 20 patients with acute middle cerebral artery (MCA) infarctions using serial 99Tcm-ECD or 99Tcm-HMPAO SPET (SPET 1 one day and SPET 2 three days after stroke onset). Neurological (NIH, SSS) and functional (Barthel, Rankin) scores were calculated simultaneously and 3 months poststroke. The two SPET scans correlated equally well with the severity of functional and neurological deficits evaluated 3 months after stroke onset. In comparison to clinical assessment, the prognostic value of SPET was relatively better on the first day than the third day. Crossed cerebellar diaschisis correlated with early SPET deficits, but did not predict functional outcome. Our results suggest that SPET, either with 99Tcm-ECD or 99Tcm-HMPAO, can be used to predict stroke outcome in acute MCA infarction up to 72 h poststroke without significant interference from luxury perfusion.

Cerebral perfusion SPECT in transient ischemic attack

PURPOSE

The purpose of our study is to evaluate the efficacy of cerebral perfusion single photon emission computerized tomography (SPECT) in patients with transient ischemic attack (TIA).

METHODS

Thirty-seven patients with TIA were collected for study. All patients had transient focal neurological symptoms or signs with complete recovery within 24 h after onset. The patients underwent cerebral perfusion SPECT between 6 h and 11 days after onset, with 10 cases performed within 24 h (group A), nine cases performed between 1 and 3 days (group B), 11 cases performed between 3 and 5 days (group C), and seven cases performed after more than 5 days (group D). A semi-quantitative method was used for analyzing the SPECT data, and the difference ratios between lesion side and contralateral normal side were calculated on each pair of regions of interest.

RESULTS

In total, 78.4% (29/37) of patients had reduced perfusion in the cerebral cortical regions or deep nuclei, and the regions with reduced perfusion corresponded with clinical presentations of the patients. The abnormal rate with reduced perfusion was 90.0% in group A, 77.8% in group B, 72.7% in group C and 71.4% in group D. Cross cerebellar diaschisis (CCD) was present in seven patients, and all of the primary cerebral perfusion defects of these patients were located at the territory of left or right middle cerebral artery.

CONCLUSION

Cerebral perfusion SPECT is a potential tool to detect cerebral perfusion defects and CCD in patients with TIA. Although the perfusion defect may persist more than 5 days after onset, we suggest cerebral perfusion SPECT should be performed as soon as possible.

Early postischemic hyperperfusion: pathophysiologic insights from positron emission tomography

Early postischemic hyperperfusion (EPIH) has long been documented in animal stroke models and is the hallmark of efficient recanalization of the occluded artery with subsequent reperfusion of the tissue (although occasionally it may be seen in areas bordering the hypoperfused area during arterial occlusion). In experimental stroke, early reperfusion has been reported to both prevent infarct growth and aggravate edema formation and hemorrhage, depending on the severity and duration of prior ischemia and the efficiency of reperfusion, whereas neuronal damage with or without enlarged infarction also may result from reperfusion (so-called "reperfusion injury"). In humans, focal hyperperfusion in the subacute stage (i.e., more than 48 hours after onset) has been associated with tissue necrosis in most instances, but regarding the acute stage, its occurrence, its relations with tissue metabolism and viability, and its clinical prognostic value were poorly understood before the advent of positron emission tomography (PET), in part because of methodologic issues. By measuring both CBF and metabolism, PET is an ideal imaging modality to study the pathophysiologic mechanism of EPIH. Although only a few PET studies have been performed in the acute stage that have systematically assessed tissue and clinical outcome in relation to EPIH, they have provided important insights. In one study, about one third of the patients with first-ever middle cerebral artery (MCA) territory stroke studied within 5 to 18 hours after symptom onset exhibited EPIH. In most cases, EPIH affected large parts of the cortical MCA territory in a patchy fashion, together with abnormal vasodilation (increased cerebral blood volume), "luxury perfusion" (decreased oxygen extraction fraction), and mildly increased CMRO2, which was interpreted as postischemic rebound of cellular metabolism in structurally preserved tissue. In that study, the spontaneous outcome of the tissue exhibiting EPIH was good, with late structural imaging not showing infarction. This observation was supported by another PET study, which showed, in a few patients, that previously hypoperfused tissue that later exhibited hyperperfusion after thrombolysis did not undergo frank infarction at follow-up. In both studies, clinical outcome was excellent in all patients showing EPIH except one, but in this case the hyperperfused area coexisted with an extensive area of severe hypoperfusion and hypometabolism. These findings from human studies therefore suggest that EPIH is not detrimental for the tissue, which contradicts the experimental concept of "reperfusion injury" but is consistent with the apparent clinical benefit from thrombolysis. However, PET studies performed in the cat have shown that although hyperperfusion was associated with prolonged survival and lack of histologic infarction when following brief (30-minute) MCA occlusion, it often was associated with poor outcome and extensive infarction when associated with longer (60-minute) MCA occlusion. It is unclear whether this discrepancy with human studies reflects a shorter window for tissue survival after stroke in cats, points to the cat being more prone to reperfusion injury, or indicates that EPIH tends not to develop in humans after severe or prolonged ischemia because of a greater tendency for the no-reflow phenomenon, for example. Nevertheless, the fact that the degree of hyperperfusion in these cat studies was related to the severity of prior flow reduction suggests that hyperperfusion is not detrimental per se. Preliminary observations in temporary MCA occlusion in baboons suggest that hyperperfusion developing even after 6 hours of occlusion is mainly cortical and associated with no frank infarction, as in humans. Overall, therefore, PET studies in both humans and the experimental animal, including the baboon, suggest that hyperperfusion is not a key factor in the development of tissue infarction and that it may be a harmless phenomenon

Outcome in acute stroke with successful intra-arterial thrombolysis and predictive value of initial single-photon emission-computed tomography

This study investigates retrospectively, in selected patients, the ischemic outcome (reversible ischemia, infarction, and hemorrhage) and neurologic outcome of acute stroke treated with intra-arterial thrombolysis and the predictive value of pretreatment single-photon emission-computed tomography (SPECT). Thirty patients with complete recanalization within 12 hours were analyzed. The extent of ischemia was outlined on SPECT, and two CBF parameters were calculated: the ratio of ischemic regional activity to CBF in the cerebellum and the asymmetry index. Reversible ischemia, infarction, and hemorrhage were identified by comparing SPECT and follow-up computed tomography. Nine patients (30%) had no or small infarction, 14 (47%) had medium or large infarction, and seven (23%) had hemorrhage. Forty-two lesions were identified (22 reversible ischemia, 13 infarction, and 7 hemorrhage). Duration of ischemia, urokinase dose, disease type, and occlusion site were nonsignificant factors, whereas neurologic outcome and CBF parameters were significant among the three patient groups and three types of ischemic lesions. Ischemic tissue with CBF greater than 55% of cerebellar flow still may be salvageable, even with treatment initiated 6 hours after onset of symptoms. Ischemic tissue with CBF greater than 35% of cerebellar flow still may be salvageable with early treatment (less than 5 hours). Ischemic tissue with with CBF less than 35% of cerebellar flow may be at risk for hemorrhage within the critical time window. Pretreatment SPECT can provide useful parameters to increase the efficacy of thrombolysis by reducing hemorrhagic complications and improving neurologic outcome.

Emission tomography contribution to clinical neurology

The role of functional neuroimaging techniques in furthering the understanding of pathophysiological mechanisms of neurological diseases and in the assessment of neurological patients is increasingly important. Here, we review data mainly from emission tomography techniques, namely positron emission tomography (PET) and single photon emission computerized tomography (SPECT), that have helped elucidate the pathophysiology of a number of neurological diseases and have suggested strategies in the treatment of neurological patients. We also suggest possible future developments of functional neuroimaging applied to clinical populations and briefly touch on the emerging role of functional magnetic resonance imaging (fMRI) in clinical neurology and neurosurgery.

Tissue at risk of infarction rescued by early reperfusion: a positron emission tomography study in systemic recombinant tissue plasminogen activator thrombolysis of acute stroke

Thrombolytic therapy of acute ischemic stroke can be successful only as long as there is penumbral tissue perfused at rates between the thresholds of normal function and irreversible structural damage, respectively. To determine the proportion of tissue at risk of infarction, cerebral perfusion was studied in 12 patients with acute ischemic stroke who underwent treatment with systemic recombinant tissue plasminogen activator (0.9 mg/kg body weight according to National Institute of Neurological Disorders and Stroke protocol) within 3 hours of onset of symptoms, using [15O]-H2O positron emission tomography (PET) before or during, and repeatedly after thrombolysis. The size of the regions of critically hypoperfused gray matter were identified on the initial PET scans, and changes of perfusion in those areas were related to the clinical course (followed by the National Institutes of Health stroke scale) and to the volume of infarcted gray matter demarcated on magnetic resonance imaging 3 weeks after the stroke. Whereas the initial clinical score was unrelated to the size of the ischemic area, after 3 weeks there was a strong correlation between clinical deficit and volume size of infarcted gray matter (Spearman's rho, 0.96; P < 0.001). All patients with a severely hypoperfused (< 12 mL/100 g/min) gray matter region measuring less than 15 mL on first PET showed full morphologic and clinical recovery (n = 5), whereas those with ischemic areas larger than 20 mL developed infarction and experienced persistent neurologic deficits of varying degree. Infarct sizes, however, were smaller than expected from previous correlative PET and morphologic studies of patients with acute stroke: only 22.7% of the gray matter initially perfused at rates below the conventional threshold of critical ischemia became necrotic. Actually, the percentage of initially ischemic voxels that became reperfused at almost normal levels clearly predicted the degree of clinical improvement achieved within 3 weeks. These sequential blood flow PET studies demonstrate that critically hypoperfused tissue can be preserved by early reperfusion, perhaps related to thrombolytic therapy. The results correspond with experimental findings demonstrating the prevention of large infarcts by early reperfusion to misery perfused but viable tissue.

Differentiation between transient ischemic attack and ischemic stroke within the first six hours after onset of symptoms by using 99mTc-ECD-SPECT

The aim of this study was to define the accuracy of 99mTc-ethyl cysteinate dimer-single photon emission computed tomography (99mTc-ECD-SPECT) in distinguishing transient ischemic attack from completed ischemic stroke at early stages after the onset of symptoms. In a prospective study we examined 82 patients within 6 hours after the onset of symptoms (neurologic deficit caused by middle cerebral artery ischemia) using both 99mTc-ECD-SPECT and computed tomography (CT). The follow-up was based on Scandinavian Stroke Scale (SSS) 24 hours and 5-7 days, as well as on CT 7 days, after the event. SPECT evaluation was performed both visually and using semiquantitative region-of-interest (ROI) analysis. According to visual SPECT analysis, on admission 59 of 82 patients had activity deficits in the symptomatic hemisphere. After 7 days, all these patients had neurologic symptoms (SSS 28 +/- 12 points), caused by a cerebral infarction as evidenced with CT. Twenty-three of 82 patients displayed no early activity deficit despite clinical symptoms. None of these patients had neurologic symptoms after 7 days (indicating transient ischemic attack or prolonged reversible ischemic neurologic deficit). In the semiquantitative SPECT analysis, all patients had abnormal count densities in the respective ROI (activity < 90% compared with the contralateral side). All patients with transient ischemia (n = 23) had count rate densities more than 70% of the respective contralateral ROI, whereas all patients with subsequent infarction (n = 59) had values < 70%. Use of 99mTc-ECD-SPECT allows transient ischemia to be distinguished from ischemic infarction using relative regional activity thresholds within the first 6 hours after onset of symptoms.

Emergency imaging of the acute stroke patient

Patients presenting with suspected acute stroke require rapid diagnosis and treatment. Neuroimaging is critical in determining acute-stroke type and thus appropriate management. A review of various neuroimaging techniques and their role in the evaluation of both acute ischemic stroke and acute hemorrhagic stroke is provided.

Cobalt-55 positron emission tomography in ischemic stroke

After acute cerebral stroke, the (peri-) infarct tissue is characterized by calcium (Ca)-mediated neuronal damage and inflammatory processes. Monitoring Ca-mediated damage using the isotope cobalt-55 (Co) as a Ca-tracer may enable PET-imaging of this tissue. Since the fate of (peri-) infarct tissue determines clinical outcome, Co-PET may have prognostic value in stroke. Six stroke patients were examined with Co-PET, MRI and a middle cerebral artery (mca) stroke scale (Orgogozo). In every patient, specific Co-accumulation in the appropriate brain region was seen, irrespective of the integrity of the blood-brain barrier. This pilot study suggests Co-PET as a diagnostic tool in stroke, which may provide additional information on the clinical outcome. Validation of method in larger patient series is necessary.

Prognostic value of single-photon emission tomography in acute ischaemic stroke

Single-photon emission tomography (SPET) is widely used in the investigation of acute stroke. We investigated the relationship between SPET data and functional outcome in a large group of acute stroke patients. One hundred and eight patients underwent cerebral computed tomography (CT) and technetium-99m hexamethylpropylene amine oxime SPET after acute ischaemic stroke. We categorised the clinical presentation according to the Oxford classification of acute stroke. Outcome was measured 1 year after stroke using mortality and the Barthel Index for survivors. SPET scans were interpreted without reference to the clinical data using a semi-automatic technique. Three experienced observers determined the presence of luxury perfusion using suitably scaled SPET images in conjunction with the CT scan. Both SPET volume and severity of deficit were significantly negatively correlated with Barthel Index at 1 year (rs=-0.310, P<0.0001, and rs=-0.316, P<0.0001 respectively). In patients scanned with SPET within 16 h of stroke onset, the correlations were more strongly negative (rs=-0.606, P<0. 001, and rs=-0.492, P<0.005 respectively). Luxury perfusion was not associated (chi2=0.073, df=1, P=0.79) with good functional outcome (Barthel score >/=60). Stepwise logistic regression identified Oxford classification, total deficit volume and patient's age as significant predictors of functional outcome. Overall predictive accuracy was 72%. Predictive accuracy was better in patients who received SPET within 16 h of stroke onset. SPET provides useful information about the functional outcome of acute stroke at 1 year. However, the accuracy of prediction decreases the longer SPET is delayed. Prognostication using SPET in combination with clinical assessment and other investigations may also be considered.

Demonstration of hypoperfusion surrounding intracerebral hematoma in humans

We undertook this study to determine whether ischemic regions are present that may contribute to poor outcome after intracerebral hemorrhage (ICH) in humans. Hypoperfusion around an ICH has not been reported in humans. Brain computed tomography (CT) and (99m)Tc-HMPAO brain single photon emission computed tomography (SPECT) perfusion studies were carried out 51 +/- 12 hours after supratentorial ICH in seven patients selected from a referral hospital over an 8-month period. The widest diameters of the hematoma on CT and of reduced perfusion on SPECT were measured and compared. The diameters of reduced perfusion were measured at the 40% and 20% reduced count levels compared with the contralateral side. Reduced perfusion in and around the hematoma was seen in all seven cases. The diameters of ICH on CT (mean, 53 +/- 12 mm) were comparable to the diameters of 40% reduction of counts (mean, 61 +/- 14 mm) measured by SPECT. The mean diameter of brain demonstrating 20% reduction in counts was 76+/-19 mm, which was 43% greater than the hematoma diameter on CT (p = .004). In conclusion, substantial regions of reduced perfusion surround ICH in humans, which might contribute to poor outcome and be amenable to anti-ischemic therapy.

Changes in cerebral tissue perfusion during the first 48 hours of ischaemic stroke: relation to clinical outcome

BACKGROUND

One major therapeutic strategy to minimise the extent of infarction after ischaemic stroke is to improve early reperfusion using thrombolytic agents. However, reperfusion may be hazardous and the period during which reperfusion may have a beneficial effect on tissue and clinical outcome is not known.

METHODS

Fifty three patients were studied with serial cerebral perfusion (99mTcHMPAO SPECT) during the first 48 hours of ischaemic stroke to determine if changes in tissue perfusion during this time were prognostically significant. Single and multiple linear regression non-parametric analyses were used to include other factors during the same period which may influence outcome.

RESULTS

In univariate analysis age, neurological score at admission, SPECT perfusion defect size in the first 24 hours, and percentage change in cerebral tissue perfusion at 24-48 hours (all P < 0.01) correlated significantly with the Barthel score at three months. In multiple linear regression analysis only age (P < 0.01) and percentage change in cerebral tissue perfusion at 24-48 hours (P < 0.01) provided independent prognostic information at three months.

CONCLUSIONS

Changes in cerebral tissue perfusion during the first 48 hours of ischaemic stroke are significant outcome predictors and therapeutic effort aimed at increasing perfusion during this period seem to be justified.

SPECT imaging of stroke

Single-photon emission computed tomography (SPECT) is a helpful tool for the management of stroke patients. Brain perfusion SPECT can help differentiate an ischemic event from peri-ictal phenomena such as Todd's paresis. Initial data suggest that SPECT may be useful in prognosticating the likelihood of an early stroke after a transient ischemic attack and in distinguishing lacunar from cortical stroke. After an acute stroke, early SPECT depicts the area of ischemia with greater accuracy than either computed tomography or magnetic resonance imaging. When the perfusion defect is large, the likelihood of hemorrhagic complications or herniation increases. Reperfusion of an arterial territory after thrombolysis can be documented more conveniently with SPECT than with angiography. SPECT before and after the injection of acetazolamide has been used to assess the vascular reserve in patients with severe stenosis of the proximal vessels of the cerebrovascular tree. Combined with transcranial Doppler studies, SPECT is used to document ischemia after subarachnoid hemorrhage. It has also been used to assess the effect of arterial ligation intended to treat arteriovenous malformations or aneurysms on brain perfusion and to evaluate ischemia secondary to pressure from an intracranial hemorrhage.

Technetium-99m HMPAO SPET in acute supratentorial ischaemic infarction, expressing deficits as millilitre of zero perfusion

A comparative interim analysis was performed of clinical parameters, computed tomographic (CT) scan results and technetium-99m hexamethylpropylene amine oxime single-photon emission tomography (SPET) findings obtained within 12 h of acute supratentorial ischaemic infarction. First, the applicability for SPET semiquantification in this study of the "method of Mountz", simultaneously accounting for extent and degrees of hypoperfusion by expressing deficits as millilitre of zero perfusion, was considered. Next, the relative contributions of perfusion SPET and CT scan in the acute stage of ischaemic infarction were compared in 27 patients (mean age 68.8 years). Finally, the correlation of SPET lesions with clinical parameters at onset was evaluated. The method of Mountz represents a workable, accurate virtual parameter, with the assumption that the contralateral brain region remains uninvolved. Interobserver reproducibility in 12 SPET studies, with lesions varying between 6 and 369 cc, showed a correlation coefficient r of 0.99. In practice, because of inconstant distribution of activities in the brain, the method can only be applied slice by slice and not on the total global volume. While the mean delay since the onset of symptomatology was approximately 7 h for both SPET and CT scan, SPET showed lesions concordant with the clinical neurological findings in 100% and CT scan in only 48%. One could hypothesize that SPET examinations performed later would show larger functional defects, because of the development of additional functional changes secondary to biochemical alterations. However, in this regard no statistically significant differences were found between two subproups, taking the median of delay before SPET examination as cut-off.(ABSTRACT TRUNCATED AT 250 WORDS)

Noninvasive assessment of intracranial perfusion in acute cerebral ischemia

Single-photon emission computed tomography (SPECT) and transcranial Doppler sonography (TCD) may help to determine a target group of patients with maximum therapeutic response for tissue rescue after acute stroke. As previously described, the cerebral perfusion index represents a combination of these techniques, and is calculated by multiplying assigned values for TCD and SPECT perfusion patterns. The three grades of cerebral perfusion index (1-5, 6-12, 15-20) may predict short-term outcome if the index is based on SPECT and TCD performed within the first 6 hours after stroke. A total of 30 consecutive patients were studied (18 with middle cerebral artery stroke and 12 with transient ischemic attack or minor stroke). Neurological deficit was scored using the Canadian Neurological Scale. SPECT and TCD were performed 4 +/- 2 hours after the onset. Forty-five minutes were required to perform both tests, evaluate the results, and calculate the cerebral perfusion index. The mean score (+/- standard deviation) of the neurological deficit on admission was 84 +/- 20 in patients with transient ischemic attack/minor stroke and 54 +/- 33 in patients with stroke (p < 0.009). The volume of ischemic lesion was measured on computed tomography scans performed more than 3 days after the ictus. Patients with transient ischemic attack/minor stroke had lesion volumes of 8 +/- 7 cm3 compared to 72 +/- 26 cm3 for those with stroke (p < 0.0001). The mean cerebral perfusion index in the transient ischemic attack group was 18 +/- 4, while in the stroke group it was 4 +/- 1 (p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Application of technetium-99m hexamethylpropylene amine oxime single-photon emission tomography to neurologic prognosis in patients undergoing urgent carotid surgery

In this study we aimed to work out a quantitative prognostic index for preoperative assessment of brain technetium-99m hexamethylpropylene amine oxime (HMPAO) single-photon emission tomography (SPET) in patients referred for urgent carotid endarterectomy due to acute obstructive disease of the internal carotid artery (ICA) and neurological deficit. To this end we compared data from preoperative SPET studies with the postinterventional changes in neurological status in 20 patients (17 males, three females; mean age 53 years, SD 4 years) with acute ischaemic cerebral disorders induced by obstruction of the ICA. Carotid obstruction was diagnosed by ultrasound B-mode study. All patients underwent urgent carotid endarterectomy from the ICA. Patients were divided into two groups in accordance with the results of postoperative follow-up: group A comprised patients with significant (more than 3 points) postoperative improvement in neurological condition as quantified by the Canadian Neurological Scale (11 patients); group B consisted of patients with minimal improvement or deterioration (nine, three of whom died). All patients were studied preoperatively by 99mTc-HMPAO SPET. The volume of nonperfused tissue (VS, cm3) was quantified using the Mountz technique. Hypoperfused volume (Vhypoperf, cm3) in the affected hemisphere was calculated as the total volume of voxels with 99mTc-HMPAO uptake < 90% of the contralateral symmetric voxels. Discriminant prognostic function was calculated by discriminant analysis as: PF = 0.072 x VS + 29.46x(VS/Vhypoperf). Patients with preoperative PF values < 8.20 demonstrated postoperative improvement in neurological status, while the group with PF > 8.90 comprised patients who demonstrated minimal improvement or deterioration. PF values in the range 8.20-8.90 carried an indefinite prognosis. We conclude that the preoperative 99mTc-HMPAO SPET can be used for the selection of patients in whom improvement in neurological status may be expected after urgent surgical correction of acute extracranial obstruction of the ICA.