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Biomedical subjects

A E Baird

Publications and source records attributed to A E Baird.

35 records · Page 2Linked to original sources
PubMed1997

Enlargement of human cerebral ischemic lesion volumes measured by diffusion-weighted magnetic resonance imaging.

We aimed to determine the frequency and time course of the enlargement of ischemic cerebral lesions following human stroke and to study the effect of the state of perfusion on lesion enlargement. Acute lesion volumes were measured on diffusion-weighted magnetic resonance images and compared with lesion volumes measured on T2-weighted images at 7 days or later. Forty-four measurements were performed between 2 and 53 hours after stroke onset in 28 patients. Thirteen patients also had magnetic resonance perfusion imaging performed. In 12 (43%) of 28 patients the initial lesion volume increased by 20% or more. The number of studies showing enlargement of the ischemic lesion volume ranged from 12 (43%) of 28 at or after 2 hours to 10 (38%) of 26 at or after 6 hours, 5 (33%) of 15 at or after 24 hours, and 2 (33%) of 6 at or after 48 hours. In 7 of the 10 patients in whom the hypoperfusion volume acutely exceeded the volume of the abnormality on diffusion-weighted images, lesion volume increased by 20% or more. This study provided evidence that substantial enlargement of human cerebral ischemic lesion volumes can occur beyond the first 6, 12, or 24 hours after onset. A mismatch acutely between the region of hypoperfusion (larger) and the region of diffusion abnormality (smaller) may be predictive of ischemic lesion enlargement.

Adult↗
PubMed1997

Ischemic lesion volumes in acute stroke by diffusion-weighted magnetic resonance imaging correlate with clinical outcome.

Diffusion-weighted magnetic resonance imaging detects ischemic injury within minutes after onset, and has been used to demonstrate drug efficacy in animal models of stroke. In 50 patients diagnosed with acute ischemic stroke (<24-hour duration) within the middle cerebral artery territory, lesion volume was measured by diffusion-weighted imaging. Thirty-four patients also had volumes measured by T2-weighted imaging chronically (median time, 7.5 weeks; mean, 15.9 weeks). Clinical severity was measured by the National Institutes of Health Stroke Scale Score and the Barthel index. Acute lesion volumes correlated with the acute stroke scale score (r = 0.56), the chronic stroke scale score (r = 0.63), and chronic lesion volumes (r = 0.84). Chronic volumes correlated with the chronic stroke scale score (r = 0.86) and the Barthel index (r = -0.60). When only cortically based lesions were considered, the correlations relating acute lesion volume measured by diffusion-weighted imaging (r = 0.61) and chronic lesion volume measured by T2-weighted imaging (r = 0.90) to the chronic stroke scale score were higher. These results provide evidence that lesion volumes determined by diffusion-weighted imaging acutely may be predictive of clinical severity and outcome, and may support a role for diffusion-weighted imaging in the assessment of acute stroke therapies in clinical trials.

Adult↗
PubMed1997

Sensitivity and specificity of 99mTc-HMPAO SPECT cerebral perfusion measurements during the first 48 hours for the localization of cerebral infarction.

BACKGROUND AND PURPOSE: There is no routinely used method for imaging the location of the extent and severity of cerebral tissue perfusion changes during the first hours of ischemic stroke, the period during which therapeutic intervention is most likely to be successful. Cerebral perfusion measurements with single-photon emission CT (SPECT) may potentially provide this information rapidly and noninvasively. In this study, the sensitivity and specificity of 99mTc-hexamethylpropyleneamine oxime (HMPAO) SPECT cerebral perfusion measurements during the first 48 hours of cerebral ischemia for the localization of cerebral infarction were determined. METHODS: One hundred and four patients with acute ischemic stroke underwent 99mTc-HMPAO SPECT and CT scanning during the first 48 hours. In each patient, the location of the SPECT perfusion abnormality was compared with the location of infarction on a second brain CT acquired at a mean of 8 days after stroke. RESULTS: During the first 48 hours of ischemic stroke, the sensitivity of 99mTc-HMPAO SPECT in locating the site of infarction was 79% (110/139), and the specificity was 95% (362/381). SPECT was more sensitive in the localization of the vascular territory of cortical infarction (sensitivity, 93%) than pure subcortical infarcts (sensitivity, 47%). During the first 48 hours, SPECT was significantly more sensitive than brain CT (sensitivity of brain CT during the first 48 hours, 35%; P < .001, Mann-Whitney U test). CONCLUSIONS: HMPAO SPECT measurement provides a widely available and practical technique of locating cerebral ischemia acutely and demonstrates high sensitivity and specificity within the first 48 hours for the localization of the vascular territory of cerebral infarction. It is most sensitive for cortical ischemia but is limited by its resolution in the subcortex, particularly of white matter perfusion changes.

Aged↗
PubMed1996

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.

Aged↗
PubMed1996

Streptokinase increases luxury perfusion after stroke.

BACKGROUND AND PURPOSE: Recent acute stroke trials have reported that intravenous streptokinase is associated with an increased risk of adverse outcomes. We aimed to study the effect of streptokinase on the nature of reperfusion and the relation between reperfusion and clinical outcome. METHODS: We studied 24 patients in the Australian Streptokinase Trial with acute middle cerebral cortical infarction using 99mTc-hexamethylpropyleneamine oxime single-photon emission CT. Eleven of the 24 patients were scanned before therapy and again 24 hours later. The remaining 13 were scanned once either before therapy (1 patient) or after therapy (12 patients). All patients had outcome scans after 3 months. Infarct hypoperfusion was measured with a validated volumetric technique. Neurological impairment and functional outcome were assessed with the Canadian Neurological Scale and the Barthel Index, respectively. RESULTS: Fifteen patients received streptokinase and 9 received placebo. There was no difference in early reperfusion between streptokinase and placebo. However, streptokinase was associated with a greater amount of nonnutritional reperfusion than was placebo (P = .04). This luxury perfusion was associated with poor functional outcome (P = .02). CONCLUSIONS: This study suggests that streptokinase augments luxury perfusion after stroke. Luxury perfusion is associated with a worse outcome, which might be due in part to reperfusion injury.

Adult↗
PubMed1995

Early reperfusion in the 'spectacular shrinking deficit' demonstrated by single-photon emission computed tomography.

The "spectacular shrinking deficit" (SSD) refers to a syndrome of profound hemispheric ischemia that resolves rapidly over hours to days, leaving patients with minimal residual neurologic deficits. The SSD is postulated to result from rapid embolic lysis, fragmentation, and migration along the internal carotid/middle cerebral artery axis, leading to restored tissue perfusion before irreversible tissue damage has occurred. We performed serial single-photon emission computed tomographic (SPECT) cerebral perfusion measurements during the first 48 hours in 36 patients admitted with major hemispheric ischemia, to compare the cerebral perfusion changes between patients who developed SSD (n = 5) and those who did not (n = 31). The two groups were similar for severity of neurologic deficit, time of SPECT study, and size of perfusion defect on the SPECT images. Patients with SSD were younger (p = 0.02, Mann-Whitney U), demonstrated significantly greater tissue reperfusion during the first 48 hours (p < 0.01), and had smaller infarcts on CT (p = 0.02). This syndrome provides an opportunity to understand the mechanism by which early reperfusion may result in early tissue salvage and clinical recovery.

Aged↗
PubMed1994

Reperfusion after thrombolytic therapy in ischemic stroke measured by single-photon emission computed tomography.

BACKGROUND AND PURPOSE: We used 99mTc-hexamethylpropyleneamine oxime single-photon emission computed tomography (SPECT) to study cerebral perfusion in patients treated with streptokinase for acute ischemic stroke in an open and prospective study. Our primary aims were (1) to compare the extent of reperfusion between patients who had received thrombolytic therapy and a control group studied during the same period who were ineligible to receive such therapy and (2) to determine if, among all patients, reperfusion led to improved outcome. METHODS: Fifty-seven patients (22 treated with streptokinase) had two SPECT studies performed, the first before streptokinase administration and the second 24 hours later. RESULTS: On the first SPECT study hyperfusion was present in the middle cerebral artery or anterior cerebral artery territories in 40 patients (17 treated with streptokinase). Patients in the treatment and control groups with initial hypoperfusion on SPECT were well matched for the volume of the perfusion defect and the severity of neurological deficit. A greater number of patients who received streptokinase developed at least partial reperfusion (streptokinase, 65%; control, 52%) on the second study but not significantly so (P = .43). Similarly, the proportion of each hypoperfused region that reperfused (P = .74) and the reduction in the size of the perfusion defect (P = .06) were higher in the streptokinase group but did not reach statistical significance. When all patients were considered, those who did not reperfuse had higher mortality rates (P = .008), less neurological improvement (P = .016), and more functional disability (P < .001) than patients who had reperfusion or normal perfusion initially. CONCLUSIONS: These findings suggest that at least some reperfusion during the first 48 hours of ischemic stroke is a common natural occurrence and is of prognostic significance. The observed trend toward better reperfusion indexes among patients treated with streptokinase is encouraging, but larger controlled trials are required to answer this definitively.

Aged↗
PubMed1994

Diagnosis and imaging of stroke.

BACKGROUND: Less than 20 years ago the diagnosis of stroke was almost entirely based on clinical features. Since the mid-1970s sophisticated ultrasonography, computed tomography, magnetic resonance imaging, angiography and spectroscopy, single-photon emission computed tomography and positron emission tomography have been developed in rapid succession. CURRENT USE OF NEUROIMAGING IN STROKE PATIENTS: By using a combination of imaging modalities it is now possible to show nearly all of the vascular tree from the left ventricle of the heart through to small arteries within the brain. Depending on clinical need, in most cases, it should be possible to define the location and mechanism of any given vascular event affecting the brain, and thus design appropriate management. THE FUTURE: Neuroimaging, clinical diagnosis and therapy are closely linked. Neuroimaging will become even more important if potential neuroprotective or thrombolytic agents prove effective. Categorization of pathophysiological subtypes of haemorrhagic and ischaemic stroke will allow more precise management of patients. If the rate of development in neuroimaging of the previous 20 years is maintained, even more precise evaluation of stroke patients will become possible.

Cerebrovascular Disorders↗
PubMed1993

Intra-arterial streptokinase in acute ischaemic stroke. A pilot study.

AIMS: To assess the safety and efficacy of the intra-arterial administration of streptokinase within 24 hours of acute ischaemic stroke. METHODS: Patients who presented to the Austin Hospital casualty department between 3 and 22 hours after an acute stroke were considered for the study. Eligible patients had pretreatment non-contrast computed tomographic scans of the brain to exclude haemorrhage. Streptokinase (250,000 units) was administered directly into the common carotid artery or the cervical portion of the internal carotid artery. MAIN OUTCOME MEASURES: The incidence of symptomatic and asymptomatic cerebral haemorrhage, haemorrhagic transformation of infarction, angiographic reperfusion, clinical outcome at seven to 10 days and the frequency of other complications. RESULTS: Thirteen patients were treated over a 16-month period. Major clinical improvement occurred in five patients (39%) at 48 hours. This was associated with angiographically demonstrated recanalisation of a middle cerebral artery occlusion in two patients and partial recanalisation in two others. Significant hypotension in two patients required therapy to be stopped. In five other cases mild hypotension developed but the streptokinase infusion was completed. Haemorrhagic transformation of the infarct occurred in four patients without clinical deterioration. CONCLUSION: Intra-arterial administration of streptokinase is safe in selected patients with acute ischaemic stroke. The theoretical benefit of an increased local thrombolytic effect and reduced systemic complications, compared with the use of higher intravenous doses, justifies a randomised clinical trial. If therapies such as this are to be successful, rapid referral to an appropriate centre is necessary.

Aged↗
PubMed1991

Preliminary experience with 99mTc-HMPAO SPECT in cerebral ischaemia.

To assess the sequential changes seen in cerebral blood flow using Single Photon Emission Computed Tomography with 99mtechnetium-hexamethylpropylene amine oxime (99mTc-HMPAO SPECT) in acute ischaemic stroke, 35 patients were prospectively studied from June 1990- to March 1991. Scans were performed during the acute phase (1-7 days), sub-acute phase (8-21 days) and chronic phase of stroke (greater than 1 month). Nine patients underwent scans in all 3 phases, 15 patients had 2 scans, and 11 patients had one scan. The majority of infarcts were in the middle cerebral territory (15 patients), while 4 infarcts were in the posterior cerebral territory and two in the anterior cerebral territory. There was a total of 4 lacunar infarcts. Image analysis was by visual inspection and by semiquantitation using homologous regions of interest in opposite hemispheres. SPECT in the acute phase identified the final vascular territory affected in 19 of 27 patients. There were 8 patients in whom early SPECT predicted the vascular territory as seen on late CT scan when the early CT scan was normal. Hyperaemia or reperfusion in the involved vascular territory was identified in 10 patients on scans performed during the sub-acute phase. Late SPECT scans showed perfusion defects greater than the infarct size seen on CT scan in the majority of patients. In all cases, the perfusion defect on the late SPECT scan was equal to or larger than the defect seen on the acute or sub-acute scan. Crossed cerebellar diaschisis was identified in 8 patients, and cortical/subcortical diaschisis in one patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1991

Mechanisms and clinical features of internal watershed infarction.

The mechanism of internal carotid watershed cerebral infarction is not well understood, but the phenomenon has been described in association with carotid occlusive disease, and more recently with distal middle cerebral artery occlusion beyond the origin of the lenticulostriate branches. The clinical correlates of these changes have not yet been described. We present 5 patients in whom acute internal watershed infarction had occurred, and correlate the clinical, neuropsychological and 99mTc-HMPAO SPECT (Single Photon Emission Computed Tomography using 99mtechnetium-hexamethylpropylene amine oxime) cerebral perfusion findings. Four patients had distal middle cerebral artery occlusion demonstrated on angiography, and one showed profound hemispheric depression in cerebral perfusion with only a small area of infarction. We have concentrated on the mechanism of distal middle cerebral artery occlusion to describe the "arc" of the watershed zone created. We propose that internal watershed infarcts can further be subdivided into anterior and posterior subtypes, outline the vascular territories involved, and propose an overall classification of cerebral watershed infarction.

Adult↗
PubMedDate not supplied

A phantom for diffusion-weighted imaging of acute stroke.

A tissue phantom for diffusion-weighted imaging was developed, basing its contrast between two compartments on different apparent diffusion coefficients, without contrast due to T2 relaxation and proton density. These contrast properties of the phantom simulate the situation found in normal gray matter and areas of acute ischemia. A possible application of the phantom was demonstrated for the investigation of the accuracy of volume measurements based on diffusion-weighted images.

Acute Disease↗
PubMedDate not supplied

Clinical correlations of diffusion and perfusion lesion volumes in acute ischemic stroke.

The aim of this study was to describe the clinico-radiological correlations of magnetic resonance (MR) perfusion and diffusion-weighted imaging (DWI) abnormalities in ischemic stroke. Eighteen patients had undergone MR imaging and clinical evaluation within 24 h of symptom onset and at or after 7 days. During the first 24 h the volume of perfusion abnormality (measured on the relative mean transit time map) was larger than the DWI lesion in 12/18 patients. In 6/18 patients the DWI lesion volume was larger. Acutely (<24 h) all lesion volumes showed a significant correlation with acute clinical severity measured by the National Institutes of Health Stroke Scale score. The correlations of the hypoperfusion volume (rho = 0.86, p = 0.0001) and the volume 'tissue at risk' (larger than the DWI and perfusion lesion volumes, rho = 0.86, p = 0. 0001) with acute clinical severity were slightly higher than for the DWI lesion volume (rho = 0.76, p = 0.0001). The difference between the volume of tissue at risk (acutely) and the infarct on follow-up T(2)-weighted imaging correlated significantly with change in clinical severity from acute to chronic time points (rho = 0.72, p = 0.001). Such clinico-radiological relationships may support the use of DWI and perfusion MR in decisions concerning the administration and evaluation of stroke therapies.

Acute Disease↗
PubMedDate not supplied

Clinical experience with diffusion-weighted MR in patients with acute stroke.

PURPOSE: Our purpose was to evaluate the clinical efficacy, sensitivity, and specificity of echo-planar diffusion-weighted MR imaging in patients with acute infarction. METHODS: We retrospectively analyzed 194 cases of acute ischemic stroke diagnosed clinically within 24 hours of onset and studied with echo-planar diffusion-weighted MR imaging. Examinations were considered to be positive for infarction when an increase in signal was noted on images acquired at a high b value but absent on images with a low b value. A final clinical diagnosis of acute stroke was used as the standard of reference. A subset of 48 patients scanned within 6 hours was also analyzed. RESULTS: Diffusion-weighted MR imaging studies were positive in 133 of 151 cases of infarction (88% sensitivity) and negative in 41 of 43 cases with no infarction (95% specificity). Two cases identified as positive on diffusion-weighted images had nonischemic diagnoses (1.5% false-positive rate). Diffusion-weighted imaging had a positive predictive value of 98.5% and a negative predictive value of 69.5%. Use of T2-weighted sequences as well as diffusion-weighted imaging produced no false-positive findings. Of the negative scans, 69.5% corresponded to transient ischemic attacks or infarcts (mostly small brain stem infarcts). When only cases scanned within 6 hours of onset were considered, the sensitivity rose to 94% and the specificity to 100%. CONCLUSION: Despite bias due to dependence between diffusion-weighted imaging and the final diagnosis, this analysis suggests high sensitivity and specificity for echo-planar diffusion-weighted imaging in the diagnosis of acute cerebral infarction, although negative scans did not rule out an ischemic pathogenesis.

Acute Disease↗