Biomedical subjects

H S Markus

Publications and source records attributed to H S Markus.

At least 19 recordsLinked to original sources

PubMed2002

Diagnostic strategies in CADASIL.

BACKGROUND: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited autosomal dominant condition characterized by migraine, recurrent stroke, and dementia. It results from mutations in the notch3 gene but mutations may occur at multiple sites making molecular diagnosis time consuming. It has been suggested that the presence of granular osmiophilic material (GOM) on skin biopsy and involvement of the anterior temporal lobe and external capsule on MRI may help in diagnosis. METHODS: The authors identified 83 potential index cases from the British population and screened exons 2 to 23 of notch3. MRI scans were scored using a modified Scheltens scale. Skin biopsy was performed in a subgroup. RESULTS: Fifteen different point mutations were identified in 48 families, 73% of which were in exon 4, 8% in exon 3, and 6% in each of exons 5 and 6. Moderate or severe involvement of the anterior temporal pole on MRI had a sensitivity of 89% and specificity of 86% for diagnosis of CADASIL, whereas external capsule involvement had a high sensitivity of 93% but a low specificity of 45%. Skin biopsy, performed in 18 cases, had a sensitivity of 45% and specificity of 100%. CONCLUSIONS: The spectrum of mutations in this study can be used to plan appropriate screening protocols; a suggested protocol is to screen exon 4, and proceed to exons 3, 5, and 6 where indicated. GOM on skin biopsy is diagnostic but can be negative. Anterior temporal pole involvement on MRI is a useful diagnostic marker.

Adult↗

PubMed2002

Patterns of cerebral blood flow reduction in patients with ischemic leukoaraiosis.

BACKGROUND: Ischemic leukoaraiosis (ILA) refers to diffuse T2-weighted white matter hyperintensity in the context of a previous clinical lacunar stroke. Reduced cerebral blood flow (CBF) in white matter has been demonstrated, but it is not known whether hypoperfusion is confined to lesions or extends into normal-appearing white matter. Demonstrating changes in normal-appearing white matter would provide clues to the importance of hypoperfusion in pathogenesis and would be an obvious target for therapies aimed at restoring white matter blood flow. METHODS: Twenty-one patients with ILA, and 16 age-matched control subjects, underwent exogenous contrast-based quantitative perfusion MRI. CBF was determined both within and outside areas of T2-weighted hyperintensity in both periventricular white matter and the centrum semiovale. RESULTS: CBF of normal-appearing white matter was reduced in periventricular regions (for patients with ILA, 17.9 +/- 5.6 mL/100 g/min; for controls, 21.6 +/- 5.1 mL/100 g/min; p = 0.046). CBF in gray matter and normal-appearing white matter of the centrum semiovale did not differ significantly between groups. In normal-appearing white matter in patients, CBF was higher in the centrum semiovale than periventricular white matter, with a similar trend in control subjects. CONCLUSIONS: Hypoperfusion may be an early feature in the development of periventricular lesions in ILA and may play a direct pathogenic role. Serial studies are now needed to determine whether these changes herald the appearance of new lesions and represent "at risk" white matter, and to determine whether pharmacological agents can restore perfusion of normal-appearing white matter.

Aged↗

PubMed2001

Normal-appearing white matter in ischemic leukoaraiosis: a diffusion tensor MRI study.

Ischemic leukoaraiosis is a consistent concomitant of vascular dementia. Conventional MRI provides little information about underlying white matter tract disruption and correlates poorly with cognitive dysfunction. Diffusion tensor MRI may provide better markers of tract integrity. Changes in the normal-appearing white matter were demonstrated in 30 patients with ischemic leukoaraiosis compared with 17 age-matched control subjects. These changes correlated with executive dysfunction assessed by the Wisconsin Card Sorting Test.

Aged↗

PubMed2001

Atrial natriuretic peptide gene G664A polymorphism and the risk of ischemic cerebrovascular disease.

The atrial natriuretic peptide (ANP) gene may underlie stroke susceptibility and sensitivity to cerebral ischemia in an animal model of stroke. The authors investigate its role in humans by genotyping a polymorphism (G664A) in 436 patients with ischemic cerebrovascular disease and 295 community control subjects. The frequency of this variant was similar in both groups and across the different stroke subtypes. The ANP gene G664A polymorphism is therefore unlikely to be an important risk factor for ischemic stroke in this population.

Aged↗

PubMed2001

Evidence for cortical "disconnection" as a mechanism of age-related cognitive decline.

BACKGROUND: Normal aging is accompanied by a decline of cognitive abilities, and executive skills may be affected selectively, but the underlying mechanisms remain obscure and preventive strategies are lacking. It has been suggested that cortical "disconnection" due to the loss of white matter fibers may play an important role. But, to date, there has been no direct demonstration of structural disconnection in humans in vivo. METHODS: The authors used diffusion tensor MRI to look for evidence of ultrastructural changes in cerebral white matter in a group of 20 elderly volunteers with normal conventional MRI scans, and a group of 10 younger controls. The older group also underwent neuropsychological assessment. RESULTS: Diffusional anisotropy, a marker of white matter tract integrity, was reduced in the white matter of older subjects and fell linearly with increasing age in the older group. Mean diffusivity was higher in the older group and increased with age. These changes were maximal in anterior white matter. In the older group, anterior mean diffusivity correlated with executive function assessed by the Trail Making Test. CONCLUSIONS: These findings provide direct evidence that white matter tract disruption occurs in normal aging and would be consistent with the cortical disconnection hypothesis of age-related cognitive decline. Maximal changes in anterior white matter provide a plausible structural basis for selective loss of executive functions. In addition to providing new information about the biological basis of cognitive abilities, diffusion tensor MRI may be a sensitive tool for assessing interventions aimed at preventing cognitive decline.

Adult↗

PubMed2001

L-arginine and S-nitrosoglutathione reduce embolization in humans.

BACKGROUND: L-Arginine reduces platelet aggregation and adhesion in ex vivo studies, but there is no evidence as yet that it has a therapeutic effect on clinical end points. Doppler ultrasound can detect cerebral emboli noninvasively. Such embolic signals are common after carotid endarterectomy, and their frequency predicts risk of stroke recurrence. We used this situation to determine the antiplatelet efficacy of L-arginine and S-nitrosoglutathione (GSNO), a physiological nitric oxide donor with possible platelet specificity. METHODS AND RESULTS: Patients undergoing carotid endarterectomy were randomized in a double-blind manner between L-arginine (n=14), GSNO (n=14), or placebo (n=14) administered intravenously for 90 minutes, starting 30 minutes after skin closure. All patients were pretreated with aspirin and given heparin during surgery. Transcranial Doppler recordings were made from the ipsilateral middle cerebral artery for 4 hours after surgery, beginning 30 minutes after skin closure, and also at 6 and 24 hours. There were highly significant reductions in the number of Doppler embolic signals in the L-arginine and GSNO groups; first 4 hours, median (range) number of embolic signals, placebo 44.7 (6 to 778), L-arginine 9.5 (0 to 225), and GSNO 0.8 (0 to 8), both P<0.001 versus control values. The reduction in the signals persisted at the 24-hour recording. CONCLUSIONS: Intravenous L-arginine and GSNO attenuate Doppler embolic signals in humans. Modulation of the NO system with these agents may have applications in the treatment of thromboembolic disease. This study demonstrates the potential application of ultrasonic embolic signal detection to examine the efficacy of new antiplatelet agents in relatively small numbers of patients.

Aged↗

PubMed2001

MRI hyperintensities of the temporal lobe and external capsule in patients with CADASIL.

BACKGROUND: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited, autosomal dominant condition caused by mutations of the Notch3 gene. Affected individuals have migraine, mood disturbance, and recurrent strokes, often progressing to subcortical dementia and premature death. MRI findings include focal lacunar infarcts and diffuse T2-weighted hyperintensity, or leukoaraiosis. However, such findings are seen much more commonly in patients with cardiovascular risk factors, particularly hypertension, where they are believed to represent cerebral small vessel disease. No previous study has sought to identify specific radiologic markers of CADASIL. METHODS: MRI scans from 20 consecutive patients with CADASIL and 20 patients with sporadic leukoaraiosis due to presumed small-vessel disease were compared using the previously validated semiquantitative MRI rating scale devised by Scheltens et al. Analysis was blinded to clinical category. RESULTS: Scores for hyperintensities of the temporal white matter and external capsule-insula region were significantly higher in patients with CADASIL. Hyperintensity confined to the pole of the temporal lobe was a characteristic finding in CADASIL, occurring in 19 patients with CADASIL but no patients with ischemic leukoaraiosis. Involvement of the external capsule, though less specific, was seen early in the disease course. In a few patients with CADASIL, involvement of the corpus callosum was observed. CONCLUSIONS: Temporal pole hyperintensity is a radiologic marker of CADASIL. Involvement of the external capsule and corpus callosum are also characteristic findings that may help to distinguish the disease.

Adult↗

PubMed2001

Evaluation of a 1 MHz transducer for transcranial Doppler ultrasound including embolic signal detection.

A 1 MHz transducer for use with transcranial Doppler ultrasound may improve the intensity and therefore the detection of embolic signals (ES) and may also reduce the number of absent acoustic windows. A series of studies was performed to investigate its potential benefits. Firstly, ES were detected using a 1 MHz and a 2 MHz transducer both in vitro and in vivo. Secondly, the time taken to identify 100 middle cerebral arteries (MCA) was recorded for both transducers and the best Doppler signal obtained was reviewed off-line and graded for quality. ES were more intense when detected with the 1 MHz compared with the 2 MHz transducer, both in vitro (p <.0001) and in vivo (p <.0001). Of the 100 MCAs studied, 81 had acoustic windows identified with both transducers. The number of acoustic windows detected with one transducer but not the other was the same for both transducers (n = 3). The time taken to identify the MCA was longer with the 1 MHz transducer (p <.0001) and the quality of the signal achieved was poorer (p <.0001). In conclusion, the 1 MHz transducer improved embolic signal intensity but the overall quality of the flow spectrum obtained was poorer with the 1 MHz than with the 2 MHz transducer. A lower frequency transducer of 1 MHz or possibly 1.5 MHz with transcranial Doppler ultrasound may improve the application of embolic signal detection but may not improve the signal for routine measurement of flow velocities.

Endarterectomy, Carotid↗

PubMed2001

MRI based diffusion and perfusion predictive model to estimate stroke evolution.

In this study we present a novel automated strategy for predicting infarct evolution, based on MR diffusion and perfusion images acquired in the acute stage of stroke. The validity of this methodology was tested on novel patient data including data acquired from an independent stroke clinic. Regions-of-interest (ROIs) defining the initial diffusion lesion and tissue with abnormal hemodynamic function as defined by the mean transit time (MTT) abnormality were automatically extracted from DWI/PI maps. Quantitative measures of cerebral blood flow (CBF) and volume (CBV) along with ratio measures defined relative to the contralateral hemisphere (r(a)CBF and r(a)CBV) were calculated for the MTT ROIs. A parametric normal classifier algorithm incorporating these measures was used to predict infarct growth. The mean r(a)CBF and r(a)CBV values for eventually infarcted MTT tissue were 0.70 +/- 0.19 and 1.20 +/- 0.36. For recovered tissue the mean values were 0.99 +/- 0.25 and 1.87 +/- 0.71, respectively. There was a significant difference between these two regions for both measures (p < 0.003 and p < 0.001, respectively). Mean absolute measures of CBF (ml/100g/min) and CBV (ml/100g) for the total infarcted territory were 33.9 +/- 9.7 and 4.2 +/- 1.9. For recovered MTT tissue, the mean values were 41.5 +/- 7.2 and 5.3 +/- 1.2, respectively. A significant difference was also found for these regions (p < 0.009 and p < 0.036, respectively). The mean measures of sensitivity, specificity, positive and negative predictive values for modeling infarct evolution for the validation patient data were 0.72 +/- 0.05, 0.97 +/- 0.02, 0.68 +/- 0.07 and 0.97 +/- 0.02. We propose that this automated strategy may allow possible guided therapeutic intervention to stroke patients and evaluation of efficacy of novel stroke compounds in clinical drug trials.

Aged↗

PubMed2001

Ischaemic heart disease and Cag A strains of Helicobacter pylori in the Caerphilly heart disease study.

OBJECTIVE: To look for the presence of the more virulent strains of Helicobacter pylori (H pylori) in men who developed ischaemic heart disease over a 10 year period and in controls. DESIGN: The Caerphilly prospective heart disease study recruited 2512 men aged 45-59 years during 1979-83. Western blot analysis or enzyme linked immunosorbent assay (ELISA) was performed on serum taken from those who subsequently died of ischaemic heart disease, or developed non-fatal myocardial infarction, to determine H pylori and Cag A status. Similar information was available on age matched controls. RESULTS: During the first decade of the study, 312 men died of ischaemic heart disease or developed non-fatal myocardial infarction. Serum was available from 172 of these (55%). There was no evidence of an association between Cag A seropositivity and incident ischaemic heart disease or ischaemic heart disease mortality, either before or after adjustment for potential confounders (adjusted odds ratios 1.18 (95% confidence interval (CI) 0.76 to 1.85) and 1.13 (95% CI 0.61 to 2.07), respectively). Further, the odds ratios for ischaemic heart disease incidence and ischaemic heart disease mortality by H pylori seropositivity did not appear to depend on the presence or absence of Cag A strains (p = 0.76 and 0.77, respectively). CONCLUSIONS: In this cohort of middle aged men, followed over a 10 year period, there is little evidence of an association between Cag A seropositivity and either incident ischaemic heart disease or ischaemic heart disease mortality.

Antigens, Bacterial↗

PubMed2001

Magnetic resonance markers of ischaemia: their correlation with vasodilatory reserve in patients with carotid artery stenosis and occlusion.

OBJECTIVES: Better methods of identifying patients with asymptomatic carotid artery stenosis who are at high risk of stroke are required. It has been suggested that proton magnetic resonance spectroscopy (MRS) may allow the identification of ongoing ischaemia in this patient group by the detection of a potentially reversible reduction of N-acetyl aspartate (NAA), a presumed marker of neuronal integrity, and the presence of lactate, a marker of anaerobic metabolism. Previous studies have reported metabolite ratios rather than absolute concentrations. This study was performed to determine if NAA was reduced ipsilateral to carotid stenosis or occlusion, and if its concentration was related to carbon dioxide reactivity, a marker of cerebrovascular reserve. METHODS: Twenty one patients with unilateral carotid stenosis (>70%) or occlusion were studied. Single voxel proton MRS was performed in the ipsilateral and contralateral hemispheres, with the voxel positioned in the arterial borderzone region between the middle and anterior cerebral artery territories. Absolute quantification of metabolite concentrations was performed. Cerebrovascular reactivity to 6% carbon dioxide was determined in both middle cerebral artery territories using transcranial Doppler ultrasonography. RESULTS: Mean (SD) cerebrovascular reactivity was significantly lower in the stenosed compared with the contralateral hemisphere (13.3 (7.7) v 19.2 (8.2)%/kPa, p=0.002). There were no significant differences in the absolute concentrations of NAA, choline, or creatine between the ipsilateral and contralateral hemispheres (for example, NAA 10.1 (1.1) v 10.5 (1.1) mmol/l, p=0.1). No lactate peak was seen in any spectra. For each metabolite measured, there was no correlation between the absolute concentration and cerebrovascular reactivity for either hemisphere. CONCLUSIONS: In patients with carotid stenosis and occlusion we found no evidence that chronic hypoperfusion is associated with a reduction in NAA or the presence of lactate. Magnetic resonance spectroscopy is unlikely to help in the selection of patients with asymptomatic carotid stenosis for endarterectomy.

Aged↗

PubMed2000

The effect of the nitric oxide donor glyceryl trinitrate on global and regional cerebral blood flow in man.

Despite their potential use as cerebral vasodilatory agents there are few studies of the effect of nitric oxide (NO) donors on the cerebral circulation in non-anaesthetised man. We determined the effect of the NO donor glyceryl trinitrate (GTN) at clinically relevant doses on global and regional cerebral blood flow (CBF) in healthy non-anaesthetised volunteers, using H(2)(15)O PET, ultrasonic colour velocity flow imaging of carotid artery flow, and transcranial Doppler (TCD) of middle cerebral artery velocities (MCAv). Three rates of GTN infusion (0.1, 0.4, 1.0 microg/kg/min) were used. There was no significant change in common or internal carotid artery flow following GTN administration although a dose dependent fall in MCAv post GTN was observed. There was no significant change in either global or regional CBF following GTN. Thus intravenous GTN at therapeutic doses in awake humans does not alter global or regional CBF. However it does produce basal cerebral artery vasodilatation as evidenced by a fall in MCAv in the absence of a change in internal carotid artery flow.

Adult↗

PubMed2000

Quantitative perfusion imaging in carotid artery stenosis using dynamic susceptibility contrast-enhanced magnetic resonance imaging.

Quantitative, multislice dynamic susceptibility contrast-enhanced MRI perfusion measurements were used to determine the patterns of cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and normalized first moment of the tissue deltaR2-time curve (N) in 11 subjects with carotid artery occlusion or stenosis. MTT correlated with degree of carotid stenosis, whereas a range of alterations in CBF and CBV were found presumably reflecting variables degrees of collateral flow. There was no significant correlation between MRI and SPET flow perfusion measurements, with increasing disparity between the two techniques at higher inter-hemispheric flow ratios. The effect of obtaining the arterial input function (AIF) from the middle cerebral artery (MCA) ipsilateral or contralateral to the stenosis was determined. Despite the use of an AIF from the MCA, which is distal to the circle of Willis, and hence the major sources of collateral supply, there was still some extra dispersion of the contrast agent bolus due to differences in arrival time.

Aged↗

PubMed2000

Optimization of processing parameters for the analysis and detection of embolic signals.

The fast Fourier transform (FFT), which is employed by all commercially available ultrasonic systems, provides a time-frequency representation of Doppler ultrasonic signals obtained from blood flow. The FFT assumes that the signal is stationary within the analysis window. However, the presence of short duration embolic signals invalidates this assumption. For optimal detection of embolic signals if FFT is used for signal processing, it is important that the FFT parameters such as window size, window type, and required overlap ratio should be optimized. The effect of varying window type, window size and window overlap ratio were investigated for both simulated embolic signals, and recorded from patients with carotid artery stenosis. An optimal compromise is the use of a Hamming or Hanning window with a FFT size of 64 (8.9 ms) or 128 (17.9 ms). A high overlap ratio should also be employed in order not to miss embolic events occurring at the edges of analysis windows. The degree of overlap required will depend on the FFT size. The minimum overlap should be 65% for a 64-point window and 80% for a 128-point window.

Blood Flow Velocity↗

PubMed2000

Genetics and ischaemic stroke.

Ischaemic stroke can be caused by a number of monogenic disorders, and in such cases stroke is frequently part of a multisystem disorder. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL), due to mutations in the NOTCH: 3 gene, is increasingly appreciated as a cause of familial subcortical stroke. The genetics and phenotypes of monogenic stroke are covered in this review. However, the majority of cases of ischaemic stroke are multifactorial in aetiology. Strong evidence from epidemiological and animal studies has implicated genetic influences in the pathogenesis of multifactorial ischaemic stroke, but the identification of individual causative mutations remains problematic; this is in part limited by the number of approaches currently available. In addition, genetic influences are likely to be polygenic, and ischaemic stroke itself consists of a number of different phenotypes which may each have different genetic profiles. Almost all human studies to date have employed a candidate gene approach. Associations with polymorphisms in a variety of candidate genes have been investigated, including haemostatic genes, genes controlling homocysteine metabolism, the angiotensin-converting enzyme gene, and the endothelial nitric oxide synthase gene. The results of these studies, and the advantages and limitations of the candidate gene approach, are presented. The recent biological revolution, spurred by the human genome project, promises the advent of novel technologies supported by bioinformatics resources that will transform the study of polygenic disorders such as stroke. Their potential application to polygenic ischaemic stroke is discussed.

Animals↗

PubMed2000

Reduced cerebral blood flow in white matter in ischaemic leukoaraiosis demonstrated using quantitative exogenous contrast based perfusion MRI.

OBJECTIVE: White matter hypoperfusion may play a part in the pathogenesis of ischaemic leukoaraiosis, but demonstration of this requires a high resolution quantitative method of cerebral blood flow (CBF) measurement. Initial exogenous contrast based MRI methods only allowed measurement of relative cerebral blood volume (CBV) values, but more recently a mathematical approach has been developed which enables absolute regional CBF and CBV to be determined. This technique was applied to patients with ischaemic leukoaraiosis to determine whether reduced white matter CBF in this patient group could be demonstrated. METHODS: Eight patients with ischaemic leukoaraiosis (radiological leukoaraiosis and clinical lacunar stroke), and nine age matched controls were studied. A spin echo echoplanar image sequence was used on a 1.5 Tesla MR system. An arterial input function was obtained from voxels placed over the middle cerebral arteries. Cerebral blood flow, CBV, and mean transit (MTT) maps were derived. Regions of interest were placed at standard positions in the white and grey matter and mean values of CBF, CBV, and MTT were compared between the two groups. RESULTS: Mean (SD) white matter CBF was significantly reduced in patients by 38% (13.40 (4.87) v 21.74 (3.53) ml/min/ 100 g, p=0.002). Significant reductions in CBF were seen in all white matter regions. By contrast there was no reduction in CBF in any grey matter region. There was no significant difference in white matter CBV between cases and controls; mean values were lower in all white matter regions for patients but this did not reach significance for any region. By contrast mean grey matter CBV was significantly higher in patients than in controls. Mean MTT values were higher in all regions of grey and white matter in the patient group, but this only achieved significance for the superior white matter. CONCLUSION: A quantitative MR perfusion method showed reduced white matter CBF in patients with ischaemic leukoaraiosis, but normal grey matter CBF. This is consistent with hypoperfusion playing a part in the pathogenesis of ischaemic leukoaraiosis. The absolute values of white matter and grey matter CBF obtained in the patient groups were very similar to those in previous PET studies, providing further evidence for the validity of the regional CBF measurements obtained using this quantitative MR perfusion technique. The high spatial resolution and lack of radioactive administration makes such techniques ideal for longitudinal studies in this condition.

Aged↗

PubMed2000

Evaluation of new online automated embolic signal detection algorithm, including comparison with panel of international experts.

BACKGROUND AND PURPOSE: The clinical application of Doppler detection of circulating cerebral emboli will depend on a reliable automated system of embolic signal detection; such a system is not currently available. Previous studies have shown that frequency filtering increases the ratio of embolic signal to background signal intensity and that the incorporation of such an approach into an offline automated detection system markedly improved performance. In this study, we evaluated an online version of the system. In a single-center study, we compared its performance with that of a human expert on data from 2 clinical situations, carotid stenosis and the period immediately after carotid endarterectomy. Because the human expert is currently the "gold standard" for embolic signal detection, we also compared the performance of the system with an international panel of human experts in a multicenter study. METHODS: In the single-center evaluation, the performance of the software was tested against that of a human expert on 20 hours of data from 21 patients with carotid stenosis and 18 hours of data from 9 patients that was recorded after carotid endarterectomy. For the multicenter evaluation, a separate 2-hour data set, recorded from 5 patients after carotid endarterectomy, was analyzed by 6 different human experts using the same equipment and by the software. Agreement was assessed by determining the probability of agreement. RESULTS: In the 20 hours of carotid stenosis data, there were 140 embolic signals with an intensity of > or =7 dB. With the software set at a confidence threshold of 60%, a sensitivity of 85.7% and a specificity of 88.9% for detection of embolic signals were obtained. At higher confidence thresholds, a specificity >95% could be obtained, but this was at the expense of a lower sensitivity. In the 18 hours of post-carotid endarterectomy data, there were 411 embolic signals of > or =7-dB intensity. When the same confidence threshold was used, a sensitivity of 95.4% and a specificity of 97.5% were obtained. In the multicenter evaluation, a total of 127 events were recorded as embolic signals by at least 1 center. The total number of embolic signals detected by the 6 different centers was 84, 93, 108, 92, 63, and 78. The software set at a confidence threshold of 60% detected 90 events as embolic signals. The mean probability of agreement, including all human experts and the software, was 0.83, and this was higher than that for 2 human experts and lower than that for 4 human experts. The mean values for the 6 human observers were averaged to give P=0.84, which was similar to that of the software. CONCLUSIONS: By using the frequency specificity of the intensity increase occurring with embolic signals, we have developed an automated detection system with a much improved sensitivity. Its performance was equal to that of some human experts and only slightly below the mean performance of a panel of human experts

Algorithms↗

PubMed2000

Transcranial Doppler ultrasound.

Transcranial Doppler ultrasound allows measurements of blood flow velocity to be made from the basal intracerebral vessels. The major advantages of transcranial Doppler ultrasound are that it is non-invasive, relatively cheap, can be performed with portable machines, allows monitoring for prolonged periods, and has a high temporal resolution making it ideal for studying dynamic cerebrovascular responses. In addition it has recently been demonstrated that it can be used to detect circulating cerebral emboli; these cannot be detected by any other currently available imaging modality.

Arterial Occlusive Diseases↗