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Biomedical subjects

Dirk W Droste

Publications and source records attributed to Dirk W Droste.

At least 19 recordsLinked to original sources
PubMed2006

The use of embolic signal detection in multicenter trials to evaluate antiplatelet efficacy: signal analysis and quality control mechanisms in the CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial.

BACKGROUND AND PURPOSE: The CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial proved the effectiveness of the combination of clopidogrel and aspirin compared with aspirin alone in reducing presence and number of microembolic signals (MES) in patients with recently symptomatic carotid stenosis. The present study aimed at installing primary and secondary quality control measures in CARESS because MES evaluation relies on subjective judgment by human experts. METHODS: As primary quality control, centers participating in CARESS evaluated a reference digital audio tape (DAT) before the study containing both MES and artifacts. Interobserver agreement of classifying signals as MES was expressed as proportions of specific agreement of positive ratings (ps+/-values). For all DATs included in CARESS (n=300), online number of MES and off-line number of MES read by the central reader were compared using correlation coefficients. As secondary control, a sample of 16 of 300 DATs was cross-validated by another independent reader (post-trial validator). RESULTS: For the reference tape, the cumulative ps+/-value was 0.894 based on 12 of 14 observers. Two observers with very different results improved after a training procedure. Agreement between post-trial validator and central reader was ps+=0.805, indicating very good agreement. Correlation between online evaluation and off-line evaluation of DATs was very good overall (cumulative rho=0.84; P<0.001). CONCLUSIONS: Multicenter studies using MES as outcome parameter are feasible. However, primary and secondary quality control procedures are important.

Aspirin↗
PubMed2005

Benefit of echocontrast-enhanced transcranial arterial color-coded duplex ultrasound.

OBJECTIVES: Proper assessment of the intracranial arteries by transcranial color-coded duplex sonography (TCCD) is occasionally made difficult by an insufficient temporal bone window, an unfavorable insonation angle, or low flow velocity or volume. In these cases, echocontrast could be helpful to increase the diagnostic confidence or to make the diagnosis at all. MATERIAL AND METHODS: We investigated 67 temporal windows of 47 patients with insufficient native transtemporal insonation conditions before and after the application of the second-generation (gas-filled) microbubble contrast agent Sonovue (in 20 patients out of these 47, both temporal windows were insufficient, in the remaining 27 only one side). RESULTS: As compared to the precontrast scans, echocontrast allowed for more segments to be evaluated by pulsed Doppler sonography (p < 0.0001) and for longer lumen segments to be displayed on color mode (p < 0.0001). With the help of contrast medium, flow velocity in the middle cerebral artery could be measured through 65 windows as compared to only 26 windows before contrast was applied (p < 0.0001). CONCLUSIONS: In patients with poor precontrast visualization of intracranial arteries, echocontrast-enhanced TCCD is very helpful.

Adult↗
PubMed2005

Dual antiplatelet therapy with clopidogrel and aspirin in symptomatic carotid stenosis evaluated using doppler embolic signal detection: the Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) trial.

BACKGROUND: Evidence for efficacy of dual antiplatelet therapy in stroke is limited. Symptomatic carotid stenosis patients are at high risk of early recurrent stroke. In this group, asymptomatic microembolic signals (MES), detected by transcranial Doppler ultrasound (TCD), are markers of future stroke and transient ischemic attack (TIA) risk. They offer a surrogate marker to evaluate antiplatelet therapy, but no multicenter study has evaluated the feasibility of this approach. METHODS AND RESULTS: Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic Carotid Stenosis (CARESS) is a randomized, double-blind study in subjects with recently symptomatic > or =50% carotid stenosis. Patients were screened with TCD, and if MES were detected, they were randomized to clopidogrel and aspirin or aspirin monotherapy. Repeated TCD recordings were made on days 2 and 7. MES were detected in 110 of 230 patients by online analysis at baseline, of whom 107 were randomized. Intention-to-treat analysis revealed a significant reduction in the primary end point: 43.8% of dual-therapy patients were MES positive on day 7, as compared with 72.7% of monotherapy patients (relative risk reduction 39.8%; 95% CI, 13.8 to 58.0; P=0.0046). The secondary end point of MES frequency per hour was reduced (compared with baseline) by 61.4% (95% CI, 31.6 to 78.2; P=0.0013) in the dual-therapy group at day 7 and by 61.6% (95% CI, 34.9 to 77.4; P=0.0005) on day 2. There were 4 recurrent strokes and 7 TIAs in the monotherapy group versus no stroke and 4 TIAs in the dual-therapy group that were treatment emergent and ipsilateral to the qualifying carotid stenosis; 2 additional ipsilateral TIAs occurred before treatment started. MES frequency was greater in the 17 patients with recurrent ipsilateral events compared with the 90 without (mean+/-SD: 24.4+/-27.7 versus 8.9+/-11.5 per hour; P=0.0003). CONCLUSIONS: In patients with recently symptomatic carotid stenosis, combination therapy with clopidogrel and aspirin is more effective than aspirin alone in reducing asymptomatic embolization. Doppler MES detection is a feasible method to evaluate the efficacy of antiplatelet therapy in multicenter studies.

Aged↗
PubMed2005

Measuring carotid artery stenosis--comparison of postmortem arteriograms with the planimetric gold standard.

OBJECTIVE: Five different calliper methods for assessing the degree of carotid artery stenosis and visual estimation ("eyeballing") of postmortem carotid arteriograms were compared with the planimetric gold standard of the area reduction at the site of the stenosis. METHODS: During autopsy 53 carotid specimens were removed in toto from 31 neurological patients. Carotid arteries were ligated and redistended to a physiological degree for standardised three-plane arteriography. Afterwards, the entire specimen was filled with an embedding medium under the same conditions and sectioned. Slices at the site of stenoses were histologically processed. Computerised planimetric analysis of the lumen area reduction was performed and compared with the arteriographic findings. Arteriograms were evaluated by two independent observers by means of linear Common Carotid Artery (CC), the European Carotid Surgery Trial (ECST) and the North American Symptomatic Carotid Endarterectomy Trial (NASCET), and squared measurements (NASCET2, ECST2) after applying the pi r2 function. Further, three independent observers performed eyeballing of the degree of stenosis from the postmortem arteriographies. RESULTS: Planimetry was carried out in 29 internal carotid artery (ICA) and 17 common carotid artery (CCA) stenoses ranging from 8.5 to 100%. The smallest mean differences of the degree of stenosis in % between planimetry and arteriography were -0.5 and 0.6%. The narrowest 95 %-limits of agreement covered a range of +/-24.1 and 26.3% of stenoses, and the highest correlation coefficients were both 0.9 for the CC and ECST2 techniques, respectively. By eyeballing, the degree of stenosis was underestimated by 13.5 to 15.8% on average. The narrowest limits of agreement between two observers for eyeballing covered a range of 35%. CONCLUSION: Three-plane arteriography has only a moderate accuracy and reproducibility in detecting and measuring carotid artery stenosis independent of the technique of measurement used.

Aged↗
PubMed2005

Comparison of a 1-MHz and a 2-MHz probe for microembolus detection using transcranial Doppler ultrasound.

OBJECTIVES: Clinically silent microembolic signals (MES) can be detected by transcranial Doppler sonography (TCD). There is theoretical evidence that lower ultrasound emission frequencies may lead to a higher signal intensity and thus sensitivity to detect MES. We compared a 1-MHz probe with a 2-MHz probe regarding sensitivity in the detection of MES. Moreover, embolus detection by transcranial Doppler ultrasound is very time consuming and semi-automated detection is mandatory. Therefore, we studied an on-line algorithm using the bi-gate technique and the two transmission frequencies. METHODS: After defining detection thresholds of > or = 12 dB (1 MHz) and > or = 10 dB (2 MHz) with eight normal subjects as MES-negative controls, taking into account natural fluctuations of the Doppler spectrum, we studied 36 patients with ischaemic events and five asymptomatic patients with incidental embolic sources. All patients subsequently underwent a 1-hour unilateral embolus detection from the middle cerebral artery (MCA) or the posterior cerebral artery (PCA), respectively, using 1 and 2 MHz for 30 minutes each in a randomized order. The software algorithm was compared with a blinded off-line analysis by an experienced observer as a gold standard. RESULTS: The investigator detected 198 MES (range 0-41 MES) in the recordings of 29 patients out of the 41 patients using the 1-MHz probe and 101 MES (range 0-32 MES) in the recordings of 14 patients using the 2-MHz probe (p = 0.0007). Sensitivity of the software to detect MES confirmed by the investigator was 31% using 1 MHz and 41% using 2 MHz. The positive predictive value was 6 and 30%, respectively. DISCUSSION: The sensitivity and positive predictive values of the automated algorithm to detect MES were unacceptably low for clinical practice with both frequencies. The use of 1 MHz instead of 2 MHz may, however, be useful when evaluating the recordings off-line by an experienced blinded observer.

Adolescent↗
PubMed2004

Microembolic signal predicts recurrent cerebral ischemic events in acute stroke patients with middle cerebral artery stenosis.

BACKGROUND AND PURPOSE: Cerebral embolism is a common cause of stroke. Microembolic signals (MES) detected by transcranial Doppler represent ongoing embolisms, but the lack of reliable data about its clinical relevance hinders its widespread use in clinical practice. METHODS: We prospectively monitored 114 consecutive acute ischemic stroke patients with middle cerebral artery (MCA) stenosis for MES. The signals on digital audio tape were analyzed by an independent observer who was blinded to all other data. All patients were followed-up for the occurrence of recurrent stroke or transient ischemic attack (TIA) in the indexed MCA territory. RESULTS: MES was detected in 25 (22%) patients. The mean number of MES was 18 (range, 1 to 102). MES were more common in patients with severe stenosis (10/21, 48%) than in those with mild-moderate stenosis (4/26, 15%) (Pearson chi2 P=0.02). During follow-up for a mean of 13.6 months (range, 1 to 32), 12 (12%) patients had further ischemic events (10 strokes and 2 TIAs) in the affected MCA region during follow-up. Among these, 7 (58%) had recurred within 1 month (1 recurred within 1 week, the other 6 patients had recurrences in week 3 or 4 after discharge), 3 within 6 months, 1 within 6 to 12 months, and the remaining 1 recurred after 1 year. The presence of MES was the only predictor of a further ischemic stroke/TIA by Cox regression (adjusted odds ratio, 8.45; 95% CI, 1.69 to 42.22; P=0.01) even after controlling for age, sex, diabetes, hypertension, previous stroke, smoking, and acute treatment. CONCLUSIONS: In acute stroke patients with MCA stenosis, MES predicts further cerebral ischemia. This procedure should be considered as part of routine investigation and might identify a group of patients who are most likely to benefit from antithrombotic treatment.

Aged↗
PubMed2004

Solid or gaseous circulating brain emboli: are they separable by transcranial ultrasound?

High-intensity transient signals (HITS) detected by transcranial Doppler (TCD) ultrasound may correspond to artifacts or to microembolic signals, the latter being either solid or gaseous emboli. The goal of this study was to assess what can be achieved with an automatic signal processing system for artifact/microembolic signals and solid/gas differentiation in different clinical situations. The authors studied 3,428 HITS in vivo in a multicenter study, i.e., 1,608 artifacts in healthy subjects, 649 solid emboli in stroke patients with a carotid stenosis, and 1,171 gaseous emboli in stroke patients with patent foramen ovale. They worked with the dual-gate TCD combined to three types of statistical classifiers: binary decision trees (BDT), artificial neural networks (ANN), and support vector machines (SVM). The sensitivity and specificity to separate artifacts from microembolic signals by BDT reached was 94% and 97%, respectively. For the discrimination between solid and gaseous emboli, the classifier achieved a sensitivity and specificity of 81% and 81% for BDT, 84% and 84% for ANN, and 86% and 86% for SVM, respectively. The current results for artifact elimination and solid/gas differentiation are already useful to extract data for future prospective clinical studies.

Algorithms↗
PubMed2004

Platelets in patients with acute ischemic stroke are exhausted and refractory to thrombin, due to cleavage of the seven-transmembrane thrombin receptor (PAR-1).

Platelet activation is involved in the pathogenesis of cerebrovascular ischemia, but the major agonist involved has yet to be identified. To investigate the role of thrombin in platelet activation in patients with acute ischemic stroke, and while thrombin is the most likely candidate for activation of the thrombin receptor PAR-1 in vivo, we assessed its cleavage and internalization using the antibodies SPAN12, binding to uncleaved PAR-1, and WEDE15, recognizing cleaved and uncleaved, but not internalized PAR-1. In contrast to healthy age-matched controls, platelets from stroke patients exhibited significant cleavage and internalization of PAR-1 (P<0.001) and failed to respond to thrombin in vitro. Enhanced surface expression of CD62P, CD63, TSP-1 and less mepacrine uptake showed platelet degranulation during stroke. Platelets from patients with acute cerebral ischemia are exhausted and desensitized to thrombin through cleavage of PAR-1, indicating that high concentrations of thrombin occur with acute cerebrovascular ischemic events in vivo.

Acute Disease↗
PubMed2004

The identification of right-to-left shunts using contrast transcranial Doppler ultrasound: performance and interpretation modalities, and absence of a significant side difference of cardiac micro-emboli.

Cardiac and extracardiac right-to-left shunts can be identified by transesophageal echocardiography (TEE) as well as by transcranial Doppler ultrasound (TCD) using contrast agents that do not pass the lungs. Currently, the appropriate performance of a Valsalva manoeuvre (VM) to provoke the shunt, the use of different contrast agents and the classification of the TCD results are still under debate. In this study, we looked also at possible side effects of provoked cardiac micro-emboli in the left and right hemisphere. Seventy-one patients were investigated by both TEE and bilateral TCD of the middle cerebral arteries. The following protocol was applied in a randomized way: (1) Echovist-300 without VM; (2) Echovist-300, VM for 5 seconds starting 5 seconds after the beginning of contrast injection; (3) repetitive short VMs in between 2 and 13 seconds after the beginning of Echovist-300 injection; and (4) repetitive short VMs in between 2 and 13 seconds after the beginning of agitated saline injection. Only if one of the tests (2-4) was negative, this particular negative test was repeated. Use of Echovist-300, but not of saline yielded 100% sensitivity in the detection of TEE-proven shunts. The repetitive VM was slightly superior to the conventional VM. Introduction of a threshold of two or even three microbubbles produced less falsely positive TCD results in comparison to the TEE. There was no difference in microbubbles. TCD using Echovist-300 is a sensitive method to identify TEE-proven cardiac right-to-left shunts. Repetitive VM is an alternative to conventional VM.

Adult↗
PubMed2004

Clinical utility of echocontrast agents in neurosonology.

INTRODUCTION: Neurosonological investigations of the extracranial and intracranial brain supplying arteries are helpful in the assessment of stroke and stroke-prone patients. METHODS: In this paper we review the indications, application and advantages of second-generation (gas-filled) microbubble contrast agents such as SonoVue. RESULTS: Gas-filled microbubbles have a strong echo enhancing effect and produce enhancement for several minutes, enabling the sonographer to perform the investigation with a single injection or two or three repeated injections without the need for continuous administration. Echocontrast agents provide better delineation of normal blood flow, occlusions, pseudo-occlusions, stenoses, and collaterals in the extracranial and intracranial vascular beds. They are of particular value during transcranial color-coded transcranial duplex investigations via the temporal and occipital window. CONCLUSIONS: Echocontrast agents give additional information on the patient's vascular situation that is often crucial to planning further diagnostic and therapeutic steps. The use of second-generation gas-filled microbubbles, such as SonoVue in transcranial neurosonology, may help to avoid unnecessary, expensive and potentially harmful additional investigations such as intra-arterial DSA. Future applications include the visualization of brain tissue perfusion.

Cerebrovascular Disorders↗
PubMed2004

[Cerebral apoplexy--importance of diagnosis and therapy in acute stroke].

Every day occur about 4 strokes in the Grand-Duchy of Luxemburg. Stroke is the third cause of death and the first cause of acquired handicap. Stroke constitutes a major individual and social problem. Stroke and TIA are neurological emergency conditions that warrant immediate hospitalisation on a stroke unit, where a dedicated equipe of neurologists, nurses, speech and occupational therapists, physiotherapists and social workers in collaboration with other medical and surgical specialties provide up-to-date diagnostic and therapeutic measures. These include the diagnostic work-up of stroke aetiology and the vascular status, monitoring to ensure the maintenance of homeostasis, thrombolysis and revascularisation, antithrombotic drug treatment relying on individual stroke pathophysiology, treatment of risk factors and early rehabilitation. By treatment on a stroke unit, death and disability can be reduced by 27%, in the case of intravenous thrombolysis even by 45%.

Emergencies↗
PubMed2003

Right-to-left-shunts detected by transesophageal echocardiography and transcranial Doppler sonography.

BACKGROUND: Transesophageal echocardiography (TEE) and transcranial Doppler sonography (TCD) can identify right-to-left-shunts that predispose to paradoxical embolism. In a large cohort we compared the results of both techniques. METHODS: 222 patients were investigated by both techniques using the contrast agent Echovist-300 and performing each test once without and once with the Valsalva maneuver (VM). RESULTS: TEE-proven right-to-left-shunts were detected by TCD with a high sensitivity of 94%. In addition, TCD revealed shunts not noted during TEE in about 20% of all patients studied. These shunts are in general smaller than those concordantly identified; however, 9% of the patients without a TEE-proven shunt presented with a shunt that allows a considerable amount of contrast medium to pass. There were 12% more microbubbles detected in the right middle cerebral artery than in the left middle cerebral artery during the TCD test performed with VM, but not during the TCD test performed without VM. CONCLUSIONS: Contrast-enhanced TEE and TCD are complementary methods in the assessment of stroke and stroke-prone patients. The side difference of microbubbles may indicate a selective streaming of cardiac emboli during VM.

Adolescent↗
PubMed2003

Image quality of the temporal bone window examined by transcranial Doppler sonography and correlation with postmortem computed tomography measurements.

BACKGROUND AND PURPOSE: The major limitation of native transcranial colour-coded duplex sonography (TCCS) in older stroke patients is the relatively frequent occurrence of an insufficient temporal window. Our goal was to investigate the relationship between the in vivo Doppler ultrasound image quality of the temporal bone, and computed tomography (CT)-determined thickness, density, and homogeneity of cadaver temporal bone. METHODS: Thirty-three moribund neurological patients who eventually died were examined by TCCS using the transtemporal approach. The sonographer categorized the quality of the TCCS image (excellent, intermediate, and poor). During autopsy, a rectangular sample of the temporal squama was removed, which corresponded to the area of the in vivo acoustic window. The thickness of the whole temporal bone, cortical, and cancellous (= diploe) bone as well as the density and homogeneity were determined by high-resolution CT. RESULTS: Thirty-seven temporal bones were obtained. The quality of the acoustic window was classified as excellent in 13, intermediate in 6 and poor in 18 cases. A significant correlation between the complete bone thickness, as well as between the absolute thickness of the diploe and the quality of the acoustic window was found: the thinner the bone/diploe, the better the colour Doppler signal. The thickness of the cortical plates and the homogeneity of the bones were identical in the three image quality categories. CONCLUSION: The transtemporal TCCS image quality depends mainly on the thickness of the cancellous component of the temporal bone.

Adult↗
PubMed2003

On the origin of microembolic signals--a clinical and postmortem study.

BACKGROUND AND PURPOSE: Clinically silent circulating microembolic signals (MES) can be identified by transcranial Doppler ultrasound (TCD). It is not yet clear whether their occurrence is always linked to the presence of embolic sources. METHODS: 24 terminally ill patients (7 women, 17 men; mean age 68 years) were investigated by TCD of the middle cerebral arteries. These findings were correlated with a complete post-mortem examination of potential embolic pathways. RESULTS: Four patients out of the 24 under investigation showed MES, 2 of them bilaterally. All these 4 MES-positive patients had a definite embolic source, i. e. bilateral carotid artery occlusive disease, endocarditis with thrombotic valvular adhesions and severe plaques in the aortic arch, dilated left atrium and a patent foramen ovale, or severe plaques in the aortic arch and a dilated left atrium, respectively. CONCLUSION: In the investigated patient group, we could demonstrate that MES can only be found when an embolic source is present. The finding of MES justifies an extensive clinical and laboratory search for potential embolic sources including extracranial and intracranial colour-coded duplex ultrasound, ECG, Holter-ECG, and TEE.

Adult↗
PubMed2003

Does ultrasound contrast agent improve the diagnostic value of colour and power Doppler sonography in superficial lymph node enlargement?

OBJECTIVE: to analyse whether ultrasound contrast agent (UCA) improves the diagnostic accuracy to differentiate between benign and malignant superficial lymph node enlargement by using colour-coded duplex sonography (CCDS) and power Doppler (PD). METHODS: 32 patients with suspected malignant superficial lymph node enlargement prospectively underwent standardised ultrasound examinations using B-mode sonography and native and contrast-enhanced CCDS and PD immediately before biopsy. Solbiati-Index (longitudinal-transverse diameter ratio) and intranodal flow patterns by using different vascularisation types were assessed. Histological and sonographical findings were correlated. RESULTS: 27 malignant and 5 benign lymph nodes were found. Solbiati-Index was lower in malignant lymph nodes than in benign nodes (mean 1.5 vs. 2.4, P<0.045). More intranodal flow patterns could be detected after UCA (53 vs. 43) but the number of correctly identified malignant nodes decreased after UCA (26 vs. 24) and the number of correctly identified benign nodes remained constant compared with native CCDS and PD. In 31% of the colour-mode studies, PD was considered to visualise more clearly intranodal vascular flow patterns than CCDS. CONCLUSION: despite depicting more intranodal vascular patterns, the use of an ultrasound contrast agent seems not to improve the diagnostic value of CCDS and PD compared with native colour-mode studies in superficial lymph node enlargement.

Adolescent↗
PubMed2003

Reduction of circulating microemboli in the subclavian vein of patients undergoing haemodialysis using pre-filled instead of dry dialysers.

BACKGROUND: Chronic microembolization that can be demonstrated by pulsed Doppler ultrasound may give rise to pulmonary side-effects during haemodialysis by direct vessel obstruction, increased complement activation or platelet aggregation. The objective of the present investigation was to study whether the use of pre-filled instead of dry dialysers would help to minimize the number of microemboli. METHODS: The study cohort consisted of 23 patients undergoing maintenance haemodialysis. Using a 2 MHz pulsed ultrasound device, the subclavian vein downstream to the dialysis fistula was investigated for 10 min during the dialysis session. The ultrasound examination was performed twice during two successive dialysis sessions, using a pre-filled or a dry dialyser in randomized order. RESULTS: In all patients investigated, numerous microembolic signals (MES) could be observed in the subclavian vein. Treatment with pre-filled dialysers was associated with significantly less MES (82 +/- 94) as compared with dry dialysers (268 +/- 296; P = 0.002). CONCLUSIONS: In comparison to dry dialysers, the use of pre-filled dialysers leads to a significant reduction in microembolization, which may prevent repeated damage to the pulmonary vasculature and, thus, cause less pulmonary damage.

Adult↗