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McKenzie AJ, Doyle BJ, Aman ZM. Micromechanical Force Measurement of Clotted Blood Particle Cohesion: Understanding Thromboembolic Aggregation Mechanisms. Cardiovasc Eng Technol 2022; 13:816-828. [PMID: 35419664 PMCID: PMC9750917 DOI: 10.1007/s13239-022-00618-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 03/19/2022] [Indexed: 01/27/2023]
Abstract
PURPOSE Arterial shear forces may promote the embolization of clotted blood from the surface of thrombi, displacing particles that may occlude vasculature, with increased risk of physiological complications and mortality. Thromboemboli may also collide in vivo to form metastable aggregates that increase vessel occlusion likelihood. METHODS A micromechanical force (MMF) apparatus was modified for aqueous applications to study clot-liquid interfacial phenomena between clotted porcine blood particles suspended in modified continuous phases. The MMF measurement is based on visual observation of particle-particle separation, where Hooke's Law is applied to calculate separation force. This technique has previously been deployed to study solid-fluid interfacial phenomena in oil and gas pipelines, providing fundamental insight to cohesive and adhesive properties between solids in multiphase flow systems. RESULTS This manuscript introduces distributed inter-particle separation force properties as a function of governing physio-chemical parameters; pre-load (contact) force, contact time, and bulk phase chemical modification. In each experimental campaign, the hysteresis and distributed force properties were analysed, to derive insight as to the governing mechanism of cohesion between particles. Porcine serum, porcine albumin and pharmaceutical agents (alteplase, tranexamic acid and hydrolysed aspirin) reduced the measurement by an order of magnitude from the baseline measurement-the apparatus provides a platform to study how surface-active chemistries impact the solid-fluid interface. CONCLUSION These results provide new insight to potential mechanisms of macroscopic thromboembolic aggregation via particles cohering in the vascular system-data that can be directly applied to computational simulations to predict particle fate, better informing the mechanistic developments of embolic occlusion.
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Affiliation(s)
- Angus J. McKenzie
- grid.1012.20000 0004 1936 7910Department of Chemical Engineering, The Centre for Long Subsea Tiebacks, Fluid Science and Resources Cluster, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 Australia
| | - Barry J. Doyle
- grid.1012.20000 0004 1936 7910Vascular Engineering Laboratory, Harry Perkins Institute of Medical Research, Nedlands, and Centre for Medical Research, The University of Western Australia, Crawley, PER Australia ,Australian Research Council Centre for Personalised Therapeutics Technologies, Parkville, Australia ,grid.4305.20000 0004 1936 7988BHF Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK
| | - Zachary M. Aman
- grid.1012.20000 0004 1936 7910Department of Chemical Engineering, The Centre for Long Subsea Tiebacks, Fluid Science and Resources Cluster, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 Australia
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2
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Detection of Weak Doppler Microembolic Signature using Two-Dimensional-Adaptive Time-Frequency Threshold from Spectrogram. Biomed Signal Process Control 2020. [DOI: 10.1016/j.bspc.2019.101811] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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3
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Serbes G, Aydin N. Analysis of embolic signals with directional dual tree rational dilation wavelet transform. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2016:3821-3824. [PMID: 28269119 DOI: 10.1109/embc.2016.7591561] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The dyadic discrete wavelet transform (dyadic-DWT), which is based on fixed integer sampling factor, has been used before for processing piecewise smooth biomedical signals. However, the dyadic-DWT has poor frequency resolution due to the low-oscillatory nature of its wavelet bases and therefore, it is less effective in processing embolic signals (ESs). To process ESs more effectively, a wavelet transform having better frequency resolution than the dyadic-DWT is needed. Therefore, in this study two ESs, containing micro-emboli and artifact waveforms, are analyzed with the Directional Dual Tree Rational-Dilation Wavelet Transform (DDT-RADWT). The DDT-RADWT, which can be directly applied to quadrature signals, is based on rational dilation factors and has adjustable frequency resolution. The analyses are done for both low and high Q-factors. It is proved that, when high Q-factor filters are employed in the DDT-RADWT, clearer representations of ESs can be attained in decomposed sub-bands and artifacts can be successfully separated.
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4
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An emboli detection system based on Dual Tree Complex Wavelet Transform and ensemble learning. Appl Soft Comput 2015. [DOI: 10.1016/j.asoc.2015.08.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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5
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Banahan C, Rogerson Z, Rousseau C, Ramnarine KV, Evans DH, Chung EML. An in vitro comparison of embolus differentiation techniques for clinically significant macroemboli: dual-frequency technique versus frequency modulation method. ULTRASOUND IN MEDICINE & BIOLOGY 2014; 40:2642-2654. [PMID: 25218455 PMCID: PMC4195753 DOI: 10.1016/j.ultrasmedbio.2014.06.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 05/12/2014] [Accepted: 06/03/2014] [Indexed: 06/03/2023]
Abstract
The ability to distinguish harmful solid cerebral emboli from gas bubbles intra-operatively has potential to direct interventions to reduce the risk of brain injury. In this in vitro study, two embolus discrimination techniques, dual-frequency (DF) and frequency modulation (FM) methods, are simultaneously compared to assess discrimination of potentially harmful large pieces of carotid plaque debris (0.5-1.55 mm) and thrombus-mimicking material (0.5-2 mm) from gas bubbles (0.01-2.5 mm). Detection of plaque and thrombus-mimic using the DF technique yielded disappointing results, with four out of five particles being misclassified (sensitivity: 18%; specificity: 89%). Although the FM method offered improved sensitivity, a higher number of false positives were observed (sensitivity: 72%; specificity: 50%). Optimum differentiation was achieved using the difference between peak embolus/blood ratio and mean embolus/blood ratio (sensitivity: 77%; specificity: 81%). We conclude that existing DF and FM techniques are unable to confidently distinguish large solid emboli from small gas bubbles (<50 μm).
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Affiliation(s)
- Caroline Banahan
- Medical Physics Department, University Hospitals of Leicester NHS Trust, Leicester, UK.
| | - Zach Rogerson
- Department of Physics, University of Leicester, Leicester, UK
| | - Clément Rousseau
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | | | - David H Evans
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
| | - Emma M L Chung
- Department of Cardiovascular Sciences, University of Leicester, Leicester, UK
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6
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Denoising performance of modified dual-tree complex wavelet transform for processing quadrature embolic Doppler signals. Med Biol Eng Comput 2013; 52:29-43. [DOI: 10.1007/s11517-013-1114-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Accepted: 09/01/2013] [Indexed: 10/26/2022]
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7
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Gonçalves IB, Leiria A, Moura MMM. STFT or CWT for the detection of Doppler ultrasound embolic signals. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2013; 29:964-976. [PMID: 23576393 DOI: 10.1002/cnm.2546] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2012] [Revised: 01/24/2013] [Accepted: 01/30/2013] [Indexed: 06/02/2023]
Abstract
Aiming reliable detection and localization of cerebral blood flow and emboli, embolic signals were added to simulated middle cerebral artery Doppler signals and analysed. Short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used in the evaluation. The following parameters were used in this study: the powers of the embolic signals added were 5, 6, 6.5, 7, 7.5, 8 and 9 dB; the mother wavelets for CWT analysis were Morlet, Mexican hat, Meyer, Gaussian (order 4) and Daubechies (orders 4 and 8); and the thresholds for detection (equated in terms of false positive, false negative and sensitivity) were 2 and 3.5 dB for the CWT and STFT, respectively. The results indicate that although the STFT allows accurately detecting emboli, better time localization can be achieved with the CWT. Among the CWT, the current best overall results were obtained with Mexican Hat mother wavelet, with optimal results for sensitivity (100% detection rate) for nearly all emboli power values studied.
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Affiliation(s)
- Ivo B Gonçalves
- DEEI/FCT, Universidade do Algarve, Campus de Gambelas 8005-139 Faro, Portugal
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8
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Anzola GP, Costa A, Magoni M, Guindani M, Cobelli M. Transcranial Doppler monitoring of cerebral embolism in atrial fibrillation and prosthetic valves. Clinical correlations. Eur J Neurol 2011; 2:566-9. [DOI: 10.1111/j.1468-1331.1995.tb00175.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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9
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Işik H, Arslan S. An Artificial Neural Network classification approach for use the ultrasound in physiotherapy. J Med Syst 2010; 35:1333-41. [PMID: 20703780 DOI: 10.1007/s10916-009-9410-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2009] [Accepted: 11/20/2009] [Indexed: 11/24/2022]
Abstract
In this study, a classification to be used in physiotherapy was realized by means of Artificial Neural Network (ANN). The aim of the classification was to determine the treatment length and appropriate ultrasound value for the age of physiotherapy patients, the area on which ultrasound will be applied, the fat rate in tissue and related factors. For this purpose, the patient information obtained from Selçuk University, Meram School of Medicine Hospital, Physiotherapy Department was used. In order to identify the appropriate ultrasound value and treatment length for the patient, the ultrasound therapy device realized with ANN was placed together in an embedded system. The results obtained by means of the designed and realized embedded system were compared with data gathered from an expert. As a result, the data obtained from the designed system were found out to be in line with the existing data.
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Affiliation(s)
- Hakan Işik
- Department of Electronic and Computer Education, Selcuk University, Konya, Turkey.
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10
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Discrimination of Types of Venous Emboli Using Doppler Ultrasound. Ann Vasc Surg 2010; 24:721-7. [DOI: 10.1016/j.avsg.2010.03.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 01/25/2010] [Accepted: 03/01/2010] [Indexed: 11/24/2022]
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11
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Voss A, Bahrmann P, Schröder R, Wagner M, Werner GS, Figulla HR. Automatic Detection of Microemboli During Percutaneous Coronary Interventions. Ann Biomed Eng 2007; 35:2087-94. [PMID: 17899377 DOI: 10.1007/s10439-007-9386-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Accepted: 09/18/2007] [Indexed: 10/22/2022]
Abstract
The objective of this study was to develop an analysis method for the automatic detection of intracoronary microemboli triggered high intensity signals (HITS) during percutaneous coronary interventions (PCI). The recorded ultrasonic Doppler velocity spectra from an intracoronary ultrasonic guide-wire were decomposed into 13 wavelet scales applying the continuous wavelet transform. From 7 wavelet scales which were most suitable for a differentiation between HITS and pulsatile flow, envelopes were calculated and combined to improve the HITS-to-background noise ratio. For different intensity thresholds the resulting number of HITS was automatically counted and compared with the number estimated by experienced observers. In a first validation trial HITS were detected within a simplified in vitro model with a sensitivity of 89.2% and a positive predictive value of 87.6%. In a following clinical study 211 HITS from 18 patients during PCI were counted manually by the observers. With the developed wavelet-based method 189 HITS were correctly detected (sensitivity of 89.6%, positive predictive value of 85.5%). The introduced new method automatically detects intracoronary HITS for the first time with a reliable accuracy. This may support further studies evaluating the incidence and consequences of coronary microembolization during coronary interventions.
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Affiliation(s)
- Andreas Voss
- Department of Medical Engineering and Biotechnology, University of Applied Sciences Jena, Carl-Zeiss-Promenade 2, 07745, Jena, Germany.
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12
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Fan L, Boni E, Tortoli P, Evans DH. Multigate transcranial Doppler ultrasound system with real-time embolic signal identification and archival. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2006; 53:1853-61. [PMID: 17036793 DOI: 10.1109/tuffc.2006.117] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
An integrated system for acquisition and processing of intracranial and extracranial Doppler signals and automatic embolic signal detection has been developed. The hardware basis of the system is a purpose-built acquisition/processing board that includes a multigate Doppler unit controlled through a computer. The signal-processing engine of the system contains a fast Fourier transform (FFT)-based, spectral-analysis unit and an embolic signal-detection unit using expert system reasoning theory. The system is designed so that up to four receive gates from a single transducer can be used to provide useful reasoning information to the embolic signal-detection unit. Alternatively, two transducers can be used simultaneously, either for bilateral transcranial Doppler (TCD) investigations or for simultaneous intra- and extracranial investigation of different arteries. The structure of the software will allow the future implementation of embolus detection algorithms that use the information from all four channels when a single transducer is used, or of independent embolus detection in two sets of two channels when two transducers are used. The user-friendly system has been tested in-vitro, and it has demonstrated a 93.6% sensitivity for micro-embolic signal (MES) identification. Preliminary in-vivo results also are encouraging.
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Affiliation(s)
- Lingke Fan
- Medical Physics Group, Department of Cardiovascular Sciences, University of Leicester, Leicester, UK.
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13
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Chappell MA, Payne SJ. A method for the automated detection of venous gas bubbles in humans using empirical mode decomposition. Ann Biomed Eng 2006; 33:1411-21. [PMID: 16240089 DOI: 10.1007/s10439-005-6045-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Accepted: 05/20/2005] [Indexed: 11/29/2022]
Abstract
Doppler ultrasound signals are widely used to grade the quantity of circulating venous bubbles in divers. Current techniques rely on trained observers, making the grading process both time-consuming and subjective. The automated detection of bubbles, however, is confounded by the presence of other signals, primarily those arising from blood motion. Empirical Mode Decomposition was used here to calculate the intrinsic mode functions (IMFs) of a number of Doppler ultrasound signals from recreational divers, post-decompression. The IMFs provide a basis set for signal decomposition, each IMF corresponding to a different timescale in the signal. Each signal was found to comprise approximately 20 IMFs: the precise number being dependent upon the nature of the signal. A method is presented to detect bubbles using the IMF; features are first identified in the individual heart cycles, these having been previously determined using a robust peak detection method, by examining deviations from the ensemble averaged IMF. Bubbles are then identified as features appearing in more than one IMF, with significant energy in the original signal. This method has been applied to a subset of the available database and appears to perform with good sensitivity even when the signal has variable signal strength.
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Affiliation(s)
- M A Chappell
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
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Hudorović N. Clinical significance of microembolus detection by transcranial Doppler sonography in cardiovascular clinical conditions. Int J Surg 2006; 4:232-41. [PMID: 17462357 DOI: 10.1016/j.ijsu.2005.12.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2005] [Revised: 12/11/2005] [Accepted: 12/13/2005] [Indexed: 11/30/2022]
Abstract
Transcranial Doppler can detect microembolic signals, which are characterized by unidirectional high intensity increase, short duration, and random occurrence, producing a "whistling" sound. Microembolic signals have been proven to represent solid or gaseous particles within the blood flow. Microemboli have been detected in a number of clinical cardiovascular settings: carotid artery stenosis, aortic arch plaques, atrial fibrillation, myocardial infarction, prosthetic heart valves, patent foramen ovale, valvular stenosis, during invasive procedures (angiography, percutaneous transluminal angioplasty) and surgery (carotid, cardiopulmonary bypass). Despite numerous studies performed so far, clinical significance of microembolic signals is still unclear. This article provides an overview of the development and current state of technical and clinical aspects of microembolus detection.
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Affiliation(s)
- Narcis Hudorović
- University Department of Vascular and Endovascular Surgery, University Hospital Sestre Milosrdnice, 10000 Zagreb, Vinogradska 29, Croatia.
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15
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Aydin N, Marvasti F, Markus HS. Embolic Doppler Ultrasound Signal Detection Using Discrete Wavelet Transform. ACTA ACUST UNITED AC 2004; 8:182-90. [PMID: 15217263 DOI: 10.1109/titb.2004.828882] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Asymptomatic circulating emboli can be detected by Doppler ultrasound. Embolic Doppler ultrasound signals are short duration transient like signals. The wavelet transform is an ideal method for analysis and detection of such signals by optimizing time-frequency resolution. We propose a detection system based on the discrete wavelet transform (DWT) and study some parameters, which might be useful for describing embolic signals (ES). We used a fast DWT algorithm based on the Daubechies eighth-order wavelet filters with eight scales. In order to evaluate feasibility of the DWT of ES, two independent data sets, each comprising of short segments containing an ES (N = 100), artifact (N = 100) or Doppler speckle (DS) (N = 100), were used. After applying the DWT to the data, several parameters were evaluated. The threshold values used for both data sets were optimized using the first data set. While the DWT coefficients resulting from artifacts dominantly appear at the higher scales (five, six, seven, and eight), the DWT coefficients at the lower scales (one, two, three, and four) are mainly dominated by ES and DS. The DWT is able to filter out most of the artifacts inherently during the transform process. For the first data set, 98 out of 100 ES were detected as ES. For the second data set, 95 out of 100 ES were detected as ES when the same threshold values were used. The algorithm was also tested with a third data set comprising 202 normal ES; 198 signals were detected as ES.
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Affiliation(s)
- Nizamettin Aydin
- School of Engineering and Electronic, The University of Edinburgh, Edinburgh EH9 3JL, UK.
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16
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Chapter 6 Large-Vessel Atherosclerosis. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/s1877-3419(09)70081-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Dittrich R, Ritter MA, Droste DW. Microembolus detection by transcranial doppler sonography. EUROPEAN JOURNAL OF ULTRASOUND : OFFICIAL JOURNAL OF THE EUROPEAN FEDERATION OF SOCIETIES FOR ULTRASOUND IN MEDICINE AND BIOLOGY 2002; 16:21-30. [PMID: 12470847 DOI: 10.1016/s0929-8266(02)00046-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Microembolic signals can be detected by transcranial ultrasound as signals of high intensity and short duration. These signals represent circulating gaseous or solid particles. To optimize the differentiation from artefacts and the background signal and to facilitate the clinical use, several attempts have been made to automatize the detection of microemboli. Microemboli occur spontaneously in various clinical situations but their clinical impact and possible therapeutical implications are still under debate. This article provides a review of the actual literature concerning the current state of technical and clinical aspects of microembolus detection.
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Affiliation(s)
- Ralf Dittrich
- Klinik und Poliklinik für Neurologie, Universitätsklinikum Münster, Albert-Schweitzer-Str 33, D-48129, Münster, Germany.
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El-Brawany MA, Nassiri DK. Microemboli detection using ultrasound backscatter. ULTRASOUND IN MEDICINE & BIOLOGY 2002; 28:1439-1446. [PMID: 12498939 DOI: 10.1016/s0301-5629(02)00547-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Microemboli detection and characterisation have recently received great attention due to its clinical importance in the management of cerebrovascular disease. The new method presented in this paper is directly based on the idea that the ultrasound (US) backscattered signal from flowing blood is chaotic (El-Brawany and Nassiri 2002). The detection technique involves building a nonlinear model of the deterministic characteristics of the chaotic backscatter signal from blood, and the use of this model to look at the prediction error as a primary decision-making criterion for the microemboli detector. A complementary feature to the prediction error, namely, the degree of coherence between the US excitation pulse and the prediction error signal is used to enhance the detection process. The detector has been built using a feed-forward neural network with error back-propagation. The detection technique is tested successfully using a vascular flow phantom with solid spheres and bubbles of known sizes introduced in the flow circuit to mimic solid and gaseous emboli. Receiver operating characteristic (ROC) curve is used to assess the performance of the detection process. The total classification rate ranges from 88% to 96%.
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Affiliation(s)
- Mohamed A El-Brawany
- Department of Medical Physics and Bioengineering, St. George's Hospital, Blackshaw Road, London, UK
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19
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Rollé F, Pengloan J, Abazza M, Halimi JM, Laskar M, Pourcelot L, Tranquart F. Identification of microemboli during haemodialysis using Doppler ultrasound. Nephrol Dial Transplant 2000; 15:1420-4. [PMID: 10978401 DOI: 10.1093/ndt/15.9.1420] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND Doppler ultrasound methods were used during haemodialysis sessions for the detection of microemboli and determination of their origin. METHODS A 2-MHz ultrasound probe (Multidop X(4) DWL((TM))) was used to assess the number of microembolic signals (MES) in the subclavian vein downstream from the arteriovenous fistula before the dialysis session and over two periods of 15 min at the beginning and end of haemodialysis sessions in 25 patients without previous cardiovascular disease. A similar probe was used during in vitro studies to detect MES at different sites in the dialysis machine (before and downstream from the blood pump, and before and downstream from the air trap). RESULTS No MES were detected during in vivo studies before haemodialysis sessions. MES were registered in all patients (100%) at the beginning and end of the haemodialysis procedure at an average of 12.7+/-9 and 16. 7+/-11.5 signals/min respectively. The average intensity of MES was 19.2+/-5.0 dB and 19.4+/-3.9 dB respectively. No MES were detected on the arterial line during in vitro studies. In contrast, 19+/-6 MES/min were detected after the blood pump, 13+/-4.2 before the air trap, and 16.5+/-5.5 thereafter. CONCLUSIONS In all patients, MES were recorded during haemodialysis sessions in the drainage vein from arteriovenous fistulae. The results of in vitro studies indicate that MES are formed by the blood pump of the haemodialysis machine. The intensity of the MES suggests that they correspond to synthetic particles or microbubbles, which are not detected by the air trap. The final destination of these microbubbles will be assessed in further studies.
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Affiliation(s)
- F Rollé
- Department of Cardiovascular Surgery of Limoges University Hospital, Limoges, France
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Abstract
Transcranial Doppler ultrasound allows noninvasive monitoring of the large intracranial vessels. Microembolic signals (MES) have been observed under a variety of circumstances, especially in symptomatic carotid stenosis, high-risk cardiac conditions, and surgical procedures (such as carotid endarterectomy and cardiopulmonary bypass surgery). Technical considerations have presented numerous challenges to the interpretation of these signals, many of which appear to represent small emboli traveling in the blood flow. The technical aspects of these MES are discussed and their significance in relation to cerebral ischemia and its prevention are examined in some detail.
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Affiliation(s)
- M Gorman
- Department of Neurology, Wayne State University, Detroit, MI, USA.
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Telman G, Reisner SA, Sprecher E, Hemli JA, Yarnitsky D. Monitoring of the extracranial and intracranial course of single emboli of cardiac origin: a preliminary report. J Neuroimaging 1999; 9:238-40. [PMID: 10540606 DOI: 10.1111/jon199994238] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Simultaneous monitoring of emboli in extracranial and intracranial arteries recorded with identical probes, in a patient with an artificial cardiac valve, allowed the identification and characterization of pairs of signals, which most likely represent single emboli flowing through the common carotid artery into the middle cerebral artery. This technique offers new insight into emboligenesis with obvious therapeutic implications.
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Affiliation(s)
- G Telman
- Department of Neurology, Rambam Medical Center, Haifa, Israel
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22
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Markus HS, Reid G. Frequency filtering improves ultrasonic embolic signal detection. ULTRASOUND IN MEDICINE & BIOLOGY 1999; 25:857-860. [PMID: 10414903 DOI: 10.1016/s0301-5629(99)00029-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Problems in detection of Doppler cerebral embolic signals primarily occur for embolic signals of low relative intensity. A characteristic feature of embolic signals is that the intensity increase is maximal over a narrow frequency band. Therefore, frequency filtering of the data might improve embolic signal relative intensity and detectability. We implemented an off-line finite impulse response filter in software running on a commercially available transcranial Doppler system, using the time-domain audio data as input. The range of the filter was chosen by placing a box around the embolic signal on the spectral display. One hundred consecutive embolic signals from patients with carotid stenosis were analyzed; all had been recorded by a bigate system and the signal was analyzed in both proximal and distal channels. There was a highly significant increase in embolic signal relative intensity following frequency filtering; mean (SD) proximal channel prefiltering 12.75 (4.83) dB, postfiltering 16.36 (4.93) dB; distal channel prefiltering 13.42 (4.98) dB, postfiltering 16.60 (5.11) dB, for both p < 0.001. Despite all embolic signals being audible and visible in at least one channel on the frequency spectral display, in 17 cases, the amplitude increase associated with the embolic signal could not be clearly seen in time-domain data of one or both channels prior to filtering. Following frequency filtering, this was reduced to 5. Incorporation of such a frequency-filtering approach to an online system is likely to improve the sensitivity of online detection for embolic signals of low relative intensity.
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Affiliation(s)
- H S Markus
- Department of Clinical Neurosciences, King's College School of Medicine and Dentistry, London, UK.
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Roy E, Montrésor S, Abraham P, Saumet JL. Spectrogram analysis of arterial Doppler signals for off-line automated hits detection. ULTRASOUND IN MEDICINE & BIOLOGY 1999; 25:349-359. [PMID: 10374979 DOI: 10.1016/s0301-5629(98)00173-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recently, a time processing of arterial Doppler signals was proposed to detect automatically high-intensity transient signals (HITS). This technique provided satisfactory detection results, but was not always constantly accurate, particularly with high-resistance blood velocity profiles. A time-frequency processing, based on the spectrogram, is presented to detect the presence of emboli in the arterial Doppler signals. The method uses the narrow-band hypothesis and extracts the detection criterion from the time-frequency representation (TFR). A first database of 560 peripheral arterial Doppler HITS was created to study microemboli and to define the normal limits to be used in our method. A threshold was experimentally defined using this database, and then applied to 38 recordings from 12 patients. Using another database, 6 human expert Doppler users reported 140, 176, 155, 161, 161 and 146 HITS, corresponding to a total of 197 different observed HITS. When an event was detected by at least 6, 5, 4, 3, 2 and 1 of the observers, sensitivity of the automatic detection was 93.9, 91.7, 89.6, 88.7, 84.7 and 73.1%, respectively. The sensitivity of our automatic detection is, thus, highly associated with the number of observers in agreement. A preliminary experiment has been performed to test the method in the case of long recording duration. In 15 patients, 6 h 24 min of recordings have been analyzed. The proposed automated processing provided an overall sensibility of 91.5%. The present work shows that this detection scheme preserves good sensibility and improves the positive predictive value compared with the time-processing recently proposed.
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Affiliation(s)
- E Roy
- Laboratoire d'Informatique de l'Université du Maine, Le Mans, France
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24
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Ringelstein EB, Droste DW, Babikian VL, Evans DH, Grosset DG, Kaps M, Markus HS, Russell D, Siebler M. Consensus on microembolus detection by TCD. International Consensus Group on Microembolus Detection. Stroke 1998; 29:725-9. [PMID: 9506619 DOI: 10.1161/01.str.29.3.725] [Citation(s) in RCA: 359] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Transcranial Doppler ultrasound is capable of detecting microembolic material, both gaseous and solid, within the intracranial cerebral arteries. To avoid discrediting this promising and exciting new technique, experts in this field met in January 1997 in Frankfurt, Germany, to discuss the limitations and problems of embolus detection and to determine guidelines for its proper use in clinical practice, as well as in scientific investigations. In particular, the authors suggest that studies report the following parameters: (1) ultrasound device, (2) transducer type and size, (3) insonated artery, (4) insonation depth, (5) algorithms for signal intensity measurement, (6) scale settings, (7) detection threshold, (8) axial extension of sample volume, (9) fast Fourier transform (FFT) size (number of points used), (10) FFT length (time), (11) FFT overlap, (12) transmitted ultrasound frequency, (13) high-pass filter settings, and (14) recording time. There was agreement that no current system of automatic embolus detection has the required sensitivity and specificity for clinical use.
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25
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Roy E, Abraham P, Montrésor S, Baudry M, Saumet JL. The narrow band hypothesis: an interesting approach for high-intensity transient signals (HITS) detection. ULTRASOUND IN MEDICINE & BIOLOGY 1998; 24:375-382. [PMID: 9587992 DOI: 10.1016/s0301-5629(97)00279-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We propose a new approach to detect microemboli automatically using the narrow band hypothesis. An initial database of 560 peripheral arterial Doppler high-intensity transient signals (HITS) was created to study microemboli and to define the normal limits to be used in our method. When a HITS occurs, our approach consists of modelling the Doppler signal using amplitude and frequency wave modulation. A threshold was defined experimentally using this database and then applied to 38 recordings from 12 patients. Using another database, six expert Doppler users reported 140, 176, 155, 161, 161 and 146 HITS, corresponding to a total of 197 different observed HITS. When an event was detected by 6, 5, 4, 3, 2 and 1 of the observers, the sensitivity of the automatic detection was 94.8%, 75.9%, 55.6%, 42.9%, 30% and 0%, respectively. The sensitivity of our automatic detection thus is highly associated with the likelihood (defined as the ratio of observers in agreement to the total number of observers) of an event: r = 0.99 for p < 0.0001. Although future research would result in improvement of the specificity, the narrow band hypothesis appears to be a promising technique for the detection of HITS.
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Affiliation(s)
- E Roy
- Laboratoire de Physiologie et d'Explorations Fonctionnelles Vasculaires, Centre Hospitalier Universitaire, Angers, France
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26
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Droste DW, Ringelstein EB. Detection of high intensity transient signals (HITS): how and why? EUROPEAN JOURNAL OF ULTRASOUND : OFFICIAL JOURNAL OF THE EUROPEAN FEDERATION OF SOCIETIES FOR ULTRASOUND IN MEDICINE AND BIOLOGY 1998; 7:23-9. [PMID: 9614287 DOI: 10.1016/s0929-8266(98)00010-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
HITS (high intensity transient signals) in transcranial Doppler recordings reflect either microemboli, both gaseous and solid, or artefacts. Various frequencies in number of microembolic signals (MES) have been reported in the same clinical condition. A possible explanation for these discrepancies may be different device settings and algorithms for embolus detection. For reproducibility of data, we suggest that studies on MES report the following parameters: (1) Ultrasound device; (2) transducer type; (3) insonated artery; (4) insonation depth; (5) algorithms for signal intensity measurement; (6) scale settings; (7) detection threshold; (8) axial extension of sample volume; (9) fast Fourier transform (FFT) size (number of points used); (10) FFT length (time); (11) FFT overlap; (12) transmitted ultrasound frequency; (13) high pass filter settings; and (14) recording time. No current system of automatic embolus detection has the full sensitivity and specificity required for clinical use. Therefore, each of the signals detected by these devices needs to be checked and verified by an experienced investigator. MES will help to identify the site and activity of the embolizing lesion. Microembolus detection might reduce the observation time and the number of patients needed to perform interventional trials. First, however, MES needs to be validated as a meaningful prognostic parameter. Microemboli originating from prosthetic cardiac valves are mainly gaseous. Therefore, they cannot serve as an indicator of the valves thromboembolic activity or the patient's stroke risk.
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Affiliation(s)
- D W Droste
- Klinik und Poliklinik für Neurologie der WWU Münster, Albert-Schweitzer-Str. 33, D-48129 Münster, Germany
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27
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Van Zuilen EV, Van Gijn J, Ackerstaff RG. The clinical relevance of cerebral microemboli detection by transcranial Doppler ultrasound. J Neuroimaging 1998; 8:32-7. [PMID: 9442588 DOI: 10.1111/jon19988132] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Affiliation(s)
- E V Van Zuilen
- Department of Clinical Neurophysiology, St. Antonius Hospital, Nieuwegein, The Netherlands
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28
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Gossetti B, Martinelli O, Guerricchio R, Irace L, Benedetti-Valentini F. Transcranial Doppler in 178 patients before, during, and after carotid endarterectomy. J Neuroimaging 1997; 7:213-6. [PMID: 9344002 DOI: 10.1111/jon199774213] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
From July 1991 to March 1995, 178 patients who underwent 198 carotid surgical repairs were investigated preoperatively, intraoperatively, and postoperatively by transcranial Doppler sonography (TCD). Preoperative TCD evaluation showed stenosis of the middle cerebral artery (MCA) in 4 patients (2.2%), siphon stenosis in 3 (1.6%), incomplete circle of Willis in 23 (12.9%), a decrease of mean blood flow velocity more than 70% of the basal value during digital common carotid compression in 31 (17.9%), and a critical reduction of vasomotor reactivity (no significant increase of mean blood flow velocity in the MCA during breath-holding test) in 34 (19.1%). Nine patients (5%) had surgery without preoperative angiography. In those patients the indication for surgery was based on color Doppler imaging and TCD investigations. Ninety surgical procedures were carried out under general anesthesia and 188 under locoregional anesthesia. In 37 surgeries (31.7%) a shunt was inserted. The use of a shunt was based on a decrease of mean blood flow velocity in the MCA below 50% of the basal value under general anesthesia or loss of consciousness combined with a decrease of mean blood flow velocity in the MCA higher than 70% of the basal value when locoregional anesthesia was employed. Intraoperative TCD monitoring showed a decrease of mean blood flow velocity in the MCA due to shunt malfunction in (8.3%) of 36 surgeries, turbulence of blood flow during declamping in 79 procedures (39.8%), and microembolic events in 10 patients (5%) that were related to one transient and one permanent neurological deficit. Another permanent deficit occurred in a patient without TCD signs. After surgery, TCD reliably detected an early asymptomatic occlusion of the carotid artery, hyperperfusion syndrome in 12 (6.0%), and an increase of vasomotor reactivity in 10 (29.4%) of 34 surgeries.
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MESH Headings
- Anesthesia, Conduction
- Anesthesia, General
- Apnea/physiopathology
- Arterial Occlusive Diseases/diagnostic imaging
- Arterial Occlusive Diseases/surgery
- Arteriovenous Shunt, Surgical
- Blood Flow Velocity
- Carotid Artery, Common/diagnostic imaging
- Carotid Stenosis/diagnostic imaging
- Carotid Stenosis/etiology
- Cerebral Angiography
- Cerebral Arterial Diseases/diagnostic imaging
- Cerebral Arterial Diseases/surgery
- Cerebral Arteries/diagnostic imaging
- Cerebrovascular Circulation
- Circle of Willis/diagnostic imaging
- Circle of Willis/surgery
- Constriction, Pathologic/diagnostic imaging
- Constriction, Pathologic/surgery
- Endarterectomy, Carotid
- Hemorheology
- Humans
- Intracranial Embolism and Thrombosis/diagnostic imaging
- Intracranial Embolism and Thrombosis/etiology
- Ischemic Attack, Transient/diagnostic imaging
- Ischemic Attack, Transient/surgery
- Monitoring, Intraoperative
- Neurologic Examination
- Postoperative Care
- Reproducibility of Results
- Ultrasonography, Doppler, Color
- Ultrasonography, Doppler, Transcranial
- Vasomotor System/diagnostic imaging
- Vasomotor System/physiopathology
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Affiliation(s)
- B Gossetti
- 2nd Chair of Vascular Surgery, La Sapienza University of Roma, Italy
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29
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Detection of Embolic Signals during and after Percutaneous Transluminal Angioplasty of Subclavian and Vertebral Arteries Using Transcranial Doppler Ultrasonography. Neurosurgery 1997. [DOI: 10.1097/00006123-199709000-00005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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30
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Sawada M, Hashimoto N, Nishi S, Akiyama Y. Detection of Embolic Signals during and after Percutaneous Transluminal Angioplasty of Subclavian and Vertebral Arteries Using Transcranial Doppler Ultrasonography. Neurosurgery 1997. [DOI: 10.1227/00006123-199709000-00005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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31
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Abstract
Abnormal high intensity transient signals detectable with transcranial Doppler (TCD) sonography have been associated with formed cerebral microembolism. Using long-term TCD monitoring, these clinically silent microembolic events can be observed in patients with cerebrovascular disease. Downstream of high grade internal carotid artery (ICA) stenosis, they occur significantly more frequently in neurologically symptomatic than in asymptomatic patients. Although the occurrence of microemboli is random, the individual rate underlies circadian fluctuations and seems to decline within the first weeks after an ischemic event. Pathoanatomic work suggests that luminal ulcer and thrombosis of the stenosed ICA are the major sources of microemboli. Thus, by tapping into an important pathomechanism, the detection of clinically silent cerebral microembolism appears to provide paraclinical evidence of "unstable carotid artery disease" and may help to evaluate more specific treatment strategies. (ECHOCARDIOGRAPHY, Volume 13, September 1996)
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Affiliation(s)
- Mario Siebler
- Department of Neurology, Heinrich-Heine-University, Moorenstrasse 5, P.O. Box 101007, D-40001 Düsseldorf, Germany
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32
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Abstract
Doppler detection of venous and arterial gas emboli has been recognized since 1968. The technology has been applied using 5-MHz ultrasound to study decompression sickness and monitor cardiopulmonary bypass and intracranial surgery. Since the advent of transcranial Doppler, which requires the use of lower ultrasonic carrier frequencies to penetrate the temporal bone, the detection of particulates moving in the bloodstream has been available. Using 2 MHz, microembolic signals have been detected in a variety of clinical situations, including cardiac conditions known to have high probabilities to produce embolic stroke. The basic features of a Doppler embolic signal have been clarified, and many investigators are applying the technology to determine the clinical significance of the detected emboli and their use in diagnosis and medical and surgical treatments. The basis for automatic sizing, counting, and characterizing the emboli is under development. The applications of Doppler detection of emboli will range from diagnosis and localization of embolic sources to improvement in surgical techniques and adjustments in medical treatments. (ECHOCARDIOGRAPHY, Volume 13, September 1996)
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Affiliation(s)
- Merrill P. Spencer
- Institute of Applied Physiology and Medicine, 701 16th Ave., Seattle, WA 98122
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33
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Georgiadis D, Goeke J, Hill M, König M, Nabavi DG, Stögbauer F, Zunker P, Ringelstein EB. A novel technique for identification of doppler microembolic signals based on the coincidence method: in vitro and in vivo evaluation. Stroke 1996; 27:683-6. [PMID: 8614930 DOI: 10.1161/01.str.27.4.683] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND AND PURPOSE The applicability of a novel differentiation technique in embolus detection based on the coincidence principle and using a multigate probe was evaluated in this study. METHODS According to the coincidence method, high-intensity transients should only be classified as microembolic signals if they appear sequentially in the two sample volumes monitored and within a defined time window calculated from the blood velocity and the spatial distance between the insonation depths. Part A: microbubbles were introduced in a continuous flow bench model of the middle cerebral artery to evaluate the accuracy of the multigate probe in embolus detection. Part B: in the subjects and patients, the minimal and maximum time delays in the appearance of microembolic signals in the two middle cerebral artery sample volumes were calculated as 0.01 second and set at 0.1 second, respectively. The multigate probe was used to monitor (1) 5 normal volunteers in whom 1008 artifact signals were produced,(2) 2 patients undergoing aortic valve replacement surgery, and (3) 12 patients with potential cardiac or carotid embolic sources. RESULTS In the bench model, 95.5% of microembolic signals produced by microbubbles appeared in the two sample volumes with a time delay between 0.02 and 0.05 second, while in the remaining 4.5% a shorter passage time of 0.01 second was measured. A total of 1968 high-intensity signals were recorded in subjects and patients. All but 20 of these (99%) appeared in both monitoring channels within the above time frame. To summarize, 996 (98.8%) of the 1004 artifact signals and 943 (98.1%) of the 961 microembolic signals were correctly classified. CONCLUSIONS Application of the coincidence theory to distinguish microembolic signals from artifacts provides a promising new technique with high sensitivity and specificity that could decisively improve the validity of embolus detection.
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Affiliation(s)
- D Georgiadis
- Department of Neurology, University of Münster, Germany
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34
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Abstract
Stroke is an emergency. Ischemic stroke is similar to myocardial infarction in that the pathogenesis is loss of blood supply to the tissue, which can result in irreversible damage if blood flow is not restored quickly. Public education is needed to emphasize the warning signs of stroke. Patients should seek medical help immediately, using emergency transport systems. Therapy geared toward minimizing the damage from an acute stroke should be started without delay in the emergency room. This includes measures to protect brain tissue, support perfusion pressure, and minimize cerebral edema. Strategies for improving recovery should also begin immediately. All major medical centers need stroke teams and stroke units. Stroke prevention should be given high priority as a public health strategy. Risk factor management should be part of general health care and should begin in childhood, with emphasis on nutrition, exercise, weight control, and avoidance of tobacco. Health screening and early treatment of hypertension and hypercholesterolemia has decreased the incidence of stroke and heart disease, but these efforts need to be expanded to reach all segments of the population. Basic research has opened the door to new therapies aimed at re-establishing blood flow and limiting tissue damage. Clinical trials have already led to changes in stroke prevention, including studies of carotid endarterectomy and ticlopidine and warfarin therapy (for patients with atrial fibrillation). Trials in progress are testing the usefulness of ancrod, neuroprotective agents, antioxidant agents, anti-inflammatory agents, low-molecular-weight heparin, thrombolytic drugs, and angioplasty. Any delay starting therapy after an acute stroke will result in progressive, irreversible loss of brain tissue. Clinicians should remember that for a stroke patient, time is brain tissue.
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Affiliation(s)
- N Futrell
- Division of Neurology, Stroke Unit, Medical College of Ohio, Toledo, USA
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35
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Smith JL, Evans DH, Fan L, Bell PR, Naylor AR. Differentiation between emboli and artefacts using dual-gated transcranial Doppler ultrasound. ULTRASOUND IN MEDICINE & BIOLOGY 1996; 22:1031-1036. [PMID: 9004426 DOI: 10.1016/s0301-5629(96)00103-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
It is well documented that transcranial Doppler ultrasound has the ability to detect cerebral emboli. During intraoperative patient monitoring studies, many signals due to artefact (probe motion, patient movement or surgical manipulation) are also detected and can be difficult to distinguish from genuine embolic events. We have constructed a Doppler system that can simultaneously range-gate at two separate depths, in order to test the hypothesis that it should be possible to distinguish between emboli and artefact by comparing the signal from the two separate regions within the vessel. The classification algorithm is based on the principle that emboli propagate with blood motion (whereas artefacts do not) and thus will be detected sequentially at different depths along the insonated cerebral artery. One hundred thirty-eight (presumed) embolic and 170 artefact signals were analysed. The median (interquartile range) gate separation was 10.01 mm (7.41-10.78 mm). The time delay between detection of embolic signals in the two channels was 11.04 ms (6.24-16.41 ms, but was only 0.08 ms (-0.48(-)+0.64 ms) for artefact (p < 0.0001). Dual-gated Doppler ultrasound is a conclusive and independent method that differentiates emboli from artefact. Incorporation of this system for long-term monitoring may eliminate the need for an experienced observer to be present.
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Affiliation(s)
- J L Smith
- Department of Surgery, Faculty of Medicine, Leicester University, UK
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36
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Markus HS, Tegeler CH. Experimental aspects of high-intensity transient signals in the detection of emboli. JOURNAL OF CLINICAL ULTRASOUND : JCU 1995; 23:81-87. [PMID: 7699103 DOI: 10.1002/jcu.1870230204] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Experimental studies in the 1960s and 1970s demonstrated the high sensitivity of Doppler ultrasound in detecting gaseous bubbles. More recent studies have shown that microscopic air bubbles, as well as glass microspheres as small as 5 mu to 20 mu, cause characteristic high-intensity signals. Recently it has been demonstrated that less echogenic embolic materials such as thrombus, platelet aggregates, and atheroma can also be detected with a high sensitivity. Such "solid," or formed-element, emboli as small as 200 mu to 400 mu can be detected; the lower size limit of detection was due to an inability to make smaller embolic particles rather than to the sensitivity of the detection process itself. Analysis of the Doppler signals provides some information about embolus size and composition, but accurate characterization in clinical practice is not possible using current technology. Studies in experimental models have allowed the detailed description of embolic signals; they appear as a short-duration, frequency-focused increase in intensity, predominantly unidirectional in the direction of flow, and usually contained within the spectral envelope. In contrast, artifacts appear as a bidirectional, high-intensity increase with maximum intensity at low frequencies. These differences have been exploited to develop automatic embolus detection programs, and an off-line version has been successfully validated in an experimental model.
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Affiliation(s)
- H S Markus
- Division of Clinical Neuroscience, St. George's Hospital Medical School, London, United Kingdom
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37
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Kaps M, Seidel G, Berg J. Is there a hemispheric side preference of cardiac valvular emboli? ULTRASOUND IN MEDICINE & BIOLOGY 1995; 21:753-756. [PMID: 8571463 DOI: 10.1016/0301-5629(95)00019-n] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Microaggregates arising from prosthetic cardiac valves offer the opportunity to examine the distribution of valvular emboli in the human cerebral circulation. Forty-four patients with different kinds of prosthetic valves underwent bilateral transcranial Doppler monitoring for 1 h to detect high intensity Doppler signals representing microemboli. Comparing the total number of embolic signals in both middle cerebral arteries (N = 1066), a side preference was not statistically evident. However, clear side preferences were obvious in some individuals. The lack of statistical evidence for hemispherical preferences of cardiac microembolism in general does not exclude selective streaming in individuals, explaining the clinical observation of lodging preferences of recurrent cardiac embolism. A cardiac source of microembolism may mimic disease activity of extracranial carotid artery stenosis and bias the localization of embolic source.
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Affiliation(s)
- M Kaps
- Department of Neurology, Medical University at Lübeck, Germany
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38
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Markus HS, Clifton A, Buckenham T, Brown MM. Carotid angioplasty. Detection of embolic signals during and after the procedure. Stroke 1994; 25:2403-6. [PMID: 7974580 DOI: 10.1161/01.str.25.12.2403] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND AND PURPOSE Carotid angioplasty may offer an effective treatment for carotid stenosis, but there has been concern about the incidence and clinical consequences of distal embolization. Transcranial Doppler monitoring in carotid endarterectomy has demonstrated embolic signals during this procedure. We used this technique in patients undergoing carotid angioplasty. METHODS Transcranial Doppler ultrasound was used to monitor for embolic signals in the ipsilateral middle cerebral artery before and during 10 technically successful carotid angioplasties and at various standardized times in the following month. RESULTS In the month before angioplasty asymptomatic embolic signals were detected in 3 of 10 patients. During angioplasty multiple embolic signals were detected immediately after balloon inflation in 9 of 10 subjects. A minor ipsilateral cerebral ischemic event occurred in 1 of these 9, but the other 8 were asymptomatic. Embolic signals were common immediately after the procedure and intra-arterial femoral catheter removal (8 of 10 subjects) but thereafter became less frequent and were present in 1 of 5 at 4 hours, 2 of 10 at 48 hours, 1 of 6 at 7 days, and 1 of 10 at 1 month. CONCLUSIONS Embolization at the time of carotid angioplasty is very common but usually asymptomatic; monitoring by means of Doppler ultrasound will allow the effectiveness of measures to reduce this embolization to be studied. Late embolization occurs in a minority of patients and may account for the small but significant risk of delayed stroke. Doppler monitoring may allow identification of patients at risk and assessment of the effectiveness of prophylactic therapy.
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Affiliation(s)
- H S Markus
- Division of Clinical Neuroscience, St George's Hospital Medical School, London, England
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39
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Halvorsen AM, Futrell N, Wang LC. Fibrin content of carotid thrombi alters the production of embolic stroke in the rat. Stroke 1994; 25:1632-6. [PMID: 8042216 DOI: 10.1161/01.str.25.8.1632] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
BACKGROUND AND PURPOSE Mechanical denudation of the endothelium of the carotid artery in animals produces a nonocclusive thrombus, but the brains of these animals have not been examined for the presence of embolic stroke. METHODS The endothelium of the right carotid artery of 16 Wistar rats was denuded using a balloon catheter. Phosphotungstic acid hematoxylin (PTAH) staining and scanning electron micrographs of the nonocclusive thrombi in the carotid arteries were compared with those produced by photochemical methods, and brains were examined for infarcts. RESULTS Although nonocclusive thrombi were present in the carotid arteries of 4 of 4 rats killed at 4 hours and in 8 of 12 killed at 24 hours, neither cerebral infarcts nor emboli were seen in the 14 brains evaluated by light microscopy. PTAH demonstrated a high fibrin content in the thrombus produced by the endothelial denudation, with almost no fibrin seen in photochemically induced thrombi. Scanning electron microscopy confirmed dense networks of fibrin in the thrombi produced by balloon denudation. CONCLUSIONS The composition of a nonocclusive thrombus may determine the embolic potential of this thrombus. A low fibrin content in a nonocclusive platelet thrombus may enhance the embolic potential. This suggests that platelet inhibition may also be indicated in patients with carotid artery disease who are being treated with anticoagulant.
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Affiliation(s)
- A M Halvorsen
- Department of Neurology, Henry Ford Health Sciences Center, Detroit, Mich
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40
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Abstract
Can asymptomatic cerebral emboli be detected? With transcranial Doppler ultrasonography of the middle cerebral artery, short-duration high-intensity asymptomatic embolic signals were detected in 6 of 25 patients with carotid stenosis and in 9 of 24 with prosthetic cardiac valves, but not in 20 normal controls. In carotid stenosis the signals were usually unilateral and ipsilateral to the stenosis. Embolic signals were significantly more common in patients with mechanical valves than with pig xenografts (8/13 vs 1/11). With mechanical valves embolic signals were usually bilateral. Detection of asymptomatic emboli may allow identification of and preventive treatment in at-risk patients.
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Affiliation(s)
- H S Markus
- Division of Clinical Neuroscience, St George's Hospital Medical School, London, UK
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41
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Markus H, Loh A, Brown MM. Detection of circulating cerebral emboli using Doppler ultrasound in a sheep model. J Neurol Sci 1994; 122:117-24. [PMID: 8195797 DOI: 10.1016/0022-510x(94)90061-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We describe a validation study of a new technique for detecting circulating pathological cerebral emboli. Theoretically one would expect solid emboli to be detectable as high intensity signals on the Doppler waveform, and such signals have been reported in humans with potential embolic sources. Pathological cerebral emboli (thrombi, platelet aggregates and atheroma) were introduced into the proximal carotid artery of an in vivo sheep model, and their passage detected in the cerebral circulation using Doppler ultrasound. All of 74 emboli, with a maximum dimension as small as 0.24 mm, were detected as short duration high intensity signals. Smaller pathological emboli could not be made but glass microspheres as small as 5-20 micron resulted in high intensity signals. A significant positive correlation was found between embolus size and relative intensity increase of the embolic signal. A significant positive correlation was also found between embolus size and duration of embolic signal. This study demonstrates that detection of circulating cerebral emboli is possible in vivo. This technique may allow selection of patients at particularly high risk of cerebral embolisation so that they can be given specific prophylactic treatment. Analysis of the Doppler signal may give information on the size of the embolus, although using current signal analysis it is impossible to distinguish between the signals produced by say a larger platelet embolus or a smaller thrombus embolus.
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Affiliation(s)
- H Markus
- Division of Clinical Neuroscience, St. George's Hospital Medical School, London, UK
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42
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Abstract
BACKGROUND The identification of gaseous emboli using Doppler ultrasound was described as early as the 1960s. Recently it has been demonstrated that this method can also detect solid emboli such as thrombi and platelet aggregates. This may make this technology useful in a large number of patients with, or at risk of, embolic stroke. SUMMARY OF REVIEW Emboli appear as short-duration, high-intensity signals in the Doppler spectrum. The intensity of the Doppler signal from an artery containing an embolus depends on the density difference between the embolic material and blood. This difference is greatest for gaseous emboli, which are therefore the most easy to detect. Gaseous emboli have been demonstrated during deep-sea diving, and their presence correlates with the occurrence of decompression sickness. Similar signals have been detected during cardiopulmonary bypass. A relation has been demonstrated between the number of emboli detected by transcranial Doppler and a decline in neuropsychological function after cardiopulmonary bypass. Solid emboli such as thrombi and platelet aggregates result in less intense signals than air emboli. Their detection, using Doppler ultrasound, has recently been described in patients with prosthetic heart valves, atrial fibrillation, and carotid artery disease. It may also help in the detection and localization of embolic sources in patients with stroke. Studies in in vitro and in vivo models demonstrate that this technique provides information on the size and type of emboli. Larger emboli produce signals of greater intensity and duration. Practical patient monitoring will require automatic emboli detectors incorporated into the Doppler machine; such programs are being developed. CONCLUSIONS Detection of solid emboli using Doppler techniques offers an exciting new diagnostic tool. It has been demonstrated that the technique can detect solid emboli. The prognostic significance of such emboli remains to be determined. It is hoped that the technique will allow detection of patients at high risk of embolic stroke in whom appropriate prophylactic treatment can then be instituted.
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Affiliation(s)
- H Markus
- Division of Clinical Neuroscience St George's Hospital Medical School, London, UK
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