Comparison of time-frequency estimators for peripheral embolus detection

Recently, a time-frequency processing of peripheral arterial Doppler signals, based on the spectrogram, was proposed to detect automatically high-intensity transient signal. Three time-frequency representations, the smooth-pseudo-Wigner-Ville, the Cho?-Williams and the cone-kernel distributions were compared with the spectrogram, following the detection scheme previously reported. The results showed that the spectrogram provided the best compromises between false-detection and no-detection compared with the other time-frequency representations.     

Distribution of artificially-produced microembolic signals into the cerebral circulation

According to clinical observations, cardiogenic embolism occurs more often in the anterior than in the posterior cerebral circulation. An ultrasound (US) contrast agent was used to artificially produce microembolic signals (MES) to imitate the intracranial distribution of systemic emboli. Systemic microemboli were simulated by IV administered US agent (Levovist(R) 300 mg/mL as bolus). A total of 20 patients were monitored by means of transcranial Doppler sonography (TCD), 3 min after the injection, with a 2-MHz transducer simultaneously at 50 mm (middle cerebral artery, MCA, on one side) and 90 mm (basilar artery, BA). Four 3-min recordings were done (two of the right MCA, two of the left MCA, with the BA, respectively). Three observers and an automatic detection system independently performed an off-line analysis. A total of 160 recordings were analyzed. The mean numbers of detected high-intensity transient signals (HITS) were 34.5 +/- 28.2 in the right MCA (simultaneously registered HITS in the BA: 9.4 +/- 16.8) and 39.1 +/- 34.2 in the left MCA (simultaneously registered HITS in the BA: 12.2 +/- 14.5). Only 21.4 to 23.7% of all HITS were recorded in the BA. Microembolic signals artificially produced by means of US contrast agent made it possible to mimic the physiologic distribution of small embolic particles. In future, these might help to investigate the distribution of systemic emboli in different vascular territories in various pathologic conditions of the cerebral blood flow.     

The dynamic bubble trap reduces microbubbles in extracorporeal circulation and high intensity transient signals in the middle cerebral artery: a case report

Microemboli during extracorporeal circulation (ECC) might be a reason for postoperative neuropsychological dysfunction. This case report shows that reduction of microbubbles in the arterial line, as well as high intensity transient signals (HITS) in the middle cerebral artery (MCA), could be accomplished by use of a dynamic bubble trap (DBT) during routine coronary artery bypass graft (CABG) surgery in a 63-year-old male. The DBT was placed after the arterial filter, an ultrasound Doppler device was used for detection of microemboli before and after the DBT. HITS were measured by a transcranial ultrasound Doppler in both MCAs. For first 32 min of ECC, the DBTwas excluded; 54 916 microbubbles and 507 HITS were counted. In the next 30 min, blood flow was directed through the DBT. This led to a significant reduction of microbubbles from 55 888 to 18 237; accordingly, only 120 HITS were registered. A DBT, integrated in ECC for routine CABG, effectively reduces air bubbles, thus protecting the cerebrovascular system from microembolization, as demonstrated by lower HITS counts.     

Significant reduction of air microbubbles with the dynamic bubble trap during cardiopulmonary bypass

Air microbubbles mostly occur unnoticed during cardiopulmonary bypass and are predominantly responsible for serious postoperative psychoneurological dysfunction. A dynamic bubble trap (DBT), which removes air microbubbles from the arterial blood, was tested in a clinical study. The aim was to evaluate the efficiency of microbubble removal under clinical conditions. As blood passes through the DBT, which is placed in the arterial line between the arterial filter and arterial cannula, it is converted into a rotating stream. The bubbles are directed to the centre of the blood flow and are collected in the distal end of the DBT, from where they are returned to the cardiotomy reservoir. Doppler ultrasonography was used to detect the microbubbles before and after the DBT, and also the number of high-intensity transient signals (HITS) in the right and left middle cerebral artery during extracorporeal circulation. A significant reduction of microbubbles in the arterial line (3,990 before DBT, 537 after, p < 0.001) and HITS in the brain (51 in the DBT group, 77 in the placebo group, p = 0.04) was measured.     

Evaluation of low back muscle surface EMG signals using wavelets

OBJECTIVE: To compare the ability of observers to correctly detect the reaction time of erector spinae response to unexpected load by inspecting nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals and versus automatic detection on the same wavelet transformed signals. BACKGROUND: Traditionally, electromyographic signal analysis is performed using Fourier transform based methods. However, muscle response to transients such as unexpected load, have limitations when using these methods of electromyographic processing. DESIGN: A comparison was made of the three methods using the same signals attained during sudden loading of the trunk. METHODS: 11 chronic low back pain patients and eleven normal subjects were investigated in sudden loading. Surface electromyographic signals were obtained from the erector spine muscle at L3. The ability of observers to detect reaction time of erector spinae muscle responses of nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals versus an automatic peak detection program was determined. RESULTS: The results have shown that the spine muscle reaction time was easier and more accurately determined in the wavelet domain rather than in its original signal representation. CONCLUSION: Wavelet transform methods improved the analysis of electromyographic signals in the time domain by facilitating the determination of the time of muscle activity. RELEVANCE: Wavelet transform could be a valuable tool for electromyographic analysis in resolving the psychophysical problem of perception involved in the analysis of nonprocessed signals. In clinical environments, where the speed and the accuracy of the analysis of electromyographic signal is critical, the wavelet based signal processing could be very important.     

Use of a large bore syringe creates significantly fewer high intensity transient signals (HITS) into a cardiopulmonary bypass system than a small bore syringe

INTRODUCTION: High intensity transient signals (HITS) have been reported to occur following perfusionist intervention during cardiac surgery. This study investigates the relationship of the syringe bore, injection rate, and HITS created. METHODS: Syringes (10 mL) with a male luer-lock connection (Large Bore) and Abboject 'jet syringes' with a 20 GA needle and male luer-lock connector (Small Bore) were filled with 10 mL of 0.9 N saline. A perfusionist was randomly assigned a set of four similar syringes followed by the other syringe bore. Each of the four syringes was injected into an in vitro saline-primed cardiopulmonary bypass (CPB) system over 5, 10, 15, or 20 sec. Sixteen randomizations of small and large bore syringes were completed at the four injection times (128 injections). HITS in the CPB arterial line were detected with transcranial Doppler (TCD) probes, were recorded for the 2 min following the injection, and were counted independently off-line by two reviewers. RESULTS: The use of a large bore syringe compared to a small bore syringe created significantly fewer HITS (29 +/- 6 versus 145 +/- 17 [mean +/- SEM], p<0.001) introduced into the CPB arterial line. Injection over a longer time produced significantly fewer HITS than shorter injection times (p<0.001). CONCLUSION: Significantly fewer HITS are introduced into the CPB system by using standard syringes and slower injection time.     

Detection of Cerebral High-Intensity Transient Signals by NeoDoppler during Cardiac Catheterization and Cardiac Surgery in Infants

There is a risk of gaseous and solid micro-embolus formation during transcatheter cardiac interventions and surgery in children with congenital heart disease (CHD). Our aim was to study the burden of high-intensity transient signals (HITS) during these procedures in infants. We used a novel color M-mode Doppler (CMD) technique by NeoDoppler, a non-invasive ultrasound system based on plane wave transmissions for transfontanellar continuous monitoring of cerebral blood flow in infants. The system displays CMD with 24 sample volumes and a Doppler spectrogram. Infants with CHD undergoing transcatheter interventions (n = 15) and surgery (n = 13) were included. HITS were manually detected based on an “embolic signature” in the CMD with corresponding intensity increase in the Doppler spectrogram. Embolus-to-blood ratio (EBR) defined HITS size. A total of 1169 HITS with a median EBR of 9.74 dB (interquartile range [IQR]: 5.10–15.80 dB) were detected. The median number of HITS in the surgery group was 45 (IQR: 11–150), while in the transcatheter group the median number was 12 (IQR: 7–24). During cardiac surgery, the highest number of HITS per hour was seen from initiation of cardiopulmonary bypass to aortic X-clamp. In this study we detected frequent HITS and determined the feasibility of using NeoDoppler monitoring for HITS detection.     

Pulsed Doppler ultrasound detection of flow disturbances in arteriosclerosis.

Pulsed Doppler ultrasound blood flow detection has been used in a noninvasive manner to detect arterial abnormalities associated with arteriosclerosis. Sound spectrograms of ultrasound signals obtained from in vitro and animal studies in which flow was disturbed by obstacles placed in the flow stream showed a different distribution of energy over frequency than signals obtained from studies with no flow disturbances. Similar findings were seen clinically. A technique has been developed which can detect disturbed flow patterns resulting from partial occlusion in important superficial arteries (e.g. femoral and carotid) up to 15 cm distal to localized arterial wall abnormalities. Thirty-five arterial examinations of normal and arteriographically abnormal arteries in 12 patients revealed a sensitivity of 83 percent and a specificity of 61 percent. This study suggests that pulsed Doppler ultrasound may be useful as a screening technique for detection of arteriosclerotic lesions in major superficial arteries.     

Assessment of Resting-State Blood Flow Through Anterior Cerebral Arteries Using Trans-cranial Doppler Recordings

Trans-cranial Doppler (TCD) recordings are used to monitor cerebral blood flow in the main cerebral arteries. The resting state is usually characterized by the mean velocity or the maximum Doppler shift frequency (an envelope signal) by insonating the middle cerebral arteries. In this study, we characterized cerebral blood flow in the anterior cerebral arteries. We analyzed both envelope signals and raw signals obtained from bilateral insonation. We recruited 20 healthy patients and conducted the data acquisition for 15 min. Features were extracted from the time domain, the frequency domain and the time-frequency domain. The results indicate that a gender-based statistical difference exists in the frequency and time-frequency domains. However, no handedness effect was found. In the time domain, information-theoretic features indicated that mutual dependence is higher in raw signals than in envelope signals. Finally, we concluded that insonation of the anterior cerebral arteries serves as a complement to middle cerebral artery studies. Additionally, investigation of the raw signals provided us with additional information that is not otherwise available from envelope signals. Use of direct trans-cranial Doppler raw data is therefore validated as a valuable method for characterizing the resting state.     

Quantification of Embolic Showers Using Radio-Frequency Based TCD Analysis

During cardiac surgery and cardiology interventions, microemboli may be generated and disperse in the systemic circulation. The amount of microemboli that ends up in cerebral blood vessels is associated with postoperative neurologic complications. During cardiac surgery a large amount of cerebral microemboli can occur at once and create so-called “cerebral embolic showers.” To correlate postoperative neurologic outcome to cerebral embolic load, a quantitative evaluation of these embolic showers is necessary. The standard monitoring technology to visualize cerebral microemboli is transcranial Doppler (TCD). Although the conventional TCD systems are equipped with software claiming to detect microembolic signals, none of the existing TCD systems is capable of an accurate estimation of the number of cerebral microemboli in embolic showers. In this study, an algorithm with a high temporal resolution, based on the radiofrequency (RF) signal of a TCD system, has been designed to quantify these showers. Evaluation by three independent observers of a training set demonstrates that the proposed method has a sensitivity of at least one order of magnitude better than the automatic detection algorithm on the existing Doppler device used. RF-based emboli detection can possibly become a standard addition to conventional Doppler methods, considering that accurate estimation of the embolic load supports quantification of neurologic risk during various surgical procedures. (E-mail: l.sauren@ctc.unimaas.nl)     

Automatic Measurements of Mitral Annular Plane Systolic Excursion and Velocities to Detect Left Ventricular Dysfunction

The purpose of the study described here was to evaluate an automatic algorithm for detection of left ventricular dysfunction, based on measurements of mitral annular motion indices from color tissue Doppler apical four-chamber recordings. Two hundred twenty-one patients, among whom 49 had systolic and 11 had diastolic dysfunction, were included. Echocardiographic evaluation by cardiologists was the reference. Twenty patients were also examined by medical students. The ability of the indices to detect systolic and diastolic dysfunction were compared in receiver operating characteristic analyses, and the agreement between automatic and reference measurements was evaluated. Mitral annular plane systolic excursion ≤10?mm detected left ventricular dysfunction with 82% specificity, 76% specificity, 56% positive predictive value and 92% negative predictive value. The automatic measurements acquired from expert recordings better agreed better with the reference than those acquired from student recordings. We conclude that automatic measurements of systolic mitral annular motion indices can be helpful in detection of left ventricular dysfunction.     

Comparison of two different extracorporeal circuits on cerebral embolization during cardiopulmonary bypass in children

OBJECTIVE: To compare the effect of two different extracorporeal circuits on the counts of high-intensity transient signals (HITS) during pediatric cardiopulmonary bypass (CPB). METHODS: Transcranial Doppler was used to detect HITS associated with extracorporeal sources during the period of aortic crossclamping in the middle cerebral artery of children undergoing CPB. Based on body size, children were assigned one of two extracorporeal circuits (A or B). Circuit A included a D-705 oxygenator and associated reservoir, and circuit B included a Lilliput oxygenator and reservoir. Patients were further classified into two groups according to the complexity of surgical repair: single simple lesions or multiple complex lesions. RESULTS: We studied 109 pediatric patients. Surgery for multiple complex lesions was associated with longer periods of aortic crossclamping and CPB (p < 0.0001). The median count of extracorporeal HITS was 12 (25th, 75th percentiles: 3, 51). The type of extracorporeal circuit (p = 0.012) and the complexity of surgical repair (p < 0.0001) had an effect on the HITS counts. The use of circuit A was associated with higher HITS counts during surgery for multiple complex lesions compared to single simple lesions (p < 0.0001). Conversely, no differences were found with the use of circuit B between these two surgical groups (p > 0.25). During surgery for multiple complex lesions, patients treated with circuit A showed higher HITS counts than those with circuit B (p < 0.01), but there were no circuit-related differences in HITS counts (p = 0.30) during single simple lesions. CONCLUSION: Variations in the design characteristics of extracorporeal circuits can increase cerebral emboli during CPB in children. This may be related to the reduced ability of some circuits to remove emboli during long periods of CPB for complex congenital heart-surgery.     

Effect of perfusionist technique on cerebral embolization during cardiopulmonary bypass

OBJECTIVE: To determine the association between high-intensity transient signals (HITS) and perfusionist interventions, purging techniques, pump flows and venous reservoir blood volume levels during cardiopulmonary bypass. METHODS: Transcranial Doppler was used to detect HITS in the middle cerebral artery during the period of aortic crossclamping in patients undergoing coronary artery bypass grafting. Perfusionist-related interventions were recorded and included blood sampling (including the number of times that the oxygenator sampling manifold was purged), drug bolus injections and infusions (vasopressors, crystalloid and mannitol). Pump flows and venous reservoir volume levels were also documented. RESULTS: There were 534 interventions in 90 patients [median number of interventions per patient: 6 (quartiles: 4, 8)]. The median total HITS count from all interventions was 17 (5, 37). This represented 38% of the total HITS counts during aortic crossclamping. Factors contributing to differences in the HITS count included type of intervention (p <0.0001) and perfusionist (p =0.0012). Blood sampling (p<0.001) and drug bolus injections (p=0.06) had higher HITS counts per patient than infusions. Repetitive purging significantly increased HITS counts (r=0.74; p <0.001). Purging perfusionists (purging: 1-10 times) had higher HITS counts per patient [5 HITS (1, 15) than nonpurgers [0 HITS (0, 1) p <0.0001]. HITS counts were significantly correlated with reservoir volumes (r= -0.20, p=0.017) and pump flow rates (r=0.21, p =0.008). Reservoir volume levels < or =800 mL were associated with higher HITS counts per intervention [11 HITS (2, 27)] during blood sampling compared with higher volume levels [3 HITS (1, 10), p =0.001]. CONCLUSIONS: Cerebral emboli associated with perfusionist interventions can be minimized by not purging the sampling manifold, using continuous infusions rather than bolus injections, and maintaining high blood-volume levels (>800mL) in the venous reservoir.     

Electrocardiographic monitoring: An overview

This article presents an overview of the key principles and methods underlying modern electrocardiographc (ECG) monitoring. Multilead processing, improved noise reduction techniques, and automatic lead-fail detection substantially enhance the reliability of ECG monitoring today. Computerized ECG signal processing provides reliable automatic arrhythmia detection, based on sophisticated waveform recognition and classification schemes. State-of-the-art ECG monitors carry out automatic ST segment analysis. They also detect and process pacemaker signals. A variety of signalprocessing methods arc described.     

The use of Doppler ultrasonography for the evaluation of cerebral artery flow patterns in infants with congenital heart disease

With the use of a two-dimensional range-gated pulsed-Doppler ultrasound system, Doppler examinations of the aorta and cerebral arteries were performed in 20 normal newborn infants and in 54 infants with various forms of congenital heart disease (i.e. patent ductus arteriosus, coarctation of the aorta, critical aortic stenosis, pulmonary atresia, truncus arteriosus). In the cerebral artery Doppler recordings of the normal infants, there was antegrade flow throughout systole and diastole. In the cerebral artery Doppler recordings of the infants with cardiac disease, various abnormal flow signals (i.e. retrograde or absent diastolic flow signals, increased systolic and diastolic flow signals, etc.) were found. Furthermore, the changes in the cerebral artery Doppler recordings were concomitant with changes in the aortic Doppler flow signals and the arterial blood pressure. Representative examples of the normal and abnormal Doppler flow patterns that were observed in the aorta and cerebral arteries are presented, and the mechanisms that could lead to these flow patterns are discussed.     

Detection of Dicrotic Notch in Arterial Pressure Signals

Objective. A novel algorithm to detect the dicrotic notch in arterial pressure signals is proposed. Its performance is evaluated using both aortic and radial artery pressure signals, and its robustness to variations in design parameters is investigated. Methods. Most previously published dicrotic notch detection algorithms scan the arterial pressure waveform for the characteristic pressure change that is associated with the dicrotic notch. Aortic valves, however, are closed by the backwards motion of aortic blood volume. We developed an algorithm that uses arterial flow to detect the dicrotic notch in arterial pressure waveforms. Arterial flow is calculated from arterial pressure using simulation results with a three-element windkessel model. Aortic valve closure is detected after the systolic upstroke and at the minimum of the first negative dip in the calculated flow signal. Results. In 7 dogs ejection times were derived from a calculated aortic flow signal and from simultaneously measured aortic flow probe data. A total of 86 beats was analyzed; the difference in ejection times was –0.6 ± 5.4 ms (mean ± SD). The algorithm was further evaluated using 6 second epochs of radial artery pressure data measured in 50 patients. Model simulations were carried out using both a linear windkessel model and a pressure and age dependent nonlinear windkessel model. Visual inspection by an experienced clinician confirmed that the algorithm correctly identified the dicrotic notch in 98% (49 of 50) of the patients using the linear model, and 96% (48 of 50) of the patients using the nonlinear model. The position of the dicrotic notch appeared to be less sensitive to variations in algorithm's design parameters when a nonlinear windkessel model was used. Conclusions. The detection of the dicrotic notch in arterial pressure signals is facilitated by first calculating the arterial flow waveform from arterial pressure and a model of arterial afterload. The method is robust and reduces the problem of detecting a dubious point in a decreasing pressure signal to the detection of a well-defined minimum in a derived signal.     

A novel hands-free carotid ultrasound detects low-flow cardiac output in a swine model of pulseless electrical activity arrest

Objective

To determine if a hands-free, noninvasive Doppler ultrasound device can reliably detect low-flow cardiac output by measuring carotid artery blood flow velocities. We compared the ability of observers to detect carotid artery flow velocity differences between pseudo-pulseless electrical activity (PEA) and true-PEA cardiac arrest.

Methods

Five swine were instrumented with aortic (Ao) and right atrial pressure-transducing catheters. The Doppler ultrasound device was adhered to the neck over the carotid artery. Continuous electrocardiogram, pressure readings, and Doppler signal were recorded. Each swine underwent multiple episodes of fibrillation and resuscitation. Episodes of true-PEA and pseudo-PEA were retrospectively identified from all resuscitation attempts by examination of electrocardiogram and Ao waveforms. The sensitivity and specificity of the device to detect pseudo-PEA was obtained using observers blinded to Ao waveform recordings.

Results

There was good interobserver reliability related to identification of pseudo- and true-PEA (κ = 0.873). The observers blinded to Ao waveform recordings agreed on 8 of the 9 episodes of pseudo-PEA, whereas 4 false positives of 26 true-PEA events were reported (sensitivity, 0.89; specificity, 0.85). The Doppler device was able to detect carotid flow velocity over a wide range of Ao blood pressures.

Conclusions

This hands-free, noninvasive Doppler ultrasound device can reliably differentiate pseudo-PEA from true-PEA during resuscitation from cardiac arrest, detecting pressure gradient changes of less than 5 mm Hg through to normotension. This device distinguishes conditions of no cardiac output from low cardiac output and may have applications for use during resuscitation from various etiologies of arrest and shock.     

Vasculature in hepatocellular carcinoma after transcatheter arterial chemoembolization: comparison of power and color Doppler sonography.

The purpose of this study was to compare power Doppler sonography with conventional color Doppler sonography for the detection of the vascularity of hepatocellular carcinomas after transcatheter arterial chemoembolization. Of the 93 embolized hepatocellular carcinomas, hypervascularity was demonstrated in 36 on angiography; power Doppler sonography correctly identified pulsatile flow signals in 33 (92%) of these 36, whereas color Doppler sonography identified flow signals in 24 (67%). A statistically significant difference was noted when the sizes of the nodules were 30 mm or less. Despite technical difficulties, such as flash artifact, power Doppler sonography is superior to color Doppler sonography for detection of hypervascularity, especially in small embolized nodules of hepatocellular carcinoma (30 mm or less in diameter).     

Comparative study of 18 gauge and 20 gauge intravenous catheters during transcranial Doppler ultrasonography with saline solution contrast

A formal technical protocol has not been established for transcranial Doppler ultrasonography in the detection of venous to arterial shunts; techniques have been adapted from contrast echocardiography. We evaluated the effect of different diameter indwelling intravenous catheters on the detection of right-to-left shunts by transcranial Doppler ultrasonography. Fifteen patients underwent transcranial Doppler sonographic evaluation with saline solution contrast using both 18 gauge and 20 gauge indwelling intravenous catheters. The larger bore intravenous catheter delivered a greater number of signals in a shorter time to the insonated middle cerebral artery. We recommend that a standardized method for transcranial Doppler sonographic contrast studies include an 18 gauge intravenous catheter.