Simulation of Doppler ultrasound signals for a laminar, pulsatile, nonuniform flow.

A simulation for Doppler ultrasound quadrature signals from pulsatile, nonuniform flow is presented. It is an extension of an earlier simulation presented by Jones and Giddens (1990a) which was valid for laminar, uniform, steady flow and which included the stochastic characteristics introduced by scattering particles which enter and leave the sample volume at random times. Fourier transform and autoregressive spectral analysis techniques are used to compare the simulated signals to Doppler signals collected from an in vitro flow setup. Power spectra, Doppler frequency estimates and standard deviations of these estimates serve as standards of comparison. Results show that the simulation model generates realistic quadrature signals. The study improves the understanding of the physics of the Doppler process and shows that it can be modeled for complex flow conditions. The input parameters of the simulation are the Doppler instrument parameters and flow characteristics. This allows the simulation to be used for transducer design as well as in the study of the applicability of signal analysis techniques to Doppler ultrasound.     

On the behavior of instantaneous frequency estimators implemented on Doppler flow imagers

Analytical and experimental results have been used to examine the behavior of the "autocorrelator" or instantaneous frequency detector (IFD) applied to color-coded Doppler flow mapping. Two effects were studied. The first was the influence of noise, as modified by a stationary echo canceler, on the Doppler frequency detector. Our theoretical considerations predict that uncorrelated input noise signals become partially correlated after cancellation, and bias the response to flow signals. This effect was confirmed by experiment. The canceler introduces a constant negative bias into the denominator of the algorithm implemented by the estimator, thus changing the indicated frequency. The second phenomenon, examined through processing computer simulated Doppler signals added to real noise, is related to the possible ambiguity, called aliasing, of measurements of the mean frequency for wide-band Doppler spectra. We show that aliasing cannot be observed with these spectra unless the signal is first processed by a canceler. Thus, regions of apparent reversed flow direction on two-dimensional flow images of turbulence must usually be due to real reversal of the flow direction.     

Color Doppler sonographic mapping of pulmonary lesions: evidence of dual arterial supply by spectral analysis.

OBJECTIVE: Within pulmonary lesions, flow signals of pulmonary arteries can be discriminated from flow signals of central bronchial and peripheral bronchial arteries on color Doppler sonography. Our aim was to evaluate the evidence and frequency of different arterial supplies of pleural-based pulmonary lesions using qualitative and quantitative color Doppler sonography. METHODS: Forty-one patients with roentgenologically confirmed pleural-based pulmonary lesions were investigated by color Doppler sonography. The following parameters were investigated: (1) qualitative color Doppler sonographic evidence of vascularization, (2) quantitative color Doppler sonographic evidence of arterial flow signals (resistive index and pulsatility index), and (3) number of different arterial flow signals in 1 lesion by color Doppler sonographic mapping. RESULTS: We found no vascularization in 5 patients, sparse vascularization in 21, and pronounced vascularization in 15. Quantitative color Doppler sonographic parameters were as follows: mean pulmonary artery resistive index, 1.2; mean central bronchial artery resistive index, 0.5; mean peripheral bronchial artery resistive index, 0.7; mean pulmonary artery pulsatility index, 7.8; mean central bronchial artery pulsatility index, 0.7; and mean peripheral bronchial artery pulsatility index, 1.6. There was a significant difference between all types of flow signals for resistive and pulsatility index values but not between pulmonary and peripheral bronchial arteries (P = .068). In 41 patients, 57 different arterial flow signals were determined; 19 (46%) of these patients had 2 or more different arterial flow signals in a lesion. There was no significant difference between benign and malignant lesions regarding the number of flow signals. CONCLUSIONS: Evidence of at least a dual arterial supply can be found on quantitative color Doppler sonography in almost 50% of pulmonary lesions. A single spectral analysis is not suitable for characterization of the arterial supply of pulmonary lesions.     

Color Doppler US pulmonary artery vessel signal: a sign for predicting the benign lesions

The lung cancer blood supply originates from the bronchial artery. If vessel signals within pulmonary lesions can be confirmed to be those of the pulmonary artery, color Doppler ultrasound (US) should be able to predict and differentiate benign lesions from lung cancers. Two hundred sixty-four patients with abutting thoracic lesions (including 125 lung cancers and 139 benign lesions) underwent color Doppler US examinations. A pulsatile flow, with the vessel signal length on sonographic appearance > or =1 cm demonstrated by color Doppler US, was arbitrarily defined as a pulmonary artery vessel signal. Of the 264 thoracic lesions, 73 (58%) lung cancers and 107 (77%) benign lesions had detectable color Doppler US pulsatile flow vessel signals. Analyzing the pulsatile flow vessel signals, the color Doppler US pulmonary artery vessel signal was present in 74 (53%) benign lesions, but was found in only two (2%) lung cancers of a specific alveolar cell carcinoma with lobar consolidation. Using the pulmonary artery vessel signal, color Doppler US can be valuable in predicting and differentiating benign lesions from lung cancers (p < 0.0001, sensitivity = 0.53, specificity = 0.98 and positive likelihood ratio 26.5). In conclusion, color Doppler US pulmonary artery vessel signal sign is useful in predicting and differentiating benign lesions from lung cancers.     

Design of Anthropomorphic Flow Phantoms Based on Rapid Prototyping of Compliant Vessel Geometries

Anatomically realistic flow phantoms are essential experimental tools for vascular ultrasound. Here we describe how these flow phantoms can be efficiently developed via a rapid prototyping (RP) framework that involves direct fabrication of compliant vessel geometries. In this framework, anthropomorphic vessel models were drafted in computer-aided design software, and they were fabricated using stereolithography (one type of RP). To produce elastic vessels, a compliant photopolymer was used for stereolithography. We fabricated a series of compliant, diseased carotid bifurcation models with eccentric stenosis (50%) and plaque ulceration (types I and III), and they were used to form thin-walled flow phantoms by coupling the vessels to an agar-based tissue-mimicking material. These phantoms were found to yield Doppler spectrograms with significant spectral broadening and color flow images with mosaic patterns, as typical of disturbed flow under stenosed and ulcerated disease conditions. Also, their wall distension behavior was found to be similar to that observed in vivo, and this corresponded with the vessel wall’s average elastic modulus (391 kPa), which was within the nominal range for human arteries. The vessel material’s acoustic properties were found to be sub-optimal: the estimated average acoustic speed was 1801 m/s, and the attenuation coefficient was 1.58 dB/(mm·MHzⁿ) with a power-law coefficient of 0.97. Such an acoustic mismatch nevertheless did not notably affect our Doppler spectrograms and color flow image results. These findings suggest that phantoms produced from our design framework have the potential to serve as ultrasound-compatible test beds that can simulate complex flow dynamics similar to those observed in real vasculature.     

Acoustically stimulated transient power scattering explains enhanced detection of the very low velocities in myocardial capillaries by power Doppler imaging: an in vitro study.

BACKGROUND: Although enhanced detection of myocardial perfusion signals by power Doppler imaging during contrast echocardiography has been noted, flow velocities in the coronary microvasculature should generally be below the threshold for Doppler motion detection. It has been suggested that in this situation nonlinear scattering related to acoustically stimulated microsphere oscillation or destruction may be responsible for the detected Doppler shift. METHODS AND RESULTS: This study examined the behavior of MRX 115 (ImaRx Pharmaceuticals) microbubbles during harmonic and nonharmonic power Doppler imaging at varying power outputs (mechanical indexes 0. 3, 0.5, 0.7, and 0.9) in a perfusion tube model under zero-flow conditions. Boluses of MRX 115 0.5-mL suspension were introduced into the model, and flow was halted during each imaging period. Once power Doppler imaging was implemented, a signal was detected as unique sparkling color pixels corresponding to individual bubble destruction events, even in the absence of contrast movement. This phenomenon continued until all contrast bubbles disappeared from the region subjected to power Doppler imaging, usually within 35 to 40 seconds. Off-line videointensity measurements showed that initial power Doppler signal intensity and maximum signal decay rates increased parallel to increasing power output and were substantially greater for nonharmonic than for harmonic imaging modes. CONCLUSION: This relationship between signal intensity and decay rate and acoustic power output suggests that transient scattering related to bubble destruction is responsible for generation of the power Doppler signal in the absence of flow. This would explain the enhanced detection of the very low velocity flows in the myocardial capillaries by power Doppler contrast imaging.     

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.     

Stimulated acoustic emission: pseudo-Doppler shifts seen during the destruction of nonmoving microbubbles

The purpose of this study was to evaluate the appearance and the characteristics of stimulated acoustic emission (SAE) as an echo contrast-specific color Doppler phenomenon with impact on myocardial contrast echocardiography (MCE). Stationary microbubbles of the new contrast agent SH-U 563A (Schering AG) were embedded within a tissue-mimicking gel material. Harmonic power Doppler imaging (H-PDI), color Doppler and pulse-wave Doppler data were acquired using an HDI-5000 equipped with a phased-array transducer (1.67/3.3 MHz). In color Doppler mode, bubble destruction resulted in random noise like Doppler signals. PW-Doppler revealed short "pseudo-Doppler" shifts with a broadband frequency spectrum. Quantification of SAE events by H-PDI demonstrated an exponential decay of signal intensities over successive frames. A strong linear relationship was found between bubble concentration and the square root of the linearized H-PDI signal for a range of concentrations of more than two orders of magnitude (R = 0.993, p < 0.0001). Intensity of the H-PDI signals correlated well with emission power (R = 0.96, p = 0.0014). SAE results from disintegration of microbubbles and can be demonstrated by all Doppler imaging modalities, including H-PDI. Intensity of SAE signals is influenced by the applied acoustic power and correlates highly with the concentration of microbubbles. Because intensity of SAE signals correlates highly with echo contrast concentrations, analysis of SAE signals might be used for quantitative MCE.     

Acoustical bubble trapper applied to hemodialysis

Gaseous microemboli can arise in extracorporeal lines and devices such as dialysis machines. They are associated with severe pulmonary side effects in patients undergoing chronic hemodialysis sessions. The goal of this study was to develop a gaseous emboli trapper using ultrasound waves to remove any air bubble from the tubing system before they reach the patient. A homemade bubble trapper, developed in the laboratory, consists of a Perspex block containing a main channel connected to the tubing of a hemodialysis machine and a second subchannel positioned perpendicularly to the main one, used to trap the air microemboli. The microemboli flowing in the main channel were insonified through an acoustic window with an ultrasound wave, at a frequency of 500 kHz and with a maximal acoustic pressure of 500 kPa, generated by a single-element transducer positioned 3 cm away from the main flow. The radiation force induced by the ultrasound beam acts directly on the flowing air emboli, by pushing them into the subchannel. Two Doppler probes operating both at 2 MHz, connected to a DWL Doppler machine were placed before and after the bubble trapper to count sequentially the number of embolic events. The flow of the machine was varied between 200 mL/min and 500 mL/min. Depending on the flow velocity, the number of microembolic signals (MES) detected by the Doppler probes before and after the trapping system was identical and ranged from 5 to 150 MES/min in absence of the ultrasound irradiation. When the air bubble trapper was activated, a reduction of the number of MES, up to 70%, was achieved. Doppler recordings suggest that the circulating bubbles were either fragmented into smaller bubble fragments or directly got pushed into the second subchannel where they were collected. This simple approach using an ultrasound-based trapping system was shown to operate adequately with the current settings and can be used to filter air microemboli.     

心脏运动对血流速度时间积分测定影响的模拟实验研究

目的 探讨体外模拟心脏运动对多普勒血流流速曲线速度时间积分(VTI)测定的影响。方法用自行设计的TD-3型心底运动模拟仪和血流模拟器，记录两者在不同速度状态下分别运动和同步运动时多普勒流速曲线的特点．观察模拟心脏运动对模拟血流流速曲线VTI测定的影响及其定量关系。结果在模拟心脏运动作用下，模拟血流改变了原有的流速曲线波形，两者同向运动时，模拟血流流速曲线VTI为两者单独运动时的VTI之和．反向运动时为两者单独运动的VTI之差．而模拟心腔运动所产生的多普勒频移信号的速度和频率没有变化。结论模拟心脏运动对模拟血流流速曲线VTI测值有明显影响，在用多普勒方法测量血流量时应当考虑到心脏运动对多普勒测值的影响并加以校正。     

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.     

彩色多普勒超声在不同类型布-加综合征诊断与治疗中的价值

目的探讨彩色多普勒超声在不同类型布-加综合征(BCS)诊断与治疗中的价值。方法应用彩色多普勒超声对临床拟诊的不同类型BCS患者106例及30例健康对照者进行检测,观察其特异性血管形态及血流动力学变化,与DSA对比,并治疗后随访。结果(1)超声诊断BCS90例,DSA确诊89例,超声诊断的敏感性97.8%,特异性82.4%,准确性95.3%,假阳性率17.7%,假阴性率2.3%。(2)血流动力学变化:与对照组相比,下腔静脉(IVC)狭窄者可见局部高速血流,阻塞者局部无血流信号;肝静脉(HV)扩张,血流减慢,并可见肝内侧枝血管;门静脉(PV)入肝血流速度减慢.(3)介入治疗及手术后随访:①介入治疗后,IVC病变处增宽,血流恢复,并可见支架回声,HV及PV血流速度加快;②手术治疗组,根治者可见IVC及HV血流恢复正常,人工血管转流者,可见人工血管呈螺旋管状,内血流清晰。结论彩色多普勒超声对BCS的诊断与血管造影具有良好的相关性,可明确BCS特异性异常血管形态及血流动力学变化,是BCS诊断及术后随访的可靠方法。     

彩色多普勒超声在浅表组织肿块良恶性鉴别诊断中的应用价值

目的：探讨彩色多普勒超声对浅表组织肿块良恶性的鉴别诊断价值。方法采用回顾性研究的方法,对我院收治的经彩色多普勒超声证实的100例浅表组织肿块进行声像图分析,并与手术和术后病理结果比较,比较浅表组织肿块良性和恶性的声像图特点和血流信号。结果100例浅表组织肿块中共有80例为良性病变：肿块长轴与皮肤平行,平均圆度系数为2．58,与术后病理诊断符合率为93．8％;有20例为恶性肿块：平均圆度系数为1．51,诊断符合率为70．0％。良性与恶性肿块的圆度系数以及后方回声衰减经统计学检验表明二者差异有显著性（P ＜0．05）,而良性与恶性肿块的内部回声、边界等二维征象方面差异无统计学意义（P ＞0．05）。彩色多普勒超声结果表明：100例软组织肿块中66例有血流信号,良性肿块收缩期峰值流速不高于20 cm/s,阻力系数低于0．70,与术后病理结果的诊断符合率分别为91．7％和86．1％,可作为良性和恶性肿块鉴别的临界值（P ＜0．05）,其特异性和敏感度分别为87.7％和83．0％。结论彩色多普勒超声在浅表组织肿块良恶性鉴别中具有较高的应用价值,其诊断符合率高,成像清晰,而肿块的圆度系数、后方回声衰减、收缩期峰值流速和阻力系数均可作为良恶性肿块鉴别依据。     

Bias and variance in the estimate of the Doppler frequency induced by a wall motion filter

In pulsed Doppler flowmeters, processing of the Doppler signals is often done digitally. The first step in the analysis of the echoes is the filtering which is needed to remove stationary components and low frequency shifts induced by wall motion. This preliminary step is of utmost importance. The influence of uncorrelated noise on the measurement of Doppler signals at the input of this filter is analysed. The frequencies of the Doppler signals are extracted by an algorithm based on correlation techniques. We observed that the filter induces a correlated noise term, which results in an overestimation of the frequency. An effect similar to frequency aliasing may appear. The level of the bias is dependent on filter characteristics and noise level. Our study was carried out on simulated Doppler signals using first and second order filters. An especially desirable solution in flow mapping is proposed in order to decrease this error.     

体外模拟实验研究心脏运动对频谱多普勒血流速度测定的影响

目的：通过体外模拟实验，研究心脏运动对频谱多普勒血流速度测定的影响。方法：设计一套仪器，使它模拟心脏运动的速度和频率并使在其内流动的模拟血液的流速和频率及这两种运动的开启和停止时间都分别可控，观察模拟血流的频谱多普勒在模拟心脏运动影响下的变化及它们之间量的关系。结果：在模拟心脏运动作用下，原来的模拟血流波形已不存在，代之以模拟心脏运动和模拟血流控速度矢量相加规律所组成的复合波，而模拟心脏运动所产生的多普勒频移信号的振幅和频率都未改变且与上述血流信号并存于频谱中，结论：通常所谓的血流速度频谱实际上是血细胞在心脏内流动速度和心脏运动速度的矢量和。即两项运动的复合频谱。所以，为减少误差，在用多普勒血流速度频谱测定血流参数时，应考虑校正问题。     

经胸壁多普勒超声心动图对冠状动脉血流的检测——与冠状动脉造影对照研究

目的探讨经胸壁多普勒超声心动图(TTDE)对冠状动脉远端血流检测的可行性.方法采用TTDE探查51例冠心病患者冠状动脉左前降支(LAD)远端及右冠状动脉后降支(PDA)血流,并与冠状动脉造影比较.结果 LAD的检出率为94%,PDA的检出率为75%,PDA未检出组的心率明显快于检出组.彩色多普勒冠脉显像为心底部朝向心尖部的舒张期持续的线状血流信号,脉冲多普勒显示以舒张期为主的双期血流频谱,有3例冠脉完全闭塞的患者检出舒张期负向血流.结论 TTDE可以较好地评价冠状动脉左前降支和右冠状动脉后降支血流,为临床提供一个无创的检查冠状动脉血流的新方法.     

Evaluation of solid breast lesions with power Doppler sonography.

PURPOSE: We compared the abilities of power and conventional color Doppler sonography to depict the vascularity of solid breast lesions and evaluated the usefulness of power Doppler sonography in differentiating between benign and malignant breast lesions. METHODS: One hundred two solid breast lesions (59 benign and 43 malignant lesions) were studied with power and color Doppler sonography. Power and color Doppler sonograms were retrospectively compared for the depiction of blood flow signals. Power Doppler images were also reviewed for the amount of Doppler signals, pattern of vascularity, and morphology of vessels. The sensitivity, specificity, and accuracy of the 2 techniques were calculated. RESULTS: Compared with color Doppler sonography, power Doppler sonography depicted flow superiorly in 61 cases (60%) and equally in 41 cases (40%). On power Doppler sonography, the incidence of marked blood flow in malignant lesions (65%) was higher than that in benign lesions (39%). The pattern of vascularity was predominantly central (86%) and/or penetrating (65%) more often in malignant lesions than in benign lesions (51% and 34%, respectively). Branching (56%) and disordered vessels (42%) were seen more often in malignant lesions than in benign lesions (22% and 8%, respectively). The sensitivity, specificity, and accuracy in diagnosing malignancy were 64%, 76%, and 71%, respectively, for power Doppler sonography and 77%, 76%, and 76% for color Doppler sonography. CONCLUSIONS: Power Doppler sonography was more sensitive than color Doppler sonography in the detection of flow in solid breast lesions. Although power Doppler sonography was not more effective in diagnosing malignant lesions, central and penetrating vascularity patterns and branching and disordered vessels seem to be helpful findings in predicting malignancy.     

Enhanced color flow images in small hepatocellular carcinoma

BACKGROUND: Features of enhanced color flow images in small hepatocellular carcinoma (HCC) are not fully elucidated. The purpose of this study was to clarify the characteristic vascular images in small HCC observed by enhanced color Doppler. METHODS: Enhanced color Doppler using the contrast agent Levovist was performed on 13 patients with HCC smaller than 30 mm. Enhanced color flow appearance was compared with angiographic findings. Time-intensity changes after injection of the contrast agent were analyzed in HCC nodules. RESULTS: Significant improvement in the detection of color flow signals was obtained in small HCC using Levovist, from 33% in precontrast to 92% in postcontrast (p < 0.005). Three patterns of enhanced color flow images, which were related to the angiographic findings, were observed. The time-intensity curve was classified into two types by "time to peak" and "time on plateau" and was associated with the patterns of enhanced images. CONCLUSION: Enhanced color flow imaging promises to be a useful method for evaluating tumor vascularity noninvasively and to contribute to the elucidation of the hemodynamics in small HCC.