Implementation of spectral width Doppler in pulsatile flow measurements

In this paper, we present an automatic beam-vector (Doppler) angle and flow velocity measurement method and implement it in pulsatile flow measurements using a clinical Doppler ultrasound system. In current clinical Doppler ultrasound flow velocity measurements, the axis of the blood vessel needs to be set manually on the B-scan image to enable the estimation of the beam-vector angle and the beam-vector angle corrected flow velocity (the actual flow velocity). In this study, an annular array transducer was used to generate a conical-shaped and symmetrically focused ultrasound beam to measure the flow velocity vectors parallel and perpendicular to the ultrasound beam axis. The beam-vector angle and flow velocity is calculated from the mode frequency (f(d)) and the maximum Doppler frequency (f(max)) of the Doppler spectrum. We develop a spectrum normalization algorithm to enable the Doppler spectrum averaging using the spectra obtained within a single cardiac cycle. The Doppler spectrum averaging process reduces the noise level in the Doppler spectrum and also enables the calculation of the beam-vector angle and flow velocity for pulsatile flows to be measured. We have verified the measurement method in vivo over a wide range of angles, from 52 degrees to 80 degrees, and the standard deviations of the measured beam-vector angles and flow velocities in the carotid artery are lower than 2.2 degrees and 12 cm/s (about 13.3%), respectively.     

The physical principles of Doppler and spectral analysis

The Doppler effect provides an ultrasonic method for the detection of echoes from moving structures, particularly flowing blood. In its most simple form, the continuous wave Doppler offers velocity information without depth resolution and is therefore used mainly for the examination of superficial structures. The pulsed Doppler, in combination with real-time imaging, provides a more flexible tool for the interrogation of selected sites in an ultrasound image for motion and flow. The recent development of Doppler flow imaging, in which limited Doppler information is displayed over an entire ultrasound image, usually in color and in real-time, promises to secure the association between Doppler and conventional ultrasound imaging techniques. Spectral analysis permits features of the Doppler signal to be identified which are associated with hemodynamic phenomena, such as flow disturbance and wave reflection. In addition, it allows the quantitative application of Doppler to the estimation of such physiological variables as velocity, flow rate, and pressure difference.     

Doppler color flow imaging

By simultaneous processing of frequency, phase, and amplitude information in the backscattered ultrasound signal, new instruments now permit the real-time display of high-resolution grey scale images of tissue combined with the simultaneous display of flow data from vessels within the scan plane. Doppler Color Flow Imaging, or DCFI, using such processing, permits blood flow direction and relative velocity to be detected and displayed in a color encoded display from throughout the ultrasound image. We have tested a new Doppler color flow imaging system over a period of two years to evaluate the carotid arteries, peripheral arteries and veins, and dialysis fistulas. In the abdomen and pelvis we have imaged blood flow to the liver, spleen, kidneys, uterus and renal transplants. Our experience in over 500 patients leads us to conclude that DCFI has significant advantages over conventional duplex Doppler sonography for blood flow evaluation. For examination of carotid and peripheral vessels, we have found DCFI to permit more rapid assessment in both normal and abnormal states. Areas of vessel narrowing or turbulent flow may be identified rapidly and accurately, and vessel orientation may be determined precisely, allowing accurate calculation of blood flow velocity from Doppler frequency shifts. The system we have used has adequate penetration and sensitivity to allow imaging of hepatic and renal blood flow and is extremely promising as a method of imaging organ perfusion and in the detection of abnormalities of perfusion that accompany disease, such as transplant rejection. Tumor vascularity may also be identified with DCFI, opening the possibility of additional clinical applications.     

超声造影对正常动脉检测能力的实验研究

目的研究生理状态下彩色多普勒血流成像(CDFI)对不同深度血管血流的显示能力以及彩色多普勒超声造影(以下简称彩超造影)与实时灰阶谐波超声造影(以下简称谐波造影)的表现。方法动物选择普通家犬5只。使用意大利百胜Technos DU8超声诊断仪及SonoVue超声造影剂。二维超声分别显示犬的髂总动脉、髂外动脉、髂内动脉、股动脉及腋动脉,并测量内径,脉冲多普勒测量收缩期峰值流速(PSV)。人为增加血管深度,CDFI检查记录该深度状态的血流强度。至CDFI不能清晰显示血流时,分别利用彩超造影与谐波造影两种方法再次检测。彩超造影检测时记录血流强度及PSV。结果随着深度增加CDFI观察到的血流信号减弱,造影后血流信号均明显增强;造影后在同一部位检测到的PSV增加36.1%,两组数据比较有显著性差异;谐波造影显示注射造影剂后动脉管腔内回声迅速增强,能够清晰显示血管管壁与管腔的分界。结论造影剂的应用可明显提高CDFI对深部血流信号的检出,而谐波造影能更直观、准确地显示血管壁及流道的轮廓。     

A Rotating Cylinder Phantom for Flow and Tissue Color Doppler Testing

Ultrasound Doppler using two-dimensional (2D) techniques is commonly used to study blood flow and myocardial tissue motion. This use includes measurement of velocity and time intervals, often in relation to the electrocardiogram (ECG) signal. 2D Doppler is frequently considered a real-time technique but in reality the acquisition time can be as long as 200 ms per image. We have developed a test-phantom using a rotating cylinder to simulate blood flow and tissue motion in a whole sector or space angle to evaluate velocity and timing characteristics. The phantom can produce constant velocities for velocity testing, as well as accelerating movement for testing the timing characteristics of ultrasound systems. Our investigation shows that the cylinder phantom is especially suitable for timing measurements in 2D Doppler imaging and that time delays between the Doppler signals and the ECG signal exist in the tested ultrasound system. (E-mail: andrew.walker@ltv.se)     

Precision and accuracy of Doppler flow measurements. In vitro and in vivo study of the applicability of the method in human fetuses

The precision of the Doppler method for quantitative blood flow measurement in the fetal descending thoracic aorta and in the umbilical vein and for estimation of the Pulsatility Index from the velocity curve from fetal aorta was tested in vivo by examination of six pregnant women eight times. Two investigators examined each patient twice in random order upon two successive days. The diameter of the vessel was measured using planimetry on a magnified time-motion image of the diameter variations during the heart cycle, while the angle between the ultrasound Doppler beam and the vessel of interest was measured on the hard copy image. No systematic variation was found between observers, days, repeated observations or repeated readings of curves and images. The mean coefficient of variations was 5.6% for the quantitative flow per kilogram estimated fetal weight measured in the fetal descending aorta, 6.8% for the quantitative flow per kilogram estimated fetal weight measured in the umbilical vein and 9.8% for the Pulsatility Index. When the diameter of aorta was calculated as the mean of the maximal and the minimal diameter measured on the hard copy image, the mean coefficient of variation for the flow increased to 9.4%. In vitro tests of the Doppler instrument and the real-time scanner revealed a systematic overestimation of Doppler measured flow of only 4.4% compared with the true flow, and a real-time scanner underestimation of vessel diameter of only 1.1%.     

Increased accuracy of echocardiographic measurement of flow using automated spherical integration of multiple plane velocity vectors.

The calculation of blood flow in the heart by surface integration of velocity vectors (SIVV) using Doppler ultrasound is independent of the angle. Flow is normally calculated from velocity in a spherical thick shell with its center located at the ultrasound transducer. In a numerical simulation, we have shown that the ratio between minor and major axes of an elliptic flow area substantially influences the accuracy of the estimation of flow in a single scan plane. The accuracy of flow measurements by SIVV can be improved by calculating the mean of the values from more than one scan plane. We have produced an automated computer program that includes an antialiasing procedure. We confirmed an improvement of flow measurements in a pulsatile hydraulic flow model, the 95% confidence interval for single estimations being reduced from 20% to 10% (p < 0.05) using the newly developed software. We think that the SIVV method has important implications for clinical transthoracic echocardiography.     

淋巴管畸形的高频超声与彩色多普勒特点

目的 研究淋巴管畸形的高频超声及彩色多普勒超声表现特点并进行分析、总结.方法 应用高频超声及彩色多普勒超声对23例淋巴管畸形的二维灰阶超声声像图及彩色血流信号进行回顾性研究.超声扫查内容包括:病变大小、边界、内部回声、彩色血流信号及用脉冲多普勒测量血流速度.结果 17例淋巴管畸形(74%,17/23)位于颈部、颌下或腋下,6例位于其他部位;21例位于皮下组织内,其中3例同时累及真皮及肌层.13例大囊型淋巴管畸型,均显示为较大的无回声区,有分隔,壁光滑,其中2例大囊型合并感染,无回声区内有稀疏低回声;5例混合型淋巴管畸形,为淋巴管畸形和血管畸形混合存在,超声显示为大小不等的无回声区有分隔,合并局部微小无回声区或不规则的小的实性低回声区,其中3例侵及肌层;5例微囊型淋巴管畸形,超声显示以无回声区为主,内有少量的低回声区,形成囊实混合性病变.所有病例无回声区内彩色多普勒扫查均无彩色血流信号.8例大囊型及3例混合型淋巴管畸形周边扫查到彩色血流信号,2例微囊型内部实性低回声内显示有彩色血流信号.脉冲多普勒检查最大血流速度18～73 cm/s,阻力指数0.55～0.72.结论 淋巴管畸形的高频超声及彩色超声多普勒成像有显著的特点,以较大的无回声区为主,多发可有分隔,无回声区内无血流信号,大部分位于皮下组织内,基于以上特点,可确诊大部分病例,因而高频超声及彩色多普勒是诊断淋巴管畸形的较好方法.     

Translabial color Doppler for imaging in urogynecology: a preliminary report.

OBJECTIVE: A prospective study was conducted to evaluate the use of color Doppler ultrasound in the investigation of female urinary incontinence. METHODS: Thirty-seven patients underwent a full urodynamic assessment and translabial ultrasound examination using color Doppler-capable equipment with 5-7-MHz curved array transducers, both in the supine and in the erect positions. RESULTS: More than minimal leakage was seen in 13 patients by Doppler and in 16 by fluoroscopic imaging. Results were in agreement in 28/37 cases (kappa 0.49). The observed discrepancies may have been due to initial technical difficulties, differences in bladder filling and the presence of a catheter on fluoroscopic imaging. In five incontinent patients, urethral flow velocities ranged from 0.064 to 0.34 m/s, which is equivalent to physiological venous and slow arterial blood flow and one to two orders of magnitude above the detection threshold of standard Doppler ultrasound equipment. CONCLUSIONS: Translabial color Doppler imaging of the lower urinary tract allows the documentation of fluid leakage from the bladder. It has the potential to become the new imaging standard for urogynecology.     

A single-ensemble-based hybrid approach to clutter rejection combining bilinear Hankel with regression

Purpose

Clutter regarded as ultrasound Doppler echoes of soft tissue interferes with the primary objective of color flow imaging (CFI): measurement and display of blood flow. Multi-ensemble samples based clutter filters degrade resolution or frame rate of CFI. The prevalent single-ensemble clutter rejection filter is based on a single rejection criterion and fails to achieve a high accuracy for estimating both the low- and high-velocity blood flow components.

Methods

The Bilinear Hankel-SVD achieved more exact signal decomposition than the conventional Hankel-SVD. Furthermore, the correlation between two arbitrary eigen-components obtained by the B-Hankel-SVD was demonstrated. In the hybrid approach, the input ultrasound Doppler signal first passes through a low-order regression filter, and then the output is properly decomposed into a collection of eigen-components under the framework of B-Hankel-SVD. The blood flow components are finally extracted based on a frequency threshold.

Results

In a series of simulations, the proposed B-Hankel-SVD filter reduced the estimation bias of the blood flow over the conventional Hankel-SVD filter. The hybrid algorithm was shown to be more effective than regression or Hankel-SVD filters alone in rejecting the undesirable clutter components with single-ensemble (S-E) samples. It achieved a significant improvement in blood flow frequency estimation and estimation variance over the other competing filters.     

Development of a Flexible Implantable Sensor for Postoperative Monitoring of Blood Flow

We have developed a blood flow measurement system using Doppler ultrasound flow sensors fabricated of thin and flexible piezoelectric‐polymer films. These flow sensors can be wrapped around a blood vessel and accurately measure flow. The innovation that makes this flow sensor possible is the diffraction‐grating transducer. A conventional transducer produces a sound beam perpendicular to its face; therefore, when placed on the wall of a blood vessel, the Doppler shift in the backscattered ultrasound from blood theoretically would be 0. The diffraction‐grating transducer produces a beam at a known angle to its face; therefore, backscattered ultrasound from the vessel will contain a Doppler signal. Flow sensors were fabricated by spin coating a poly(vinylidene fluoride–trifluoroethylene) copolymer film onto a flexible substrate with patterned gold electrodes. Custom‐designed battery‐operated continuous wave Doppler electronics along with a laptop computer completed the system. A prototype flow sensor was evaluated experimentally by measuring blood flow in a flow phantom and the infrarenal aorta of an adult New Zealand White rabbit. The flow phantom experiment demonstrated that the error in average velocity and volume blood flow was less than 6% for 30 measurements taken over a 2.5‐hour period. The peak blood velocity through the rabbit infrarenal aorta measured by the flow sensor was 118 cm/s, within 1.7% of the measurement obtained using a duplex ultrasound system. The flow sensor and electronics operated continuously during the course of the 5‐hour experiment after the incision on the animal was closed.     

肾脏血流灌注的评估:造影增强彩色多普勒时间-强度曲线分析

背景超声评价肾脏功能主要通过测量较粗大的肾脏各级动脉的血流参数或肾切面内动脉彩色血流面积所占的比例来推断,误差较大.目的应用超声仪器随机配置的彩色多普勒时间-强度曲线软件评价肾脏血流灌注情况.设计动物实验观察.单位广州市第一人民医院功能检查科.材料实验于1999-01/2000-04在广州军区广州总医院动物实验室完成,选择8只健康新西兰兔,雌雄各4只,体质量2.5～3.5 kg.观察肾脏16个.声学造影剂为全氟显,主要成分为声振白蛋白的微泡,微泡内有一定浓度的全氟丙烷气体.方法兔外周静脉团注造影剂全氟显后用彩色多普勒能量图、彩色多普勒血流显像和彩色多普勒能量谐波成像连续采集肾脏彩色血流图像,随机配置软件显示时间-强度曲线.主要观察指标造影增强肾脏血流灌注时间-强度曲线的形态.结果进入结果分析8只家兔.肾脏血流造影增强的时间-强度曲线呈单峰状,上升支陡直,下降支平缓.调节时间轴上的感兴趣线可作定量分析,回放显示注射造影剂后对应某一时刻的造影增强的彩色多普勒图像.结论造影增强彩色多普勒血流显像和彩色多普勒能量图的时间-强度曲线能有效的观察肾脏血流灌注特征,既可显示整个肾脏的血流灌注情况,也用于观察低血流灌注区域,发现病灶进一步绘制肾功能图.     

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。     

彩色多谱勒对IUGR脐动脉血流的检测

目的：应用彩色多谱勒检测正常妊娠和胎儿宫内发育迟缓（以简称ＩＵＧＲ）的脐动脉血流指标ＰＩ、ＲＩ、Ｓ／Ｄ值。材料和方法：应用彩色多谱勒检测了２００例正常妊娠和１１１例ＩＵＧＲ的脐动脉血流,孕周从２６－４１周。结果：正常妊娠组及ＩＵＧＲ组的脐动脉血流指标均随妊娠周数的增高而降低,但ＩＵＧＲ组的脐动脉血流ＰＩ、ＲＩ、Ｓ／Ｄ值明显高于正常妊娠组（Ｐ〈０．０１）。孕３０周后,脐动脉血流Ｓ／Ｄ值〉４,揭示胎儿预后不良。结论：脐动脉血流检测不仅是胎儿监护的一种方法,而且可作为诊断ＩＵＧＲ的一个指标及对估计胎儿预后有一定的临床价值。     

A double beam doppler ultrasound method for quantitative blood flow velocity measurement

A method for measuring the absolute blood flow velocity waveform is reported. Two independent beams of ultrasound illuminate a vessel simultaneously, producing complementary Doppler signals. The two Doppler frequency shift signals are processed by subtraction and addition at the receiver. The optimum probe position where blood flow velocity is detected can be found as the position where the subtractor output reaches zero. At this position the blood flow velocity is the output from the adder. By this means the influence of the angle between the probe and blood flow is eliminated so that a quantitative measurement is obtained. Both in vitro and clinical results are reported.     

彩色多普勒超声在获得性子宫动静脉瘘的诊断及疗效评估中的应用

目的探讨获得性子宫动静脉瘘（AVM）的二维及多普勒超声特征，分析二维及彩色多普勒超声在经子宫动脉栓塞治疗后疗效观察中的价值。 方法选择11例获得性子宫AVM患者为研究对象。回顾性分析其子宫及病灶区二维声像图、彩色多普勒血流（CDFI）表现，量化分析多普勒流速曲线特点，包括收缩期峰值速率（PSV）和阻力指数（RI），结合临床症状对经子宫动脉栓塞术（UAE）治疗后病灶的声像图变化，进行分析。 结果11例患者均经彩色多普勒超声诊断为子宫AVM，二维超声图像显示为子宫肌层内见单发类圆形无回声区和（或）多个小无回声区伴低回声呈"蜂窝状"，彩色多普勒显示无回声区内有丰富红蓝镶嵌血流信号充填，呈"马赛克"或"湖泊样"改变；脉冲多普勒呈高速低阻血流流速曲线，典型者表现出静脉血流动脉化表现，11例超声检查结果与子宫动脉造影结果基本一致。患者均接受了UAE治疗，10例栓塞术后1周~6个月复查，二维超声见病灶均有明显减小或逐渐消失，彩色多普勒超声表现为低速静脉血流信号或异常血流信号消失；1例随访1周~11个月表现为病灶减小但低速低阻动脉流速曲线持续存在，再次栓塞后仍复发出血，患者因无生育需求最终切除子宫。 结论彩色多普勒超声对获得性子宫动静脉瘘的诊断及UAE后对其治疗效果的评估监测有重要价值。     

Measurement of blood flow by ultrasound: accuracy and sources of error

Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level.     

Blood flow velocity profiles in the aortic annulus: a 3-dimensional freehand color flow Doppler imaging study.

BACKGROUND: The use of a single sample volume in Doppler measurements of the velocity time integral (VTI) in the aortic annulus may introduce errors in calculations of stroke volumes, shunts, regurgitant fractions, and aortic valve area. To study the blood flow velocity distribution and assess this potential error, we used a dynamic 3-dimensional color flow Doppler imaging method. METHODS AND RESULTS: Seventeen healthy volunteers were studied. The ultrasound data were captured from 10 to 20 heartbeats at a high frame rate (mean 57 frames per second) while freely tilting the transducer in the apical position. A magnetic position-sensor system recorded the spatial position and orientation of the probe. The raw digital ultrasound data were analyzed off-line with no loss of temporal resolution. Blood flow velocities were integrated across a spherical surface that tracked the aortic annulus during systole. The ratios of the systolic maximum to the systolic mean VTI ranged from 1.2 to 1.5 (mean 1.4). At the time of systolic peak flow, the ratios of the maximum to the mean velocity ranged from 1.1 to 2.0 (mean 1.5). The location of the maximum velocities and VTI showed individual variation. CONCLUSION: The blood flow velocity profile was nonuniform. By using a single sample volume in Doppler measurements of the VTI in the aortic annulus, errors ranging from 20% to 50% may be introduced in calculations of stroke volumes.     

定量分析多普勒血流信号评价甲状腺功能亢进症的血流变化

目的探讨定量超声能量多普勒血流信号对甲状腺功能亢进症的诊断价值。方法采用“DFY型超声图像分析仪”对30例实验组（甲亢患者）和30例对照组（健康志愿者）的超声能量多普勒图像提取彩色信号,定量分析多普勒信号与总感兴趣区面积比以及平均彩色信号强度,并进行两组间对比分析。结果实验组与对照组的多普勒信号与总感兴趣区面积比分别为64．80±7．17和6．03±1．83,实验组与对照组的平均彩色信号强度分别为78．60±3．73和57．43±5．15,组间比较差异具有统计学意义,P〈0．01。结论“DFY型超声图像分析仪”可定量甲状腺功能亢进症的血流增多情况,可为该疾病提供更多有价值的诊断信息。