Time delays in ultrasound systems can result in fallacious measurements

Even short time delays (less than 30 ms) in cardiac motion pattern may have clinical relevance. These delays can be measured with echocardiography, using techniques such as flow and tissue Doppler and M-mode together with external signals (e.g., ECG and phonocardiography). If one or more of these signals are delayed in relation to the other signals (asynchronous), an incorrect definition of cardiac time intervals can occur, the consequence of which is invalid measurement. To determine if this time delay in signal processing is a problem, we tested three common ultrasound (US) systems using the ECG as the reference signal. We used a digital ECG simulator and a Doppler string phantom to obtain test signals for flow and tissue pulsed Doppler, M-mode, phonocardiography, auxiliary and ECG signals. We found long time delays of up to 90 ms in one system, whereas delays were mostly short in the two other systems. The time delays varied relative to system settings. Consequently, to avoid these errors, precise knowledge of the characteristics of the system being used is essential.     

High-Frame-Rate Power Doppler Ultrasound Is More Sensitive than Conventional Power Doppler in Detecting Rheumatic Vascularisation

Early recognition of joint inflammation will increase treatment efficacy in rheumatoid arthritis (RA). Yet, conventional power Doppler (PD) ultrasound might not be sufficiently sensitive to detect minor inflammation. We investigated the sensitivity of high-frame rate Doppler, combined with singular value decomposition technique, to suppress tissue signals, for microvascular flow in a flow phantom setup and in a proof-of-principle study in healthy controls and in RA patients with different disease activities. In the flow phantom, minimal detectable flow velocity was a factor 3 lower with high-frame-rate PD than with conventional PD ultrasound. In the proof-of-principle study we detected a positive PD signal in all volunteers, diseased or healthy, with high-frame-rate PD ultrasound. We saw a gradual increase in PD signal in RA patients depending on disease activity. In conclusion, high-frame rate Doppler is more sensitive in detecting vascularisation than conventional PD ultrasound.     

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.     

彩色多普勒超声对骨巨细胞瘤的诊断价值

目的：探讨彩色多普勒超声在骨巨细胞瘤诊断中的价值。方法：回顾性分析39例经病理证实的骨巨细胞瘤的二维及彩色多普勒超声声像图特征、血流分布和血流动力学变化。按照Campanacci分级对血流动力学参数进行统计分析。结果：组间收缩期峰值流速（PSV）的差异不明显（P>0.05）,舒张末期流速（EDV）I级低于III级（P<0.05）。阻力指数（RI）I级与II、III级之间存在差异（P<0.05）,而后两者之间无统计学差异（P>0.05）。结论：通过二维图像及CDFI观察肿瘤形态及血流动力学参数对骨巨细胞瘤的诊断及临床分级的鉴别诊断有一定的意义。     

多普勒组织显像对脑梗死患者腹主动脉壁运动的研究

目的评价多普勒组织显像(DTI)对脑梗死患者腹主动脉(AAo)前壁运动速度定量检测的应用价值.方法对43例脑梗死患者的AAo前壁进行PW-DTI检查,结合同步心电图描记,对PW-DTI频谱进行观察,分别测量E、S1、S2、D峰值;测量S1峰起始至S1峰顶点的上升斜率(AC)及S1峰顶点至S1峰结束的下降斜率(DC);同时测量电-机械时间(EMT)、左室射血前期(PEP)、脉搏波传递时间(PWT,PWT=EMT-PEP),并分别与健康组比较加以统计分析.结果脑梗死患者AAo前壁的PW-DTI频谱E、S1、S2、D峰值均有下降,与正常对照组比较有显著性差异(P＜0.001);AC及DC减低,PWT间期缩短,与对照组比较有显著性差异(P＜0.001).结论脑梗死患者AAo前壁DTI技术的检测,可作为评价脑梗死患者腹主动脉壁弹性和顺应性的一项新指标.     

Non-invasive Small Vessel Imaging of Human Thyroid Using Motion-Corrected Spatiotemporal Clutter Filtering

Reliable assessment of small vessel blood flow in the thyroid, without using any contrast agents, can be challenging because of increased physiological motion resulting from its proximity to the pulsating carotid artery. In this study, we hypothesized that correction of tissue motion prior to singular value decomposition (SVD)-based clutter filtering can improve the coherency of the tissue components and, thus, may allow better clutter suppression and visualization of small vessels in the thyroid. We corroborated this hypothesis by conducting phantom and in vivo studies using a clinical ultrasound scanner implemented with compounded plane wave imaging. The phantom studies were conducted using a homogeneous tissue-mimicking phantom to study the impact of motion on the covariance of the spatiotemporal Doppler data, in the absence of blood activity. The non-invasive in vivo study was conducted on a 74-y-old woman with a thyroid nodule suspicious of malignancy. A rigid body-based motion correction was performed using tissue displacements obtained from 2-D normalized cross-correlation–based speckle tracking. Subsequently, the power Doppler images were computed using SVD-based spatiotemporal clutter filtering. The results from the phantom study revealed that motion can considerably reduce the covariance of the spatiotemporal data and, thus, increase the rank of the tissue components. When the phantom was subjected to a total translation displacement of 6 pixels over the entire ensemble, in each direction (axial and lateral), the covariance dropped by more than 25%. The results obtained from the non-invasive in vivo study indicated that visualization of small vessel blood flow improved with motion correction of the power Doppler ensemble. The contrast-to-noise ratio of the blood signal in motion-corrected power Doppler images was considerably higher (8.17 and 8.32 dB), compared with that obtained using the standard SVD approach at an optimal threshold (0.87 and 4.33 dB) and a lower singular value threshold (1.92 and 3.05 dB). Further, the covariance of the in vivo thyroid spatiotemporal data increased by approximately 10% with motion correction. These preliminary results indicate that motion correction can be used to improve the visualization of small vessel blood flow in the thyroid, without using any contrast agents. The results of this feasibility study were encouraging, and warrant further development and more in vivo validation in moving tissues and organs.     

High-frequency ultrasound Doppler system for biomedical applications with a 30-MHz linear array

In this paper, we report the development of the first high-frequency (HF) pulsed-wave Doppler system using a 30-MHz linear array transducer to assess the cardiovascular functions in small animals. This array-based pulsed-wave Doppler system included a 16-channel HF analog beamformer, a HF pulsed-wave Doppler module, timing circuits, HF bipolar pulsers and analog front ends. The beamformed echoes acquired by the 16-channel analog beamformer were fed directly to the HF pulsed-wave Doppler module. Then the in-phase and quadrature-phase (IQ) audio Doppler signals were digitized by either a sound card or a Gage digitizer and stored in a personal computer. The Doppler spectrogram was displayed on a personal computer in real time. The two-way beamwidths were determined to be 160 microm to 320 microm when the array was electronically focused at different focal points at depths from 5 to 10 mm. A micro-flow phantom, consisting of a polyimide tube with an inner diameter of 127 microm and the wire phantom were used to evaluate and calibrate the system. The results show that the system is capable of detecting motion velocity of the wire phantom as low as 0.1 mm/s, and detecting blood-mimicking flow velocity in the 127-microm tube lower than 7 mm/s. The system was subsequently used to measure the blood flow in vivo in two mouse abdominal superficial vessels, with diameters of approximately 200 microm, and a mouse aorta close to the heart. These results demonstrated that this system may become an indispensable part of the current HF array-based imaging systems for small animal studies.     

A wall-less vessel phantom for Doppler ultrasound studies

Doppler ultrasound flow measurement techniques are often validated using phantoms that simulate the vasculature, surrounding tissue and blood. Many researchers use rubber tubing to mimic blood vessels because of the realistic acoustic impedance, robust physical properties and wide range of available sizes. However, rubber tubing has a very high acoustic attenuation, which may introduce artefacts into the Doppler measurements. We describe the construction of a wall-less vessel phantom that eliminates the highly attenuating wall and reduces impedance mismatches between the vessel lumen and tissue mimic. An agar-based tissue mimic and a blood mimic are described and their acoustic attenuation coefficients and velocities are characterised. The high attenuation of the latex rubber tubing resulted in pronounced shadowing in B-mode images; however, an image of a wall-less vessel phantom did not show any shadowing. We show that the effects of the highly attenuating latex rubber vessels on Doppler amplitude spectra depend on the vessel diameter and ultrasound beam width. In this study, only small differences were observed in spectra obtained from 0.6 cm inside diameter thin-wall latex, thick-wall latex and wall-less vessel phantoms. However, a computer model predicted that the spectrum obtained from a 0.3-cm inside diameter latex-wall vessel would be significantly different than the spectrum obtained from a wall-less vessel phantom, thus resulting in an overestimation of the average fluid velocity. These results suggest that care must be taken to ensure that the Doppler measurements are not distorted by the highly attenuating wall material. In addition, the results show that a wall-less vessel phantom is preferable when measuring flow in small vessels.     

彩色多普勒超声在骨肿瘤诊断中的应用价值

目的：探讨彩色多普勒超声在诊断骨肿瘤中的价值。方法：应用二维及彩色多普勒超声显像对22例恶性和27例良性骨肿瘤进行检查，观察分析病变的声像图特征、血流分布和血流动力学变化。结果：良、恶性组问血流分级有显著差异（P＜0．01），组间收缩期峰值流速（PSV）及舒张末期流速（EDV）的差异不明显（P〉0．05），阻力指数（RI）差异显著（P＜0．01）。Pearson线性相关分析显示骨肿瘤的声像图特征和血流情况与良、恶性均有良好的相关性。结论：超声对骨肿瘤病变周围软组织浸润的判断具有独特的优势，CDFI对良、恶性的鉴别诊断有一定的意义。     

A real time system for quantifying and displaying two-dimensional velocities using ultrasound

This paper describes a system that has been developed for measuring two-dimensional velocities in real time using ultrasound. The instrument tracks interframe speckle pattern motion using a Sum-Absolute-Difference (SAD) algorithm in order to produce a vector map of 2D velocities. The system's parallel architecture allows calculation of approximately 20,000 vectors per second using the current tracking geometry. A programmable graphics processor encodes individual velocity vectors with color and displays them superimposed on the B-mode image in real time. In vitro tests indicate that the system can track velocities well over the Doppler aliasing limit in any direction in the scan plane with greater than 94% accuracy. A color encoded image obtained from a flow phantom highlights the system's ability to display lateral motion with uniform coloration, in contrast to the two-color display of current ultrasonic Doppler instruments.     

Vector Doppler imaging of a spinning disc ultrasound Doppler phantom

Vector Doppler methods are used to obtain angle independent in-plane velocity information. Velocity magnitude as well as direction are reconstructed from regular steered colour flow and from split-aperture Doppler acquisitions. Spatially resolved in-plane velocity was obtained through Doppler colour flow mode and subsequent data triangulation. A depth-invariant constant Doppler angle was achieved by using a depth expanding transmit-receive Doppler aperture. Velocities of up to 50 cm s(-1) and 360 degrees vector velocity directions were measured. This was achieved by creating a spinning solid disc phantom. Such a phantom was built to allow underwater mounting and spinning of a solid disc-shaped ultrasound phantom (maximum velocity of 50 cm s-1). Doppler triangulation was realised by steered Doppler and by a split-aperture approach. Results of both imaging methods are shown. Split-aperture results showed errors of less then 10% for velocity magnitude estimation and less then 2.5 degrees for directional information.     

彩色多普勒超声及能量图对软组织蔓状血管瘤的诊断

目的探讨彩色多普勒超声及多普勒能量图在诊断蔓状血管瘤中的应用价值。方法对27例软组织不同部位的蔓状血管瘤行二维、彩色多普勒血流检查及多普勒能量图分析。结果蔓状血管瘤二维形态表现为呈梭形或长条状,内为网格或蜂窝样低或无回声区。相互交通。CDFI:内充满闪烁明亮的红蓝相间的彩流,或以低速静脉血流为主,或以高速低阻型动脉血流信号为主。加用能量图见血流信号极其丰富,连续性好,形成血管树样网状结构分布。乏氏试验,加压或体位改变后其大小形态及血流状态随之发生变化。结论彩色多普勒超声及能量图对蔓状血管瘤的诊断具有重要的临床应用价值。     

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。     

Doppler myocardial imaging in the assessment of normal and ischemic myocardial function--past, present and future

Myocardial ischemia is associated with impaired regional myocardial function. Echocardiography is a suitable technique for the assessment of regional myocardial function as it is easily applicable and commonly available. However, most of the currently used echo-techniques are based on 2D images or M-mode traces. Therefore, they are limited either to the assessment of myocardial segments that can be insonated at 90° or are based on visually assessed wall motion scoring which is semiquantitative at best. Doppler myocardial imaging (DMI) is a new ultrasound technique which assesses the velocity of myocardial motion. Different parameters can be derived from this velocity information such as velocity time integrals, intramural velocity gradients and strain/strain-rate information. Moreover, DMI provides information of the timing of regional motion related to myocardial contraction and relaxation. These parameters are all assessed quantitatively, therefore, DMI is a promising technique to quantify myocardial function, avoiding the disadvantages of observer-dependant judgement of myocardial contraction.     

Doppler velocity histogram analysis of hepatocellular carcinoma

To study the characteristics of tumor blood flow, flow profiles from hepatocellular carcinomas (39 profiles) and normal hepatic arteries (23 profiles) were evaluated using velocity histograms obtained with Doppler ultrasound. The histograms were classified into three types: (1) high-peak, (2) flat, and (3) low-peak. Characteristically, the low-peak types and the flat types, with flows in opposing directions, were seen only in the tumor vessels. The turbulence in a phantom flow model was of the low-peak type. Spectral analysis revealed that the velocity profile of tumor blood flow was different from that of noncancerous flow and that tumor blood flow was characterized by turbulence. © 1995 John Wiley & Sons, Inc.     

The Leicester Doppler Phantom—A Digital Electronic Phantom for Ultrasound Pulsed Doppler System Testing

Doppler flow and string phantoms have been used to assess the performance of ultrasound Doppler systems in terms of parameters such as sensitivity, velocity accuracy and sample volume registration. However, because of the nature of their construction, they cannot challenge the accuracy and repeatability of modern digital ultrasound systems or give objective measures of system performance. Electronic Doppler phantoms are able to make use of electronically generated test signals, which may be controlled precisely in terms of frequency, amplitude and timing. The Leicester Electronic Doppler Phantom uses modern digital signal processing methods and field programmable gate array technology to overcome some of the limitations of previously described electronic phantoms. In its present form, it is able to give quantitative graphical assessments of frequency response and range gate characteristics, as well as measures of dynamic range and velocity measurement accuracy. The use of direct acoustic coupling eliminates uncertainties caused by Doppler beam effects, such as intrinsic spectral broadening, but prevents their evaluation. (E-mail: john.gittins@uhl-tr.nhs.uk)     

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。     

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。     

High-frequency subharmonic pulsed-wave Doppler and color flow imaging of microbubble contrast agents

A recent study has shown the feasibility of subharmonic (SH) flow imaging at a transmit frequency of 20 MHz. This paper builds on these results by examining the performance of SH flow imaging as a function of transmit pressure. Further, we also investigate the feasibility of SH pulsed-wave Doppler (PWD) imaging. In vitro flow experiments were performed with a 1-mm-diameter wall-less vessel cryogel phantom using the ultrasound contrast agent Definity and an imaging frequency of 20 MHz. The phantom results show that there is an identifiable pressure range where accurate flow velocity and power estimates can be made with SH imaging at 10 MHz (SH10), above which velocity estimates are biased by radiation force effects and unstable bubble behavior, and below which velocity and power estimates are degraded by poor SNR. In vivo validation of SH PWD was performed in an arteriole of a rabbit ear, and blood velocity estimates compared well with fundamental (F20) mode PWD. The ability to suppress tissue signals using SH signals may enable the use of higher frame rates and improve sensitivity to microvascular flow or slow velocities near large vessel walls by reducing or eliminating the need for clutter filters.