On the measurement of the mean velocity of blood flow over the cardiac cycle using Doppler ultrasound

A number of modern duplex scanners now have facilities for determining volumetric blood flow through intact vessels. The methods these machines use to arrive at an answer must presuppose a number of conditions which may not be met in practice. This paper examines the effect that nonuniform insonation of the target blood vessel (using continuous wave or wide-gate pulsed ultrasound) has on the mean velocity, as determined using mean, root mean square (RMS) and maximum frequency processors. It is shown that for a given beam/vessel geometry the error is dependent only on the shape of the mean component of the velocity profile which, depending on the arterial site, may be flat, parabolic or intermediate. Mean processors may overestimate the mean velocity of established flow by up to 33%, but this could be turned to advantage when it is impracticable to insonate a vessel uniformly. Maximum frequency processors are of value when either plugflow or fully established flow of low pulsatility is present in the target vessel. In the first case the mean flow is the same as the maximum flow, while in the second the mean flow is half the time averaged maximum flow, irrespective of the size and shape of the ultrasound beam. RMS processors are probably best avoided in volumetric flow measurement applications.     

Pulsed Doppler with B-mode imaging for quantitative blood flow measurement.

A technique is described, using the UI Octoson and a frequency-offset pulsed Doppler system, to obtain fully quantitative blood flow measurements in deep-lying vessels. By uniformly insonating the vessel and using a mean frequency Doppler demodulator, average velocity is obtained regardless of the velocity profile. B-scan imaging provides the necessary anatomic information to calculate volume flow from this average velocity. Results of in vitro flow measurement tests indicate accuracies of ± 14% rms error, ± 32% maximum error. The causes of error appear to be well understood, and in a number of cases they can be corrected. Preliminary clinical measurements of fetal umbilical vein flow and adult right branch portal vein flow are also presented.     

Accuracy and limitations of the ultrasonic Doppler blood velocimeter and zero crossing detector.

The zero crossing detector processes blood velocity signals from a Doppler ultrasonic velocimeter to give an output that can be recorded on paper. Although this output gives an indication of the instantaneous velocity averaged across the vessel the system does have limitations when used for quantitative work. This paper explains the working of the zero crossing detector and illustrates how errors can arise due to changes in amplitude and frequency content of the signal. Suggestions are made for reducing the errors, and other more accurate methods of analysis are discussed.     

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。     

胎儿脐动脉血流速度与新生儿结局的关系(附166例分析)

目的 :探讨胎儿脐动脉血流速度与新生儿结局的关系。方法 :对 166名孕妇的脐动脉收缩期峰值 (S)与舒张末期峰值 (D)比值 (S/D比值 )测定结果、新生儿结局进行回顾性分析。结果 :S/D比值异常者 17例 ,其中小于胎龄儿 12例 (70 % ) ,新生儿死亡 3例 (18% ) ;正常 149名中小于胎龄儿7例 (5 % ) ,无新生儿死亡。两组比较有显著性差异。结论 :胎儿脐动脉 S/D比值可作为评估新生儿结局的一个重要指标。     

应用超声微泡直接测量微小血管血流速度

目的应用超声微泡直接、非侵入性测量微小血管的血流速度。方法体外实验：用硅胶管建立一种模拟血流的体外模型,应用谐波超声追踪超声微泡在管内的流动,并录像。用“DFY型超声图像定量分析诊断仪”分析每帧中微泡的位置,以微泡的移动距离除以时间,得到微泡的移动速度。体内实验：建立9只大鼠直肠癌移植瘤模型,用与体外实验相同的方法测量大鼠直肠癌移植瘤内微小血管的血流速度。肿瘤切片HE染色,显微镜下测量肿瘤血管内径。结果体外实验：在体外模型中的血流标准速度分别为37．14mm／s,21．01mm／s和4．35mm／s,应用本法测得的血流速度为（37．03±2．45）1mm／s、（24．40±2．10）mm／s和（4．86±0．45）mm／s,两者间无统计学差异。体内实验：在肿瘤模型中所测得的小血管内血流速度为5．38～20．82mm／s;HE染色发现9个肿瘤外周的最大血管内径平均为（142．76±24．03）μm,肿瘤内部的最大血管内径平均为（40．82±11．17）μm。这些小血管在常规多普勒超声下不能被探及。结论本实验测试了一种直接测量小血管的血流速度的新技术。结果表明,应用超声微泡可以准确测量小血管内的血流速度。经过对自动化跟踪技术的优化,这种新技术极有可能成为临床上非侵入性直接测量小血管血流速度的有效工具。     

Effect of microbubble contrast on intracranial blood flow velocity assessed by transcranial Doppler

Purpose

Ultrasound contrast agents (UCA) salvage a considerable number of transcranial Doppler (TCD) exams which would have failed because of poor bone window. UCA bolus injection causes an undesirable increase in measured blood flow velocity (BFV). The effect of UCA continuous infusion on measured BFV has not been investigated, and some in vitro experiments suggest that gain reduction during UCA administration may also influence measured BFV. This study aimed to investigate the effect of UCA continuous infusion on BFV measured by TCD and the influence of gain reduction on these measurements in a clinical setting.

Methods

The right middle cerebral artery of ten patients with optimal bone window was insonated using a 2 MHz probe. UCA were administered using an infusion pump. BFV was measured (1) at baseline, (2) during UCA infusion, (3) during UCA infusion with gain reduction, and (4) after UCA wash-out phase. Gain reduction was based on the agreement between two neurosonographers on the degree of gain reduction necessary to restore baseline Doppler signal intensity (DSI). Actual DSI was estimated offline by analysis of raw data.

Results

BFV measured during UCA infusion with no gain adjustment was significantly higher than baseline BFV [peak systolic velocity (PSV): 85.1 ± 19.7 vs. 74.4 ± 19.7 cm/s, p < 0.0001; Mean velocity (MV): 56.5 ± 11.8 vs. 50.2 ± 12.3 cm/s, p < 0.0001]. BFV measured during UCA infusion with gain reduction was not significantly higher than baseline BFV (PSV: 74.3 ± 18.9 vs. 74.4 ± 19.4 cm/s, p = 0.8; MV: 49.4 ± 11.0 vs. 50.2 ± 12.3 cm/s, p = 0.8). Actual DSI during UCA infusion with gain reduction was not significantly higher than baseline DSI (13 ± 1 vs. 13 ± 1 dB).

Conclusion

This study shows that UCA continuous infusion leads to an increase in measured BFV which may be counteracted by reducing Doppler gain thus restoring pre-contrast DSI.     

Quantitative transcutaneous measurements of blood flow in carotid artery by means of pulse and continuous wave Doppler methods.

The authors present results of quantitative measurements of blood in vivo in the carotid artery of man. The Doppler pulse technique was used after being previously verified for steady state flows in tubes and for pulsating flows in a canine aorta where the electromagnetic method was also used for comparison.An ultrasonic probe with two transducers was adapted for determination of the angle of the ultrasonic beam in relation to the vessel allowing the measurement of the vessel diameter which was also determined by means of the ultrasonographic B-mode technique.By means of the Doppler pulse method profiles of the blood velocity in the carotid artery were determined as a function of time.The continous wave Doppler technique together with the zero-crossing system and spectral analysis were also used for making measurements.The flow velocity and the shape of the flow curve with time obtained with the above techniques showed good agreement. The measured flow rate in the carotid artery amounted to Q_M = 1.61/min (maximum instantaneous value) and Q₀ - 0.531/min (mean time value).     

Doppler color flow imaging in the detection and quantitative measurement of the gastroduodenal artery blood flow

The purpose of this article was to investigate the detection rate of gastroduodenal artery blood flow (GDABF), and to measure its velocity and volume flow rate using Doppler color imaging. The GDABF was detected in 40 of 41 (98%) normal subjects with longitudinal scanning and in 36 (88%) with transverse scanning. The velocity of the GDABF was 21 ± 8 cm/sec (m ± SD) and the volume flow rate was 67 ± 20 mL/min. Without color Doppler, the vascular lumina of the GDA was demonstrated in 27 (66%) subjects by longitudinal scanning and in 26 (63%) by transverse scanning. The hemodynamics of the GDA were revealed noninvasively using Doppler ultrasonography in a patient with a malignant islet cell tumor of the pancreas and one with a ductal cell carcinoma of the pancreas. © 1993 John Wiley & Sons, Inc.     

An esophageal Doppler probe for aortic flow velocity monitoring

An ultrasonic Doppler transducer suitable for intra-esophageal use in humans has been constructed, tested, and its function as a flow monitoring device assessed on a series of 15 unselected anaesthetized human subjects undergoing surgery. Doppler flow signals from the descending thoracic aorta have been obtained in all cases. Once correctly positioned, the probe can give continuous qualitative monitoring of pulsatile aortic blood flow velocity for extended periods. It is possible to observe flow waves in the descending thoracic aorta from the aortic arch distally for about 20 cm and observe the change from disturbed to laminar flow patterns over this length.     

Blood flow velocity changes in migraine attacks-a transcranial Doppler study

A pulsed Doppler device was used to measure blood flow velocities in the common carotid artery, the extracranial part of the internal carotid artery, the external carotid artery, the middle cerebral artery, and the anterior cerebral artery in 31 migraineurs without aura (n = 27) and with aura (n = 4), both during and outside an attack. The aims were to compare blood flow velocity during and between migraine attacks and to study asymmetries of the blood flow velocity. Compared with blood flow velocity values obtained in the attack-free interval, blood flow velocity was lower during attacks without aura in both common carotid arteries, but not in the other extra- and intracranial vessels which were examined. However, during attacks of migraine with aura, blood flow velocity tended to be lower in all examined vessels. There were no asymmetries of the blood flow velocity. We suggest that during migraine attacks without aura there is a dissociation in blood flow regulation in the common carotid and middle cerebral arteries.     

Doppler ultrasound tracking instrument for monitoring blood flow velocity

Doppler ultrasound (US) is potentially a valuable method for monitoring changes of blood flow velocity over a period of many minutes or even hours, but is seldom used in this way. One difficulty that may have contributed to this is the problem of maintaining a fixed geometry between the US beam and the blood vessel. A method of improving the success of monitoring might be to actively steer the US beam so as to maintain an adequate signal even when small displacements of the transducer occur. We have designed and built a prototype system for this purpose. The system comprises a continuous-wave phased-array transducer controlled by a purpose-built Doppler unit. The system constantly evaluates the quality of the returning Doppler signal in terms of total power and signal-to-noise ratio (SNR) (evaluated by assessing the quality of derived envelope signals), and steers the ultrasonic beam in a manner so as to improve the signal, should this be necessary. The system was tested in vitro, where the automatic tracking of the Doppler signal doubled the effective beam width of the transducer. Further developments that increase sensitivity and steering range should result in US Doppler systems that are better suited to long-term monitoring.     

On increasing the range of pulsed Doppler systems for blood flow measurement

Existing pulsed Dopplers have a fundamental limitation which makes them unable to measure a velocity v at a range R greater than that given by the limit Rv = c²/8φ₀ where c is the sound velocity and f₀ the transmitted ultrasound frequency. This limit makes it impossible for conventional pulsed Dopplers to measure blood velocity transcutaneously in such locations as stenosed or regurgitant heart valves in adults.This paper described a principle using periodic changes of the repetition frequency of the transmitted signal. This increases the range limit of pulsed Doppler systems by the ratio of the Doppler spectrum enter frequency to its bandwidth. This technique which is easily applicable to existing pulsed Dopplers, should extend the clinical applicability of these systems to long range or high velocity flows whose Doppler spectra are sufficiently narrow     

Redistribution of skin blood flow during leg dependency in peripheral arterial occlusive disease

Summary A disturbed autoregulation of cutaneous blood flow in legs with peripheral arterial occlusive disease (PAOD) has previously been demonstrated for circumscribed skin areas. In the present study, posturally-induced changes of skin perfusion distribution along ischaemic limbs were investigated topographically in 35 PAOD patients by means of fluorescein perfusography. Among the 68 legs studied, 7 had patent arteries and 61 could be assigned to FONTAINE stages I to IV. Limbs with peripheral skin lesions (stage IV) were further differentiated according to either healing (stage IV+) or non-healing (stage IV-) on conservative treatment. Sitting-up always led to prolonged calf as well as foot fluorescein appearance times (AT) except for legs in stage III or IV- disease. In the latter two groups, decreased sitting as compared to supine AT foot-to-calf ratios indicated a relative shift of dye delivery from proximal towards distal skin regions during posture. In contrast, this measure of blood flow redistribution did not change in the other groups. The redirection of fluorescein influx was significantly correlated with the systolic arterial pressure ankle-to-arm ratios. In conclusion, besides small perfusion pressure increases or passive microvessel distension, a shift of the peripheral resistance ratios may contribute to the improved blood supply of ischaemic skin regions during leg dependency. An arteriolar vasoparalysis does not regularly exist in limbs with skin lesions not primarily originating from ischaemia (stage IV+).     

Neonatal cerebral venous flow velocity measurement using a color flow Doppler system.

Color flow Doppler provides a simple means for studying blood flow velocity from the central cerebral veins in newborn infants. Twenty-two term infants were examined during the first four days of life to establish a normal range for velocity from the vein of Galen. A wide range of velocities was found between individuals (2.3 cm.s-1 to 9.5 cm.s-1), but short-term intraindividual variation was small (root mean square variation 1.1 cm.s-1). Light bilateral jugular venous compression was performed in 17 of the infants and produced a fall of up to 63% in venous flow velocity in 12 infants (p = 0.0005).     

Color and conventional image-directed Doppler ultrasonography: accuracy and sources of error in quantitative blood flow measurements.

Accuracy of two systems--conventional (DRF 400, Diasonics) and color-coded (Angiodynograph, Quantum/Phillips) image-directed Doppler ultrasonography--was investigated using an in vitro model that generated both monophasic and triphasic pulsatile flow patterns. Estimated and actual blood volume flow rates showed good correlations, but the sampling with a hand-held transducer led to wide variations in measurement error for the conventional (-69.2% to 50%) and the color-coded (-79.3% to 265.7%) systems. By performing multiple measurements, one could improve accuracy considering only the maximal values of a series instead of the mean values. Accuracy was impaired by interposed muscular or fatty tissue due to false low time-average velocity measurements caused by a loss of Doppler signal. Comparison of both systems revealed significant differences between pulsatility index values (p less than 0.001), blood flow velocities (p less than 0.001), and blood volume flow rates (p less than 0.05 for program flow, p less than 0.001 for manual and automatic flow program of the color-coded system).     

Quantitative measurement of abdominal arterial blood flow using image-directed Doppler ultrasonography: Superior mesenteric,splenic, and common hepatic arterial blood flow in normal adults

To measure volume blood flow quantitatively in human abdominal arteries, we used an ultrasonic image-directed Doppler system and electromagnetic flow-meter to first measure volume flow in canine arteries. In dogs, there was a strong linear correlation (R = 0.98) between the product of the time average of the maximum blood flow velocity and the average cross-sectional area and the volume blood flow measured by an electromagnetic flow-meter. These results enabled measurement of volume blood flow in the human superior mesenteric (SMA), splenic (SPA), and common hepatic (CHA) arteries from the abdominal wall. Comparison of pulsatility index values indicated a larger vascular resistance in the SMA than in the SPA or CHA.     

Strain gauge plethysmography and Doppler ultrasound in the measurement of limb blood flow

Abstract The maintenance of adequate oxygen delivery (DO₂) and tissue uptake (VO₂) has become central dogma in the management of the critically ill. However, these parameters are derived using gas tensions measured in mixed venous blood and may not reflect changes in regional blood flow. Therefore, it has become necessary to provide estimates of blood flow to specific organs and to evaluate the most adequate techniques available. In order to define the best means of assessing blood flow to the lower limb noninvasively in normal subjects, measurements of superficial femoral arterial blood flow using Doppler ultrasound (DU) and strain gauge plethysmography (SGP) were compared in 10 normal volunteers at rest and during exercise. To evaluate the effect of strain gauge positioning, results of measurements made under four different combinations of cuff/strain gauge placement were compared in 15 other volunteers. The correlation of the limb blood flow obtained using the two methods at rest and exercise was 0·57 and 0·62 and the limits of agreement (d±2SD) were 0·40±2·49 and -0·86±5·22 ml 100 ml^-1 tissue min^-1 at rest and on exercise, respectively. Results obtained using SGP were more reproducible (Coef. repeat. 0·45 vs. 0·94 ml 100 ml^-1 tissue min^-1, for SGP and DU, respectively). The various combinations of cuff/strain gauge positioning showed a tendency to over-read when the latter was placed on the thigh, but were not significantly different (P<0·05). Measurements of limb blood flow obtained using DU and SGP correlate poorly over a wide range of blood flow and do not agree, the results from the latter being more reproducible. Although the same position of cuff and strain gauge should be maintained throughout an experiment, varying the positions studied yields comparable results.     

Some aspects of the relationship between instantaneous volumetric blood flow and continuous wave doppler ultrasound recordings—III. The calculation of doppler power spectra from mean velocity waveforms, and the results of processing these spectra with maximum, mean, and rms frequency processors

A method of predicting velocity profiles and hence Doppler relative power spectra (RPS) from mean volumetric flow waveforms using an extension of Womersley's theory is described. The effect on the RPS of using an ultrasound beam which is smaller than the blood vessel is calculated, and comparisons are made between RPS found in this way and experimental RPS measured in a dog model. Finally the effect of making ultrasonic Doppler measurements on complex velocity profiles with different combinations of processing technique and ultrasonic beam size are considered.