An Automatic Angle Tracking Procedure for Feasible Vector Doppler Blood Velocity Measurements

Two-dimensional angle-independent blood velocity estimates typically combine the Doppler frequencies independently measured by two ultrasound beams with known interbeam angle. A different dual-beam approach was recently introduced in which one (reference) beam is used to identify the flow direction, and the second (measuring) beam directly estimates the true flow velocity at known beam-flow angle. In this paper, we present a procedure to automatically steer the two beams along optimal orientations so that the velocity magnitude can be measured. The operator only takes care of locating the Doppler sample volume in the region of interest and, through the extraction of appropriate parameters from the Doppler spectrum, the reference beam is automatically steered toward right orientation to the flow. The velocity magnitude is thus estimated by the measuring beam, which is automatically oriented with respect to the (known) flow direction at a suitable Doppler angle. The implementation of the new angle tracking method in the ULtrasound Advanced Open Platform (ULA-OP), connected to a linear array transducer, is reported. A series of experiments shows that the proposed method rapidly locks the flow direction and measures the velocity magnitude with low variability for a large range of initial probe orientations. In vitro tests conducted in both steady and pulsatile flow conditions produced coefficients of variability (CV) below 2.3% and 8.3%, respectively. The peak systolic velocities have also been measured in the common carotid arteries of 13 volunteers, with mean CV of 7%. (E-mail: piero.tortoli@unifi.it).     

Accuracy and Precision of a Plane Wave Vector Flow Imaging Method in the Healthy Carotid Artery

The objective of the study described here was to investigate the accuracy and precision of a plane wave 2-D vector flow imaging (VFI) method in laminar and complex blood flow conditions in the healthy carotid artery. The approach was to study (i) the accuracy for complex flow by comparing the velocity field from a computational fluid dynamics (CFD) simulation to VFI estimates obtained from the scan of an anthropomorphic flow phantom and from an in vivo scan; (ii) the accuracy for laminar unidirectional flow in vivo by comparing peak systolic velocities from VFI with magnetic resonance angiography (MRA); (iii) the precision of VFI estimation in vivo at several evaluation points in the vessels. The carotid artery at the bifurcation was scanned using both fast plane wave ultrasound and MRA in 10 healthy volunteers. The MRA geometry acquired from one of the volunteers was used to fabricate an anthropomorphic flow phantom, which was also scanned using the fast plane wave sequence. The same geometry was used in a CFD simulation to calculate the velocity field. Results indicated that similar flow patterns and vortices were estimated with CFD and VFI in the phantom for the carotid bifurcation. The root-mean-square difference between CFD and VFI was within 0.12?m/s for velocity estimates in the common carotid artery and the internal branch. The root-mean-square difference was 0.17?m/s in the external branch. For the 10 volunteers, the mean difference between VFI and MRA was ?0.17?m/s for peak systolic velocities of laminar flow in vivo. The precision in vivo was calculated as the mean standard deviation (SD) of estimates aligned to the heart cycle and was highest in the center of the common carotid artery (SD?=?3.6% for velocity magnitudes and 4.5° for angles) and lowest in the external branch and for vortices (SD?=?10.2% for velocity magnitudes and 39° for angles). The results indicate that plane wave VFI measures flow precisely and that estimates are in good agreement with a CFD simulation and MRA.     

Accuracy and Reproducibility of a Novel Dynamic Volume Flow Measurement Method

In clinical practice, blood volume flow (BVF) is typically calculated assuming a perfect parabolic and axisymmetric velocity distribution. This simple approach cannot account for the complex flow configurations that are produced by vessel curvatures, pulsatility and diameter changes and, therefore, results in a poor estimation. Application of the Womersley model allows compensation for the flow distortion caused by pulsatility and, with some adjustment, the effects of slight curvatures, but several problems remain unanswered. Two- and three-dimensional approaches can acquire the actual velocity field over the whole vessel section, but are typically affected by a limited temporal resolution. The multigate technique allows acquisition of the actual velocity profile over a line intersecting the vessel lumen and, when coupled with a suitable wall-tracking method, can offer the ideal trade-off among attainable accuracy, temporal resolution and required calculation power. In this article, we describe a BVF measurement method based on the multigate spectral Doppler and a B-mode edge detector algorithm for wall-position tracking. The method has been extensively tested on the research platform ULA-OP, with more than 1700 phantom measurements at flow rates between 60 and 750 mL/min, steering angles between 10° and 22° and constant, sinusoidal or pulsed flow trends. In the averaged BVF measurement, we found an underestimation of about −5% and a coefficient of variability (CV) less than 6%. In instantaneous measurements (e.g., systolic peak) the CV was in the range 2%–8.5%. These results were confirmed by a preliminary test on the common carotid artery of 10 volunteers (CV = 2%–11%).     

Novel Flow Quantification of the Carotid Bulb and the Common Carotid Artery with Vector Flow Ultrasound

Abnormal blood flow is usually assessed using spectral Doppler estimation of the peak systolic velocity. The technique, however, only estimates the axial velocity component, and therefore the complexity of blood flow remains hidden in conventional ultrasound examinations. With the vector ultrasound technique transverse oscillation the blood velocities of both the axial and the transverse directions are obtained and the complexity of blood flow can be visualized. The aim of the study was to determine the technical performance and interpretation of vector concentration as a tool for estimation of flow complexity. A secondary aim was to establish accuracy parameters to detect flow changes/patterns in the common carotid artery (CCA) and the carotid bulb (CB). The right carotid bifurcation including the CCA and CB of eight healthy volunteers were scanned in a longitudinal plane with vector flow ultrasound (US) using a commercial vector flow ultrasound scanner (ProFocus, BK Medical, Denmark) with a linear 5 MHz transducer transverse oscillation vector flow software. CCA and CB areas were marked in one cardiac cycle from each volunteer. The complex flow was assessed by medical expert evaluation and by vector concentration calculation. A vortex with complex flow was found in all carotid bulbs, whereas the CCA had mainly laminar flow. The medical experts evaluated the flow to be mainly laminar in the CCA (0.82 ± 0.14) and mainly complex (0.23 ± 0.22) in the CB. Likewise, the estimated vector concentrations in CCA (0.96 ± 0.16) indicated mainly laminar flow and in CB (0.83 ± 0.07) indicated mainly turbulence. Both methods were thus able to clearly distinguish the flow patterns of CCA and CB in systole. Vector concentration from angle-independent vector velocity estimates is a quantitative index, which is simple to calculate and can differentiate between laminar and complex flow.     

Combined Vector Velocity and Spectral Doppler Imaging for Improved Imaging of Complex Blood Flow in the Carotid Arteries

Color flow imaging and pulsed wave (PW) Doppler are important diagnostic tools in the examination of patients with carotid artery disease. However, measurement of the true peak systolic velocity is dependent on sample volume placement and the operator's ability to provide an educated guess of the flow direction. Using plane wave transmissions and a duplex imaging scheme, we present an all-in-one modality that provides both vector velocity and spectral Doppler imaging from one acquisition, in addition to separate B-mode images of sufficient quality. The vector Doppler information was used to provide automatically calibrated (angle-corrected) PW Doppler spectra at every image point. It was demonstrated that the combined information can be used to generate spatial maps of the peak systolic velocity, highlighting regions of high velocity and the extent of the stenotic region, which could be used to automate work flow as well as improve the accuracy of measurement of true peak systolic velocity. The modality was tested in a small group (N = 12) of patients with carotid artery disease. PW Doppler, vector velocity and B-mode images could successfully be obtained from a single recording for all patients with a body mass index ranging from 21 to 31 and a carotid depth ranging from 16 to 28 mm.     

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     

糖尿病患者颈动脉彩超检测的应用价值

目的 应用彩色多普勒超声检测Ⅱ型糖尿病患者颈动脉病变情况。方法 对117例糖尿病患者双侧颈动脉检测结果与对照组127例健康人群进行比较分析。结果 糖尿病组Ⅲ级粥样斑块检出率(44.4％)与对照组(9.6％)有明显差异(P<0.01);糖尿病组血流速度降低、血管阻力指数及搏动指数增高,与对照组存在差异(P<0.05)。结论 糖尿病患者颈动脉病变以粥样硬化斑块形成、血流减速、血管阻力增高为主要特点。彩超可直观反映病变的分期、轻重程度,在糖尿病血管病变的诊断中具有重要的实用价值。     

Accuracy and repeatability of pediatric cardiac output measurement using Doppler: 20-year review of the literature

Objective Review of the accuracy and repeatability of Doppler cardiac output (CO) measurements in children.Design Publications in the scientific literature retrieved using a computerized Medline search from 1982–2002 and a manual review of article bibliographies. Studies comparing Doppler flow measurements with thermodilution, Fick, or dye dilution methods in the pediatric critical care setting were identified to assess the bias, precision, and intra- and interobserver repeatability of Doppler CO measurement. Where results were not suitable for comparison and the original measurements available, data were re-analyzed using appropriate statistical methods and presented in comparative tables.Results The precision of pediatric Doppler CO measurements compared to thermodilution, dye dilution, or Fick methods is around 30% and repeatability varies from less than 1% to 22%. Bias is generally less than 10% but varies considerably.Conclusions The bias, precision, and repeatability from study to study indicate that Doppler CO measurements are acceptably reproducible in children, with best results when used to track changes rather than absolute values, and using the transesophageal approach.     

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).     

Geometric modeling of the carotid bifurcation in humans: implications in ultrasonic Doppler and radiologic investigations

A geometric representation of the carotid bifurcation is presented with data obtained from biplane angiograms of normal branches and branches exhibiting less than 5% vessel diameter reduction. Three features are identified that are of importance in the interpretation of ultrasonic Doppler velocity information and in the design of engineering flow models for evaluation of carotid branch hemodynamics: the variability of the bifurcation angles, the degree of tortuosity, and the nonplanar nature of the branches. In addition, data collected demonstrate the potential usefulness of the common carotid artery as a reference diameter in evaluating stenosis of the carotid bulb.     

Vector and Doppler Ultrasound Velocities Evaluated in a Flow Phantom and the Femoropopliteal Vein

Ultrasound is used for evaluating the veins of the lower extremities. Operator and angle dependency limit spectral Doppler ultrasound (SDUS). The aim of the study was to compare peak velocity measurements in a flow phantom and the femoropopliteal vein of 20 volunteers with the angle-independent vector velocity technique vector flow imaging (VFI) and SDUS. In the flow phantom, VFI underestimated velocity (p = 0.01), with a lower accuracy of 5.5% (p = 0.01) and with no difference in precision, that is, error factor, compared with SDUS (VFI: 1.02 vs. SDUS: 1.02, p = 0.58). In vivo, VFI estimated lower velocities (femoral: p = 0.001; popliteal: p = 0.001) with no difference in precision compared with SDUS (femoral: VFI 1.09 vs. SDUS 1.14, p = 0.37; popliteal: VFI 1.13 vs. SDUS 1.06, p = 0.09). In conclusion, the precise VFI technique can be used to characterize venous hemodynamics of the lower extremities despite its underestimation of velocities.     

二维多普勒超声对1000名健康人颈动脉及椎动脉血流参数正常值的测定研究

本文作者应用二维多普勒超声诊断技术对１０００名健康人颈总动脉、颈外动脉、颈内动脉及椎动脉进行了诸多血流参数的定量研究，建立了不同性别各年龄段的正常值范围，并深入研究了影响检测血流参数正常值的常见技术因素，为临床判断颈动脉、椎动脉供血情况，提供了评定方法和客观依据。     

冠心病患者颈动脉内径及血流参数的多普勒超声测定

对１０３例经选择性冠状动脉造影的患者作双侧颈动脉多普勒超声检查。探讨多普勒超声检查颈动脉内径及血流参数的方法学以及正常颈动脉的多普勒频谱特征。分析不同冠脉病变组颈动脉内径及血流参数的差异，提出颈内动脉和颈总动脉血流速度的比值有助于检出轻度颈动脉粥样硬化性狭窄。     

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.     

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.     

彩色多普勒检测颈内动脉狭窄的方法和准确性

目的探讨彩色多普勒诊断颈内动脉狭窄的方法及准确性。方法采用彩色多普勒检测８３例颈动脉硬化症患者,１２８侧颈内动脉起始处有不同程度狭窄。按狭窄程度分成三组,轻度（１～３９％）６９侧,中度（４０～６９％）４４侧,重度（７０～９９％）１５侧。测定颈内动脉收缩期峰值流速（ＩＣＡＳＰＶ）及颈内动脉与颈总动脉流速之比（ＶＩＣＡ／ＣＣＡ）。结果轻度狭窄时血流无明显改变,中度狭窄时,ＩＣＡＳＰＶ及ＶＩＣＡ／ＣＣＡ轻度增加;重度狭窄时,狭窄口呈现五彩色血流信号,ＩＣＡＳＰＶ及ＶＩＣＡ／ＣＣＡ均明显增加;尤以ＶＩＣＡ／ＣＣＡ敏感。部分超声检测结果与动脉造影及／或手术对照符合率为８９７１％。结论超声检查诊断颈内动脉起始处狭窄准确、无创,可作为临床首选方法;判断狭窄程度应以颈内与颈总动脉流速之比作为主要依据,结合峰值流速及二维切面图检测情况;中度狭窄,ＶＩＣＡ／ＣＣＡ＞１４,ＩＣＡＳＰＶ＞９５ｃｍ／ｓ;重度狭窄,ＶＩＣＡ／ＣＣＡ＞３０,ＩＣＡＳＰＶ＞２００ｃｍ／ｓ。     

Pulsed doppler techniques for measuring instantaneous maximum and mean flow velocities in carotid arteries

A 5 MHz pulsed Doppler instrument measuring instantaneous maximum and mean flow velocities is presented. The maximum velocity estimator is based on the principle of frequency variable filtering controlled by a feedback loop to follow the velocity spectrum envelope.Findings by Doppler and bilateral selective carotid arteriography in 216 patients were compared. Extracranial carotid stenoses were identified by the finding of a vessel segment with locally increased flow velocity. Peak Velocity Ratio (PVR) was calculated from maximum velocities measured in the stenosis and in more distal Internal Carotid Artery (ICA) segments. Using PVR, ICA stenoses > 20% were detected with sensitivity 96%, specificity 94%, positive accuracy 94% and negative accuracy 96%. Total ICA occlusions were identified with sensitivity 97% and specificity 99%.     

A Comparison Study of Vector Velocity,Spectral Doppler and Magnetic Resonance of Blood Flow in the Common Carotid Artery

Magnetic resonance phase contrast angiography (MRA) is the gold standard for blood flow evaluation. Spectral Doppler ultrasound (SDU) is the first clinical choice, although the method is angle dependent. Vector flow imaging (VFI) is an angle-independent ultrasound method. The aim of the study was to compare VFI- and SDU-estimated peak systolic velocities (PSV) of the common carotid artery (CCA) with PSV obtained by MRA. Furthermore, intra- and inter-observer agreement was determined. MRA estimates were significantly different from SDU estimates (left CCA: p?<?0.001, right CCA: p?<?0.001), but not from VFI estimates (left CCA: p?=?0.28, right CCA: p?=?0.18). VFI measured lower PSV in both CCAs compared with SDU (p?<?0.001) with improved precision (VFI: left: 24%, right: 18%; SDU: left 38%, right: 23%). Intra- and inter-observer agreement was almost perfect for VFI and SDU (inter-observer correlation coefficient: VFI 0.88, SDU 0.91; intra-observer correlation coefficient: VFI 0.96, SDU 0.97). VFI is more accurate than SDU in evaluating PSV compared with MRA.     

Method for the measurement of the maximum Doppler frequency

This paper describes a method for detection of the maximum Doppler frequency from a histogram of Doppler signals (HDS). The performance of the system is described, and its behavior in analysis of noise signals that have known lower and upper cut off frequencies is discussed. Experimental investigations show that the device correctly measures the maximum frequency envelope and can be useful in evaluating the maximum flow velocities in the blood circulation system.     

糖尿病、高血压患者的颈动脉彩色多普勒超声分析

目的 探讨彩色多普勒超声检测糖尿病、高血压患者颈动脉粥样硬化的诊断特点与应用价值。方法 对临床确诊的92例糖尿病、高血压患者的颈动脉超声检查资料进行回顾性分析。结果 92例患者颈动脉粥样硬化发生率79．3％。其中糖尿病及高血压患者的颈动脉粥样硬化率分别为81．7％，75．0％；粥样硬化斑块多发生在分叉部，占54．7％。结论 颈动脉粥样硬化是糖尿病、高血压靶器官损害的标志之一，彩色多普勒超声能评价颈动脉病变的程度，临床上具有重要的实用价值。