Interobserver variability of carotid Doppler peak velocity measurements among technologists in an ICAVL-accredited vascular laboratory

Quantitative 2-Dimensionsal Digital Subtraction Venography for Venous Interventions: Validation in Phantom and In Vivo Porcine Models

PURPOSE

To determine the feasibility of using a 2-dimensional quantitative digital subtraction venography (qDSV) technique that employs a temporally modulated contrast medium injection to quantify blood velocity in phantom, normal, and stenotic porcine iliac vein models.

MATERIALS AND METHODS

Blood velocity was calculated using qDSV following temporally modulated pulsed injections of iodinated contrast medium and compared with Doppler ultrasound (US) measurements (phantom, in-line sensor; in vivo, diagnostic linear probe). Phantom evaluation was performed in a compliant polyethylene tube phantom with simulated venous flow. In vivo evaluation of qDSV was performed in normal (n = 7) and stenotic (n = 3) iliac vein models. Stenoses were created using endovenous radiofrequency ablation, and blood velocities were determined at baseline, after stenosis, after venoplasty, and after stent placement.

RESULTS

In the phantom model, qDSV-calculated blood velocities (12-50 cm/s) had very strong correlations with US-measured velocities (13-51 cm/s) across a range of baseline blood velocities and injection protocols (slope, 1.01-1.13; R2 = 0.96-0.99). qDSV velocities were similar to US velocities regardless of injection method: (a) custom injector, (b) commercial injector, or (c) hand injection. In the normal in vivo model, qDSV-calculated velocities (5-18 cm/s) had strong correlation (slope, 1.22; R2 = 0.90) with US-measured velocities (3-20 cm/s). In the stenosis model, blood velocities at baseline, after stenosis, after venoplasty, and after stent placement were similar on qDSV and US at all time points.

CONCLUSIONS

Venous blood velocity was accurately quantified in a venous phantom and in vivo porcine models using qDSV. Intraprocedural changes in porcine iliac vein blood velocity were quantified with qDSV after creation of a stenosis and subsequently treating it with venoplasty and stent placement.

Automated mitral inflow Doppler peak velocity measurement using deep learning

Doppler echocardiography is a widely utilised non-invasive imaging modality for assessing the functionality of heart valves, including the mitral valve. Manual assessments of Doppler traces by clinicians introduce variability, prompting the need for automated solutions. This study introduces an innovative deep learning model for automated detection of peak velocity measurements from mitral inflow Doppler images, independent from Electrocardiogram information. A dataset of Doppler images annotated by multiple expert cardiologists was established, serving as a robust benchmark. The model leverages heatmap regression networks, achieving 96% detection accuracy. The model discrepancy with the expert consensus falls comfortably within the range of inter- and intra-observer variability in measuring Doppler peak velocities. The dataset and models are open-source, fostering further research and clinical application.

Correlation of Common Carotid Artery Blood Flow Parameters With Transthoracic Echocardiographic Cardiac Output for Assessing Fluid Responsiveness After Passive Leg Raising (PLR) Test in Critically Ill Patients

Introduction The passive leg raising (PLR) test is a simple, non-invasive method of knowing fluid responsiveness by acting as an internal-fluid challenge. The PLR test coupled with a non-invasive assessment of stroke volume would be the ideal method to assess fluid responsiveness. This study aimed to determine the correlation between transthoracic echocardiographic cardiac output (TTE-CO) and common carotid artery blood flow (CCABF) parameters in determining fluid responsiveness with the PLR test. Methods  We performed a prospective observational study on 40 critically ill patients. Patients were evaluated with a 7-13 MHz linear transducer probe for CCABF parameters calculated using time-averaged mean velocity (TAmean) and with a 1-5 MHz cardiac probe equipped with tissue doppler imaging (TDI) for TTE-CO calculated using left ventricular outflow tract velocity time integral (LVOT VTI) with an apical five-chamber view. Two separate PLR tests (five minutes apart) were done within 48 hours of ICU admission. The first PLR test was to assess the effects on TTE-CO. The second PLR test was performed to assess the effects on CCABF parameters. Patients were designated as fluid responders (FR) if changes in TTE-CO (Δ TTE-CO) ≥ 10 %. Results  A positive PLR test was observed in 33% of patients. A strong correlation was present between absolute values of TTE-CO calculated using LVOT VTI and the absolute values of CCABF calculated using TAmean (r=0.60, p<0.05). However, a weak correlation was found between Δ TTE-CO and changes in CCABF (Δ CCABF) during the PLR test (r=0.05, p<0.74). A positive PLR test response could not be detected by Δ CCABF (area under the curve (AUC): 0.59 ± 0.09). Conclusions We found a moderate correlation between TTE-CO and CCABF at baseline. However, Δ TTE-CO had a very poor correlation with Δ CCABF, during the PLR test. Considering this, CCABF parameters may not be recommended as a means to detect fluid responsiveness with PLR tests in critically ill patients.

Assessment of extracranial carotid artery disease using digital twins - A pilot study

To improve risk stratification in extracranial internal carotid artery disease (CAD), patients who would benefit maximally from revascularization must be identified. In cardiology, the fractional flow reserve (FFR) has become a reference standard for evaluating the functional severity of coronary artery stenosis, and noninvasive surrogates thereof relying on computational fluid dynamics (CFD) have been developed. Here, we present a CFD-based workflow using digital twins of patients' carotid bifurcations derived from computed tomography angiography for the noninvasive functional assessment of CAD. We reconstructed patient-specific digital twins of 37 carotid bifurcations. We implemented a CFD model using common carotid artery peak systolic velocity (PSV) acquired with Doppler ultrasound (DUS) as inlet boundary condition and a two-element Windkessel model as oulet boundary condition. The agreement between CFD and DUS on the PSV in the internal carotid artery (ICA) was then compared. The relative error for the agreement between DUS and CFD was 9% ± 20% and the intraclass correlation coefficient was 0.88. Furthermore, hyperemic simulations in a physiological range were feasible and unmasked markedly different pressure drops along two ICA stenoses with similar degree of narrowing under comparable ICA blood flow. Hereby, we lay the foundation for prospective studies on noninvasive CFD-based derivation of metrics similar to the FFR for the assessment of CAD.

Effects of a single dose of long-acting FSH on testicular blood flow, testicular echotexture, and circulating testosterone, estradiol, and nitric oxide in rams during the non-breeding season

The present study investigated the effect of a single administration of long-acting follicle simulation hormone (FSH) on testicular blood perfusion as measured by pulsed-wave Doppler ultrasonography, testicular echotexture, and circulating testosterone (T), estradiol (E2), and nitric oxide (NO) in the plasma of rams in the non-breeding season. Twelve Ossimi rams were subjected to either a single administration of long-acting FSH subcutaneously (FSH group; n = 6) or the vehicle (control group; n = 6). Assessment of testicular hemodynamics at the level of the supratesticular artery was performed just before administration (0 h), and at 4, 24, 48, 72, 96, and 168 h after FSH or the vehicle administrations. Testicular volume (TV), and echotexture of testicular parenchyma including pixel intensity and heterogeneity were derived by the computer analysis software. Concentrations of T, E2, and NO were measured using commercial kits. Results revealed significant decreases (P ˂ 0.05) in the values of Doppler indices (resistive index: RI and pulsatility index: PI), especially at 48 h after administration of FSH (RI: 0.42 ± 0.02, PI: 0.56 ± 0.04) compared to their values in the control group (RI: 0.54 ± 0.03, PI: 0.77 ± 0.04). FSH administration induced significant decreases (P ˂ 0.05) in the pixel intensity of testicular parenchyma. Testicular volume and T concentrations were not significantly changed (P ˃ 0.05). Concentrations of E2 increased significantly (P ˂ 0.05) at 48 h and 72 h after FSH administration. (30.07 ± 5.23 pg/ml, 29.93 ± 1.44 pg/ml, respectively) compared to their values before FSH administration (14.63 ± 1.37 pg/ml). Concentrations of NO increased significantly (P ˂ 0.05) in the FSH group between 4 h to 48 h compared to the values in the control one. In conclusion, a single administration of long-acting FSH enhanced testicular blood perfusion as measured by pulsed Doppler ultrasonography in rams during the non-breeding season. Concurrently, significant increases in the concentrations of E2 and NO were found.

Safety and efficacy of a novel robotic transcranial doppler system in subarachnoid hemorrhage

Delayed cerebral ischemia (DCI) secondary to vasospasm is a determinate of outcomes following non-traumatic subarachnoid hemorrhage (SAH). SAH patients are monitored using transcranial doppler (TCD) to measure cerebral blood flow velocities (CBFv). However, the accuracy and precision of manually acquired TCD can be operator dependent. The NovaGuide robotic TCD system attempts to standardize acquisition. This investigation evaluated the safety and efficacy of the NovaGuide system in SAH patients in a Neuro ICU. We retrospectively identified 48 NovaGuide scans conducted on SAH patients. Mean and maximum middle cerebral artery (MCA) CBFv were obtained from the NovaGuide and the level of agreement between CBFv and computed tomography angiography (CTA) for vasospasm was determined. Safety of NovaGuide acquisition of CBFv was evaluated based on number of complications with central venous lines (CVL) and external ventricular drains (EVD). There was significant agreement between the NovaGuide and CTA (Cohen’s Kappa = 0.74) when maximum MCA CBFv ≥ 120 cm/s was the threshold for vasospasm. 27/48 scans were carried out with CVLs and EVDs present without negative outcomes. The lack of adverse events associated with EVDs/CVLs and the strong congruence between maximal MCA CBFv and CTA illustrates the diagnostic utility of the NovaGuide.

Evaluation of Transient Ischemic Attack and Minor Stroke: A Rapid Outpatient Model for the COVID-19 Pandemic and Beyond

The grim circumstances of the COVID-19 pandemic have highlighted the need to refine and adapt stroke systems of care. Patients' care-seeking behaviors have changed due to perceived risks of in-hospital treatment during the pandemic. In response to these challenges, we optimized a recently implemented, novel outpatient approach for the evaluation and management of minor stroke and transient ischemic attack, entitled RESCUE-TIA. This modified approach incorporated telemedicine visits and remote testing, and proved valuable during the pandemic. In this review article, we provide the evidence-based rationale for our approach, describe its operationalization, and provide data from our initial experience.

A New Doppler-Derived Parameter to Quantify Internal Carotid Artery Stenosis: Maximal Systolic Acceleration

OBJECTIVE

Doppler ultrasonography (DUS) is used as initial measurement to diagnose and classify carotid artery stenosis. Local distorting factors such as vascular calcification can influence the ability to obtain DUS measurements. The DUS derived maximal systolic acceleration (ACCmax) provides a different way to determine the degree of stenosis. While conventional DUS parameters are measured at the stenosis itself, ACCmax is measured distal to the internal carotid artery (ICA) stenosis. The value of ACCmax in ICA stenosis was investigated in this study.

MATERIAL AND METHODS

All carotid artery DUS studies of a tertiary academic center were reviewed from October 2007 until December 2017. Every ICA was included once. The ACCmax was compared to conventional DUS parameters: ICA peak systolic velocity (PSV), and PSV ratio (ICA PSV/ CCA PSV). ROC-curve analysis was used to evaluate accuracy of ACCmax, ICA PSV and PSV ratio as compared to CT-angiography (CTA) derived stenosis measurement as reference test.

RESULTS

The study population consisted of 947 carotid arteries and was divided into 3 groups: <50% (710/947), 50-69% (109/947), and ≥70% (128/947). Between these groups ACCmax was significantly different. Strong correlations between ACCmax and ICA PSV (R² 0.88) and PSV ratio (R² 0.87) were found. In ROC subanalysis, the ACCmax had a sensitivity of 90% and a specificity of 89% to diagnose a ≥70% ICA stenosis, and a sensitivity of 82% and a specificity of 88% to diagnose a ≥50% ICA stenosis. For diagnosing a ≥50% ICA stenosis the area under the curve (AUC) of ACCmax (0.88) was significantly lower than the AUC of PSV ratio (0.94) and ICA PSV (0.94). To diagnose a ≥70% ICA stenosis there were no significant differences in AUC between ACCmax (0.89), PSV ratio (0.93) and ICA PSV (0.94).

CONCLUSIONS

ACCmax is an interesting additional DUS measurement in determining the degree of ICA stenosis. ACCmax is measured distal to the stenosis and is not hampered by local distorting factors at the site of the stenosis. ACCmax can accurately diagnose an ICA stenosis, but was somewhat inferior compared to ICA PSV and PSV ratio to diagnose a ≥50% ICA stenosis.

Common Carotid Artery Volume Flow: A Comparison Study between Ultrasound Vector Flow Imaging and Phase Contrast Magnetic Resonance Imaging

Volume flow estimation in the common carotid artery (CCA) can assess the absolute hemodynamic effect of a carotid stenosis. The aim of this study was to compare a commercial vector flow imaging (VFI) setup against the reference method magnetic resonance phase contrast angiography (MRA) for volume flow estimation in the CCA. Ten healthy volunteers were scanned with VFI and MRA over the CCA. VFI had an improved precision of 19.2% compared to MRA of 31.9% (p = 0.061). VFI estimated significantly lower volume flow than MRA (mean difference: 63.2 mL/min, p = 0.017), whilst the correlation between VFI and MRA was strong (R² = 0.81, p < 0.0001). A Bland–Altman plot indicated a systematic bias. After bias correction, the percentage error was reduced from 41.0% to 25.2%. This study indicated that a VFI setup for volume flow estimation is precise and strongly correlated to MRA volume flow estimation, and after correcting for the systematic bias, VFI and MRA become interchangeable.

Is Doppler Echocardiography Adequate for Surgical Planning of Single Ventricle Patients?

PURPOSE

Surgical planning has shown great potential for optimizing outcomes for patients affected by single ventricle (SV) malformations. Phase-contrast magnetic resonance imaging (PC-MRI) is the routine technique used for flow acquisition in the surgical planning paradigm. However, PC-MRI may suffer from possible artifacts in certain cases; furthermore, this technology may not be readily available for patients in low and lower-middle-income countries. Therefore, this study aims to investigate the effectiveness of using Doppler echocardiography (echo-Doppler) for flow acquisitions of SV surgical planning.

METHODS

This study included eight patients whose blood flow data was acquired by both PC-MRI and echo-Doppler. A virtual surgery platform was used to generate two surgical options for each patient: (1) a traditional Fontan conduit and (2) a Y-graft. Computational fluid dynamics (CFD) simulations were conducted using the two flow acquisitions to assess clinically relevant hemodynamic metrics: indexed power loss (iPL) and hepatic flow distribution (HFD).

RESULTS

Differences exist in flow data acquired by PC-MRI and echo-Doppler, but no statistical significance was obtained. Flow fields, therefore, exhibit discrepancies between simulations using flow acquisitions by PC-MRI and echo-Doppler. In virtual surgery, the two surgical options were ranked based on these metrics. No difference was observed in the ranking of surgical options between using different flow acquisitions.

CONCLUSION

Doppler echocardiography is an adequate alternative approach to acquire flow data for SV surgical planning. This finding encourages broader usage of SV surgical planning with echo-Doppler when MRI may present artifacts or is not available, especially in low and lower-middle-income countries.

Flow Complexity Estimation in Dysfunctional Arteriovenous Dialysis Fistulas using Vector Flow Imaging

Non-invasive assessment is preferred for monitoring arteriovenous dialysis fistulas (AVFs). Vector concentration assesses flow complexity, which may correlate with stenosis severity. We determined whether vector concentration could assess stenosis severity in dysfunctional AVFs. Vector concentration was estimated in four stenotic phantoms at different pulse repetition frequencies. Spectral Doppler peak velocity and vector concentration were measured in 12 patients with dysfunctional AVFs. Additionally, 5 patients underwent digital subtraction angiography (DSA). In phantoms, vector concentration exhibited an inverse relationship with stenosis severity and was less affected by aliasing in severe stenoses. In nine stenoses of 5 patients undergoing DSA, vector concentration correlated strongly with stenosis severity (first stenosis: r = -0.73, p = 0.04; other stenoses; r = -0.69, p = 0.02) and mid-stenotic diameter (first stenosis: r = 0.87, p = 0.006; other stenoses: r = 0.70, p = 0.02) as opposed to peak velocities (p > 0.05). Vector concentration is less affected by aliasing in severe stenoses and correlates with DSA in patients with dysfunctional AVF.

Measurement, Analysis and Interpretation of Pressure/Flow Waves in Blood Vessels

The optimal performance of the cardiovascular system, as well as the break-down of this performance with disease, both involve complex biomechanical interactions between the heart, conduit vascular networks and microvascular beds. ‘Wave analysis’ refers to a group of techniques that provide valuable insight into these interactions by scrutinizing the shape of blood pressure and flow/velocity waveforms. The aim of this review paper is to provide a comprehensive introduction to wave analysis, with a focus on key concepts and practical application rather than mathematical derivations. We begin with an overview of invasive and non-invasive measurement techniques that can be used to obtain the signals required for wave analysis. We then review the most widely used wave analysis techniques—pulse wave analysis, wave separation and wave intensity analysis—and associated methods for estimating local wave speed or characteristic impedance that are required for decomposing waveforms into forward and backward wave components. This is followed by a discussion of the biomechanical phenomena that generate waves and the processes that modulate wave amplitude, both of which are critical for interpreting measured wave patterns. Finally, we provide a brief update on several emerging techniques/concepts in the wave analysis field, namely wave potential and the reservoir-excess pressure approach.

Carotid Stenosis Assessment with Vector Concentration before and after Stenting

Digital subtraction angiography (DSA) is considered the reference method for the assessment of carotid artery stenosis; however, the procedure is invasive and accompanied by ionizing radiation. Velocity estimation with duplex ultrasound (DUS) is widely used for carotid artery stenosis assessment since no radiation or intravenous contrast is required; however, the method is angle-dependent. Vector concentration (VC) is a parameter for flow complexity assessment derived from the angle independent ultrasound method vector flow imaging (VFI), and VC has shown to correlate strongly with stenosis degree. The aim of this study was to compare VC estimates and DUS estimated peak-systolic (PSV) and end-diastolic velocities (EDV) for carotid artery stenosis patients, with the stenosis degree obtained with DSA. Eleven patients with symptomatic carotid artery stenosis were examined with DUS, VFI, and DSA before and after stent treatment. Compared to DSA, VC showed a strong correlation (r = -0.79, p < 0.001), while PSV (r = 0.68, p = 0.002) and EDV (r = 0.51, p = 0.048) obtained with DUS showed a moderate correlation. VFI using VC calculations may be a useful ultrasound method for carotid artery stenosis and stent patency assessment.

The role of multislice computerized tomography angiography in assessing postoperative vascular complications in liver transplant patients

Background/aim

Vascular complications can be detected in liver transplant patients. Digital subtraction angiography has served as the gold standard to make this diagnosis; however, due to its invasive nature, ultrasonography is used for the preliminary evaluation. The purpose of this study was to evaluate the role of multislice computerized tomography angiography (MSCTA) in the detection of vascular complications of symptomatic and asymptomatic liver transplant patients and to compare the results with Doppler ultrasound (Doppler US) findings.

Materials and methods

Fifty-three liver transplant patients (6 symptomatic, 47 asymptomatic) underwent Doppler US examination followed by an MSCTA. The findings in each modality were interpreted in a blinded fashion and then compared.

Results

MSCTA detected 15 abnormalities, none of which were detected by Doppler US. There were hepatic and splenic artery aneurysms (n = 4) and various stenoses (n = 4), infrarenal aortic anastomosis (n = 4), vena cava inferior thrombosis (n = 1), arteriovenous malformation (n = 1), and esophageal varices (n = 1).

Conclusion

MSCTA detected more lesions and we believe that it should be considered as a road map for Doppler US follow-ups as well as a routine screening modality for early detection of vascular complications in symptomatic and asymptomatic liver transplantation patients that may be missed by Doppler US.

Association between age and progression of carotid artery atherosclerosis: a serial high resolution magnetic resonance imaging study

This study aimed to investigate the association between age and progression of carotid atherosclerotic plaques using serial high resolution magnetic resonance imaging (MRI). Symptomatic patients who had carotid atherosclerosis with 30-70% stenosis were enrolled in this study. Carotid MRI was performed at baseline and follow-up time point (≥ 6 months after baseline), respectively. The characteristics of carotid plaque progression among different age groups (> 75 years old, 60-75 years old and < 60 years old) were compared. Logistic regression was performed to relate age with carotid plaque progression. Of recruited 84 patients, 73 (mean age, 66.5 ± 11.4 years old; males, 82.2%) with 96 plaques were included in the final analysis. Compared with younger patients, older ones had significantly higher incidence of calcification in carotid plaques (> 75 years old: 91.3%, 60-75 years old: 65.7% and < 60 years old: 55.3%, p = 0.013), greater annual change of carotid wall volume (> 75 years old: 39.0 (4.3-104.6) mm³, 60-75 years old: 28.7 (- 28.0 to 73.7) mm³ and < 60 years old: 4.8 (- 27.1-31.9) mm³, p = 0.032) and maximum carotid wall area (> 75 years old: 6.1 (- 3.5 to 17.2) mm², 60-75 years old: 2.4 (- 4.7 to 15.1) mm² and < 60 years old: 1.4 (- 5.8 to 6.9) mm², p = 0.046). Age (OR 1.44; 95% CI 1.10-1.89; p = 0.009) and hypertension (OR 4.61; 95% CI 1.41-15. 02; p = 0.011) were independent predictors in discriminating upper quartile of annual change of carotid wall volume after adjusting for all clinical factors. Older patients have faster progression rate in carotid plaques than younger ones and age is independently associated with carotid plaque progression. Our findings suggest that the carotid plaques of older patients need to be monitored more frequently.

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.

Association of Progression of Carotid Artery Wall Volume and Recurrent Transient Ischemic Attack or Stroke: A Magnetic Resonance Imaging Study

BACKGROUND AND PURPOSE

This study aimed to investigate the association between carotid plaque progression and subsequent recurrent events using magnetic resonance imaging.

METHODS

Sixty-three symptomatic patients with ipsilateral carotid atherosclerotic stenosis (30%-69% stenosis) determined by ultrasound underwent first and second carotid artery magnetic resonance imaging for carotid artery at baseline and ≥6 months after the first scan, respectively. All the patients had clinical follow-up after the second magnetic resonance scan for ≤5 years until the onset of recurrent transient ischemic attack or stroke. Presence/absence of carotid plaque compositional features, particularly intraplaque hemorrhage and fibrous cap rupture was identified. The annual progression of carotid wall volume between 2 magnetic resonance scans was measured. Univariate and multivariate Cox regression was used to calculate the hazard ratio and corresponding 95% confidence interval of carotid plaque features in discriminating recurrent events. Receiver-operating-characteristic-curve analysis was conducted to determine the area-under-the-curve of carotid plaque features in predicting recurrent events.

RESULTS

Sixty-three patients (mean age: 66.5±10.0 years old; 54 males) were eligible for final statistics analysis. During a mean follow-up duration of 55.1±13.6 months, 14.3% of patients (n=9) experienced ipsilateral recurrent transient ischemic attack/stroke. The annual progression of carotid wall volume was significantly associated with recurrent events before (hazard ratio, 1.14 per 10 mm³; 95% confidence interval, 1.02-1.27; P=0.019) and after (hazard ratio, 1.19 per 10 mm3; 95% confidence interval, 1.03-1.37; P=0.022) adjusted for confounding factors. In discriminating the recurrence of transient ischemia attack/stroke, receiver-operator curve analysis indicated that combined with annual progression of wall volume, there was a significant incremental improvement in the area-under-the-curve of intraplaque hemorrhage (area-under-the-curve: 0.69-0.81) and fibrous cap rupture (area-under-the-curve: 0.73-0.84).

CONCLUSIONS

The annual progression of carotid wall volume is independently associated with recurrent ischemic cerebrovascular events, and this measurement has added value for intraplaque hemorrhage and fibrous cap rupture in predicting future events.

Comparison of carotid artery blood velocity measurements by vector and standard Doppler approaches

Although severely affected by the angle dependency, carotid artery peak systolic velocity measurements are widely used for assessment of stenosis. In this study, blood peak systolic velocities in the common and internal carotid arteries of both healthy volunteers and patients with internal carotid artery stenosis were measured by two vector Doppler (VD) methods and compared with measurements obtained with the conventional spectral Doppler approach. Although the two VD techniques were completely different (using the transmission of focused beams and plane waves, respectively), the measurement results indicate that these techniques are nearly equivalent. The peak systolic velocities measured in 22 healthy common carotid arteries by the two VD techniques were very close (according to Bland-Altman analysis, the average difference was 3.2%, with limits of agreement of ± 8.6%). Application of Bland-Altman analysis to comparison of either VD technique with the spectral Doppler method provided a 21%-25% average difference with ± 13%-15% limits of agreement. Analysis of the results obtained from 15 internal carotid arteries led to similar conclusions, indicating significant overestimation of peak systolic velocity with the spectral Doppler method. Inter- and intra-operator repeatability measurements performed in a group of 8 healthy volunteers provided equivalent results for all of the methods (coefficients of variability in the range 2.7%-6.9%), even though the sonographers were not familiar with the VD methods. The results of this study suggest that the introduction of vector Doppler methods in commercial machines may finally be considered mature and capable of overcoming the angle-dependent overestimation typical of the standard spectral Doppler approach.

Accurate blood peak velocity estimation using spectral models and vector doppler

Ultrasound blood peak velocity estimates are routinely used for diagnostics, such as the grading of a stenosis. The peak velocity is typically assessed from the Doppler spectrum by locating the highest frequency detectable from noise. The selected frequency is then converted to velocity by the Doppler equation. This procedure contains several potential sources of error: the frequency selection is noise dependent and sensitive to the spectral broadening, which, in turn, is affected by the Doppler angle uncertainty. The result is, often, an inaccurate estimate. In this work we propose a new method that removes the aforementioned errors. The frequency is selected by exploiting a mathematical model of the Doppler spectrum that has recently been introduced. When a very large sample volume is used, which includes all the vessel section, the model is capable of predicting the exact threshold to be used without the need of broadening compensation. The angle ambiguity is solved by applying the threshold to the Doppler spectra measured from two different directions, according to the vector Doppler technique. The proposed approach has here been validated through Field II simulations, phantom experiments, and tests on volunteers by using defocused waves to insonify a large region from a linear array probe. A mean error lower than 1% and a mean coefficient of variability lower than 5% were measured in a variety of experimental conditions.

An improved Doppler model for obtaining accurate maximum blood velocities

Maximum blood velocity estimates are frequently required in diagnostic applications, including carotid stenosis evaluation, arteriovenous fistula inspection, and maternal-fetal examinations. However, the currently used methods for ultrasound measurements are inaccurate and often rely on applying heuristic thresholds to a Doppler power spectrum. A new method that uses a mathematical model to predict the correct threshold that should be used for maximum velocity measurements has recently been introduced. Although it is a valuable and deterministic tool, this method is limited to parabolic flows insonated by uniform pressure fields. In this work, a more generalized technique that overcomes such limitations is presented. The new approach, which uses an extended Doppler spectrum model, has been implemented in an experimental set-up based on a linear array probe that transmits defocused steered waves. The improved model has been validated by Field II simulations and phantom experiments on tubes with diameters between 2mm and 8mm. Using the spectral threshold suggested by the new model significantly higher accuracy estimates of the peak velocity can be achieved than are now clinically attained, including for narrow beams and non-parabolic velocity profiles. In particular, an accuracy of +1.2±2.5 cm/s has been obtained in phantom measurements for velocities ranging from 20 to 80 cm/s. This result represents an improvement that can significantly affect the way maximum blood velocity is investigated today.

Improving the reliability of venous Doppler flow measurements: relevance of combined ECG, training and repeated measures

The nature of venous Doppler waves is highly variable. An additional electrocardiogram (ECG) improves the interpretation of venous Doppler wave characteristics and allows measurement of venous pulse transit time. The purpose of this study was to assess the reproducibility of ECG-guided repeated measurements of venous Doppler flow characteristics before and after sonographer training and the inter- and intra-observer variability. In four groups of 25 healthy women, venous Doppler flow measurements were performed at the level of the kidneys and liver according to a standardized protocol. Intra-observer Pearson correlation coefficients of the renal interlobar vein Doppler indices were ≥ 0.80 with the addition of the ECG, which are higher than the results of a former study. The inter-observer correlation between an experienced ultrasonographer and an inexperienced ultrasonographer improved from ≥ 0.71 to ≥ 0.91 after training. The correlation range of all parameters between two independent observers improved when values were based on repeated measures. The addition of an ECG to the Doppler image, training and repeated measurements are helpful in improving venous Doppler wave interpretation.

Real-time vector velocity assessment through multigate Doppler and plane waves

Several ultrasound (US) methods have been recently proposed to produce 2-D velocity vector fields with high temporal and spatial resolution. However, the real-time implementation in US scanners is heavily hampered by the high calculation power required. In this work, we report a real-time vector Doppler imaging method which has been integrated in an open research system. The proposed approach exploits the plane waves transmitted from two sub-arrays of a linear probe to estimate the velocity vectors in 512 sample volumes aligned along the probe axis. The method has been tested for accuracy and reproducibility through simulations and in vitro experiments. Simulations over a 0° to 90° angle range of a 0.5 m/s peak parabolic flow have yielded 0.75° bias and 1.1° standard deviation for direction measurement, and 0.6 cm/s bias with 3.1% coefficient of variation for velocity assessment. In vitro tests have supported the simulation results. Preliminary measurements on the carotid artery of a volunteer have highlighted the real-time system capability of imaging complex flow configurations in an intuitive, easy, and quick way, as shown in a sample supplementary movie. These features have allowed reproducible peak velocity measurements to be obtained, as needed for quantitative investigations on patients.

A reliability study of colour-Doppler sonography for the diagnosis of chronic cerebrospinal venous insufficiency shows low inter-rater agreement

OBJECTIVE

Chronic cerebrospinal venous insufficiency (CCSVI) has been extremely variable, associated with multiple sclerosis in colour-Doppler sonographic studies. We aimed to evaluate inter-rater agreement in a colour-Doppler sonography venous examination.

DESIGN

Inter-rater agreement study.

SETTING

First-referral multiple sclerosis centre.

PARTICIPANTS

38 patients with multiple sclerosis and 55 age-matched (±5 years) controls.

INTERVENTION

Sonography was carried out in accordance with Zamboni's five criteria by eight sonographers with different expertise, blinded to the status of cases and controls. Each participant was evaluated by two operators.

PRIMARY AND SECONDARY OUTCOME MEASURES

Inter-rater agreement was measured through the κ statistics and the intraclass correlation coefficient.

RESULTS

The agreement was no higher than chance for criterion 2-reflux in the deep cerebral veins (κ=-0.02) and criterion 4-flow not Doppler detectable in one or both the internal jugular veins (IJVs) or vertebral veins (VVs; -0.09). It was substantially low for criterion 1-reflux in the IJVs and/or VVs (0.29), criterion 3-IJV stenosis or malformations (0.23) and criterion 5-absence of IJV diameter increase when passing from the sitting to the supine position (0.22). The κ value for CCSVI as a whole was 0.20 (95% confidence limit -0.01 to 0.42). Intraclass correlation coefficients for the measure of cross-sectional area ranged from 0.05 to 0.25. Inter-rater agreement was low for CCSVI experts (κ=0.24; -0.11 to 0.59) and non-experts (0.20; -0.33 to 0.73); neurologists (0.21; -0.06 to 0.47) and non-neurologists (0.18; -0.20 to 0.56); cases (0.19; -0.14 to 0.52) and controls (0.21; -0.08 to 0.49). Zamboni-trained neurosonographers ascertained CCSVI more frequently than the non-trained neurosonographers.

CONCLUSIONS

Agreement was unsatisfactory for the diagnosis of CCSVI as a whole, for each of its five criteria and according to the different subgroups. Standardisation of the method is urgently needed prior to its further application in studies of patients with multiple sclerosis or other neurological diseases.

Finding the peak velocity in a flow from its Doppler spectrum

The signal backscattered by blood cells crossing a sample volume produces a Doppler power spectrum determined by the scatterers¿ velocity distribution. Because of intrinsic spectral broadening, the peak Doppler frequency observed does not correspond to the peak velocity in the flow. Several methods have been proposed for estimating the maximum velocity component--an important clinical parameter--but these methods are approximate, based on heuristic thresholds that can be inaccurate and strongly affected by noise. Reported here is a method of modeling the Doppler power spectrum of a flow, and from that model, determining what Doppler frequency on the descending slope of the power spectrum corresponds to the peak velocity in the insonated flow. It is shown that, for a fully insonated flow with a parabolic velocity distribution, the peak velocity corresponds to the Doppler frequency at the half-power point on that slope. The method is demonstrated to be robust with regard to the effects of noise and valid for a wide range of acquisition parameters. Experimental maximum velocity measurements on steady flows with rates between 100 and 300 mL/min (peak velocity range 6.6 cm/s to 19.9 cm/s) show a mean bias error that is smaller than 1%.

Effect of velocity profile skewing on blood velocity and volume flow waveforms derived from maximum Doppler spectral velocity

Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (V(max)) can lie outside the Doppler sample volume (SV). The link between V(max) and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected V(max) waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in V(max) waveforms when using a small, centered SV, although peak V(max) was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from V(max) was typically within ±15%, although substantial skewing and use of a small SV caused 10%-25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. V(max) pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into V(max)-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the V(max) and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies.

Noninvasive assessment of the carotid and cerebrovascular atherosclerotic plaques by multidetector CT in type-2 diabetes mellitus patients with transient ischemic attack or stroke

BACKGROUND

The cerebrovasuclar artery disease as a common complication of type-2 diabetes mellitus (T2DM) caused huge economic burden and lives threatening to patients. We evaluated the prevalence and morphology of carotid and cerebrovascular atherosclerotic plaques in T2DM patients with transient ischemic attack (TIA) or stroke using multidetector CT (MDCT).

METHODS

64-MDCT and dual-source CT (DSCT) angiographies were performed in 195 T2DM patients with TIA or stroke (mean age 65.7+/-12.8 years; 118 men) between January 2009 to August 2011. During the process, plaque type, its distribution, extensive and obstructive natures were determined for each segment derived from the patients.

RESULTS

Atherosclerotic plaques were detected in 183 (93.8%) patients. A total of 1056 segments with plaque were identified, of which 450 (42.6%) were non-calcified, 192 (18.2%) were mixed and 414 (39.2%) calcified ones. Among them, 562 (53.2%) resulted in mild stenosis, 291 (27.6%) moderate stenosis, 170 (16.1%) severe stenosis and 33 (3.1%) occlusion. Non-calcified plaques contributed 91.8% to non-obstructive lumen narrowing, while mixed and calcified plaques contributed 89.0% and 65.0% respectively.

CONCLUSIONS

MDCT angiography detected a high prevalence of plaques in T2DM patients with TIA or stroke. A relatively high proportion of plaques were non-calcified, as well as with non-obstructive stenosis. MDCT angiography might further enhance the detection and management of carotid and cerebrovascular atherosclerosis in T2DM patients with TIA and stroke.

Carotid stenosis: change of treatment plan based on repeat duplex ultrasonography

BACKGROUND

This study was conducted to evaluate the change in the treatment plan observed when clinical decisions are made based on initial carotid duplex ultrasonography (DU) performed at an outside center before surgical consultation versus those made based on DU performed in a dedicated vascular laboratory.

METHODS

A prospective study of patients who underwent initial DU at an outside facility and repeat DU in a dedicated vascular laboratory for evaluation of carotid stenosis was performed. Initial DU was compared with repeat DU to evaluate clinical impact.

RESULTS

Ninety-six consecutive patients were evaluated. Disagreement between initial DU and repeat DU was observed in 27.1% of patients. This disagreement led to a change of treatment plan in 23 of 146 (15.8%) carotid arteries studied.

CONCLUSIONS

Reliance on 1 DU in clinical practice, when performed outside a dedicated vascular laboratory, may lead to both unnecessary surgery and missed opportunities for surgery to prevent stroke.

Measurement of carotid artery stenosis: correlation analysis between B-mode ultrasonography and contrast arteriography

Purpose

To evaluate the efficacy of B-mode ultrasonography (US) in measurement of carotid stenosis% (CS%).

Methods

One hundred and thirth-three carotid arteries in 96 patients who underwent both carotid US and carotid arteriography (CA) were included in this retrospective study. To measure CS% on US, a cross sectional view of the most stenotic segment of the internal carotid artery was captured and residual diameter and original diameter of that segment were measured with electronic caliper on the same plane and in the same direction. To measure CS% on an angiogram, we used European Carotid Surgery Trial (ECST) and the North American Symptomatic Carotid Endarterectomy Trial (NASCET) methods. Pearson's correlation analysis and linear regression analysis were used to determine the correlation between CS% on an US and angiogram.

Results

Pearson's correlation coefficient (R) between CS% measured in US and CA were 0.853 (ECST method, P < 0.001) and 0.828 (NASCET method, P < 0.001). Accuracies of B-mode US were 93.2%, 88.0%, and 81.2% for estimating CS% by ECST method and 86.5%, 82.7%, and 82% for estimating CS% by NASCET method.

Conclusion

CS% measured in B-mode US was simpler and showed a strong positive correlation with that measured on an arteriogram either ECST or NASCET method.

The reproducibility of transcranial Doppler middle cerebral artery velocity measurements: Implications for clinical practice

Use of transcranial Doppler (TCD) to diagnose vasospasm has been criticised. We examined reproducibility of TCD middle cerebral artery (MCA) velocity measurements. Thirty-six healthy adult volunteers were recruited. Four operators, two experienced and two inexperienced, participated. MCA velocity was measured twice by one operator and once by a second operator. Mean (95% limits of agreement) interoperator agreement was 2.4(+/-36.7) cm/s. Experienced vs. inexperienced, inexperienced vs. inexperienced, and experienced vs. experienced operators were -2.8(+/-39.3), -5.6(+/-40.1), 1.8(+/-22.1) cm/s, respectively. Intraoperator agreement across all operators, experienced and inexperienced were -0.5(+/-16.9), -1.6(+/-19.3), 0.7(+/-13.7) cm/s, respectively. Interoperator limits of agreement for experienced operators were almost half that of inexperienced operators. Intraoperator reproducibility was much better, regardless of level of experience, but aberrant results did occur even with experienced operators. If TCD measurements are used to guide management it is essential that operators are adequately trained, and readings repeated before potentially harmful treatments are instituted.

Flow volume and cross-sectional area of the extracranial vertebral arteries and its relation to vascular lesions or anatomical variations in the posterior circulation

We examined whether the time-averaged maximum velocity (TAMV), flow volume (FV) or cross-sectional area (CA) in the vertebral arteries (VA) as determined by ultrasonography was related to vascular lesions or variations in the intracranial part of the posterior circulation. Three hundred nine patients without severe stenosis in the carotid circulation (159 males, 150 females, mean age of 69.1 years) underwent both colour duplex ultrasonography and magnetic resonance angiography (MRA) and were thus analyzed. According to the MRA findings, the patients were divided as follows; 22 patients with severe stenosis in the bilateral PCA or VA or basilar artery (V group) and 287 patients without (N group). The N group was then further divided as follows; 144 patients with no (P0 group); 89 with one (P1) and 54 with both posterior communicating arteries (P2) detected on MRA. TAMV, FV and CA were compared among these groups. Both TAMV and FV of V group were significantly lower than those of N group (35.3 vs. 42.6 cm/sec in TAMV, 98.2 vs. 135.3 mL/min in FV, p < 0.001 and 0.0001, respectively). The FVs and CAs in the P0 through P2 groups were all significantly different according to the number of posterior communicating arteries (149.3 vs. 128.0 vs. 109.8 mL/min, 22.5 vs. 20.2 vs. 16.5 mm2, both p < 0.001) while TAMVs in these groups did not differ substantially. The FV in both VAs were thus found to be related to the vascular lesions or variations in the posterior circulation.

Velocity variability in ultrasonic Doppler examinations

Ultrasonic Doppler examination with spectral waveform has been used for the classification and surveillance of carotid artery stenosis for over 25 years. Progression/regression between examinations can be identified with 95% confidence if the velocity measurements change by more than two times the root mean square difference (RMSD) of the repeat measurement. Peak systolic velocity and end diastolic velocity measurements at a Doppler angle of 60 degrees were repeated in 47 carotid examinations. Measurement difference between sonographers and between instruments was tabulated. Root mean square difference was 11 cm/s (RMS%D = 11%) for systolic and 7 cm/s (RMS%D = 21%) for diastolic velocity measurements (excluding one severe stenosis case). Results for differences between sonographers and between instruments were similar to the overall results. In serial arterial studies using this Doppler velocimetry method, a difference exceeding 23 cm/s (21%) systolic, or 14 cm/s (42%) diastolic velocity indicates a significant (2 x RMSD) hemodynamic change.

Accuracy and reproducibility of a novel dual-beam vector Doppler method

Conventional Doppler ultrasound (US) investigations are limited to detect only the axial component of the blood velocity vector. A novel dual-beam method has been recently proposed in which the Doppler angle is estimated through a reference US beam, and the velocity magnitude through a measuring US beam, respectively. In this study, the performance of such a method has been assessed quantitatively through in vitro and in vivo measurements made in different experimental conditions. In vitro, more than 300 acquisitions were completed using seven transducers to insonify a straight tube phantom at different Doppler angles. In steady laminar flow conditions, the velocity magnitude was measured with mean error of -1.9% (95% confidence interval: -2.33% to -1.47%) and standard deviation of 3.4%, with respect to a reference velocity. In pulsatile flow conditions, reproducibility tests of the entire velocity waveforms provided an average coefficient of variation (CV) of 6.9%. For peak velocity measurements made at five Doppler angles and three flow rates, the intrasession and intersession CVs were in the range 0.8-3.7% and 2.9-10.6%, respectively. The peak systolic velocities (PSVs) in the common carotid arteries of 21 volunteers were estimated with 95% limits of agreement of +/- 9.6 cm/s (intersession). This analysis shows that the proposed dual-beam method is capable of overcoming the Doppler angle ambiguity by producing reliable velocity measurements over a large set of experimental conditions.

Computer vision approach for ultrasound Doppler angle estimation

Doppler ultrasound is an important noninvasive diagnostic tool for cardiovascular diseases. Modern ultrasound imaging systems utilize spectral Doppler techniques for quantitative evaluation of blood flow velocities, and these measurements play a crucial rule in the diagnosis and grading of arterial stenosis. One drawback of Doppler-based blood flow quantification is that the operator has to manually specify the angle between the Doppler ultrasound beam and the vessel orientation, which is called the Doppler angle, in order to calculate flow velocities. In this paper, we will describe a computer vision approach to automate the Doppler angle estimation. Our approach starts with the segmentation of blood vessels in ultrasound color Doppler images. The segmentation step is followed by an estimation technique for the Doppler angle based on a skeleton representation of the segmented vessel. We conducted preliminary clinical experiments to evaluate the agreement between the expert operator's angle specification and the new automated method. Statistical regression analysis showed strong agreement between the manual and automated methods. We hypothesize that the automation of the Doppler angle will enhance the workflow of the ultrasound Doppler exam and achieve more standardized clinical outcome.

Human factors as a source of error in peak Doppler velocity measurement

OBJECTIVE

The study was conducted to assess the error and variability that results from human factors in Doppler peak velocity measurement. The positioning of the Doppler sample volume in the vessel, adjustment of the Doppler gain and angle, and choice of waveform display size were investigated. We hypothesized that even experienced vascular technologists in a laboratory accredited by the Intersocietal Commission for Accreditation of Vascular Laboratories make significant errors and have significant variability in the subjective adjustments made during measurements.

METHODS

Problems of patient variability were avoided by having the four technologists measure peak velocities from an in vitro pulsatile flow model with unstenosed and 61% stenosed tubes. To evaluate inaccurate angle and sample volume positioning, a probe holder was used in some of the experiments to fix the Doppler angle at 60 degrees. The effect of Doppler gain was studied at three settings--low, ideal, and saturated gains--that were standardized from the ideal level chosen by consensus amongst the technologists. Two waveform display sizes were also investigated. Peak velocity measurement was assessed by comparison with true peak velocities. For each variable studied, average peak velocities were calculated from the 10 measurements made by each technologist and used to find the percent error from the true value, and the coefficient of variation was used to measure the variability.

RESULTS

Doppler angle, sample volume placement, and the Doppler gain were the most significant sources of error and variability. Inaccurate angle and placement increased the variability in measurements from 1% to 2% (range) to 4% to 6% for the straight tube and from 1% to 2% to 3% to 9% for the 61% stenosis. The peak velocity error was increased from 9% to 13% to 7% to 28% for the stenosis. Both measurement error and variability were strongly dependent on the Doppler gain level. At low gain, the error was approximately 10% less than the true value and at saturated gain, 20% greater. The display size only affected measurements from the stenosed tube, increasing the error from 9% to 13% to 15% to 24%.

CONCLUSIONS

Major factors affecting Doppler peak velocity measurement error and variability were identified. Inaccurate angle and sample volume placement increased the variability. The presence of a stenosis was found to increase the measurement errors. The error was found to depend on the Doppler gain setting, with greater variability at low and saturated gains and on the display size with a stenosis.

CLINICAL RELEVANCE

Doppler ultrasound peak velocity measurements are widely used for the diagnostic assessment of the severity of arterial stenoses. However, it is known that these measurements are often in error. We have identified subjective human factors introduced by the technologist and assessed their contribution to peak velocity measurement error and variability. It is to be hoped that by understanding this, improvements in the machine design and measurement methods can be made that will result in improved measurement accuracy and reproducibility.

Sensitivity and specificity of color duplex ultrasound measurement in the estimation of internal carotid artery stenosis: A systematic review and meta-analysis

BACKGROUND

Duplex ultrasound is widely used for the diagnosis of internal carotid artery stenosis. Standard duplex ultrasound criteria for the grading of internal carotid artery stenosis do not exist; thus, we conducted a systematic review and meta-analysis of the relation between the degree of internal carotid artery stenosis by duplex ultrasound criteria and degree of stenosis by angiography.

METHODS

Data were gathered from Medline from January 1966 to January 2003, the Cochrane Central Register of Controlled Trials and Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, ACP Journal Club, UpToDate, reference lists, and authors' files. Inclusion criteria were the comparison of color duplex ultrasound results with angiography by the North American Symptomatic Carotid Endarterectomy Trial method; peer-reviewed publications, and >/=10 adults.

RESULTS

Variables extracted included internal carotid artery peak systolic velocity, internal carotid artery end diastolic velocity, internal carotid artery/common carotid artery peak systolic velocity ratio, sensitivity and specificity of duplex ultrasound scanning for internal carotid artery stenosis by angiography. The Standards for Reporting of Diagnostic Accuracy (STARD) criteria were used to assess study quality. Sensitivity and specificity for duplex ultrasound criteria were combined as weighted means by using a random effects model. The threshold of peak systolic velocity >/=130 cm/s is associated with sensitivity of 98% (95% confidence intervals [CI], 97% to 100%) and specificity of 88% (95% CI, 76% to 100%) in the identification of angiographic stenosis of >/=50%. For the diagnosis of angiographic stenosis of >/=70%, a peak systolic velocity >/=200 cm/s has a sensitivity of 90% (95% CI, 84% to 94%) and a specificity of 94% (95% CI, 88% to 97%). For each duplex ultrasound threshold, measurement properties vary widely between laboratories, and the magnitude of the variation is clinically important. The heterogeneity observed in the measurement properties of duplex ultrasound may be caused by differences in patients, study design, equipment, techniques or training.

CONCLUSIONS

Clinicians need to be aware of the limitations of duplex ultrasound scanning when making management decisions.

[Significance of Doppler ultrasound procedures for diagnosis of carotid stenoses]

Determining degree and morphology of stenoses is important for surgical planning or stent implantation. Vascular ultrasound is usually the first modality to evaluate carotid artery stenosis. Due to rapid development various methods of vascular ultrasound are applied including continuous wave (CW) Doppler, duplex Doppler, colour-coded duplex sonography (CCDS), power Doppler and B-flow technique. For quantitative assessment of the degree of stenosis the most frequently used parameters are peak systolic velocity (PSV), end-diastolic velocity (EDV) in the internal carotid artery (ICA), as well as ICA to CCA ratios of PSV and EDV. Different results reported in the literature may reflect differences in defining the degree of stenosis and methodological differences in protocol or imaging techniques. Differences in defining the degree of stenosis, advantages and disadvantages of the different Doppler techniques and future developments are discussed in detail.