[B-flow and contrast medium-enhanced power Doppler (Optison(R))--preoperative diagnosis of high-grade stenosis of the internal carotid artery]

Duplex ultrasound for diagnosing symptomatic carotid stenosis in the extracranial segments

BACKGROUND

Carotid artery stenosis is an important cause of stroke and transient ischemic attack. Correctly and rapidly identifying patients with symptomatic carotid artery stenosis is essential for adequate treatment with early cerebral revascularization. Doubts about the diagnostic value regarding the accuracy of duplex ultrasound (DUS) and the possibility of using DUS as the single diagnostic test before carotid revascularization are still debated.

OBJECTIVES

To estimate the accuracy of DUS in individuals with symptomatic carotid stenosis verified by either digital subtraction angiography (DSA), computed tomography angiography (CTA), or magnetic resonance angiography (MRA).

SEARCH METHODS

We searched CRDTAS, CENTRAL, MEDLINE (Ovid), Embase (Ovid), ISI Web of Science, HTA, DARE, and LILACS up to 15 February 2021. We handsearched the reference lists of all included studies and other relevant publications and contacted experts in the field to identify additional studies or unpublished data.

SELECTION CRITERIA

We included studies assessing DUS accuracy against an acceptable reference standard (DSA, MRA, or CTA) in symptomatic patients. We considered the classification of carotid stenosis with DUS defined with validated duplex velocity criteria, and the NASCET criteria for carotid stenosis measures on DSA, MRA, and CTA. We excluded studies that included < 70% of symptomatic patients; the time between the index test and the reference standard was longer than four weeks or not described, or that presented no objective criteria to estimate carotid stenosis.

DATA COLLECTION AND ANALYSIS

The review authors independently screened articles, extracted data, and assessed the risk of bias and applicability concerns using the QUADAS-2 domain list. We extracted data with an effort to complete a 2 × 2 table (true positives, true negatives, false positives, and false negatives) for each of the different categories of carotid stenosis and reference standards. We produced forest plots and summary receiver operating characteristic (ROC) plots to summarize the data. Where meta-analysis was possible, we used a bivariate meta-analysis model.

MAIN RESULTS

We identified 25,087 unique studies, of which 22 were deemed eligible for inclusion (4957 carotid arteries). The risk of bias varied considerably across the studies, and studies were generally of moderate to low quality. We narratively described the results without meta-analysis in seven studies in which the criteria used to determine stenosis were too different from the duplex velocity criteria proposed in our protocol or studies that provided insufficient data to complete a 2 × 2 table for at least in one category of stenosis. Nine studies (2770 carotid arteries) presented DUS versus DSA results for 70% to 99% carotid artery stenosis, and two (685 carotid arteries) presented results from DUS versus CTA in this category. Seven studies presented results for occlusion with DSA as the reference standard and three with CTA as the reference standard. Five studies compared DUS versus DSA for 50% to 99% carotid artery stenosis. Only one study presented results from 50% to 69% carotid artery stenosis. For DUS versus DSA, for < 50% carotid artery stenosis, the summary sensitivity was 0.63 (95% confidence interval [CI] 0.48 to 0.76) and the summary specificity was 0.99 (95% CI 0.96 to 0.99); for the 50% to 69% range, only one study was included and meta-analysis not performed; for the 50% to 99% range, the summary sensitivity was 0.97 (95% CI 0.95 to 0.98) and the summary specificity was 0.70 (95% CI 0.67 to 0.73); for the 70% to 99% range, the summary sensitivity was 0.85 (95% CI 0.77 to 0.91) and the summary specificity was 0.98 (95% CI 0.74 to 0.90); for occlusion, the summary sensitivity was 0.91 (95% CI 0.81 to 0.97) and the summary specificity was 0.95 (95% CI 0.76 to 0.99). For sensitivity analyses, excluding studies in which participants were selected based on the presence of occlusion on DUS had an impact on specificity: 0.98 (95% CI 0.97 to 0.99). For DUS versus CTA, we found two studies in the range of 70% to 99%; the sensitivity varied from 0.57 to 0.94 and the specificity varied from 0.87 to 0.98. For occlusion, the summary sensitivity was 0.95 (95% CI 0.80 to 0.99) and the summary specificity was 0.91 (95% CI 0.09 to 0.99). For DUS versus MRA, there was one study with results for 50% to 99% carotid artery stenosis, with a sensitivity of 0.88 (95% CI 0.70 to 0.98) and specificity of 0.60 (95% CI 0.15 to 0.95); in the 70% to 99% range, two studies were included, with sensitivity that varied from 0.54 to 0.99 and specificity that varied from 0.78 to 0.89. We could perform only a few of the proposed sensitivity analyses because of the small number of studies included.

AUTHORS' CONCLUSIONS

This review provides evidence that the diagnostic accuracy of DUS is high, especially at discriminating between the presence or absence of significant carotid artery stenosis (< 50% or 50% to 99%). This evidence, plus its less invasive nature, supports the early use of DUS for the detection of carotid artery stenosis. The accuracy for 70% to 99% carotid artery stenosis and occlusion is high. Clinicians should exercise caution when using DUS as the single preoperative diagnostic method, and the limitations should be considered. There was little evidence of the accuracy of DUS when compared with CTA or MRA. The results of this review should be interpreted with caution because they are based on studies of low methodological quality, mainly due to the patient selection method. Methodological problems in participant inclusion criteria from the studies discussed above apparently influenced an overestimated estimate of prevalence values. Most of the studies included failed to precisely describe inclusion criteria and previous testing. Future diagnostic accuracy studies should include direct comparisons of the various modalities of diagnostic tests (mainly DUS, CTA, and MRA) for carotid artery stenosis since DSA is no longer considered to be the best method for diagnosing carotid stenosis and less invasive tests are now used as reference standards in clinical practice. Also, for future studies, the participant inclusion criteria require careful attention.

[Current developments in vascular ultrasound]

Ultrasound plays a central role in the diagnostic imaging of venous and arterial vessels, especially for the assessment or exclusion of arteriosclerotic vessel obstructions as well as venous or arterial thrombosis. Due to its excellent patient acceptance and its broad availability, ultrasound is considered the standard method of choice for vascular imaging. New techniques and methods have greatly enhanced its diagnostic accuracy, the most notable of which are the B-flow technique, a variant of Doppler signal read-out for reduction of artifacts in duplex sonography, as well as other techniques, such as tissue harmonic imaging, the cross-beam technique and the speckle-reduction technique, which employ different echo processing methods for contrast improvement and enhanced delineation of body structures adjacent to the vessels. The introduction of contrast enhanced ultrasound represents an important advancement and has brought a substantial improvement in sensitivity. This article describes and discusses these new techniques and methods of vascular ultrasound diagnostics with respect to their diagnostic value.

[Value of vascular ultrasound in the evaluation of hemodialysis fistulas]

Vascular ultrasound has been proven to be effective in the assessment of hemodialysis fistulas providing noninvasive diagnostic work-up of vascular morphology and hemodynamics. The most common reason for hemodialysis fistula failure is thrombosis due to stenosis. Therefore, early identification of stenosis is essential to avoid complications. Ultrasound-based identification of hypoechoic plaques and intimal proliferation helps to reach therapeutic decisions. An estimation of the grade of stenosis is also feasible. An occlusion rate of up to 45% due to reduced blood flow justifies follow-up examinations. Due to frequent puncture of the fistula the risk of hemodynamically relevant stenoses is increased. Establishment of new ultrasound methods like B-flow and advanced dynamic flow (ADF) enable direct visualization of the flow in the area of the anastomosis. In addition, high-resolution ultrasound techniques allow improved flow detection without aliasing. Our report addresses the topics of examination strategy, possible complications, and treatment like percutaneous intervention techniques.

[Ultrasound diagnosis of vascular complications following transfemoral puncture]

Percutaneous catheter interventions are performed increasingly often for the purposes of both diagnosis and therapy. The incidence of local complications reported after transfemoral catheterization in the literature is 0.1-9%. Such complications should be detected as early and reliably as possible, and sonography is a good means of finding them during follow-up, not least because it is suitable for use in examinations at the bedside. The clinical value of sonography compared with other examination techniques is made clear with reference to specimen cases.

Color Doppler, power Doppler and B-flow ultrasound in the assessment of ICA stenosis: Comparison with 64-MD-CT angiography

The purpose of this study is to investigate the diagnostic potential of color-coded Doppler sonography (CCDS), power-Doppler (PD) and B-flow ultrasound in assessing the degree of extracranial internal carotid artery (ICA) stenosis in comparison to CT-angiography (MD-CTA). Thirty-two consecutive patients referred for CTA with 41 ICA-stenoses were included in this prospective study. MD-CTA was performed using a 64 row scanner with a CTDIvol of 13.1 mGy/cm. In CTA, CCDS, PD and B-flow, the degree of stenosis was evaluated by the minimal intrastenotic diameter in comparison to the poststenotic diameter. Two radiologists performed a quantitative evaluation of the stenoses in consensus blinded to the results of ultrasound. These were correlated to CTA, CCDS, PD and B-flow, intraoperative findings and clinical follow-up. Grading of the stenoses in B-flow ultrasound outperformed the other techniques in terms of accuracy with a correlation coefficient to CTA of 0.88, while PD and CCDS measurements yield coefficients of 0.74 and 0.70. Bland-Altman analysis additionally shows a very little bias of the three US methods between 0.5 and 3.2 %. There is excellent correlation (coefficient 0.88, CI 0.77-0.93) with 64-MD-CTA and B-flow ultrasound in terms of accuracy for intrastenotic and poststenotic diameter. Duplex sonography is useful for screening purposes.

High-grade stenoses of the internal carotid artery: comparison of high-resolution contrast enhanced 3D MRA, duplex sonography and power Doppler imaging

PURPOSE

The objective of this study was to determine the agreement and diagnostic accuracy of high-resolution contrast enhanced magnetic resonance angiography (MRA) with integrated parallel acquisition techniques (iPAT), color coded duplex ultrasound (CCDS) and power Doppler ultrasound (PD) in the assessment of high-grade stenoses of the internal carotid artery (ICA).

METHODS

Forty-four patients with 52 known or suspected stenoses of the internal carotid artery (ICA) were included in this prospective study. High-resolution MRA scans with a spatial resolution of 0.9 mm x 0.7 mm x 0.9 mm were acquired with an iPAT acceleration factor of 2 on a 1.5T MR system (Sonata Maestro Class, Siemens Medical Solutions, Erlangen, Germany) with a head, neck and body coil. For the 3D-CE MRA a fast spoiled gradient echo sequence (FLASH) was used. To compensate for the inherent signal loss with parallel imaging, a 1M contrast agent (gadobutrol, Gadovist, Schering, Berlin, Germany) was used. Stenoses were quantified by two readers in consensus in cross-sectional area measurements and graded according to the NASCET criteria. Using color coded duplex ultrasound (CCDS) and power Doppler (PD; Logiq 9, GE), the stenoses were also graded by two readers in consensus according to the NASCET criteria from intra- and post-stenotic diameter measurements. The results of MRA, CCDS and PD were compared to intraoperative findings or to follow-up examinations.

RESULTS

High-resolution MRA allowed an excellent grading of vascular stenoses. In 70-90% degrees of stenosis there was an underestimation of the degree of stenosis in MRA as well as in CCDS. However, there was an overestimation of 90% stenoses in both MRA and CCDS. Pseudoocclusions with a lumen of less than one millimeter were occasionally rated as a complete occlusion in MRA.

CONCLUSION

A combination of MRA and duplex sonography seems reasonable for the accurate grading of stenoses and determination of distal stenoses downstream. However, the accuracy of duplex ultrasound depends on the examiner's experience.

Diagnostics and characterisation of preocclusive stenoses and occlusions of the internal carotid artery with B-flow

The purpose was to evaluate whether B-flow can improve the ultrasonographic diagnosis of preocclusive stenosis and occlusion of the internal carotid artery (ICA) compared with colour-coded Doppler and power Doppler. Ninety patients with occlusions or preocclusive stenoses of the ICA suspected by Doppler sonography were examined with B-flow in comparison with colour-coded Doppler sonography (CCDS), power Doppler (PD) and intra-arterial digital subtraction angiography (DSA). Intrastenotic flow detection and lengths of stenoses were the main criteria. Ulcerated plaques found by surgery in 42/90 patients were compared by ultrasonography (US). Diagnosis of ICA occlusion with CCDS, PD and B-flow was correct in all 42 cases. A preocclusive ICA stenosis in DSA was detected correctly in all 48/48 cases (100%) for B-flow, in 44/48 (92%) for PD and in 39/48 (81%) for CCDS. Surgical findings showed in 17/42 cases ulcerated plaques; 15/17 (89%) of these cases were detected with B-flow, 12/17 (71%) with PD, 10/17 (59%) with CCDS, and 8/17 (47%) with DSA. With B-flow the extent of stenosis was appraised more precisely than with PD and CCDS (P<0.0001). In conclusion, B-flow is a reliable method for preocclusive stenosis of the ICA with less intrastenotic flow artefacts. B-flow facilitates the characterization of plaque morphologies.

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.

Improved diagnosis of vascular dissection by ultrasound B-flow: a comparison with color-coded Doppler and power Doppler sonography

The purpose was to evaluate the diagnostic results of different ultrasound techniques: color-coded Doppler (CCD), power Doppler (PD) and B-flow in the diagnosis of vascular dissection. Findings from 68 patients with arterial dissection proven either by vascular ultrasound (US) or by magnetic resonance angiography (MRA), computed tomographic angiography (CTA) or intra-arterial digital subtraction angiography (DSA) were reviewed in retrospect. The study compared results from three different modes of ultrasound, i.e., CCD, PD and B-flow, in dissections of the carotid artery (n=11), of the vertebral artery (n=9), of the abdominal aorta (n=13), of the iliac artery (n=12) and of the femoral artery (n=23). MRA, CTA and DSA were considered as reference standard. The sensitivity of CCD for detecting all dissections was 78%, 84% for the PD and 98% for B-flow. For carotid artery dissection, the sensitivity of CCD, PD and B-flow was 82, 91 and 98%, for the vertebral artery 67, 78 and 98%, for the abdominal aorta 85, 85 and 98%, for the iliac artery 67, 75 and 98%, for the femoral artery 83, 87 and 98%, respectively. Intima flaps, fissures of membranes and residual flow within the true and false lumen were better detected by B-flow than by CCD and PD. The lack of angle dependence of the US probe in B-flow made the examination procedure easier. In the cine mode of B-flow, the pulse synchronic movement of the membrane was more apparent than in any other imaging method. With B-flow, accuracy for the diagnosis of arterial dissection is improved compared to CCD and PD. Flow within the true and false lumen, low-echo thrombi, intramural hematoma and even movements of the dissection membrane are clearly distinguished.