Wall Shear Stress Measurements Based on Ultrasound Vector Flow Imaging: Theoretical Studies and Clinical Examples.

Wall shear stress (WSS) is considered as a key factor for atherosclerosis development. Previous WSS research based on pulsed wave Doppler (PWD) showed limitations in complex flows. To improve accuracy for nonlaminar flow, a commercial ultrasound vector flow imaging (UVFI)-based WSS calculation is proposed. Errors for PWD are presented theoretically when flow is not laminar. Based on this, simulations of WSS calculations between PWD and UVFI were set up for different turbulent flows. Our simulations show that UVFI has obviously better performance than PWD in WSS calculations. Wall shear stress results in different flow conditions at carotid bifurcations are described.

High-Frame Rate Vector Flow Imaging of the Carotid Bifurcation in Healthy Adults: Comparison With Color Doppler Imaging.

OBJECTIVES: To evaluate the carotid bifurcation in healthy adults using a commercial system equipped with high-frame rate vector flow imaging (VFI) based on the plane wave and to compare VFI with color Doppler imaging. METHODS: Carotid bifurcation diameters and flow characteristics of 60 vessels in 60 healthy volunteers were evaluated quantitatively and qualitatively to assess complex flow patterns and their extension and duration. RESULTS: Complex flow in the internal carotid artery (ICA) was associated with a statistically significant difference in the ΔICA sinus-to-common carotid artery (CCA) diameter ratio (the relative change in diameter between the CCA and ICA sinus.) Vector flow imaging and color Doppler imaging were in accordance when detecting complex flow in 96.7% of cases; in 3.3% of cases, only VFI identified small recirculation areas of short duration. Vector flow imaging highlighted a larger extension of the complex flow (mean ± SD, 47.7 ± 28.5 mm2 ; median, 45.5 mm2 ) compared with color Doppler imaging (mean, 29.2 ± 19.9 mm2 ; median, 29.5 mm2 ) and better depicted different complex flow patterns; a strong correlation (r = 0.84) was found between the ΔICA sinus-to-CCA diameter ratio and the complex flow extension. Vector flow imaging showed a longer duration of the flow disturbances (mean, 380 ± 218 milliseconds; median, 352.5 milliseconds) compared with color Doppler imaging (mean, 325 ± 206 milliseconds; median, 333 milliseconds), and there was a strong correlation (r = 0.92). CONCLUSIONS: Vector flow imaging is as effective as color Doppler imaging in the detection of flow disturbances, but it is more powerful in the assessment of complex flow patterns.

Vector flow imaging techniques: An innovative ultrasonographic technique for the study of blood flow.

Doppler ultrasonography is routinely used to identify abnormal blood flow. Nevertheless, conventional Doppler can be used to determine only the axial component of blood flow velocity and is angle dependent. A new method of multidimensional angle-independent estimation of flow velocity, called Vector Flow Imaging (VFI), has been proposed. It quantitatively evaluates the true velocity vector's amplitude and direction at any location into a vessel and displays a more intuitive depiction of the flow movements. High frame rate VFI, based on plane wave imaging, allows a detailed dynamic visualization of complex flow by showing even transient events, otherwise undetectable. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:582-588, 2017.

Calcific tendinopathy of the rotator cuff: the correlation between pain and imaging features in symptomatic and asymptomatic female shoulders.

OBJECTIVE: To provide new epidemiological data regarding the prevalence, distribution and macroscopic features of shoulder rotator cuff calcific tendinopathy (calcific tendinopathy), and to identify the characteristics of calcific deposits associated with shoulder pain. MATERIALS AND METHODS: Three hundred and two female volunteers (604 shoulders) who had been referred to a gynaecological clinic participated in the study. The subjects underwent a high-resolution ultrasonography of both shoulders, and those with a diagnosis of calcific tendinopathy compiled a standardized questionnaire relating to shoulder symptoms. We determined the prevalence of symptomatic and asymptomatic rotator cuff calcific tendinopathy, and compared differences in distribution and macroscopic features of the symptomatic and asymptomatic calcifications. RESULTS: The prevalence of calcific tendinopathy was 17.8% (103 shoulders). Ninety-five shoulders (15.7%) were symptomatic; of these, calcific tendinopathy was found in 34 shoulders (33%) on imaging. Of the 509 asymptomatic (84.3%) shoulders, calcific tendinopathy was observed in 69 cases (67%). Among tendons, supraspinatus (53.4%) and infraspinatus (54.6%) were the most frequently involved. The majority of calcific deposits were of maximum diameter between 2 and 5 mm (77.9%), and were linear in form (69.9%). The involvement of multiple tendons and a location in the supraspinatus tendon were found to be significantly correlated with pain (p = 0.023, p = 0.043 respectively), as were age (p = 0.041) and an excessive body mass index (p = 0.024). CONCLUSION: In this sample from the general population of working age females, both intrinsic factors (location in supraspinatus, multiple tendon involvement) and extrinsic variables (age, abnormally high BMI) were correlated with pain in calcific tendinopathy. LEVEL OF EVIDENCE: Level III, cross-sectional study, prevalence study.

Implanted blood vessel external support device for the treatment of distal hypoperfusion ischemic syndrome in arteriovenous fistulas and high-frame-rate Vector Flow quality assessment.

INTRODUCTION: Distal hypoperfusion ischemic syndrome (DHIS) is a complication occurring after arteriovenous fistula (AVF) creation. Different surgical alternatives haves been proposed in case of severe DHIS. Aim of the present paper is to present a new technique for DHIS treatment. MATERIAL AND METHODS: Between the 1st of January 2021 and the 31st December 2021 all the patients referred to our center for DHIS grade 2-4 were treated with a new surgical technique. It consists of AVF remodeling using an external nitinol support (VasQ®) to reduce the risk of outflow vein enlargement and DHIS recurrence. To better appreciate the hemodynamic effects of the surgery, a new ultrasound technique called high-frame-rate Vector Flow (HiFR-VF) was used. RESULTS: Seven patients (M:F 1:3; mean age 43 ± 12 years, range 29-65) were included in this study. Central line was never necessary, and technical success was 100% at 12 months. The comparison with historical data demonstrated lower recurrence of symptoms in comparison to simple artery-to-vein redo (p 0.50). The HiFR-VF showed flow with limited turbulent characteristics at the anastomosis site. DISCUSSION AND CONCLUSION: The new technique proposed demonstrated to be safe and effective for treatment of DHIS, preventing symptoms recurrence. Ultrasound examination and HiFR-VF can be considered a valuable method to evaluate complex flows at the levels of vascular anastomosis.

Velocity vector comparison between vector flow imaging and computational fluid dynamics in the carotid bifurcation.

It has been largely documented that local hemodynamic conditions, characterized by low and oscillating wall shear stresses, play a key role in the initiation and progression of vascular atherosclerotic lesions. Thus, investigation of the flow field in the carotid bifurcation can lead to early identification of vulnerable plaques. In this scenario, the development of novel non-invasive imaging tools that can be used in routine clinical practice to identify disturbed and recirculating blood flow becomes crucial. In this context, Vector Flow Imaging is becoming a relevant tool as it provides an angle independent assessment of blood flow velocity and multidimensional flow vector visualization. The purpose of the present study was to validate, in several locations of the carotid bifurcation, the high-frame rate vector flow imaging (HiFR-VFI) technique by comparing with computational fluid dynamic simulations (CFD). In all eight carotid bifurcations, HiFR-VFI accurately detected regions of laminar flow as well as recirculation and unsteady flow areas. An accurate and statistically significant agreement was observed between velocity vectors obtained by HiFR-VFI and those computed by CFD, both for vector magnitude (R = 0.85) and direction (R = 0.74). Our study demonstrated that HiFR-VFI is a valid technique for rapid and advanced visual representation of velocity field in large arteries. Thus, it has a great potential in research-based clinical practice for the identification of flow recirculation, low and oscillating velocity gradients near vessel wall. The use of HiFR-VFI may provide a great improvement in the investigation of the role of local hemodynamics in vascular pathologies, as well in the assessment of the effect of pharmacological treatments.

Real-time tissue elastography for testicular lesion assessment.

OBJECTIVES: To assess the ability of Real-time Elastography (RTE) to differentiate malignant from benign testicular lesions. METHODS: In 88 testicles ultrasound identified 144 lesions, which were examined by RTE. Elasticity images of the lesions were assigned the colour-coded score of Itoh (Radiology 2006), according to the distribution of strain induced by light compression. RTE findings were analysed considering shape (nodular/pseudo-nodular), size (<5 mm, 6-10 mm, >11 mm) and score (SC1-5) of the lesions. RESULTS: 93.7% of all benign lesions showed a complete elastic pattern (SC1). 92.9% of benign nodules <5 mm and 100% of the pseudonodules showed a nearly complete elastic pattern (mainly SC1). 87.5% of malignant nodules showed a stiff pattern (SC4-5). RTE gave 87.5% sensitivity, 98.2% specificity, 93.3% positive predictive value, 96.4% negative predictive value and 95.8% accuracy in differentiating malignant from benign lesions. CONCLUSIONS: RTE is a useful technique in assessing small testicular nodules and pseudo-nodules. This is relevant in clinical practice allowing expectant management in RTE selected cases. The role of RTE seems less relevant for larger lesions because most of them are malignant at clinical and ultrasound assessment, limiting RTE to simply confirmation role. KEY POINTS: An emerging role for Elastography in allowing surveillance for small testicular lesions. Elastography can better differentiate benign from malignant testicular lesions. Follow up can be reduced for elastic testicular lesions at Elastography.

High-frame rate vector flow imaging of the carotid bifurcation.

Carotid artery atherosclerotic disease is still a significant cause of cerebrovascular morbidity and mortality. A new angle-independent technique, measuring and visualizing blood flow velocities in all directions, called vector flow imaging (VFI) is becoming available from several vendors. VFI can provide more intuitive and quantitative imaging of vortex formation, which is not clearly distinguishable in the color Doppler image. VFI, as quantitative method assessing disturbed flow patterns of the carotid bifurcation, has the potential to allow better understanding of the diagnostic value of complex flow and to enhance risk stratification. This pictorial review article will show which new information VFI adds for the knowledge of hemodynamics in comparison to the conventional ultrasound techniques. TEACHING POINTS: • VFI is an angle-independent technique measuring flow velocities in all directions. • This kind of VFI is based on a plane wave multidirectional excitation technique. • VFI allows quantitative assessment of carotid streamlines progression and visualizes vorticity. • VFI does not allow a precise comprehension of streamlines' 3D shape. • VFI allows a better understanding of carotid artery complex flows.

Ultrasound Vector Flow Imaging - could be a new tool in evaluation of arteriovenous fistulas for hemodialysis?

INTRODUCTION: We report the use of a new ultrasound technique to evaluate the axial and lateral components of a complex flow in the arteriovenous fistula (AVF). Vector Flow Imaging (VFI) allows to identify different components of the flow in every direction, even orthogonal to the flow streamline, represented by many single vectors. VFI could help to identify flow alterations in AVF, probably responsible for its malfunction. METHODS: From February to June 2016, 14 consecutive patients with upper-limb AVF were examined with a Resona 7 (Mindray, Shenzhen, China) ultrasound scanner equipped with VFI. An analysis of mean velocity, angular direction and mean number of vectors impacting the vessel wall was carried out. We also identified main flow patterns present in the arterial side, into the venous aneurysm and in correspondence of significant stenosis. RESULTS: A disturbed flow with the presence of vectors directed against the vessel walls was found in 9/14 patients (64.28%): in correspondence of the iuxta-anastomotic venous side (4/9; 44.4%), into the venous aneurysmal tracts (3/9; 33.3%) and in concomitance of stenosis (2/9; 22.2%). The mean velocity of the vectors was around 20-25 cm/s, except in presence of stenosis, where the velocities were much higher (45-50 cm/s). The vectors directed against the vessel walls presented high angle attack (from 45° to 90°, with a median angular deviation 65°). CONCLUSIONS: VFI was confirmed to be an innovative and intuitive imaging technology to study the flow complexity in the arteriovenous fistulas.

In vitro analysis of ultrasound second generation contrast agent diluted in saline solution.

PURPOSE: To evaluate the changes in response of a second-generation sonographic contrast agent diluted in saline solution at different concentrations when different scanning techniques, and saline solution temperatures and pH were used. MATERIALS AND METHODS: A series of tests was devised to analyse the behaviour of the sonographic contrast agent at different concentrations, temperatures, pH and scanning techniques. Latex balloons were used as phantoms. These were filled with 0.9% Sodium Chloride solution mixed with a suspension of sulphur hexafluoride microbubbles stabilised with phospholipids (SonoVue ) and scanned with the harmonic imaging technique at low acoustic pressure. For each image obtained, we calculated the mean grey-scale level values and the standard deviations of grey-scale level were calculated within a ROI on the US images obtained; the resulting data were used to create echogenicity curves of UCA the echo-enhancer over time at the different conditions tested. RESULTS: We noted that SonoVue maintains adequate backscatter properties even at low concentration (0.15%) in N/S solution. The amount of echogenicity can be considered adequate for the average duration of an ultrasound examination. These properties are not affected by the scanning technique used on the phantom containing the UCA contrast agent/NaCl solution. The pH of the saline solution does not affect the survival of the microbubbles. Temperature becomes a significant value beyondover 33-37 degrees C; this condition favours rupture of the microbubbles with subsequent reduction of the echogenicity after 10-15 min, and complete disappearance after 30 min. US beam attenuation related to the concentration of the microbubbles in the saline solution volume has a non-linear behaviour; at low amplification levels, attenuation becomes more significant when using SonoVue concentrations higher than 0.4%. Unexpected greater improvement in US beam transmission was experienced for each of the three SonoVue concentrations tested, and especially for 0.2% and 0.4%, compared to saline solution alone. CONCLUSIONS: Our results show that a second-generation contrast agent may be used even diluted at low concentration in saline solution. This characteristic opens up new diagnostic perspectives possibilities for the use of contrast-enhanced harmonic imaging; in particular, its can be suggested used in hollow organs and functional studies. These in vitro results require by confirmation by clinical applications which are under evaluation and experimentation.