Robotic tomographic ultrasound and artificial intelligence for management of haemodialysis arteriovenous fistulae.

BACKGROUND: Arteriovenous fistulae (AVF) and Arteriovenous Grafts (AVG) may present a problematic vascular access for renal replacement therapy (RRT), reliant on recurrent specialist nurse and medical evaluation. Dysfunctional accesses are frequently referred 'out of the dialysis clinic' for specialist sonographic examination, with associated delays potentiating loss of vascular access viability and/or need for emergency intervention. Definitive anatomical and functional diagnostics based in the dialysis unit may help to solve these delays and associated complications. OBJECTIVES: This publication reports a novel vascular access monitoring concept, Robotic Tomographic Ultrasound (RTU). RESEARCH DESIGN: Robotic Tomographic Ultrasound incorporates a semi-autonomous, robotic vascular ultrasound system and purpose designed analysis software that can be deployed at the point of care. Three-dimensional scan data, as well as conventional B-Mode and Doppler data are obtained by the system and transferred to a cloud based reporting and analysis software. Scans are remotely annotated and interpreted by a sonographer, with diagnostic data presented securely to clinicians on their preferred web based application/web connected device. RESULTS: Software developed specifically for pre AVF mapping, maturation and monitoring protocols, analyse the data and then present interpreted results to all caring clinicians to assist with decision making. Vascular access planning can be determined with high confidence with data from the Map module. Maturation data can be presented in line with institutional requirements to the dialysis nurse, facilitating precocious needle access. CONCLUSION: Robotic Tomographic Ultrasound is a novel approach to vascular access management that may reduce the risk of loss of functional access by regular monitoring with the system; automated alerts guiding clinicians to the need for pre-emptive intervention, and the potential to increase longevity of the vascular access.

A longitudinal study of the arterio-venous fistula maturation of a single patient over 15 weeks.

Arterio-venous fistula creation is the preferred vascular access for haemodialysis, but has a large failure rate in the maturation period. Previous research, considering the remodelling mechanisms for failure-to-mature patients, has been limited by obtaining the patient-specific boundary conditions at only a few points in the patient history. Here, a non-invasive imaging system was used to reconstruct the three-dimensional vasculature, and computational fluid dynamics was used to analyse the haemodynamics for one patient over 15 weeks. The analysis suggested evidence of a control mechanism, which adjusts the lumen diameter to keep the wall shear stress near constant in the proximal regions of the vein and artery. Additionally, the vein and artery were shown to remodel at different growth rates, and the blood flow rate also saw the largest increase within the first week. Wall shear stress at time of creation may be a useful indicator for successful AVF maturation.

Arteriovenous fistula maturation and the influence of fluid dynamics.

Arteriovenous fistula creation is the preferred vascular access for haemodialysis therapy, but has a large failure rate in the maturation period. This period generally lasts 6 to 8 weeks after surgical creation, in which the vein and artery undergo extensive vascular remodelling. In this review, we outline proposed mechanisms for both arteriovenous fistula maturation and arteriovenous fistula failure. Clinical, animal and computational studies have not yet shown a definitive link between any metric and disease development, although a number of theories based on wall shear stress metrics have been suggested. Recent work allowing patient-based longitudinal studies may hold the key to understanding arteriovenous fistula maturation processes.

Tracking geometric and hemodynamic alterations of an arteriovenous fistula through patient-specific modelling.

BACKGROUND AND OBJECTIVE: The use of patient-specific CFD modelling for arteriovenous fistulae (AVF) has shown great clinical potential for improving surveillance, yet the use of imaging modes such as MRI and CT for the 3D geometry acquisition presents high costs and exposure risks, preventing regular use. We have developed an ultrasound based procedure to bypass these limitations. METHODS: A scanning procedure and processing pipeline was developed specifically for CFD modelling of AVFs, using a freehand ultrasound setup combining B-mode scanning with 3D probe motion tracking. The scanning procedure involves sweeping along the vasculature to create a high density stack of B-mode frames containing the lumen geometry. This stack is converted into a continuous volume and transient flow waveforms are recorded at the boundaries, synchronised with ECG and automatically digitised, forming realistic boundary conditions for the CFD models. This is demonstrated on a diseased patient-specific AVF. RESULTS: The three scans obtained using this procedure varied in geometry and flow behaviour, with regions of disease located in the first two scans. The outcome of the second procedure seen in the third scan indicated successful restoration with no sites of disease and higher flow. The models gave insight into the lumenal changes in diameter for both the artery and vein segments, as well as characterising hemodynamic behaviours in both the diseased and restored states. Vascular segment resistances obtained from the CFD models indicate a significant reduction once disease was removed, resulting in much higher flows enabling the patient to resume dialysis. CONCLUSION: The methodology described in this study allowed for a multifaceted analysis and high level tracking in terms of both geometry and flow behaviours for a patient case, demonstrating significant clinical utility and practicality, as well as enabling further research into vascular disease progression in AVFs through longitudinal analysis.

A Methodology for Non-Invasive 3-D Surveillance of Arteriovenous Fistulae Using Freehand Ultrasound.

OBJECTIVE: Surveillance techniques for arteriovenous fistulae are required to maintain functional vascular access, with two-dimensional duplex ultrasound the most widely used imaging modality. This paper presents a surveillance method for an arteriovenous fistula using a freehand three-dimensional (3-D) ultrasound system. A patient-case study highlights the applicability in a clinical environment. METHODS: The freehand ultrasound system uses optical tracking to determine the vascular probe location, and as the probe is swept down a patient's arm, each B-mode slice is spatially arranged to be post-processed as a volume. The volume is segmented to obtain the 3-D vasculature for high detail analysis. RESULTS: The results follow a patient with stenosis, undergoing surgery to have a stent placement. A surveillance scan was taken pre-surgery, postsurgery, and at a two-month follow-up. Vasculature changes are quantified using detailed analysis, and the benefits of using 3-D imaging are shown through 3-D printing and visualization. CONCLUSION AND SIGNIFICANCE: Non-invasive 3-D surveillance of arteriovenous fistulae is possible, and a patient-specific geometry was created using ultrasound and optical tracking. Access to this non-invasive 3-D surveillance technique will enable future studies to determine patient-specific remodeling behavior, in terms of geometry and hemodynamics over time.