Mathematical Models for Blood Flow Quantification in Dialysis Access Using Angiography: A Comparative Study.

Nischal Koirala,Gordon Mclennan

doi:10.3390/diagnostics11101771

Abstract

Blood flow rate in dialysis (vascular) access is the key parameter to examine patency and to evaluate the outcomes of various endovascular interve7ntions. While angiography is extensively used for dialysis access–salvage procedures, to date, there is no image-based blood flow measurement application commercially available in the angiography suite. We aim to calculate the blood flow rate in the dialysis access based on cine-angiographic and fluoroscopic image sequences. In this study, we discuss image-based methods to quantify access blood flow in a flow phantom model. Digital subtraction angiography (DSA) and fluoroscopy were used to acquire images at various sampling rates (DSA—3 and 6 frames/s, fluoroscopy—4 and 10 pulses/s). Flow rates were computed based on two bolus tracking algorithms, peak-to-peak and cross-correlation, and modeled with three curve-fitting functions, gamma variate, lagged normal, and polynomial, to correct errors with transit time measurement. Dye propagation distance and the cross-sectional area were calculated by analyzing the contrast enhancement in the vessel. The calculated flow rates were correlated versus an in-line flow sensor measurement. The cross-correlation algorithm with gamma-variate curve fitting had the best accuracy and least variability in both imaging modes. The absolute percent error (mean ± SEM) of flow quantification in the DSA mode at 6 frames/s was 21.4 ± 1.9%, and in the fluoroscopic mode at 10 pulses/s was 37.4 ± 3.6%. The radiation dose varied linearly with the sampling rate in both imaging modes and was substantially low to invoke any tissue reactions or stochastic effects. The cross-correlation algorithm and gamma-variate curve fitting for DSA acquisition at 6 frames/s had the best correlation with the flow sensor measurements. These findings will be helpful to develop a software-based vascular access flow measurement tool for the angiography suite and to optimize the imaging protocol amenable for computational flow applications.

Highlights

The ability to measure blood flow using digital images is of significant clinical interest that permits management, diagnosis, and treatment planning of vascular disease [1,2,3]
Blood flow measurement using angiography is based on tracking the passage of the radiopaque contrast material (CM) at two regions of interest (ROIs) and measuring the corresponding transit time, spatial displacement, and vessel dimension [35]
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Summary

Introduction

The ability to measure blood flow using digital images is of significant clinical interest that permits management, diagnosis, and treatment planning of vascular disease [1,2,3]. Because of artificial shunting (fistula/graft), the fistula vein registers an abnormal surge in blood flow and invokes a complex pathophysiological process to accommodate the neo-fluidic stress [7,8] This results in vascular remodeling (intimal hyperplasia) that, over time, leads to narrowing of the lumen and predisposes to stenosis and thrombosis [9,10,11,12]. As per the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF/KDOQI), the minimum flow threshold to ensure patent access is 400–500 mL/min for arteriovenous fistula and 600 mL/min for arteriovenous grafts [14]. Based on these guidelines, the measurement of post-procedural blood flow can provide a reliable assessment of the radio-surgical endpoint

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