Improving Blood Flow Visualization of Recirculation Regions at Carotid Bulb in 4D Flow MRI Using Semi-Automatic Segmentation with ITK-SNAP.

Minh Tri Ngo,Dong Hwan Lee,Ui Yun Lee,Hyo Sung Kwak,Hojin Ha,Jinmu Jung

doi:10.3390/diagnostics11101890

Abstract

Assessment of carotid bulb hemodynamics using four-dimensional (4D) flow magnetic resonance imaging (MRI) requires accurate segmentation of recirculation regions that is frequently hampered by limited resolution. This study aims to improve the accuracy of 4D flow MRI carotid bulb segmentation and subsequent recirculation regions analysis. Time-of-flight (TOF) MRI and 4D flow MRI were performed on bilateral carotid artery bifurcations in seven healthy volunteers. TOF-MRI data was segmented into 3D geometry for computational fluid dynamics (CFD) simulations. ITK-SNAP segmentation software was included in the workflow for the semi-automatic generation of 4D flow MRI angiographic data. This study compared the velocities calculated at the carotid bifurcations and the 3D blood flow visualization at the carotid bulbs obtained by 4D flow MRI and CFD. By applying ITK-SNAP segmentation software, an obvious improvement in the 4D flow MRI visualization of the recirculation regions was observed. The 4D flow MRI images of the recirculation flow characteristics of the carotid artery bulbs coincided with the CFD. A reasonable agreement was found in terms of velocity calculated at the carotid bifurcation between CFD and 4D flow MRI. However, the dispersion of velocity data points relative to the local errors of measurement in 4D flow MRI remains. Our proposed strategy showed the feasibility of improving recirculation regions segmentation and the potential for reliable blood flow visualization in 4D flow MRI. However, quantitative analysis of recirculation regions in 4D flow MRI with ITK-SNAP should be enhanced for use in clinical situations.

Highlights

Studies have shown that local hemodynamic conditions at the carotid bulbs, such as deceleration of blood flow or recirculation flow, have a significant impact on the initiation of atherosclerosis [1,2,3,4]
We improved the accuracy of 4D flow magnetic resonance imaging (MRI) carotid bulb segmentation, and, subsequent recirculation regions analysis
Each graph contains the velocity values according to time, and the velocity values were analyzed with three different approaches (4D flow MRI without ITK-SNAP, 4D flow MRI with ITK-SNAP, and computational fluid dynamics (CFD) simulation)

Summary

Introduction

Studies have shown that local hemodynamic conditions at the carotid bulbs, such as deceleration of blood flow or recirculation flow, have a significant impact on the initiation of atherosclerosis [1,2,3,4]. Current 4D flow MRI acquisition schemes could provide information on the hemodynamics of human major arteries (aorta, pulmonary arteries, carotid arteries, and intracranial arteries) [8], but the trade-off between image resolution quality and scanning time still limits its widespread use in clinical practice [9]. One of the most important disadvantages of 4D flow MRI is a challenge in image segmentation caused by the low resolution and poor contrast between interested flow and surrounding tissues [10]. Complex flow in recirculation regions causes further segmentation problems in these 4D flow MRI datasets [11,12]

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