Accuracy of flow volume estimation in the dilated aorta using 4D flow MRI: a pulsatile phantom study

<i>Objectives.</i>Aortic dilatation is a severe pathology that increases the risk of rupture and its hemodynamics could be accurately assessed by using the 4D flow cardiovascular magnetic resonance (CMR) technique but flow assessment under complex flow patterns require validation. The aim of this work was to develop an<i>in vitro</i>system compatible with CMR to assess the accuracy of volume flow measurements in dilated aortas.<i>Approach.</i>Two latex models, one with ascending and the other with abdominal aortic aneurysms were manufactured to ensure a constant and controlled net flow volume along the aortic length. A pneumatic piston driven by a stepper motor and controlled by an embedded system located in the control room modulated a pulsatile fluid flow using a pump with an elastic membrane placed in the magnet near the elastic models. All the visualization and measurement algorithms were integrated into a custom computer platform. 4D flow imaging was used to estimate the flow rate and volume through multiple aortic planes and compared to the reference assessed by weight method and to 2D flow measurements.<i>Main results.</i>The errors of flow volume assessment using 4D flow remained within reasonable limits along the length of the aortic models. Mean differences in net flow volume from the reference were less than 2 ml (range -4 to 6 ml), corresponding to mean relative differences of less than 4% (range -8% to 11%). Averaged net, forward and backward flow volume estimations along the aortic length were similar using 2D and 4D flow measurements (<i>p</i>> 0.05). Peak forward and backward flow rates increased in the dilated regions and were comparable to those observed in patients.<i>Significance.</i>The accuracy of flow volume estimates in complex flow patterns, such as those observed in patients with aneurysms, was validated<i>in vitro</i>using 4D flow.