J. Birjiniuk4, J. M. Ruddy3, E. Iffrig4, T. Henry5, B. G. Leshnower6, J. N. Oshinski4,5, D. N. Ku1, R. K. Veeraswamy2 1Georgia Institute Of Technology,George W. Woodruff School Of Mechanical Engineering,Atlanta, GA, USA 2Emory University School Of Medicine,Division Of Vascular Surgery And Endovascular Therapy, Department Of Surgery,Atlanta, GA, USA 3Medical University Of South Carolina,Division Of Vascular Surgery, Department Of Surgery,Charleston, Sc, USA 4Georgia Institute Of Technology,Wallace H. Coulter Department Of Biomedical Engineering,Atlanta, GA, USA 5Emory University School Of Medicine,Department Of Radiology,Atlanta, GA, USA 6Emory University School Of Medicine,Division Of Cardiothoracic Surgery, Department Of Surgery,Atlanta, GA, USA
Introduction:
Aortic dissection is a tearing of the intimal layer of the aorta leading to two distinct aortic flow lumens with varying degrees of communication between them. This results in a complex biomechanical system with poorly understood fluid dynamics throughout the aorta. Ultimately, these changes may affect tear propagation, intraluminal thrombogenesis, and end-organ perfusion. Developing novel therapies to manage aortic dissection has been limited by the lack of a reproducible system to investigate this pathology. We present a novel method for studying hemodynamic measurements in a dissected aorta.
Methods:
CT images of several clinical aortic dissections were collected. Rapid prototypes of aortic dissections were created and served as molds for constructing silicone models. These models have a mobile membrane, which has dimensions and elasticity similar to those of an intimal flap. A positive displacement perfusion pump (COBE, Century HeartLung) with a blood-mimic agent was utilized at a rate of 5 L/min. and magnetic resonance sequences for anatomical data were obtained. In addition, four dimensional phase-contrast magnetic resonance (4D PCMR) imaging was used to determine velocities in three axes. All images were processed using Siemens 4D Flow (Siemens Medical Solutions USA, Malvern, PA) for particle streams and a custom-made analysis software for flow calculations. Planes perpendicular to aortic wall were chosen at multiple points along the model. In the dissected portion, the two lumens were treated independently after manual segmentation. Luminal regions of interest were drawn manually and used to calculate lumen areas and velocity profiles. Flow parameters were individually measured at each point. Flow rates were calculated using velocity profiles and averaged over several time points in the 4D scan.
Results:
MRI particle streams confirmed flow communicating between the lumens. Flow rate in the true lumen averaged 3.1 +/- 0.8 L/m with 68% of the total flow. The false lumen had a mean flow rate of 1.4 +/- 0.6 L/min (p<0.05). The luminal shapes changed along the length, with a crescent shape proximally, and an elliptical shape distally, for the true lumen. Area in the true lumen decreased along the descending thoracic aorta, while the false lumen increased from 35 to 39%.
Conclusion:
Our model successfully recapitulates the flow behavior in a Type III b dissected thoracic aorta, and our method successfully utilizes 4D PCMR imaging to make relevant hemodynamic measurements. For this particular example, we found that the flow in each lumen was proportional to its share of luminal area. Future studies will yield detailed hemodynamics with entrance and exit tears.
