Virtual Stenting

Motivation

b1Aortic coarctation is a narrowing of the aorta in the region of the transition between the aortic arch and the descending aorta where the fetal ductus arteriosus is joined. It occurs in about 7% of all congenital heart defects. The high afterload induced by the stenosis can lead to ventricular dysfunction and thus a major therapy goal is to remove the pressure gradient. According to the AHA Guidelines, balloon angioplasty with stenting is a minimally invasive recommended therapy for patients with a systolic pressure gradient of more than 20 mmHg (Feltes, et al. 2011). optimal stent placement is however a non-trivial task.

b2Care must be taken with respect to several associated complications such as occlusion of the subclavian artery, (Waltham et al. 2005), stent migration, formation of aneurysms, and aortic dissection, (Godart 2011), to name a few. and associated complications to avoid include the occlusion of the subclavian artery (Waltham, et al. 2005) as well as a stent placement that causes stent migration or the formation of aneurysms or aortic dissection (Godart 2011). It is therefore desirable to simulate treatment options prior to the intervention in order to decide on an optimal stent placement that would result in reasonable changes in diameter and acceptable post-interventional hemodynamics provided by the guidelines.

 

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Pipeline

Our prototype works with arbitrary 3D datasets of the patient’s anatomy and 4D PC MRI data of the patient’s blood flow. The software enables the extraction of the vessel geometry using an interactive approach that combines the watershed transformation with manual correction tools. The extracted anatomy is then fused with the pre-processed PC MRI data that contains the blood flow velocity information for one heart cycle. With these data blood flow as well as pressure differences can be visualized and quantified. (Hennemuth, et al. 2011) (Drexl, et al. 2013) (Meier, et al. 2013). b3In order to explore intervention strategies, it is then possible to interactively change the aorta anatomy through simulating a stenting procedure.

The extracted anatomy is converted into a high quality surface mesh and the centreline of the vessel is computed. The user selects pre-, post- and stenosis locations by interactively placing cross-sectional contours on the vessel surface. Hemodynamic data is provided as contextual information. A pressure map and the pressure curve along the centreline allows for a detailed qualitative and quantitative analysis of the pressure gradient.

All necessary parameters (e.g. stent length, balloon diameter) are derived from these contours. The vessel segment affected by the stent is deformed accord- ingly. The user can interactively alter the suggested deformation by changing the stent parameters (stiffness, radial force), relocating the stent or change its diameter. The resulting geometry as well as the in- flow conditions derived from the 4D PC MRI data are then used as input information for a simulation of the hemodynamic situation after stenting.

Outlook

Computational fluid dynamics (CFD) simulations in this pipeline provide one of its kind data quantifying hemodynamics for patients with coarctation of the aorta.

b4After the virtual treatment of the vascular geometry a meshless CFD approach based on the lattice Boltzmann method is applied to simulate the velocity field after a treatment.Based on this field the pressure values are computed and ultimately the pressure gradients are visualized. Our preliminary results on a stenosis phantom data depicted below indicate a good agreement between simulation and measured 4D PC MRI data.

 

Author: Hanieh Mirzaee

This article was originally published in Cardioproof Newsletter-Issue 1

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References:

Feltes TF, Bacha E, Beekman RH 3rd, Cheatham JP, Feinstein JA, Gomes AS, Hijazi ZM, Ing FF, de Moor M, Morrow WR, Mull- ins CE, Taubert KA, Zahn EM. Indications for cardiac catheteri- zation and intervention in pediatric cardiac disease: a scientific statement from the American Heart Association. Circulation, 2011: 2607-52.
Godart, F., Intravascular stenting for the treatment of coarcta- tion of the aorta in adolescent and adult patients. “Archives of Cardiovascular Diseases, 2011: 627-635.
Waltham, M., V. Agrawal, L. Bowman, C. Hughes, und G.H. White. Right arm ischemia following intentional stent-graft coverage of an anomalous right subclavian artery.“ J Endovasc Ther, 2005: 110-4.
Hennemuth, A., Friman, O., Schumann, C., Bock, J., Drexl, J., Huellebrand, M., et al. “Fast interactive exploration of 4D MRI flow data” SPIE Medical Imaging 2011.
Drexl, J., Mirzaee, H., Harloff, A., Hüllebrand, M., Hennemuth, A., Hahn, H.. (2013). A Software Tool for the Computation of Arterial Pulse Wave Velocity from Flow-sensitive 4D MRI Data. CinC – Computing in Cardiology Conference 2013.
Meier, S., Hennemuth, A., Drexl, J., Bock, J., Jung, B., & Preusser, T. “A fast and noise-robust method for computation of intravascular pressure difference maps from 4D PC-MRI data.” Statistical Atlases and Computational Models of the Heart 2013: 215–224