Real-time magnetic resonance-guided endovascular repair of experimental abdominal aortic aneurysm in swine

Venkatesh K Raman, Parag V Karmarkar, Michael A Guttman, Alexander J Dick, Dana C Peters, Cengizhan Ozturk, Breno S S Pessanha, Richard B Thompson, Amish N Raval, Ranil DeSilva, Ronnier J Aviles, Ergin Atalar, Elliot R McVeigh, Robert J Lederman, Venkatesh K Raman, Parag V Karmarkar, Michael A Guttman, Alexander J Dick, Dana C Peters, Cengizhan Ozturk, Breno S S Pessanha, Richard B Thompson, Amish N Raval, Ranil DeSilva, Ronnier J Aviles, Ergin Atalar, Elliot R McVeigh, Robert J Lederman

Abstract

Objectives: This study tested the hypotheses that endografts can be visualized and navigated in vivo solely under real-time magnetic resonance imaging (rtMRI) guidance to repair experimental abdominal aortic aneurysms (AAA) in swine, and that MRI can provide immediate assessment of endograft apposition and aneurysm exclusion.

Background: Endovascular repair for AAA is limited by endoleak caused by inflow or outflow malapposition. The ability of rtMRI to image soft tissue and flow may improve on X-ray guidance of this procedure.

Methods: Infrarenal AAA was created in swine by balloon overstretch. We used one passive commercial endograft, imaged based on metal-induced MRI artifacts, and several types of homemade active endografts, incorporating MRI receiver coils (antennae). Custom interactive rtMRI features included color coding the catheter-antenna signals individually, simultaneous multislice imaging, and real-time three-dimensional rendering.

Results: Eleven repairs were performed solely using rtMRI, simultaneously depicting the device and soft-tissue pathology during endograft deployment. Active devices proved most useful. Intraprocedural MRI provided anatomic confirmation of stent strut apposition and functional corroboration of aneurysm exclusion and restoration of laminar flow in successful cases. In two cases, there was clear evidence of contrast accumulation in the aneurysm sac, denoting endoleak.

Conclusions: Endovascular AAA repair is feasible under rtMRI guidance. Active endografts facilitate device visualization and complement the soft tissue contrast afforded by MRI for precise positioning and deployment. Magnetic resonance imaging also permits immediate post-procedural anatomic and functional evaluation of successful aneurysm exclusion.

Figures

Figure 1
Figure 1
Active-stent endograft. (A) Components of homemade active endograft, constructed from 0.009-inch nitinol wire and expanded poly-tetrafluoroethylene graft material. (B) Completed one-channel active-stent device mounted on a 5-F catheter and constrained within a 10-F nylon sheath (arrowhead). Matching tuning circuitry is housed in a separate box (arrow).
Figure 2
Figure 2
Schematic of endograft designs. (A) Unmodified commercial device imaged on the basis of intrinsic magnetic susceptibility (signal void). (B) Homemade endograft device with active opposed loop solenoid coils as markers delineating proximal and distal stent edges. (C) Homemade endograft device with active stent connected to delivery system shaft by a detachable cable that, after deployment and removal of the delivery catheter, renders the stent inactive. (D) Homemade endograft device with active stent as described in (C) and second active marker composed of a multilooped coil on the delivery shaft just beyond the distal stent edge.
Figure 3
Figure 3
Real-time multislice imaging and three-dimensional rendering during endograft positioning. In the left column, real-time magnetic resonance imaging multislice axial, sagittal, and coronal images shown simultaneously facilitate precise device positioning. Concomitant three-dimensional rendering on the right integrates multislice information. Positioning three axial slices at the caudal renal artery origin, the middle of the aneurysm, and the aortic bifurcation, respectively, allows simultaneous capture of the most important anatomy for device placement. The coronal and sagittal slices provide an overall “bird’s eye” view of the aorta. Orientation markers indicate: S = superior, I = inferior, A = anterior, P = posterior, R = right, L = left. Blue arrow indicates aneurysm.
Figure 4
Figure 4
Stent strut apposition. (A) Fast spin echo image shows nitinol stent well apposed to target proximal infrarenal aorta (arrows show signal void from stent struts). (B) Spin-echo axial image at level of aneurysm, showing excluded sac (dashed outline). Orientation markers as in Figure 3.
Figure 5
Figure 5
Magnetic resonance angiogram (maximum-intensity projection) before and after endograft delivery. (A) Conventional contrast-enhanced magnetic resonance angiography shows infrarenal abdominal aortic aneurysm after balloon overstretch. (B) Abdominal aortic aneurysm is excluded by nitinol endograft (causing luminal artifact). Orientation markers as in Figure 3.
Figure 6
Figure 6
Phase-contrast flow assessments before and after endograft deployment. Axial overlays of in-plane (vector flow map) and through-plane (color map) flow within ruptured experimental aneurysm. Before endovascular repair, there is marked turbulence and evidence of retrograde flow (blue) within the aneurysm (dashed outline). The vena cava is collapsed in this hemorrhagic state. Laminar flow is restored after endograft (dashed outline) deployment. Solid lines border vena cava, identified on cine loops by constant nonpulsatile flow. Orientation markers as in Figure 3.

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