Selective embolization with magnetized microbeads using magnetic resonance navigation in a controlled‐flow liver model

Abstract

Purpose The purpose of this study was to demonstrate the feasibility of using a custom gradient sequence on an unmodified 3T magnetic resonance imaging (MRI) scanner to perform magnetic resonance navigation (MRN) by investigating the blood flow control method in vivo, reproducing the obtained rheology in a phantom mimicking porcine hepatic arterial anatomy, injecting magnetized microbead aggregates through an implantable catheter, and steering the aggregates across arterial bifurcations for selective tumor embolization. Materials and Methods In the first phase, arterial hepatic velocity was measured using cine phase‐contrast imaging in seven pigs under free‐flow conditions and controlled‐flow conditions, whereby a balloon catheter is used to occlude arterial flow and saline is injected at different rates. Three of the seven pigs previously underwent selective lobe embolization to simulate a chemoembolization procedure. In the second phase, the measured in vivo controlled‐flow velocities were approximately reproduced in a Y‐shaped vascular bifurcation phantom by injecting saline at an average rate of 0.6 mL/s with a pulsatile component. Aggregates of 200‐μm magnetized particles were steered toward the right or left hepatic branch using a 20‐mT/m MRN gradient. The phantom was oriented at 0°, 45°, and 90° with respect to the B0 magnetic field. The steering differences between left–right gradient and baseline were calculated using Fisher's exact test. A theoretical model of the trajectory of the aggregate within the main phantom branch taking into account gravity, magnetic force, and hydrodynamic drag was also designed, solved, and validated against the experimental results to characterize the physical limitations of the method. Results At an injection rate of 0.5 mL/s, the average flow velocity decreased from 20 ± 15 to 8.4 ± 5.0 cm/s after occlusion in nonembolized pigs and from 13.6 ± 2.0 to 5.4 ± 3.0 cm/s in previously embolized pigs. The pulsatility index measured to be 1.7 ± 1.8 and 1.1 ± 0.1 for nonembolized and embolized pigs, respectively, decreased to 0.6 ± 0.4 and 0.7 ± 0.3 after occlusion. For MRN performed at each orientation, the left–right distribution of aggregates was 55%, 25%, and 75% on baseline and 100%, 100%, and 100% (P < 0.001, P = 0.003, P = 0.003) after the application of MRN, respectively. According to the theoretical model, the aggregate reaches a stable transverse position located toward the direction of the gradient at a distance equal to 5.8% of the radius away from the centerline within 0.11 s, at which point the aggregate will have transited through a longitudinal distance of 1.0 mm from its release position. Conclusion In this study, we showed that the use of a balloon catheter reduces arterial hepatic flow magnitude and variation with the aim to reduce steering failures caused by fast blood flow rates and low magnetic steering forces. A mathematical model confirmed that the reduced flow rate is low enough to maximize steering ratio. After reproducing the flow rate in a vascular bifur...

Magnetic Resonance Imaging System–Driven Medical Robotics

“…To provide stronger forces, an additional MRI gradient coil insert unit has been used to steer the microparticles. This method has been demonstrated to be used for embolization with magnetic microparticles in MRI devices . e) Conceptual depiction of an MRI‐driven swimmer .…”

“…This gradient coil insert can generate 400 mT m −1 gradients. This study has been further improved upon by Michaud et al to investigate the performance of this application under realistic medical environments . In this study, animal experiments are conducted to acquire clinically relevant physical conditions in pig arteries.…”

Estudo de anatomia comparada suína por angiotomografia: contribuições para modelos de pesquisa e treinamento em cirurgia vascular e endovascular

“…5 Classic studies, based on surgical dissections, such as "The anatomy of domestic animals", were published in 1910, 9 and were followed by others that described use of pigs for a variety of procedures. 1,2,[5][6][7][8][10][11][12][13][14][15][16] Over recent decades, the complexity of open and endovascular surgery has been increasing. Noninvasive imaging methods, such as computed tomography (CT), have become routine for treatment planning and monitoring of cases and are progressively substituting traditional angiography.…”

Swarm of magnetic nanoparticles steering in multi-bifurcation vessels under fluid flow

“…BBB) is involved [20]. Moreover, gravity plays a major role in microbids (200 µm) steering [21,22], but for much smaller sized 0.75 to 1 µm magnetic particles, the aggregation size was controlled by introducing discontinuity in the magnetic field. Thus, reducing the severity of the gravitational effects [20].…”

“…In realistic scenarios, as introduced in [23], modulated flow control (MFC) and successive targeted embolization (STE) methods can be applied to reduce and control the blood flow, which makes the proposed scheme applicable. More recent works also cover in vitro and in vivo studies using MRI based navigation systems [21,22]. Despite the recent developments, no electromagnetic steering strategy for swarm of nanoparticles under fluid flow have been studied.…”