Mathieu Jean-Baptiste, Beaudoin Gilles, Martel Sylvain
Ecole Polytechnique de Montréal, QC, Canada.
IEEE Trans Biomed Eng. 2006 Feb;53(2):292-9. doi: 10.1109/TBME.2005.862570.
This paper reports the use of a magnetic resonance imaging (MRI) system to propel a ferromagnetic core. The concept was studied for future development of microdevices designed to perform minimally invasive interventions in remote sites accessible through the human cardiovascular system. A mathematical model is described taking into account various parameters such as the size of blood vessels, the velocities and viscous properties of blood, the magnetic properties of the materials, the characteristics of MRI gradient coils, as well as the ratio between the diameter of a spherical core and the diameter of the blood vessels. The concept of magnetic propulsion by MRI is validated experimentally by measuring the flow velocities that magnetized spheres (carbon steel 1010/1020) can withstand inside cylindrical tubes under the different magnetic forces created with a Siemens Magnetom Vision 1.5 T MRI system. The differences between the velocities predicted by the theoretical model and the experiments are approximately 10%. The results indicate that with the technology available today for gradient coils used in clinical MRI systems, it is possible to generate sufficient gradients to propel a ferromagnetic sphere in the larger sections of the arterial system. In other words, the results show that in the larger blood vessels where the diameter of the microdevices could be as large as a couple a millimeters, the few tens of mT/m of gradients required for displacement against the relatively high blood flow rate is well within the limits of clinical MRI systems. On the other hand, although propulsion of a ferromagnetic core with diameter of approximately 600 microm may be possible with existing clinical MRI systems, gradient amplitudes of several T/m would be required to propel a much smaller ferromagnetic core in small vessels such as capillaries and additional gradient coils would be required to upgrade existing MRI systems for operations at such a scale.
本文报道了利用磁共振成像（MRI）系统推动铁磁芯的研究。该概念是为未来微型设备的发展而研究的，这些微型设备旨在对可通过人体心血管系统到达的偏远部位进行微创干预。文中描述了一个数学模型，该模型考虑了各种参数，如血管大小、血液的流速和粘性特性、材料的磁性特性、MRI梯度线圈的特性，以及球形芯直径与血管直径的比值。通过测量在西门子Magnetom Vision 1.5 T MRI系统产生的不同磁力作用下，磁化球体（碳钢1010/1020）在圆柱管内能够承受的流速，对MRI磁推进概念进行了实验验证。理论模型预测的速度与实验结果之间的差异约为10%。结果表明，利用当今临床MRI系统中可用的梯度线圈技术，有可能产生足够的梯度，以在动脉系统的较大部分推动铁磁球体。换句话说，结果表明，在微型设备直径可达几毫米的较大血管中，克服相对较高的血流速度进行位移所需的几十mT/m的梯度完全在临床MRI系统的限制范围内。另一方面，虽然现有临床MRI系统可能能够推动直径约600微米的铁磁芯，但在诸如毛细血管等小血管中推动小得多的铁磁芯则需要几T/m的梯度幅度，并且需要额外的梯度线圈来升级现有MRI系统以进行这种规模的操作。
