Strick Debra S, Nunnally Ray L, Smith Jolinda C, Clark W, Mills Dixie J, Cohen Mark S, Judy Jack W
Biomedical Engineering Interdepartmental program, University of California, LA 90095, USA.
Annu Int Conf IEEE Eng Med Biol Soc. 2008;2008:2047-50. doi: 10.1109/IEMBS.2008.4649594.
Implantable RF-coils have enabled sub-mm resolution magnetic resonance images (MRI) of deep structures. Scaling down the size of RF coils has similarly provided a gain in signal-to-noise ratio in nuclear-magnetic-resonance spectroscopy. By combining both approaches we designed, fabricated, and imaged with an implantable microcoil catheter. While typical implantable catheters use a transverse magnetization, the axial magnetization of the microcoil provides improved sensitivity and allows visualization of the tissue beyond the distal end of the catheter. The microcoil catheter was designed with a diameter of 1 mm for future integration with intracranial devices, and for intraductal use in breast oncology. We modified the NMR-microcoil design to allow implantation of the RF coil, by winding the microcoil on medical-grade silicone tubing and incorporating leads on the catheter to connect circuit components. In order to achieve proper turn spacing, we coated copper wire with 25 microm of biocompatible polymer (Parylene C). Tuning and matching circuitry insured that the impedance of the RF coil was approximately 50 ohm at the operating frequency for 3-T proton MR applications. A duplexer was used to enable use of the microcoil catheter as a transceiver. Experimental verification of the coil design was achieved through ex vivo imaging of neural tissue. As expected, the microcoil catheter provided microscale images with 20-microm in-plane-resolution and 170-microm-thick slices. While 3-T MRI typically provides 1 to 30 voxels per-cubic-millimeter, in this paper we report that the MRI microcoil can provide hundreds, and even thousands of voxels in the same volume.
可植入射频线圈已实现对深部结构的亚毫米分辨率磁共振成像（MRI）。缩小射频线圈的尺寸同样提高了核磁共振波谱的信噪比。通过结合这两种方法，我们设计、制造并使用可植入微线圈导管进行了成像。虽然典型的可植入导管使用横向磁化，但微线圈的轴向磁化提高了灵敏度，并能使导管远端以外的组织可视化。微线圈导管的设计直径为1毫米，以便未来与颅内设备集成，并用于乳腺肿瘤学的导管内应用。我们对核磁共振微线圈设计进行了改进，通过将微线圈缠绕在医用级硅胶管上，并在导管上设置引线以连接电路组件，从而实现射频线圈的植入。为了实现合适的匝间距，我们用25微米的生物相容性聚合物（聚对二甲苯C）包覆铜线。调谐和匹配电路确保射频线圈在3-T质子MR应用的工作频率下阻抗约为50欧姆。使用双工器使微线圈导管能够用作收发器。通过对神经组织的离体成像实现了对线圈设计的实验验证。正如预期的那样，微线圈导管提供了具有20微米平面分辨率和170微米厚切片的微观图像。虽然3-T MRI通常每立方毫米提供1到30个体素，但在本文中我们报告，MRI微线圈在相同体积内可以提供数百甚至数千个体素。
