Towards a microcoil for intracranial and intraductal MR microscopy

• Published in: 2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society Vol. 2008; pp. 2047 - 2050
• Main Authors: Strick, Debra S., Nunnally, Ray L., Smith, Jolinda C., Clark, W. Gilbert, Mills, Dixie J., Cohen, Mark S., Judy, Jack W.
• Format: Conference Proceeding Journal Article
• Language: English
• Published: United States IEEE 01-01-2008
• Subjects: Animals; Biocompatible Materials; Brain - anatomy & histology; Breast - anatomy & histology; Catheterization; Equipment Design; Humans; Magnetic Resonance Imaging - instrumentation; Sheep; Transducers
• ISBN: 9781424418145; 1424418143
• ISSN: 1094-687X; 1557-170X; 1558-4615
• 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 magneti-zation, 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 μm of biocompatible polymer (Parylene C). Tuning and matching circuitry insured that the impedance of the RF coil was approximately 50 Ω 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-μm in-plane-resolution and 170-μm-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.