There’s also considerable research on retinal and brain implants for vision, as well as efforts to give people with prosthetic hands a sense of touch. Prosthetic implants for hearing have advanced the furthest, with designs that interface with theĬochlear nerve of the inner ear or directly into the auditory brain stem. Neuroprosthetics have come a long way in the past two decades. The first version of the brain-computer interface gave the volunteer a vocabulary of 50 practical words. The design provides space for the liquid helium bath to reach all of the coil and keep the temperature low, and it also allows engineers to place the best-performing coils at the center of the system, which improves the precision of the magnetic field. However, a miswound pancake can simply be swapped out for a new one. Védrine explains that this reduces the chances for error: Making a mistake in the winding phase using a single helical coil could ruin the whole magnet. The whole magnet will consist of 170 of these double pancakes connected in series. Instead of winding the wire into one long coil, as is standard in systems with lower fields, engineers are using a “double pancake” design, in which the wire is coiled into two reels that are spliced together, one on top of the other. The company made another 58 km for two secondary coils, which will produce an opposing magnetic field to shield the area outside the machine from stray magnetic fields. Ultimately, Luvata produced 170 km of wire for the main superconducting coil. “We are pushing the superconducting material niobium-titanium very close to its limits,” Védrine says.Īnother material, niobium-tin, can produce magnetic fields stronger than 20 T, but it was passed over for the job because it’s more expensive than niobium-titanium and very brittle, making it difficult to wind. That requires specialized manufacturing and precise control of the dimensions of the wire, allowing it to be coiled so the cables are aligned to within a few micrometers of precision. To reach the required field strength, the electromagnet must be able to carry 1500 amperes at 12 T and be cooled by superfluid liquid helium to 1.8 kelvins. But it will experience some uncommon conditions as part of INUMAC. The wire in the INUMAC magnet is made from niobium-titanium, a common superconductor alloy. Improved superconducting wire is key to making such a powerful machine. Most MRI machines rely on imaging the nuclei of hydrogen atoms, but stronger scanners might gain useful physiological information by looking for weaker signals from sodium or potassium nuclei.
High-field MRI could also allow scientists to explore different methods of imaging. “You cannot really discriminate today what is happening inside your brain at the level of a few hundred neurons,” Védrine says. It would also allow much more precise functional imaging of the brain at work than is currently available.
With this type of resolution, MRIs could detect early indications of brain diseases such as Alzheimer’s or Parkinson’s and perhaps measure the effects of any methods developed to treat those illnesses. The INUMAC will be able to image an area of about 0.1 mm, or 1000 neurons, and see changes occurring as fast as one-tenth of a second, according to Pierre Védrine, director of the project at the French Alternative Energies and Atomic Energy Commission, in Paris.
Standard hospital scanners have a spatial resolution of about 1 millimeter, covering about 10 000 neurons, and a time resolution of about a second.
STRONGEST MAGNET IN THE WORLD PLUS
“We’re pretty proud of having met all the requirements, plus given them a little extra,” says Hem Kanithi, vice president of business development at Luvata, in Waterbury, Conn., which built the superconductor. The project reached a key milestone this summer with delivery of more than 200 kilometers of superconducting cable, which is now being wound into coils that will produce the scanner’s magnetic field. The development of the scanner, known as INUMAC (for Imaging of Neuro disease Using high-field MR And Contrastophores), has been in progress since 2006 and is expected to cost €200 million, or about US $270 million. Superconducting magnets used in the Large Hadron Collider, which last year was used in the discovery of the Higgs boson, produce a field of 8.4 T. A few institutions, including the University of Illinois at Chicago and Maastricht University, in the Netherlands, have recently installed human scanners that can reach 9.4 T. Most standard hospital MRIs produce 1.5 or 3 T. The imager’s superconducting electromagnet is designed to produce a field of 11.75 teslas, making it the world’s most powerful whole-body scanner.
0 kommentar(er)
