Most presently installed full-body MRI systems are based on 1.5 T liquid-He- cooled NbTi magnets, but the rate of installation of 3.0 T systems is rapidly increasing. However, the increasing cost of helium is well documented, and this leads to increases in the life cycle cost of MRI systems, which could limit ready access for traditional patient groups, and limit the ability to expand availability to traditionally less well served patient groups. The root cause of the problem is the growing shortage of helium worldwide. The major MRI magnet manufacturers (Siemens, GE, and Phillips) each have development programs focused on converting the 1.5T solenoid coils from liquid helium bath cooling to dry (cryogen free) conduction cooling. Indeed, freedom from the need for liquid-helium cooling (i.e. cryogen free, conduction-cooled, operation) is becoming more and more important. While NbTi designs have been explored for 1.5 T systems, the much higher demands of 3 T systems makes that route untenable. The larger thermal margin of MgB2 and affordability makes MgB2 based 3 T systems the most feasible. Even beyond the liquid cryogen issues for MRI, the development of cryocooled MRI magnets could allow for new geometries and MRI applications, opening up new treatment possibilities. However, we must focus where the industry can transition this new technology commercially. Accordingly, the proposed program focuses on developing the technology to enable cryogen free 3 T systems using a cryocooled mode. We proposed to do this by (1) Continuing to increase MgB2 Je in ranges appropriate to 3 T MRI (4-10 K, 0-6 T), but focus on a protectable conductor with n > 30 guaranteed over long lengths, (2) Optimizing our present magnet models (FEM/numerical) targeting reduced peak fields on the wire in order to reduce required conductor length and structural support (making present proof-of principle competitive and highly attractive), (3) Demonstrating reliable and higher performance persistent joints as well as a persistent switch, both working in conjunction with a full size segment coil, (4) Demonstrating a react and wind coil segment with 3 T design performance and an integrated active protection scheme with high reliability (as shown experimentally with coil operating in persistent mode), (5) Developing alternative magnetic/mechanical designs for specialty applications including image guided applications. 1
This proposed program aims to develop essential technology to permit MRI systems which can operate using a cryocooling mode, maintain access as helium costs rise. This will also enable new MRI applications not constrained by the designs requiring liquid cryogen cooling, thus opening up new treatment possibilities. In order to do this, improvements in conductor, wire joints, magnet design, and magnet protection are needed, which is the focus of this proposal. 1
