In anticipation of the return of the 11.7 T human system to NIH, now expected in early 2018, we have continued our efforts in developing the enabling technology for flexible contrast generation at this challenging field strength. Specifically, over the last year, much progress has been made in the area of RF transmission. We have further developed technology based on voltage-controlled current source amplification integrated with the transmit conductor. The use of switch-mode amplifiers has allowed miniaturization of the electronics and reduction of cabling, increasing the practicality of this approach. Over the last year, we have developed and tested a modular 2-channel system with a fiber-optic interface for use with NIHs Siemens 7 T and 11.7 T systems, that could be readily expanded to more channels. Tests on the 7 T human system and LFMIs 11.7 T animal system have demonstrated the feasibility of the approach confirming efficient inter-channel decoupling and accurate control over conductor current and associated B1 through feedback provided by a B1 pickup loop adjacent to each coil (Gudino, Duan et al. 2015). It is estimated that the peak B1 fields attainable with this approach are limited to about 20 T for a 16-channel version, higher B1 fields are possible when using higher current transistors or placing multiple transistors in parallel. This proof of principle is not only a major step forward in obtaining better control of B1 at high field, but also has significant practical implications. For example, the fiber-optic control obviates the need for long, low-loss RF cables, which are costly and compete for precious space in the magnet bore. In addition, the cost of the proposed RF system is estimated to be an order of magnitude lower than conventional systems that rely on very costly RF power amplifiers. This is not only the case for 11.7 T, but applies to 7 T as well. We are currently building a second prototype for operation at 7 T that will incorporate eight independent channels.
| Gudino, Natalia; de Zwart, Jacco A; Duan, Qi et al. (2018) Optically controlled on-coil amplifier with RF monitoring feedback. Magn Reson Med 79:2833-2841 |
| Liu, Jiaen; de Zwart, Jacco A; van Gelderen, Peter et al. (2018) Effect of head motion on MRI B0 field distribution. Magn Reson Med 80:2538-2548 |
| van Gelderen, Peter; Jiang, Xu; Duyn, Jeff H (2017) Rapid measurement of brain macromolecular proton fraction with transient saturation transfer MRI. Magn Reson Med 77:2174-2185 |
| Jiang, Xu; van Gelderen, Peter; Duyn, Jeff H (2017) Spectral characteristics of semisolid protons in human brain white matter at 7 T. Magn Reson Med 78:1950-1958 |
| Gudino, Natalia; Duan, Qi; de Zwart, Jacco A et al. (2016) Optically controlled switch-mode current-source amplifiers for on-coil implementation in high-field parallel transmission. Magn Reson Med 76:340-9 |
| Duan, Qi; Nair, Govind; Gudino, Natalia et al. (2015) A 7T spine array based on electric dipole transmitters. Magn Reson Med 74:1189-97 |
| van Gelderen, Peter; Mandelkow, Hendrik; de Zwart, Jacco A et al. (2015) A torque balance measurement of anisotropy of the magnetic susceptibility in white matter. Magn Reson Med 74:1388-96 |
| Duan, Qi; Duyn, Jeff H; Gudino, Natalia et al. (2014) Characterization of a dielectric phantom for high-field magnetic resonance imaging applications. Med Phys 41:102303 |
| Duyn, Jeff H (2014) Frequency shifts in the myelin water compartment. Magn Reson Med 71:1953-5 |
| Duyn, Jeff H; Barbara, Thomas M (2014) Sphere of Lorentz and demagnetization factors in white matter. Magn Reson Med 72:1-3 |
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