We have continued developing technology for RF transmission at high field strength. Specifically, over the last year, we have further developed technology based on voltage-controlled current source amplification integrated with the transmit conductor. This technology is being developed at 7 T with the goal of using it at the 11.7 T system that is expected to come on-line late 2018/early 2019. During 2018 we made additional amplifier improvements to minimize cabling and amplifier/interface footprint to allow assembling an 8 channel system and to start working on increasing the RF frequency to allow efficient operation at 11.7 T . For this purpose, we redesigned the envelope amplifier board to increase dynamic range of the RF monitored signal and to accept optical control for ADCs and DACs implemented on the amplifier board. We also redesigned coil-amplifier former in collaboration with the Section of Instrumentation at NIH. Lastly we designed an 8-channel interface box for optical control of transmit amplifiers and optical reception of monitored signal (Section of Instrumentation provided machined box with power supply for direct plug to standard power outlet). In a second project, we explored a novel acquisition method to detect myelin loss in the brain that has particular advantages at high field. The method is based on previous work that showed that magnetization transfer (MT) is sensitive to the concentration of myelin lipids, and deficits in the latter are characteristic of demyelinating diseases such as Multiple Sclerosis. The method uses a novel way to perform MT that eliminates the often overwhelming background signal from water not participating in the MT process and interferes with the MT detection. It was evaluated at 7T and preliminary results have been presented at scientific meetings. In a third project, we continued to explore ways to reduce motion sensitivity in susceptibility weighted MRI. While susceptibility weighted MRI is finding increasing clinical application, and is particularly promising at high field, its motion sensitivity renders image quality unreliable. We have investigated the origin of this motion sensitivity and found that it relates to complex changes in the magnetic field. This work was published in Magnetic Resonance in Medicine. As motion-induced field changes scale with MRI field strength, their mitigation is particularly important for experiments at 7T and 11.7 T. For this reason, we have started to develop a strategy to account for field changes by measuring them during an MRI scan. This is done by a so-called navigator measurement incorporated in the pulse sequence of the MRI scan. The navigator allows a course measurement of the magnetic field which is then used to correct motion-induced field variations during image reconstruction. Preliminary results indicate that this approach is promising; we are now incorporating this strategy in our acquisition techniques and make them compatible with parallel imaging approaches.
| 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 |
Showing the most recent 10 out of 43 publications
