The have been further setbacks with the repair of the 11.7T human MRI system, resulting in additional delays. Its magnet appears now ready for testing and the system is expected to return to NIH early 2016. In the meantime, at NIH, work has proceeded towards developing novel radiofrequency (RF) transmission technology. Specifically, two multi-channel transmit technologies have been developed: one based on dipole antennas, and one based on coils directly driven by current amplifiers within the MRI magnet. With the first approach, an array was built for imaging the spine at 7T, and was shown to provide superior performance compared to conventional RF technology. With the second approach, an prototype array was built for 7T and evaluated on test objects. It was demonstrated that the direct current drive of the RF transmit coils allows improved control of the B1 transmit fields as compared to conventional technology. Both the dipole antenna approach and the direct current drive approach are easily adaptable to 11.7T, where their improved control of B1 fields is critically important for imaging the human brain. In the area of contrast manipulation, progress was made in revealing the mechanisms underlying MRI contrast in particular that of magnetization transfer (MT) and T1 relaxation contrast. It was found that quantification of these contrast can be much improved when taking into account their inter-relationship and the effects of RF transmission fields on the way they affect the MRI signal. Based on this novel understanding, novel RF irradiation schemes were designed to more robustly measure and quantify MT and T1 contrast, and used these contrasts to infer macromolecular proton fraction in brain tissue. The latter is expected to relate closely to brain myelin content and thus may be important in the study of demyelinating diseases.
| 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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