Human magnetic resonance imaging at 8 T

TLDR

Based on 4 T measurements, 1–2 J was expected for a 90° excitation at 8 T, but lower energy would mitigate SAR concerns. The study presents the first human MRI at 8 T. The authors show that 8 T imaging yields reasonable head image quality, requires only ~0.085 J for a 90° pulse—much less than the 1–2 J predicted—and enables RF‑intensive sequences without significant SAR risk. © 1998 John Wiley & Sons, Ltd.

Abstract

In this work, we present the first human magnetic resonance image (MRI) obtained at ultrahigh field strengths (8 T). We demonstrate that clinical imaging will be possible at 8 T and that reasonable quality head images can be obtained at this field strength. Most importantly, we emphasize that the power required to excite the spins at 8 T is much lower than had previously been predicted by the nuclear magnetic resonance theory. A 90° pulse in the head at 8 T requires only ∼0.085 J of energy (90 W for a 2-lobe 4 ms sinc pulse). Based on measurements at 4 T, 1–2 J of energy should have been utilized to achieve a 90° excitation at 8 T. The fact that the energy required for spin excitation at 8 T is much lower than predicted by the NMR theory, will be extremely important to the viability of ultrahigh field imaging, since concerns related to power absorption and specific absorption rate (SAR) violations at ultrahigh field are alleviated. As such, it will be possible to utilize RF intensive pulse sequences and adiabatic spin excitation at 8 T without significant risk to the subject. © 1998 John Wiley & Sons, Ltd.