HUMAN MAGNETIC-RESONANCE-IMAGING AT 8 T

In this work, we present the first human magnetic resonance image (MRI ) obtained at ultrahigh field strengths (8 T). We demonstrate that cli nical imaging will be possible at 8 T and that reasonable quality head images can be obtained at this field strength. Most importantly, we e mphasize that the power required to excite the spins at 8 T is much lo wer than had previously been predicted by the nuclear magnetic resonan ce theory. A 90 degrees pulse in the head at 8 T requires only similar to 0.085 J of energy (90 W for a 2-lobe 3 ms sine pulse). Based on me asurements at 4 T, 1-2 J of energy should have been utilized to achiev e a 90 degrees excitation at 8 T. The fact that the energy required fo r spin excitation at 8 T is much lower than predicted by the NMR theor y, will be extremely important to the viability of ultrahigh field ima ging, since concerns related to power absorption and specific absorpti on rate (SAR) violations at ultrahigh field are alleviated. As such, i t will be possible to utilize RF intensive pulse sequences and adiabat ic spin excitation at 8 T without significant risk to the subject. (C) 1998 John Wiley & Sons, Ltd.