Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
Magn Reson Med. 2013 Aug;70(2):328-32. doi: 10.1002/mrm.24816. Epub 2013 Jun 14.
Zero echo time (ZTE) imaging is a robust and silent 3D radial technique suitable for direct MRI of tissues with very rapid transverse relaxation. Given its successful application on micro- and animal MRI systems, the purpose of this work is to enable and demonstrate ZTE imaging in humans using a whole-body magnet.
A commercial 7 T MRI scanner was complemented by rapid high-power transmit-receive switches, a custom-built spectrometer, and a proton-free detector coil. With this setup, transmit-receive switching is achieved within 1 µs, radiofrequency (RF) excitation is performed in 3 µs, and digital bandpass filtering takes 5.3 µs, resulting in an effective dead time of only 5 µs.
ZTE imaging was performed at 250 and 500 kHz bandwidth with central k-space gaps of 1.2 and 2.5 Nyquist intervals and repetition times of 739 and 471 µs. The technique was applied for silent 3D imaging of the head and joints of human volunteers at an isotropic resolution down to 0.83 mm. A sound pressure level of 41 dB(A) was measured, which is a reduction of more than 40 dB(A) compared to gradient-switched MRI.
ZTE imaging in humans was demonstrated for the first time, enabled by dedicated, high-performing RF hardware.
零回波时间（ZTE）成像是一种强大且无声的 3D 径向技术，适用于具有极快横向弛豫的组织的直接 MRI。鉴于其在微系统和动物 MRI 系统上的成功应用，本工作旨在使用全身磁体实现和演示 ZTE 成像。
一台商业 7 T MRI 扫描仪配备了快速高功率发射-接收开关、定制的光谱仪和质子自由探测器线圈。通过这种设置，发射-接收切换可在 1 µs 内完成，射频（RF）激励在 3 µs 内完成，数字带通滤波需要 5.3 µs，从而有效死区时间仅为 5 µs。
在 250 和 500 kHz 带宽下进行了 ZTE 成像，中心 k 空间间隙为 1.2 和 2.5 奈奎斯特间隔，重复时间为 739 和 471 µs。该技术应用于无声 3D 成像，志愿者头部和关节的各向同性分辨率可低至 0.83 mm。测量到的声压级为 41 dB(A)，与梯度切换 MRI 相比降低了超过 40 dB(A)。
首次通过专用的高性能 RF 硬件实现了人体 ZTE 成像。
