Department of Radiology, University of California, San Diego, San Diego, California 92103-8756, USA.
Magn Reson Med. 2010 Feb;63(2):447-55. doi: 10.1002/mrm.22257.
Imaging of short-T(2) species requires not only a short echo time but also efficient suppression of long-T(2) species in order to maximize the short-T(2) contrast and dynamic range. This paper introduces a method of long-T(2) suppression using two long adiabatic inversion pulses. The first adiabatic inversion pulse inverts the magnetization of long-T(2) water and the second one inverts that of fat. Short-T(2) species experience a significant transverse relaxation during the long adiabatic inversion process and are minimally affected by the inversion pulses. Data acquisition with a short echo time of 8 mus starts following a time delay of inversion time (TI1) for the inverted water magnetization to reach a null point and a time delay of TI2 for the inverted fat magnetization to reach a null point. The suppression of long-T(2) species depends on proper combination of TI1, TI2, and pulse repetition time. It is insensitive to radiofrequency inhomogeneities because of the adiabatic inversion pulses. The feasibility of this dual inversion recovery ultrashort echo time technique was demonstrated on phantoms, cadaveric specimens, and healthy volunteers, using a clinical 3-T scanner. High image contrast was achieved for the deep radial and calcified layers of articular cartilage, cortical bone, and the Achilles tendon.
短 T2 物质的成像是不仅需要短回波时间，还需要高效地抑制长 T2 物质，以最大化短 T2 对比度和动态范围。本文介绍了一种使用两个长绝热反转脉冲抑制长 T2 物质的方法。第一个绝热反转脉冲反转长 T2 水的磁化，第二个反转脉冲反转脂肪的磁化。短 T2 物质在长绝热反转过程中经历显著的横向弛豫，反转脉冲对其影响最小。在反转水磁化达到零点的反转时间 (TI1) 后，以及反转脂肪磁化达到零点的 TI2 后，采用 8μs 的短回波时间开始采集数据。长 T2 物质的抑制取决于 TI1、TI2 和脉冲重复时间的适当组合。由于采用了绝热反转脉冲，该方法对射频不均匀性不敏感。该双反转恢复超短回波时间技术的可行性已在体模、尸体标本和健康志愿者上进行了临床 3T 扫描仪上的验证。在关节软骨的深层放射状层和钙化层、皮质骨和跟腱上实现了高的图像对比度。
