Department of Radiology, University of California, San Diego, California.
Radiology Service, VA San Diego Healthcare System, San Diego, California.
Magn Reson Med. 2019 Dec;82(6):2178-2187. doi: 10.1002/mrm.27885. Epub 2019 Jul 17.
To design a soft-hard composite pulse for fat suppression and water excitation in ultrashort echo time (UTE) imaging with minimal short T signal attenuation.
The composite pulse contains a narrow bandwidth soft pulse centered on the fat peak with a small negative flip angle (-α) and a short rectangular pulse with a small positive flip angle (α). The fat magnetization experiences both tipping-down and -back with an identical flip angle and thus returns to the equilibrium state, leaving only the excited water magnetization. Bloch simulations, as well as knee, tibia, and ankle UTE imaging studies, were performed to investigate the effectiveness of fat suppression and corresponding water signal attenuation. A conventional fat saturation (FatSat) module was used for comparison. Signal suppression ratio (SSR), defined as the ratio of signal difference between non-fat-suppression and fat-suppression images over the non-fat-suppression signal, was introduced to evaluate the efficiency of the composite pulse.
Numerical simulations demonstrate that the soft-hard pulse has little saturation effect on short T water signals. Knee, tibia, and ankle UTE imaging results suggest that comparable fat suppression can be achieved with the soft-hard pulse and the FatSat module. However, much less water saturation is induced by the soft-hard pulse, especially for short T tissues, with SSRs reduced from 71.8 ± 6.9% to 5.8 ± 4.4% for meniscus, from 68.7 ± 5.5% to 7.7 ± 7.6% for bone, and from 62.9 ± 12.0% to 4.8 ± 3.2% for the Achilles tendon.
The soft-hard composite pulse can suppress fat signals in UTE imaging with little signal attenuation on short T tissues.
设计一种软硬复合脉冲，用于在超短回波时间 (UTE) 成像中抑制脂肪信号并激发水信号，同时最小化短 T 信号衰减。
复合脉冲包含一个中心位于脂肪峰的窄带软脉冲，其翻转角为负 (-α)，并带有一个小的正翻转角 (α) 的短矩形脉冲。脂肪磁化经历了相同翻转角的倾倒和恢复，因此回到平衡状态，只剩下激发的水磁化。通过布洛赫模拟以及膝、胫骨和踝关节 UTE 成像研究，研究了脂肪抑制的效果和相应的水信号衰减。使用传统的脂肪饱和 (FatSat) 模块进行比较。引入信号抑制比 (SSR) 来评估复合脉冲的效率，定义为非脂肪抑制和脂肪抑制图像之间的信号差异与非脂肪抑制信号的比值。
数值模拟表明，软硬脉冲对短 T 水信号的饱和效应很小。膝、胫骨和踝关节 UTE 成像结果表明，软硬脉冲和 FatSat 模块可以实现相当的脂肪抑制效果。然而，软硬脉冲引起的水饱和程度要小得多，特别是对于短 T 组织，对于半月板，SSR 从 71.8±6.9%降至 5.8±4.4%；对于骨骼，从 68.7±5.5%降至 7.7±7.6%；对于跟腱，从 62.9±12.0%降至 4.8±3.2%。
软硬复合脉冲可在 UTE 成像中抑制脂肪信号，同时对短 T 组织的信号衰减很小。
