Li Cheng, Magland Jeremy F, Zhao Xia, Seifert Alan C, Wehrli Felix W
Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Magn Reson Med. 2017 Mar;77(3):989-997. doi: 10.1002/mrm.26178. Epub 2016 Feb 24.
To design and evaluate an optimized PETRA (point-wise encoding time reduction with radial acquisition) sequence with long-T suppression at 3 Tesla.
An adiabatic inversion recovery-based scheme was used to null the long-T signal. To minimize scan time, the signal was sampled multiple times after each inversion with variable excitation flip angles designed to yield constant short-T signal amplitude. The excitation pulses were phase-modulated, allowing for increased flip angle and higher signal-to-noise ratio (SNR). A fast, noniterative image reconstruction algorithm was designed to minimize image artifacts due to nonuniform excitation profile.
Phase-modulated pulse excitation, along with the noniterative reconstruction algorithm, allows the use of larger radiofrequency pulse flip angles, resulting in effective suppression of long-T protons and improved image SNR without causing image artifacts. Midtibia images representative of collagen-bound water yielded SNR of 15 at 1-mm isotropic resolution in 6.5 minutes with a standard extremity coil. Further, the technology is shown to be suited for generating multi-angle projection images of bone akin to X-ray images displaying subtle anatomic detail.
Optimized long-T suppressed PETRA allows imaging of bone matrix water unencumbered by long-T soft tissue and pore water protons, opening up new possibilities for anatomic bone imaging at isotropic resolution and quantification in clinically practical scan times. Magn Reson Med 77:989-997, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
设计并评估一种在3特斯拉磁场下具有长T抑制功能的优化PETRA（径向采集逐点编码时间减少）序列。
采用基于绝热反转恢复的方案来消除长T信号。为了最小化扫描时间，在每次反转后对信号进行多次采样，采用可变激发翻转角以产生恒定的短T信号幅度。激发脉冲进行相位调制，以允许增大翻转角并提高信噪比（SNR）。设计了一种快速、非迭代的图像重建算法，以最小化由于不均匀激发轮廓导致的图像伪影。
相位调制脉冲激发与非迭代重建算法一起，允许使用更大的射频脉冲翻转角，从而有效抑制长T质子并提高图像SNR，而不会导致图像伪影。使用标准肢体线圈，在6.5分钟内以1毫米各向同性分辨率获得的代表胶原结合水的胫骨中部图像的SNR为15。此外，该技术被证明适用于生成类似于显示细微解剖细节的X射线图像的骨骼多角度投影图像。
优化的长T抑制PETRA能够对不受长T软组织和孔隙水质子影响的骨基质水进行成像，为在各向同性分辨率下进行解剖学骨成像以及在临床实际扫描时间内进行定量分析开辟了新的可能性。《磁共振医学》77:989 - 997, 2017。© 2016国际磁共振医学学会。
