Techawiboonwong Aranee, Song Hee Kwon, Magland Jeremy F, Saha Punam K, Wehrli Felix W
Laboratory for Structural NMR Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104, USA.
J Magn Reson Imaging. 2005 Nov;22(5):647-55. doi: 10.1002/jmri.20432.
To investigate the SNR and image properties of 3D steady-state free precession (SSFP), fast large-angle spin echo (FLASE), gradient-recalled acquisition in steady state (GRASS), and spoiled GRASS (SPGR) for structural imaging of trabecular bone (TB).
SNR was examined theoretically and experimentally on phantoms, bone specimens, and in vivo. The bone volume fraction, TB thickness, and echo time (TE) dependence of the thickness were compared. The trabecula was modeled as a cylinder in simulations to examine the intra-voxel spin-dephasing in SSFP and GRASS. Images were acquired on a 1.5 T Siemens Sonata system (40 mT/m maximum gradient, 200 T/m/s peak slew rate).
Within the hardware and safety limit constraints, SNR of FLASE was superior, followed by SSFP, GRASS, and SPGR. The trabecular thickness derived from gradient-echo images was 10-45% greater than that obtained with FLASE. Conversely, SSFP images delineated partial volume trabeculae better than FLASE. Simulations indicated that the artifactual thickening was more severe in SSFP than in GRASS, which was attributed to off-resonance effects from the induced gradients at the bone/marrow interface.
FLASE had the highest SNR and was insensitive to susceptibility dephasing. Although SSFP has superior SNR compared to GRASS, off-resonance effects and duty cycle limitations may compromise its practicality in this application. Inc.
研究三维稳态自由进动（SSFP）、快速大角度自旋回波（FLASE）、稳态梯度回波采集（GRASS）和扰相GRASS（SPGR）用于小梁骨（TB）结构成像的信噪比（SNR）和图像特性。
在体模、骨标本及体内对SNR进行了理论和实验研究。比较了骨体积分数、TB厚度以及厚度对回波时间（TE）的依赖性。在模拟中将小梁建模为圆柱体，以研究SSFP和GRASS中的体素内自旋去相位。图像在1.5T西门子Sonata系统上采集（最大梯度为40mT/m，峰值 slew率为200T/m/s）。
在硬件和安全限制范围内，FLASE的SNR最佳，其次是SSFP、GRASS和SPGR。梯度回波图像得出的小梁厚度比FLASE获得的厚度大10% - 45%。相反，SSFP图像比FLASE能更好地描绘部分体积小梁。模拟表明，SSFP中的伪增厚比GRASS更严重，这归因于骨/骨髓界面处感应梯度产生的失谐效应。
FLASE具有最高的SNR，且对磁化率去相位不敏感。虽然与GRASS相比，SSFP具有更高的SNR，但失谐效应和占空比限制可能会影响其在该应用中的实用性。公司
