SHAPING THE SIGNAL RESPONSE DURING THE APPROACH TO STEADY-STATE IN 3-DIMENSIONAL MAGNETIZATION-PREPARED RAPID GRADIENT-ECHO IMAGING USING VARIABLE FLIP ANGLES
SHAPING THE SIGNAL RESPONSE DURING THE APPROACH TO STEADY-STATE IN 3-DIMENSIONAL MAGNETIZATION-PREPARED RAPID GRADIENT-ECHO IMAGING USING VARIABLE FLIP ANGLES
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DOI：
10.1002/mrm.1910280202
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发表时间：
1992-12-01
影响因子：
3.3
通讯作者：
BROOKEMAN, JR
中科院分区：
文献类型：
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作者：
MUGLER, JP;EPSTEIN, FH;BROOKEMAN, JR
已开发并实施了一种理论算法，用于在三维磁化准备快速梯度回波（3D MP‐回波）脉冲序列中接近稳态时对信号响应进行整形。该算法推导出在3D MP‐ MRI序列的数据采集段期间产生特定选择的信号强度时间演变所需的翻转角系列。在1.5 T全身成像仪上使用掺杂水体模对未成形、均匀和单指数衰减信号响应情况的理论预测进行了定量验证，在所有情况下，理论值和实验值之间均非常一致。还研究了RF不均匀性和涡流对信号响应整形的影响。为了证明该技术的潜在实用性，将信号响应整形算法应用于T1加权3D MP‐ MRI序列，以推导出理论上产生与所选响应形状一致的最大白色物质/灰质信号差（WGSD）的采集翻转角系列。将使用该可变翻转角序列从健康志愿者获得的图像与在相同总成像时间内获得的3D RF干扰稳态梯度回波图像进行比较。3D MP‐ MRI图像显示WGSD噪声比增加了41%。这些最初的非常有希望的结果表明，通过进一步改进以消除一些强度伪影，可变翻转角3D MP-回波技术可以在某些图像属性方面提供比当前可用的3D梯度回波成像技术相当大的改进。
A theoretical algorithm for shaping the signal response during the approach to steady state in three‐dimensional magnetization‐prepared rapid gradient‐echo (3D MP‐RAGE) pulse sequences has been developed and implemented. This algorithm derives the flip angle series required to produce specifically chosen time evolutions of the signal intensities during the data acquisition segment of 3D MP‐RAGE sequences. Theoretical predictions for the cases of unshaped, uniform, and mono‐exponential decay signal responses were quantitatively validated with a doped‐water phantom on a 1.5‐T whole‐body imager and in all cases there was excellent agreement between the theoretical and experimental values. The effects of RF inhomogeneities and eddy currents on the signal response shaping were also investigated. To demonstrate the potential utility of the technique, the signal response shaping algorithm was applied to a Tl‐weighted 3D MP‐RAGE sequence to derive the acquisition flip angle series which theoretically yields the maximum white matter/gray matter signal difference (WGSD) consistent with the chosen response shape. Images obtained from a healthy volunteer using this variable flip angle sequence were compared with 3D RF‐spoiled steady‐state gradient‐echo images obtained in the same total imaging time. The 3D MP‐RAGE images demonstrated a 41% increase in the WGSD‐to‐noise ratio. These initial very promising results indicate that with further refinement to eliminate some intensity artifacts, the variable flip angle 3D MP‐RAGE technique may, with respect to certain image properties, provide considerable improvements over currently available 3D gradient‐echo imaging techniques.© 1992 Academic Press,Inc.