Sveinsson B, Chaudhari A S, Gold G E, Hargreaves B A
Department of Radiology, Stanford University, Stanford, CA, United States.
Department of Radiology, Stanford University, Stanford, CA, United States.
Magn Reson Imaging. 2017 May;38:63-70. doi: 10.1016/j.mri.2016.12.018. Epub 2016 Dec 23.
To introduce a simple analytical formula for estimating T from a single Double-Echo in Steady-State (DESS) scan.
Extended Phase Graph (EPG) modeling was used to develop a straightforward linear approximation of the relationship between the two DESS signals, enabling accurate T estimation from one DESS scan. Simulations were performed to demonstrate cancellation of different echo pathways to validate this simple model. The resulting analytic formula was compared to previous methods for T estimation using DESS and fast spin-echo scans in agar phantoms and knee cartilage in three volunteers and three patients. The DESS approach allows 3D (256×256×44) T-mapping with fat suppression in scan times of 3-4min.
The simulations demonstrated that the model approximates the true signal very well. If the T is within 20% of the assumed T, the T estimation error was shown to be less than 5% for typical scans. The inherent residual error in the model was demonstrated to be small both due to signal decay and opposing signal contributions. The estimated T from the linear relationship agrees well with reference scans, both for the phantoms and in vivo. The method resulted in less underestimation of T than previous single-scan approaches, with processing times 60 times faster than using a numerical fit.
A simplified relationship between the two DESS signals allows for rapid 3D T quantification with DESS that is accurate, yet also simple. The simplicity of the method allows for immediate T estimation in cartilage during the MRI examination.
介绍一种通过单次稳态双回波（DESS）扫描估算T的简单分析公式。
使用扩展相位图（EPG）建模来建立两个DESS信号之间关系的直接线性近似，从而能够从一次DESS扫描中准确估算T。进行模拟以证明不同回波路径的抵消，从而验证这个简单模型。将所得的分析公式与之前使用DESS和快速自旋回波扫描在琼脂模型以及三名志愿者和三名患者的膝关节软骨中估算T的方法进行比较。DESS方法允许在3 - 4分钟的扫描时间内进行具有脂肪抑制的三维（256×256×44）T映射。
模拟表明该模型能很好地逼近真实信号。如果T在假设T的20%范围内，对于典型扫描，T估算误差显示小于5%。由于信号衰减和相反信号贡献，模型中固有的残余误差被证明很小。从线性关系估算的T与参考扫描结果在模型和体内均吻合良好。该方法导致的T低估比之前的单扫描方法少，处理时间比使用数值拟合快60倍。
两个DESS信号之间的简化关系允许通过DESS进行快速的三维T定量，既准确又简单。该方法的简单性使得在MRI检查期间能够立即对软骨中的T进行估算。
