Objective

To study the need for inclusion of shaped RF pulses and magnetic field gradients in simulations of basis sets for the analysis of proton MR spectra of single voxels of the brain acquired with a semi-LASER pulse sequence.

Materials and methods

MRS basis sets where simulated at different echo times with hard RF pulses as well as with shaped RF pulses without or with magnetic field gradients included. The influence on metabolite concentration quantification was assessed using both phantom and in vivo measurements. For comparison, simulations and measurements were performed with the PRESS pulse sequence.

Results

The effect of including gradients in the simulations was smaller for semi-LASER than for PRESS, however, still noticeable. The difference was larger for strongly coupled metabolites and at longer echo times. Metabolite quantification using semi-LASER was thereby less dependent on the inclusion of gradients than PRESS, which was seen in both phantom and in vivo measurements.

Discussion

The inclusion of the shaped RF pulses and magnetic field gradients in the simulation of basis sets for semi-LASER is only important for strongly coupled metabolites. If computational time is a limiting factor, simple simulations with hard RF pulses can provide almost as accurate metabolite quantification as those that include the chemical-shift related displacement.

中文翻译：

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半激光的模拟基组：包括成形射频脉冲和磁场梯度的影响

客观的

研究在基组模拟中包含成形射频脉冲和磁场梯度的必要性，以分析使用半激光脉冲序列获取的大脑单个体素的质子 MR 谱。

材料和方法

MRS 基组在不同回波时间使用硬射频脉冲以及不包含或包含磁场梯度的成形射频脉冲进行模拟。使用体模和体内测量来评估对代谢物浓度定量的影响。为了进行比较，使用 PRESS 脉冲序列进行了模拟和测量。

结果

在模拟中包含梯度的影响对于半激光比对于 PRESS 小，但是，仍然很明显。对于强耦合代谢物和更长的回波时间，差异更大。因此，与 PRESS 相比，使用半激光的代谢物定量更不依赖于梯度的包含，这在体模和体内测量中都可以看到。

讨论

在半激光的基组模拟中包含成形的 RF 脉冲和磁场梯度仅对强耦合代谢物很重要。如果计算时间是一个限制因素，那么使用硬射频脉冲的简单模拟可以提供几乎与包括化学位移相关位移的代谢物定量一样准确的代谢物定量。