GSTF-based pre-emphasis to investigate the possibilities of a perfectly balanced steady state-free precession sequence

梯度系统传递函数(GSTF)全面描述了硬件系统的行为，如核磁共振扫描仪。它将输入信号与真实输出信号联系起来，而真实输出信号由于硬件缺陷或感应涡流而产生偏差。尤其是涡流会对图像质量产生灾难性的影响，在非线性或非笛卡尔读出设计或非相干欠采样的情况下，涡流的影响最为严重。平衡稳态自由进动(BSSFP)序列由于其固有的快速扫描时间、高信号产量和独特的对比度，是一种非常有趣的加速和量化MRI检查的候选序列。不幸的是，这种类型的MR序列对涡流诱导的扰动高度敏感。如果在测量过程中播放不完美的梯度波形或出现去相现象，则会出现图像伪影。然而，由于大多数新的成像和加速程序依赖于灵活的读出设计，这种设计与bSSFP的组合是主要感兴趣的。本项目的目的是调查基于GSTF的bSSFP测量预强调的可能性。这样的预加重将允许在测量期间实现完全平衡的梯度方案和相位校正，以避免稳态的破坏，从而避免图像伪影。然后，预加重的bSSFP序列的图像质量将独立于读出设计或欠采样图案。因此，打开了需要bSSFP与加速技术相结合的广泛应用。此外，未受干扰的bSSFP序列的信号行为将密切遵循标准信号模型。因此，基于模型的重建可以从bSSFP测量中推导出定量的组织参数。总之，基于GSTF的bSSFP预加重可以帮助解决MR成像中的两个主要缺点：扫描时间长和图像非定量。

The gradient system transfer function (GSTF) comprehensively describes the behaviour of a hardware system, like an MRI-scanner. It relates the input signal to the true output signal, which deviates due to hardware imperfections or induced eddy currents. Especially eddy currents can have a disastrous effect on image quality and their effect is most severe in cases of non-linear or non-cartesian read-out designs or incoherent undersampling.The balanced steady state free precession (bSSFP) -sequence is a very interesting candidate for the acceleration and quantification of MRI examinations, due to its inherently fast scan times, high signal yield and unique contrast. Unfortunately, this type of MR sequence is highly sensitive towards eddy current induced disturbances. Image artefacts arise if imperfect gradient waveforms are played out or dephasing occurs during the measurement. Nevertheless, as most novel imaging and acceleration procedures rely on a flexible read-out design, the combination of such designs with bSSFP is of major interest. The aim of this project is to investigate the possibilities of a GSTF-based pre-emphasis for bSSFP measurements. Such a pre-emphasis will allow implementing a perfectly balanced gradient scheme and a phase correction during the measurement, to avoid disruptions of the steady state and thereby image artefacts.Image quality of the pre-emphasized bSSFP-sequence will then be independent of read-out designs or undersampling patterns. Thus, opening a wide range of applications that require bSSFP in combination with acceleration techniques.Additionally, the signal behavior of an undisturbed bSSFP sequence will closely follow standard signal models. A model-based reconstruction can thus allow the deduction of quantitative tissue parameters from a bSSFP measurement.In conclusion, the GSTF-based pre-emphasis of bSSFP can help to solve two of the major drawbacks in MR imaging: long scan times and non-quantitative images.