Fuderer Miha, Liu Hongyan, van der Heide Oscar, van den Berg Cornelis A T, Sbrizzi Alessandro
Computational Imaging Group for MR Diagnostics & Therapy, Center for Image Sciences, University Medical Center Utrecht, Heidelberglaan 100, 3585CX, Utrecht, The Netherlands.
MAGMA. 2025 Sep 11. doi: 10.1007/s10334-025-01293-9.
Within gradient-spoiled transient-state MR sequences like Magnetic Resonance Fingerprinting or Magnetic Resonance Spin TomogrAphy in Time-domain (MR-STAT), it is examined whether an optimized RF phase modulation can help to improve the precision of the resulting relaxometry maps.
Using a Cramer-Rao based method called BLAKJac, optimized sequences of RF pulses have been generated for two scenarios (amplitude-only modulation and amplitude + phase modulation) and for several conditions. These sequences have been tested on a phantom, a healthy human brain and a healthy human leg, to reconstruct parametric maps ( and ) as well as their standard deviations.
The amplitude + phase modulation scenario systematically resulted in lower noise levels than the amplitude-only modulation scenario. On average, the difference was around 34%, but it was substantially larger for scans acquired under SAR restrictions. Compared to amplitude-only, in the amplitude + phase modulation scenario, the relevance of an inversion pulse and of a pause were greatly reduced, at least considering overall precision and in-phantom accuracy.
The application of an optimized RF phase modulation in quantitative transient-states MRI is beneficial for almost all tested scenarios and conditions, in particular under SAR restrictions Furthermore, RF phase modulation reduces the need for inversions pulses and pauses.
在诸如磁共振指纹识别或时域磁共振自旋断层扫描（MR-STAT）等梯度扰相瞬态磁共振序列中，研究优化的射频相位调制是否有助于提高所得弛豫测量图的精度。
使用一种基于克拉美罗界的方法BLAKJac，针对两种情况（仅幅度调制和幅度+相位调制）以及几种条件生成了优化的射频脉冲序列。这些序列已在体模、健康人脑和健康人腿部进行测试，以重建参数图（ 和 ）及其标准差。
幅度+相位调制情况系统地导致比仅幅度调制情况更低的噪声水平。平均而言，差异约为34%，但在受比吸收率（SAR）限制下采集的扫描中差异要大得多。与仅幅度调制相比，在幅度+相位调制情况下，反转脉冲和暂停的相关性大大降低，至少考虑到总体精度和体模内准确性时是这样。
在定量瞬态磁共振成像中应用优化的射频相位调制几乎对所有测试的情况和条件都有益，特别是在受SAR限制的情况下。此外，射频相位调制减少了对反转脉冲和暂停的需求。
