Weigand-Whittier Jonah, Wendland Michael, Lam Bonnie, Velasquez Mark, Vandsburger Moriel H
Department of Bioengineering, University of California Berkeley, Berkeley, California, USA.
Berkeley Preclinical Imaging Core, University of California Berkeley, Berkeley, California, USA.
Magn Reson Med. 2025 Apr;93(4):1793-1806. doi: 10.1002/mrm.30382. Epub 2024 Nov 28.
Electrocardiography (ECG) and respiratory-gated preclinical cardiac CEST-MRI acquisitions are difficult because of variable saturation recovery with T, RF interference in the ECG signal, and offset-to-offset variation in Z-magnetization and cardiac phase introduced by changes in cardiac frequency and trigger delays.
The proposed method consists of segmented saturation modules with radial FLASH readouts and golden angle progression. The segmented saturation blocks drive the system to steady-state, and because center k-space is sampled repeatedly, steady-state saturation dominates contrast during gridding and reconstruction. Ten complete Z-spectra were acquired in healthy mice using both ECG and respiratory-gated and ungated methods. Z-spectra were also acquired at multiple saturation B values to optimize for amide and Cr contrasts.
There was no significant difference between CEST contrasts (amide, Cr, magnetization transfer) calculated from images acquired using ECG and respiratory-gated and ungated methods (p = 0.27, 0.11, 0.47). A saturation power of 1.8μT provides optimal contrast amplitudes for both amide and total Cr contrast without significantly complicating CEST contrast quantification because of water direct saturation, magnetization transfer, and RF spillover between amide and Cr pools. Further, variability in CEST contrast measurements was significantly reduced using the ungated radial FLASH acquisition (p = 0.002, 0.006 for amide and Cr, respectively).
This method enables CEST mapping in the murine myocardium without the need for cardiac or respiratory gating. Quantitative CEST contrasts are consistent with those obtained using gated sequences, and per-contrast variance is significantly reduced. This approach makes preclinical cardiac CEST-MRI easily accessible, even for investigators without prior experience in cardiac imaging.
心电图（ECG）和呼吸门控的临床前心脏CEST-MRI采集具有挑战性，这是由于T1饱和恢复的变化、ECG信号中的射频干扰，以及心脏频率和触发延迟变化所导致的Z轴磁化和心脏相位的偏移间变化。
所提出的方法由带有径向FLASH读出和黄金角递进的分段饱和模块组成。分段饱和块驱动系统达到稳态，并且由于中心k空间被重复采样，稳态饱和在网格化和重建过程中主导对比度。使用ECG、呼吸门控和非门控方法在健康小鼠中采集了十条完整的Z谱。还在多个饱和B值下采集Z谱以优化酰胺和Cr对比度。
使用ECG、呼吸门控和非门控方法采集的图像计算得到的CEST对比度（酰胺、Cr、磁化传递）之间无显著差异（p = 0.27、0.11、0.47）。1.8μT的饱和功率为酰胺和总Cr对比度提供了最佳对比度幅度，且不会因水直接饱和、磁化传递以及酰胺和Cr池之间的射频溢出而使CEST对比度定量显著复杂化。此外，使用非门控径向FLASH采集可显著降低CEST对比度测量的变异性（酰胺和Cr的p值分别为0.002和0.006）。
该方法无需心脏或呼吸门控即可在小鼠心肌中进行CEST成像。定量CEST对比度与使用门控序列获得的结果一致，且每个对比度的方差显著降低。这种方法使临床前心脏CEST-MRI易于实现，即使对于没有心脏成像经验的研究人员也是如此。
