Mohanta Zinia, Stabinska Julia, Gilad Assaf A, Barker Peter B, McMahon Michael T
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA.
Magn Reson Med. 2025 May;93(5):1954-1968. doi: 10.1002/mrm.30410. Epub 2025 Jan 20.
To optimize a 100 ms pulse for producing CEST MRI contrast and evaluate in mice.
A gradient ascent algorithm was employed to generate a family of 100 point, 100 ms pulses for use in CEST pulse trains (proton resonance enhancement for CEST imaging and shift exchange). Gradient ascent optimizations were performed for exchange rates = 500, 1500, 2500, 3500, and 4500 s; and labile proton offsets (Δω) = 9.6, 7.8, 4.2, and 2.0 ppm. Seven proton resonance enhancement for CEST imaging and shift exchange pulse shapes were tested on an 11.7 T scanner using a phantom containing three representative CEST agents with peak saturation B = 4 μT. The pulse producing the most contrast in phantoms was then evaluated for CEST MRI pH mapping of the kidneys in healthy mice after iopamidol administration.
The most promising pulse in terms of contrast performance across all three phantoms was the 9.6 ppm, 2500 s optimized pulse with ˜2.7 × increase in asymmetric magnetization transfer ratio (MTR) over Gaussian, and ˜ 1.3 times over Fermi pulses for the same B = 4 μT. This pulse also displayed a large improvement in contrast over the Gaussian pulse after administration of iopamidol in live mice.
A new 100-ms pulse was developed based on gradient ascent optimizations, which produced better contrast compared to standard Gaussian and Fermi pulses in phantoms. This shape also showed a substantial improvement for CEST MRI pH mapping in live mice over the Gaussian shape and appears promising for a wide range of CEST applications.
优化用于产生化学交换饱和转移（CEST）磁共振成像（MRI）对比的100毫秒脉冲，并在小鼠中进行评估。
采用梯度上升算法生成一系列100个点、100毫秒的脉冲，用于CEST脉冲序列（用于CEST成像和位移交换的质子共振增强）。针对交换率=500、1500、2500、3500和4500秒；以及不稳定质子偏移（Δω）=9.6、7.8、4.2和2.0 ppm进行梯度上升优化。在11.7 T扫描仪上，使用含有三种代表性CEST剂且峰值饱和B = 4 μT的体模，测试了七种用于CEST成像和位移交换的质子共振增强脉冲形状。然后在给予碘帕醇后，对健康小鼠肾脏的CEST MRI pH映射评估在体模中产生最大对比度的脉冲。
在所有三种体模中，就对比性能而言，最有前景的脉冲是9.6 ppm、2500秒优化脉冲，在相同B = 4 μT时，其不对称磁化转移率（MTR）比高斯脉冲增加约2.7倍，比费米脉冲增加约1.3倍。在活体小鼠中给予碘帕醇后，该脉冲与高斯脉冲相比，对比度也有大幅提高。
基于梯度上升优化开发了一种新的100毫秒脉冲，与体模中的标准高斯和费米脉冲相比，它产生了更好的对比度。这种形状在活体小鼠的CEST MRI pH映射方面也比高斯形状有显著改善，并且在广泛的CEST应用中似乎很有前景。
