Li Tianzhe, de La Cerda Jorge, Tran Renee L, Schuler F William, Kotrotsou Aikaterini, Zhang Shu, Jones Kyle M, Trakru Priya N, Pagel Mark D
Department of Cancer Systems Imaging, UT MD Anderson Cancer Center, Houston, Texas, USA.
The University of Texas Health Science Center, Houston, Texas, USA.
Magn Reson Med. 2025 Sep;94(3):1218-1226. doi: 10.1002/mrm.30511. Epub 2025 May 5.
AcidoCEST MRI measures tumor extracellular pH by fitting chemical exchange saturation transfer (CEST) Z-spectra with modified Bloch-McConnell equations, known as a Bloch fitting method. We evaluated Bloch fitting with Z-spectra and T, T, B, and B MR information with phantoms. We applied the Bloch fitting method to in vivo acidoCEST MRI of a preclinical tumor model.
We studied 120 phantoms of iopamidol with a range of pH values, concentrations, and T values. We collected 180 Z-spectra for each phantom, along with T, T, B, and B measurements. The data were analyzed with the Bloch fitting method to estimate pH. AcidoCEST MRI was performed with five mice with 4T1 mammary carcinoma using the Bloch fitting method.
Bloch fitting generated accurate and precise pH estimates without also including experimental T, T, B, or B values. Accurate and precise pH estimates of phantoms were achieved with 3-μT saturation power, ≥1-s saturation time, ≥15 mM of iopamidol, and temperature control of 37.0 ± 1.5°C. Similar to our phantom studies, fixing one or more fitting parameters did not significantly alter the extracellular pH estimates from acidoCEST MRI of a 4T1 tumor model, which estimated a tumor extracellular pH of 6.8.
Although fixing Bloch fitting parameters with experimental measurements saved computation time, fixing these parameters did not significantly improve the accuracy or precision of measuring pH in phantoms or within in vivo tumors, Therefore, measurements of T, T, B, and/or B are not needed for acidoCEST MRI.
酸化学交换饱和转移（AcidoCEST）磁共振成像（MRI）通过使用修正的布洛赫 - 麦康奈尔方程（称为布洛赫拟合方法）对化学交换饱和转移（CEST）Z谱进行拟合来测量肿瘤细胞外pH值。我们使用体模评估了Z谱以及T1、T2、B1和B0磁共振信息的布洛赫拟合。我们将布洛赫拟合方法应用于临床前肿瘤模型的体内AcidoCEST MRI。
我们研究了120个具有一系列pH值、浓度和T1值的碘帕醇体模。我们为每个体模收集了180个Z谱，以及T1、T2、B1和B0测量值。使用布洛赫拟合方法对数据进行分析以估计pH值。使用布洛赫拟合方法对五只患有4T1乳腺癌的小鼠进行了AcidoCEST MRI。
布洛赫拟合在不包括实验性T1、T2、B1或B0值的情况下也能产生准确且精确的pH估计值。在3μT饱和功率、≥1秒饱和时间、≥15 mM碘帕醇以及37.0±1.5°C的温度控制条件下，实现了对体模准确且精确的pH估计。与我们的体模研究相似，固定一个或多个拟合参数不会显著改变4T1肿瘤模型的AcidoCEST MRI的细胞外pH估计值，该模型估计肿瘤细胞外pH为6.8。
尽管通过实验测量固定布洛赫拟合参数节省了计算时间，但固定这些参数并未显著提高在体模或体内肿瘤中测量pH的准确性或精确性。因此，AcidoCEST MRI不需要测量T1、T2、B1和/或B0。
