Gammaraccio Francesco, Villano Daisy, Irrera Pietro, Anemone Annasofia A, Carella Antonella, Corrado Alessia, Longo Dario Livio
Department of Molecular Biotechnology and Health Sciences, University of Turin, 10126 Torino, Italy.
Institute of Biostructures and Bioimaging (IBB), National Research Council of Italy (CNR), 10126 Torino, Italy.
J Imaging. 2024 Jul 12;10(7):166. doi: 10.3390/jimaging10070166.
CEST-MRI is an emerging imaging technique suitable for various in vivo applications, including the quantification of tumor acidosis. Traditionally, CEST contrast is calculated by asymmetry analysis, but the presence of fat signals leads to wrong contrast quantification and hence to inaccurate pH measurements. In this study, we investigated four post-processing approaches to overcome fat signal influences and enable correct CEST contrast calculations and tumor pH measurements using iopamidol. The proposed methods involve replacing the Z-spectrum region affected by fat peaks by (i) using a linear interpolation of the fat frequencies, (ii) applying water pool Lorentzian fitting, (iii) considering only the positive part of the Z-spectrum, or (iv) calculating a correction factor for the ratiometric value. In vitro and in vivo studies demonstrated the possibility of using these approaches to calculate CEST contrast and then to measure tumor pH, even in the presence of moderate to high fat fraction values. However, only the method based on the water pool Lorentzian fitting produced highly accurate results in terms of pH measurement in tumor-bearing mice with low and high fat contents.
化学交换饱和转移磁共振成像（CEST-MRI）是一种新兴的成像技术，适用于各种体内应用，包括肿瘤酸中毒的定量分析。传统上，CEST对比是通过不对称分析计算得出的，但脂肪信号的存在会导致错误的对比定量，进而导致pH测量不准确。在本研究中，我们研究了四种后处理方法，以克服脂肪信号的影响，并使用碘帕醇实现正确的CEST对比计算和肿瘤pH测量。所提出的方法包括通过以下方式替换受脂肪峰影响的Z谱区域：（i）使用脂肪频率的线性插值，（ii）应用水池洛伦兹拟合，（iii）仅考虑Z谱的正部分，或（iv）计算比例值的校正因子。体外和体内研究表明，即使在存在中等到高脂肪分数值的情况下，使用这些方法计算CEST对比并进而测量肿瘤pH也是可能的。然而，只有基于水池洛伦兹拟合的方法在低脂肪和高脂肪含量的荷瘤小鼠的pH测量方面产生了高度准确的结果。
