Molecular Imaging Center, Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.
National Engineering School of Tunis, University al Manar, Tunis, Tunisia.
Magn Reson Med. 2021 Jun;85(6):3479-3496. doi: 10.1002/mrm.28676. Epub 2021 Jan 26.
Chemical exchange saturation transfer MRI provides new approaches for investigating tumor microenvironment, including tumor acidosis that plays a key role in tumor progression and resistance to therapy. Following iopamidol injection, the detection of the contrast agent inside the tumor tissue allows measurements of tumor extracellular pH. However, accurate tumor pH quantifications are hampered by the low contrast efficiency of the CEST technique and by the low SNR of the acquired CEST images, hence in a reduced detectability of the injected agent. This work aims to investigate a novel denoising method for improving both tumor pH quantification and accuracy of CEST-MRI pH imaging.
An hybrid denoising approach was investigated for CEST-MRI pH imaging based on the combination of the nonlocal mean filter and the anisotropic diffusion tensor method. The denoising approach was tested in simulated and in vitro data and compared with previously reported methods for CEST imaging and with established denoising approaches. Finally, it was validated with in vivo data to improve the accuracy of tumor pH maps.
The proposed method outperforms current denoising methods in CEST contrast quantification and detection of the administered contrast agent at several increasing noise levels with simulated data. In addition, it achieved a better pH quantification in in vitro data and demonstrated a marked improvement in contrast detection and a substantial improvement in tumor pH accuracy in in vivo data.
The proposed approach effectively reduces the noise in CEST images and increases the sensitivity detection in CEST-MRI pH imaging.
化学交换饱和转移磁共振成像为研究肿瘤微环境提供了新的方法，包括在肿瘤进展和对治疗的抵抗中起关键作用的肿瘤酸中毒。在注射碘帕醇后，通过检测肿瘤组织内的对比剂，可以测量肿瘤细胞外 pH 值。然而，CEST 技术的低对比效率和所获取的 CEST 图像的低 SNR 阻碍了对肿瘤 pH 值的准确量化，从而降低了对注射剂的检测能力。本研究旨在探讨一种新的去噪方法，以提高 CEST-MRI pH 成像的肿瘤 pH 值定量和准确性。
研究了一种基于非局部均值滤波器和各向异性扩散张量方法相结合的 CEST-MRI pH 成像的混合去噪方法。该去噪方法在模拟和体外数据中进行了测试，并与 CEST 成像的先前报道方法以及已建立的去噪方法进行了比较。最后，使用体内数据进行了验证，以提高肿瘤 pH 图谱的准确性。
与 CEST 对比度定量和在模拟数据中在几个增加的噪声水平下检测已用对比剂的当前去噪方法相比，所提出的方法在 CEST 对比度检测中表现出色。此外，它在体外数据中实现了更好的 pH 值定量，并在体内数据中在对比度检测方面有明显改善，并且在肿瘤 pH 值准确性方面有了很大的提高。
该方法有效地降低了 CEST 图像中的噪声，并提高了 CEST-MRI pH 成像中的灵敏度检测。
