Viswanathan Malvika, Kurmi Yashwant, Jiang Xiaoyu, Xu Junzhong, Zu Zhongliang
Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
Magn Reson Med. 2025 Aug 24. doi: 10.1002/mrm.70041.
To provide a comprehensive analysis of the contributors to the amide proton transfer-weighted (APTw) imaging signal using an asymmetry analysis method, as well as its contrast between tumors and the contralateral normal tissues at 4.7 T.
First, a signal model was developed to demonstrate the dependence of APTw signal on various contributors, including water T, reference signal containing direct water saturation (DS) and magnetization transfer (MT), as well as APT, amine CEST, and nuclear Overhauser enhancement (NOE) effects. Second, these effects were measured in rat brains bearing 9 L tumors, with saturation field strengths (B) of 2 and 3 μT, at 4.7 T to assess their relative contributions. Specifically, the reference signal was determined using an extrapolated MT reference approach. The amine CEST effect was isolated using an auxiliary asymmetry analysis method, while the APT and NOE effects were quantified through a multiple-pool Lorentzian fit of CEST Z-spectra acquired at 15.2 T.
Our findings reveal that at 2 μT, the APT effect is comparable to the NOE/asymmetric MT effects in tumors. Whereas at 3 μT, the APT effect becomes greater than the NOE/asymmetric MT effects in tumors. At these two B levels, the contribution from the amine CEST effect cannot be ignored. APTw contrast between tumors and normal tissues primarily arises from decreased NOE/asymmetric MT effects, with an additional spillover-dilution effect from the reduced MT effect in tumors.
This study provides insights into the contributors to APTw signal and its contrast between tumors and normal tissues, thereby enhancing our understanding of APTw imaging.
使用不对称分析方法对酰胺质子转移加权（APTw）成像信号的贡献因素进行全面分析，并在4.7T条件下分析肿瘤与对侧正常组织之间的对比度。
首先，建立一个信号模型来证明APTw信号对各种贡献因素的依赖性，这些因素包括水质子横向弛豫时间（T₂）、包含直接水饱和（DS）和磁化传递（MT）的参考信号，以及酰胺质子转移（APT）、胺化学交换饱和转移（CEST）和核Overhauser增强（NOE）效应。其次，在患有9L肿瘤的大鼠脑中测量这些效应，饱和场强（B₁）为2和3μT，在4.7T条件下评估它们的相对贡献。具体而言，使用外推MT参考方法确定参考信号。使用辅助不对称分析方法分离胺CEST效应，而APT和NOE效应则通过在15.2T采集的CEST Z谱的多池洛伦兹拟合进行量化。
我们的研究结果表明，在2μT时，肿瘤中的APT效应与NOE/不对称MT效应相当。而在3μT时，肿瘤中的APT效应大于NOE/不对称MT效应。在这两个B₁水平下，胺CEST效应的贡献不可忽视。肿瘤与正常组织之间的APTw对比度主要源于NOE/不对称MT效应的降低，以及肿瘤中MT效应降低带来的额外溢出稀释效应。
本研究深入探讨了APTw信号的贡献因素及其在肿瘤与正常组织之间的对比度，从而增进了我们对APTw成像的理解。
