Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Tennessee, Nashville, USA.
Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Magn Reson Med. 2023 Sep;90(3):1025-1040. doi: 10.1002/mrm.29691. Epub 2023 May 8.
Quantifications of amide proton transfer (APT) and nuclear Overhauser enhancement (rNOE(-3.5)) mediated saturation transfer with high specificity are challenging because their signals measured in a Z-spectrum are overlapped with confounding signals from direct water saturation (DS), semi-solid magnetization transfer (MT), and CEST of fast-exchange pools. In this study, based on two canonical CEST acquisitions with double saturation powers (DSP), a new data-postprocessing method is proposed to specifically quantify the effects of APT and rNOE.
For CEST imaging with relatively low saturation powers ( ), both the fast-exchange CEST effect and the semi-solid MT effect roughly depend on , whereas the slow-exchange APT/rNOE(-3.5) effect do not, which is exploited to isolate a part of the APT and rNOE effects from the confounding signals in this study. After a mathematical derivation for the establishment of the proposed method, numerical simulations based on Bloch equations are then performed to demonstrate its specificity to detections of the APT and rNOE effects. Finally, an in vivo validation of the proposed method is conducted using an animal tumor model at a 4.7 T MRI scanner.
The simulations show that DSP-CEST can quantify the effects of APT and rNOE and substantially eliminate the confounding signals. The in vivo experiments demonstrate that the proposed DSP-CEST method is feasible for the imaging of tumors.
The data-postprocessing method proposed in this study can quantify the APT and rNOE effects with considerably increased specificities and a reduced cost of imaging time.
由于酰胺质子转移 (APT) 和核 Overhauser 增强 (rNOE(-3.5)) 的信号在 Z 谱中与直接水饱和 (DS)、半固态磁化转移 (MT) 和快交换池的 CEST 的混杂信号重叠，因此具有高特异性的 APT 和 rNOE 定量测量具有挑战性。在这项研究中，基于具有双饱和功率 (DSP) 的两个典型 CEST 采集，提出了一种新的数据后处理方法来特异性地定量 APT 和 rNOE 的影响。
对于相对较低饱和功率 ( ) 的 CEST 成像，快交换 CEST 效应和半固态 MT 效应大致取决于 ，而慢交换 APT/rNOE(-3.5) 效应则不然，这在本研究中被用来从混杂信号中分离出一部分 APT 和 rNOE 效应。在对所提出的方法进行数学推导后，然后基于 Bloch 方程进行数值模拟，以证明其对检测 APT 和 rNOE 效应的特异性。最后，使用动物肿瘤模型在 4.7 T MRI 扫描仪上进行了该方法的体内验证。
模拟表明，DSP-CEST 可以定量 APT 和 rNOE 的影响，并大大消除混杂信号。体内实验表明，所提出的 DSP-CEST 方法可用于肿瘤成像。
本研究提出的数据后处理方法可以以更高的特异性和更低的成像时间成本来定量 APT 和 rNOE 的影响。
