Youngdee W, Planinsic G, Lurie D J
Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen, Foresterhill, UK.
Phys Med Biol. 2001 Oct;46(10):2531-44. doi: 10.1088/0031-9155/46/10/302.
A numerical model of the behaviour of the magnetization in a field-cycled dynamic nuclear polarization (DNP) experiment is presented, with the aim of optimizing pulse sequence parameters in field-cycled proton-electron double-resonance free radical imaging. The model is used to predict the observed enhancement of the NMR signal as a function of the magnetic field strength, EPR irradiation frequency and pulse sequence timing, as well as the properties of the sample including the NMR and EPR relaxation times. The model allowed optimization of parameters in the field-cycled DNP experiment, in particular the EPR irradiation frequency, to find the value which would give the largest difference between NMR signals recorded with and without EPR irradiation. Experiments to verify the model were carried out using aqueous solutions of TEMPOL, which exhibits three hyperfine lines in its EPR spectrum and triarylmethyl (TAM), which has a single, narrow line. It was found that the model predicted very well the variation in DNP enhancement with EPR irradiation power for both samples. The behaviour of the NMR signal with EPR irradiation frequency in studies using TEMPOL was also accurately modelled, with the optimum frequency lying between 60 and 80 MHz, depending on the EPR irradiation power. The optimum frequency obtained from the model also agreed with the experimental data obtained using the TAM free radical, but with this sample the theoretical curves tended to deviate from the experimental data at irradiation frequencies below 70 MHz.
本文提出了一种场循环动态核极化（DNP）实验中磁化行为的数值模型，旨在优化场循环质子 - 电子双共振自由基成像中的脉冲序列参数。该模型用于预测作为磁场强度、电子顺磁共振（EPR）照射频率、脉冲序列定时以及包括核磁共振（NMR）和EPR弛豫时间在内的样品特性的函数所观察到的NMR信号增强。该模型允许在场循环DNP实验中优化参数，特别是EPR照射频率，以找到在有和没有EPR照射记录的NMR信号之间产生最大差异的值。使用TEMPOL水溶液和三芳基甲基（TAM）进行了验证该模型的实验，TEMPOL在其EPR谱中显示三条超精细线，而TAM有一条单一的窄线。结果发现，该模型很好地预测了两种样品的DNP增强随EPR照射功率的变化。在使用TEMPOL的研究中，NMR信号随EPR照射频率的行为也被精确建模，最佳频率在60至80 MHz之间，这取决于EPR照射功率。从模型获得的最佳频率也与使用TAM自由基获得的实验数据一致，但对于该样品，在照射频率低于70 MHz时理论曲线往往偏离实验数据。
