Duan Qi, Duyn Jeff H, Gudino Natalia, de Zwart Jacco A, van Gelderen Peter, Sodickson Daniel K, Brown Ryan
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York 10016.
Med Phys. 2014 Oct;41(10):102303. doi: 10.1118/1.4895823.
In this work, a generic recipe for an inexpensive and nontoxic phantom was developed within a range of biologically relevant dielectric properties from 150 MHz to 4.5 GHz.
The recipe includes deionized water as the solvent, NaCl to primarily control conductivity, sucrose to primarily control permittivity, agar-agar to gel the solution and reduce heat diffusivity, and benzoic acid to preserve the gel. Two hundred and seventeen samples were prepared to cover the feasible range of NaCl and sucrose concentrations. Their dielectric properties were measured using a commercial dielectric probe and were fitted to a 3D polynomial to generate a recipe describing the properties as a function of NaCl concentration, sucrose concentration, and frequency.
Results indicated that the intuitive linear and independent relationships between NaCl and conductivity and between sucrose and permittivity are not valid. A generic polynomial recipe was developed to characterize the complex relationship between the solutes and the resulting dielectric values and has been made publicly available as a web application. In representative mixtures developed to mimic brain and muscle tissue, less than 2% difference was observed between the predicted and measured conductivity and permittivity values.
It is expected that the recipe will be useful for generating dielectric phantoms for general magnetic resonance imaging (MRI) coil development at high magnetic field strength, including coil safety evaluation as well as pulse sequence evaluation (including B₁(+) mapping, B₁(+) shimming, and selective excitation pulse design), and other non-MRI applications which require biologically equivalent dielectric properties.
在这项工作中，开发了一种通用配方，用于制备一种价格低廉且无毒的体模，其介电特性在150兆赫兹至4.5吉赫兹的生物相关范围内。
该配方包括去离子水作为溶剂，氯化钠主要用于控制电导率，蔗糖主要用于控制介电常数，琼脂用于使溶液凝胶化并降低热扩散率，苯甲酸用于保存凝胶。制备了217个样品以覆盖氯化钠和蔗糖浓度的可行范围。使用商用介电探头测量它们的介电特性，并将其拟合到三维多项式，以生成一个描述特性随氯化钠浓度、蔗糖浓度和频率变化的配方。
结果表明，氯化钠与电导率之间以及蔗糖与介电常数之间直观的线性和独立关系并不成立。开发了一个通用多项式配方来表征溶质与所得介电值之间的复杂关系，并已作为一个网络应用程序公开提供。在为模拟脑和肌肉组织而开发的代表性混合物中，预测的和测量的电导率及介电常数之间的差异小于2%。
预计该配方将有助于生成用于高磁场强度下通用磁共振成像（MRI）线圈开发的介电体模，包括线圈安全性评估以及脉冲序列评估（包括B₁(+)映射、B₁(+)匀场和选择性激发脉冲设计），以及其他需要生物等效介电特性的非MRI应用。
