Development of a phantom compatible for MRI and hyperthermia equivalent to relaxation times and dielectric properties of the human tissues

我们开发了一种与MRI和热疗相兼容的幻影，相当于人体组织的松弛时间和介电特性。幻影由0 -140 μmol/kg GdCl_3、0 - 1.6%琼脂糖、0 - 0.7% NaCl、3%卡拉胶和0.03% NaN_3组成，其余为水。该模体在1.5 T时T1值为202 ~ 1904 ms， T2值为38 ~ 423 ms，在5 ~ 130 MHz频率范围内电导率为0.27 ~ 1.26 S/m，相对介电常数为78.1 ~ 98.9。开发的幻影具有以下特点；1)幻体含有卡拉胶作为固化剂，并允许其用于制造躯干幻体，而无需使用物理增强剂。2)不同浓度的GdCl_3 （Tv）和琼脂糖（T2）可以独立改变膜体的T1和T2弛豫时间。因此，可以调整幻影的T1和T2弛豫时间的范围，使其与人体所有组织的弛豫时间相对应。3)随着NaCl浓度的变化，膜体的电导率会发生变化。4)由于NaN_3作为防腐剂混合在一起，幻影在很长一段时间内保持化学和物理稳定。5)根据实验数据推导出的经验公式，可以确定GdCl_3、琼脂糖和NaCl的合适浓度，从而制备出具有所需弛豫时间和电导率的特定模体。因此，所开发的模体可用于MRI和热疗的基础研究、MRI设备的质量保证以及MRI操作员和放射科医生的培训。

We developed a phantom compatible for MRI and hyperthermia equivalent to relaxation times and dielectric properties of the human tissues. The phantom consists of 0 -140 μmol/kg GdCl_3, 0 -1.6 % agarose, 0 -0.7 % NaCl, 3 % carrageenan and 0.03 % NaN_3, with water as the remainder. The phantom has a T1 value of 202 to 1,904 ms and a T2 value of 38 to 423 ms at 1.5 T, and has conductivity of 0.27 to 1.26 S/m and relative permittivity of 78.1 to 98.9 for the frequency range of 5 -130 MHz.The phantom developed has the following characteristics;1) The phantom contains carrageenan as a solidifying agent, and allows its use in producing a torso phantom without the use of physical reinforcements.2) T1 and T2 relaxation times of the phantom are independently changeable by varying the concentrations of GdCl_3 as Tv modifier and agarose as T2 modifier. Thus, the range of the T1 and T2 relaxation times of the phantom can be adjusted to correspond to those of all human tissues.3) Conductivity of the phantom is changeable by changing the concentration of NaCl.4) As NaN_3 is admixed as a preservative, the phantom remains chemically and physically stable over extended periods.5) The appropriate concentrations of GdCl_3, agarose and NaCl can be determined from the empirical formulae which are deduced from the experimental data, when making a specified phantom that has the required relaxation times and conductivity.Thus, the phantom developed is useful for basic studies of MRI and hyperthermia, QA of MRI equipment, and training MRI operators and radiologists.