Maryanski M J, Gore J C, Kennan R P, Schulz R J
Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT 06510.
Magn Reson Imaging. 1993;11(2):253-8. doi: 10.1016/0730-725x(93)90030-h.
A new type of tissue-equivalent medium for magnetic resonance imaging of the dose distributions produced by ionizing radiation has been developed. Agarose gel is infused with acrylamide and N,N'-methylene-bis-acrylamide (Bis) comonomers, which are readily polymerized by free radical initiators in de-aerated aqueous solutions. Polymerization and cross-linking induced locally by free radical products of water radiolysis increase the rate of water proton spin relaxation gradually up to doses of about 15 Gy. The slopes of the dose-response curves at 64 MHz are 0.015 and 0.28 s-1 Gy-1 for R1 and R2, respectively. The agarose matrix as well as the high (50% by weight) relative concentration of the cross-linker (Bis) per total comonomer limit the spread of polymerization so that the spatial distribution of the radiation dose is faithfully represented in the resultant spatial distribution of relaxation rates. The gel can be imaged with conventional magnetic resonance imaging devices with high spatial resolution and accuracy. In addition, due to the well established effect of the precipitation of insoluble agglomerates of highly cross-linked acrylamide, the optical turbidity of the gel increases gradually with the absorbed dose. This may provide an additional means of visualizing the dose distribution in three dimensions. The major advantage of the acrylamide-Bis-agarose gels over those that depend on ionic chemical dosimeters, for example, Fricke-infused gels, lies in the lack of diffusion of radiation-induced chemical changes subsequent to or concurrent with irradiation.
一种用于磁共振成像电离辐射产生的剂量分布的新型组织等效介质已被开发出来。琼脂糖凝胶中注入了丙烯酰胺和N，N'-亚甲基双丙烯酰胺（双丙烯酰胺）共聚单体，它们在脱气水溶液中很容易被自由基引发剂聚合。水辐射分解产生的自由基在局部引发的聚合和交联作用，使水质子自旋弛豫速率逐渐增加，直至剂量达到约15 Gy。在64 MHz时，R1和R2的剂量响应曲线斜率分别为0.015和0.28 s-1 Gy-1。琼脂糖基质以及交联剂（双丙烯酰胺）相对于总共聚单体的高（50%重量）相对浓度限制了聚合的扩散，从而使辐射剂量的空间分布忠实地反映在所得的弛豫速率空间分布中。这种凝胶可以用具有高空间分辨率和精度的传统磁共振成像设备进行成像。此外，由于高度交联的丙烯酰胺不溶性团聚物沉淀的既定效应，凝胶的光学浊度随吸收剂量逐渐增加。这可能提供一种在三维空间中可视化剂量分布的额外方法。与那些依赖离子化学剂量计（例如注入弗里克试剂的凝胶）相比，丙烯酰胺-双丙烯酰胺-琼脂糖凝胶的主要优点在于，在辐照后或辐照过程中，辐射诱导的化学变化不会扩散。
