Improved polymer gels for radiation dosimetry by MRI

改进的聚合物凝胶用于 MRI 辐射剂量测定

• 批准号: 6435756
• 负责人: JOHN C GORE
• 金额: $ 13.17万
• 依托单位: YALE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-15 至 2002-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6435756
• 关键词: acidity /alkalinity; bioengineering /biomedical engineering; bioimaging /biomedical imaging; biomaterial development /preparation; biotechnology; gel; magnetic resonance imaging; magnetism; molecular weight; nuclear magnetic resonance spectroscopy; polymers; radiation dosage; radiation sensitivity; temperature; xenon

The studies proposed aim to develop improved polymer gels that may be used for accurate measurements of radiation dose distributions in three dimensions. Polymer gel dosimeters were first developed in our laboratory for use with MRI, which records the changes in NMR relaxation times of water protons produced by irradiation of mixtures of monomers in an aqueous gel. Such gels are tissue equivalent and provide unique and accurate measurements of integrated dose distributions in three dimensions with high spatial resolution. Nonetheless, there remain significant problems in the use of currently available polymer gels in practice that have limited their wider use. These include difficulties of preparation and storage of gels, which must be made and kept hypoxic until used and which therefore cannot be poured in plastic or arbitrary containers: their variable sensitivity, which largely arises from the influence of trace amounts of oxygen which inhibit their response: and the limited dose response, which is based on measuring changes in T2 values that are subject to errors. The studies proposed would lead to significantly improved gels that are more sensitive, more stable, and which can be made in a normal atmosphere and any container by a hospital physicist without special procedures. In preliminary studies we have produced gels in room air that are much more sensitive than current gels. These use a novel initiator system based on copper ion and ascorbic acid which combines with and requires molecular oxygen to start polymerization when the gel is irradiated. We will optimize the performance of these dosimeters by exploring the effects of different concentrations and components of this system. We have also shown that relaxation in irradiated gels occurs via magnetization transfer (MT) between free water and labile protons in contact with a semi-solid pool in the polymer. We will design and verify the performance of MT-sensitive sequences that avoid the pitfalls of T2 measurements for imaging gels to extract accurate dose information. We also postulate that the dose- response of polymer gels simply reflects a linear increase in the size of this semi-solid proton pool with increasing dose and we will perform novel NMR and other physical measurements to verify this model. Overall we aim to produce much improved gels for practical applications and obtain a better and more quantitative understanding of how they respond to radiation.

该研究旨在开发改进的聚合物凝胶，用于三维辐射剂量分布的精确测量。聚合物凝胶剂量计最初是在我们的实验室开发的，用于核磁共振成像，它记录了水凝胶中单体混合物辐照产生的水质子的核磁共振弛豫时间的变化。这种凝胶是组织等效的，并提供独特和精确的测量综合剂量分布在三维与高空间分辨率。尽管如此，目前可用的聚合物凝胶在实际应用中仍然存在重大问题，限制了它们的广泛应用。其中包括制备和储存凝胶的困难，凝胶在使用前必须在低氧条件下制造和保存，因此不能倒入塑料或任意容器中；它们的敏感性变化很大，这主要是由于微量氧气的影响而抑制了它们的反应；以及有限的剂量反应，这是基于测量T2值的变化而产生的，而T2值的变化是有误差的。提出的研究将显著改善凝胶的性能，使其更敏感、更稳定，并且可以由医院物理学家在正常气氛和任何容器中制造，而无需特殊程序。在初步研究中，我们已经在室内空气中制造出了比现有凝胶灵敏得多的凝胶。这些方法使用一种基于铜离子和抗坏血酸的新型引发剂系统，当凝胶照射时，它与分子氧结合并需要分子氧来开始聚合。我们将通过探索该系统的不同浓度和组分的影响来优化这些剂量计的性能。我们还证明了辐照凝胶中的弛豫是通过与聚合物中半固体池接触的自由水和不稳定质子之间的磁化转移（MT）发生的。我们将设计和验证mt敏感序列的性能，以避免成像凝胶的T2测量陷阱，以提取准确的剂量信息。我们还假设聚合物凝胶的剂量响应仅仅反映了半固体质子池的大小随剂量增加而线性增加，我们将进行新的核磁共振和其他物理测量来验证这一模型。总的来说，我们的目标是为实际应用生产出更好的凝胶，并对它们对辐射的反应有更好、更定量的了解。