Imaging Research, Sunnybrook Health Sciences Centre, S6-35, 2075 Bayview Avenue, Toronto, Ontario M4N 3M5, Canada.
Med Phys. 2009 Oct;36(10):4409-20. doi: 10.1118/1.3213516.
Iodinated phantoms are of value in x-ray imaging for quality control measurements, system calibration, and for use in the research setting; however, the liquid phantoms that are most often used have several limitations including variability between repeated dilutions, inhomogeneities from air bubbles or precipitants, and long set up times. Although suitable materials have been investigated for projection radiography, quantitative measurements of contrast enhancement in computed tomography (CT) have become increasingly important in the clinic, and a need exists for a durable and reproducible iodinated phantom material. In this work, the authors describe a solid radiographic phantom material that has an accurately known concentration of iodine distributed uniformly throughout its volume and that has stable properties over time. This material can be molded or machined into a desired shape to create a test object or for use in an anthropomorphic phantom.
Two sets of calibration phantoms were produced with a clinically relevant range of iodine concentrations. Measurements were made on these phantoms to characterize the material properties in terms of accuracy of iodine concentration, radiographic uniformity, temporal stability of x-ray attenuation, and manufacturing repeatability. Experimentally measured linear x-ray attenuation coefficients were compared to those predicted by a theoretical model. The uniformity of the iodine distribution in the material was assessed by measuring image intensity variation, both in projection images and in reconstructed CT volumes. The reproducibility of manufacture was estimated on a set of independently produced samples. A longitudinal study was performed to assess the stability of the material x-ray characteristics over time by making measurements at 6 month intervals.
Good agreement was seen between the experimental measurements of effective attenuation and the theoretically predicted values. It is estimated that a desired iodine concentration could be produced to within 0.04 mg/ml. Comparison of the measured effective linear iodine attenuation coefficients of eight 1.0 mg/ml samples indicated a manufacturing reproducibility of +/-0.03 mg/ml iodine. Variations in uniformity across each of the samples were on the order of image intensity fluctuations (sigma). No inhomogeneities due to mixing or settling were apparent. An analysis of longitudinal data collected for both calibration sets revealed no perceptible change in radiographic properties over the first 6 months after manufacture, nor over a subsequent 1.5 yr period from 1 yr postmanufacture onward.
The uniformity, stability, and precision of this iodinated material suggest that it is suitable for use in accurate calibration tools for contrast tomographic imaging.
碘造影剂在 X 射线成像中具有重要的价值，可用于质量控制测量、系统校准以及研究用途；然而，最常使用的液体造影剂存在一些局限性，包括重复稀释之间的可变性、气泡或沉淀引起的不均匀性以及较长的设置时间。尽管已经研究了适合投影射线照相的材料，但在临床实践中，对计算机断层扫描（CT）对比度增强的定量测量变得越来越重要，因此需要一种耐用且可重复的碘化造影剂材料。在这项工作中，作者描述了一种具有均匀分布的准确已知碘浓度的固态射线照相造影剂材料，并且该材料的性能随时间稳定。该材料可以模制或机械加工成所需的形状，以创建测试物体或用于人体模型。
制作了两组具有临床相关碘浓度范围的校准造影剂。对这些造影剂进行测量，以根据碘浓度、射线照相均匀性、X 射线衰减的时间稳定性和制造重复性来描述材料特性。将实验测量的线性 X 射线衰减系数与理论模型预测的值进行比较。通过测量投影图像和重建的 CT 体积中的图像强度变化来评估材料中碘分布的均匀性。通过对一组独立生产的样品进行估计，来评估制造的可重复性。通过每 6 个月进行一次测量，进行纵向研究以评估材料 X 射线特性随时间的稳定性。
实验测量的有效衰减与理论预测值之间存在良好的一致性。可以估计可以在 0.04mg/ml 的精度内生产出所需的碘浓度。对 8 个 1.0mg/ml 样品的有效线性碘衰减系数的测量结果进行比较表明，碘的制造重现性为 +/-0.03mg/ml。每个样品的均匀性变化在图像强度波动（sigma）的量级内。没有由于混合或沉淀引起的不均匀性。对两套校准集收集的纵向数据进行分析，结果表明，在制造后的头 6 个月内，或者在制造后 1 年开始的随后 1.5 年期间，射线照相特性没有明显变化。
这种碘化材料的均匀性、稳定性和精度表明它适用于用于对比度断层成像的精确校准工具。
