Analyzing Ferric Ion Diffusion Phenomenon in Fricke-Agarose Gel by Using MR Image-Based Differential Technique

• Main Authors: Yin-Jiun Tseng, 曾尹俊
• Other Authors: Woei-Chyn Chu
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/55169629997963969429

博士 === 國立陽明大學 === 醫學工程研究所 === 91 === Ferric ion diffusion is a detrimental factor in MRI-Fricke-infused gel dosimetry. In this study, a mathematical modeling was adopted to calculate the ferric ion diffusion coefficient based on the radiation induced magnetic resonance (MR) image intensity change in Fricke-agarose gels. The image-based approach requires less than five minutes of MR imaging time thus allows studying dose profile degradation within minutes post-irradiation. The relationship between the rate of dose profile deterioration and dose distribution gradients can be elucidated with the improved imaging temporal resolution also. This efficient dosimetry technique was also employed to avoid smearing of the acquired data due to ferric ion diffusion. Our results showed that for a Fricke-agarose gel contained 1mM ammonium ferrous sulfate, 1% agarose, 1mM sodium chloride and 50mM sulfuric acid; ferric ion diffusion effects is significant 0.5 — 1 h post-irradiation for a dose distribution with gradient 4 Gy/mm or above. For a gradual dose profile gradient change of 2.1 Gy/mm or smaller, dose profile degradation appears insignificant for a two-hour elapsed diffusion time. The calculated ferric ion diffusion coefficient is 1.5010-2cm2h-1 in room temperature. This value is within the 1.00 ~ 2.0010-2cm2h-1 range previously reported under varying concentrations of gel ingredients. Because of this irreversible movement due to inhomogeneous distribution of the substance, knowledge of the ferric ion diffusion phenomenon is important in experimental designs in order to avoid potential measurement errors in MRI-Fricke-agarose gel dosimetry.