The radiation induced magnetic resonance image intensity change provides amore efficient three-dimensional dose measurement in MRI-Fricke-agarose gel dosimetry

A detailed methodology has been developed to map the spatial dose distribut ion in a Fricke-agarose gel based on the radiation induced image intensity change in the gel's magnetic resonance (MR) images. Besides the linear corr elation between the change in the gel's spin-lattice relaxation rate and th e absorbed dose, it is shown here that the radiation induced image intensit y change for T1-weighted spin-echo images with TE much less than TR correla tes exponentially to the absorbed dose. Furthermore, at the lower dose regi on (<15 Gy), the correlation is fairly linear and its sensitivity is high. The minimum detectable dose is shown to be equivalent to the one obtained u sing the conventional R1-based approach. Since only one T1-weighted image i s required for the dose evaluation, compared to the R1-based method, the to tal MR imaging time can be reduced from hours to a few minutes. This extens ive time reduction avoids ferric ion diffusion effects and provides a pract ical way to simply and effectively measure the three-dimensional dose distr ibution using the Fricke-agarose dosimeter gel. (C) 1998 American Associati on of Physicists in Medicine. [S0094-2405(98)01512-0].