3D MRI gel dosimetry based on image intensity (A new approach)

Background: Since 1984 MRI gel dosimetry has been introduced as a potential technique for 3D dosimetry. Most of the studies have measured R1 (1/T1) or R2 (1/T2) properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Methods: Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques. Results: Our results showed that linear response exists between the variations of image intensity with absorbed dose (1-15 Gy). Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo (GRE) imaging technique also have been studied in comparison with classic spin echo (SE) imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel dosimetry. Reduction of imaging time is achievable in image intensity technique so that it’s possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel. Iran . J. Radiat. Res., 2003 1(1): 45 - 50.