[Evaluation of Absorbed Dose by MRI Read-Out]

Three dimensional dose distribution by gel dosimeters is often read out by an MRI scanner, which is readily available in most hospitals. Both the T₁ and T₂ relaxation rates are used to evaluate the absorbed dose. This paper will describe the principle of the imaging sequences (spin echo, multiple spin echo, and inversion recovery methods) to measure the relaxation rate and the factors to affect the precision (signal noise ratio, temperature during scanning, coil, imaging artefact). Additionally, the magnetization transfer method will be mentioned as an alternative for low-density foam gel dosimeters.