An investigation into the effect of magnetic resonance imaging (MRI) echo time spacing and number of echoes on the sensitivity and dose resolution of PAGATUG polymer-gel dosimeter

Background: There are various methods to read out responses of a polymer-gel dosimeter, among which the Magnetic Resonance Imaging (MRI) technique is the most common one. Optimizing imaging protocols can have significant effect on the sensitivity and the dose resolution of polymer gel dosimeters. This study has investigated the effects of the number of echoes (NOE) and the echo time spacing (ES) parameters on the response of the PAGATUG polymer gel dosimeter. Materials and Methods: The polymer gel dosimeters were produced under the normal atmospheric condition, then irradiated using a 60Co clinical radiation source. The polymer gel dosimeters were imaged using MRI technique with different imaging protocols. Afterwards, the effects of the ES and the NOE on the R2-sensitivity and the dose resolution of PAGATUG polymer gel dosimeter have been investigated. Results: Results showed that the sensitivity decreased with increasing NOE. However, it was found that the resolution got better with increasing NOE. Furthermore, the investigation of signal intensity decay curve showed that the R2 values in NOE less than 5 was less reliable.  According to the results, no significant difference were found between the sensitivities of the polymer gel dosimeters which were imaged with different ESs, except for ES=22 ms. However, dose resolution suffered from ES increasing. Conclusion: Dosimetric parameters of PAGATUG polymer gel dosimeter reaches to their optimum values by imaging with ES=25ms and NOE=10.