Polyacrylamide gels are a powerful tool to measure radiation dose by quantifying the NMR T 2 relaxation times of the irradiated gel. The exploitation of these radiation sensitive gels in clinical radiotherapy requires accurate mapping of T 2 values. This paper describes the optimization strategy used to identify accurate and practical methods of measuring the range of T 2 values typical of gel dosimeters (140-700 ms). The MR imaging techniques used to measure T 2 values and the choice of image acquisition parameters are described. Four sequences are compared and the results are analysed in terms of accuracy, signal-to-noise ratio and acquisition time. A multiple spin echo sequence was found to yield the most accurate results (98.9%). Single spin echo sequences, such as Hahn spin echo and EPI spin echo, were found to measure gel T 2 values with an accuracy of 90.1%. This paper reports the importance of careful selection and optimization of the MR imaging sequences for accurate and reliable polyacrylamide gel dosimetry.
Baustert, IC., Oldham, M., Smith, T. A. D., Hayes, C., Webb, S., & Leach, M. (2000). Optimised MR imaging for polyacrylamide gel dosimetry. Physics in Medicine and Biology, 45(4), 845-857. https://doi.org/10.1088/0031-9155/45/4/303