Artefacts in multi-echo T-2 imaging for high-precision gel dosimetry: III.Effects of temperature drift during scanning

In high-precision 3D gel dosimetry, long MR measurement times together with a high amount of RF energy being absorbed by the phantom are very common, and result in a spatially dependent temperature rise in the gel. As T-2 of the dosimeter gel is temperature dependent, dose estimation will be affecte d. In this study we assess the temperature rise in the dosimeter gel by use of MR temperature mapping and computer modelling. It is shown that in conv entional MR sequences, where linear k-space sampling is used, a temperature rise of 3 degreesC results in a dose underestimation of 10% over the whole dose map. To correct for these dose errors, a compensation method involvin g centric k-space ordering is suggested. Computer simulations have been per formed to analyse the robustness of the proposed method. Applying the compe nsated sequence. a temperature rise of 3 degreesC leads to a narrow dose ar tefact of the order of 3% for a 'worst case' situation in which a single pi xel dose gradient is assumed. Negligible deviations are found in the rest o f the dose map.