Review of quantitative MRI principles for gel dosimetry

The radiation dose distribution absorbed by polymer gel dosimeters can be read out by several methods such as magnetic resonance imaging (MRI), optical CT, X-ray CT and ultrasound. MRI was the first method that was explored to read out polymer gel dosimeters. Although MRI was soon recognised as a promising technique, limited access to MRI scanners and the often (wrongly perceived) complexity in optimizing the imaging protocol has led to a search for other imaging modalities. In this paper we hope to unveil the mysticism of magnetic resonance imaging. Firstly, the basic principles of magnetic resonance image acquisition will be explained. Also, quantitative properties to describe the image quality are defined. Secondly, some sequences for quantitative T1 and T2 imaging will be analysed and specific issues concerning optimization and accuracy will be highlighted. Thirdly, we provide the reader with some easy guidelines and tools to investigate the accuracy of quantitative imaging sequences. It should also be noted that many of the parameters that describe the accuracy of the imaging technique also apply to other imaging modalities.