The use of contrast agents with fast field-cycling magnetic resonance imaging

Fast field-cycling (FFC) MRI allows switching of the magnetic field during an imaging scan. FFC-MRI takes advantage of the T 1 dispersion properties of contrast agents to improve contrast, thus enabling more sensitive detection of the agent. A new contrast agent designed specifically for use with FFC was imaged using both a homebuilt FFC-MRI system and a 3 T Philips clinical MRI scanner. T 1 dispersion curves were obtained using a commercial relaxometer which showed large changes in relaxation rate between fields. A model of magnetization behaviour was used to predict optimum evolution times for the maximum T 1 contrast between samples at each field. Images were processed and analysed to create maps of R1 values using a set of images at each field. The R 1 maps produced at two different fields were then subtracted from each other in order to create a map of ΔR 1 in which pixel values depend on the change in R 1 of the sample between the two fields. The dispersion properties of the agent resulted in higher contrast in a ΔR 1 image compared with a standard T 1-weighted image.