Nuclear magnetic resonance imaging of freeze-drying

The objective of this study was to determine the feasibility of using magnetic resonance imaging (MRI) to observe the shape and position of the ice sublimation front during primary drying for subsequent comparison of these images with those predicted by mathematical model of heat and mass transfer during primary drying. One-dimensional (1D) profile studies on both ice and 2% HSA during in situ freeze-drying were performed with a single point imaging (SPI) sequence, and demonstrated that the SPI technique can be used in capturing the ice signal during freeze-drying. In order to perform two-dimensional imaging, it was found that the ice must be "doped" in order to increase the apparent transverse relaxation time (T2*) and decrease the longitudinal relaxation time (T1) of ice. HBr at a level of 0.1 mM was shown to be an effective dopant. As a result, 2D images of ice and 5% HSA doped with 0.1 mM HBr were successfully collected, and the shape and position of the ice sublimation front during in situ freeze-drying were observed.