Edme H. Hardy

Monitoring the formation of an Aureobasidium pullulans biofilm in a bead-packed reactor via flow-weighted magnetic resonance imaging

The biofilm-forming fungus, Aureobasidium pullulans DSM 2404, was grown in a bead-packed reactor. Alterations within the reactor were analysed in several cross-sectional slices by magnetic resonance imaging (MRI) with flow contrast. For the first time, biofilm accumulation could be continuously elucidated without using any contrast agents, and the non-stationary flow through the fixed-bed reactor could be visualized. The results indicate that the non-stationary flow through the biofilm reactor changes significantly due to the changing reactor morphology. Preferential flow lines arise during biofilm formation. The accumulation of the biomass was determined and compared to gravimetrical biomass data. The described technique can be used to monitor hydrodynamic transport, and to combine flow-field characteristics with morphological data for the prediction of undesirable reactor processes, e.g. clogging.

Automated phase correction via maximization of the real signal

Due to improved quantification capabilities and enhanced signal-to-noise ratio (SNR), phase-corrected real reconstruction in magnetic resonance imaging is superior to the common magnitude reconstruction, especially at low SNR. This requires the development of an automated phase-correction algorithm. Existing methods are not well suited for multiple unconnected regions of very low SNR. For this situation, a method based on the real-signal maximization is implemented, in which the experimental image phase is approximated by a three-dimensional polynomial of up to third order. The presented implementation was successfully applied to data originating from different samples and pulse sequences.