In vitro evaluation of MR hypointensity in Aspergillus colonies.

PURPOSE To demonstrate that paramagnetic elements in fungal colonies can cause hypointensity in MR images.

METHODS Aspergillus fumigatus grown in vitro was imaged with CT and MR at the time of initial inoculation and 5 days later. CT and MR images, T2 values, scanning electron microscopy, energy-dispersive analysis, and furnace atomic absorption spectrometry were performed.

RESULTS After 5 days of growth, MR images of A fumigatus revealed curvilinear hypointensities on T2-weighted images corresponding to the fungal growth. Gradient-echo images revealed two distinct components of hypointensity with different calculated T2 values. Phase-angle-difference images revealed a phase shift characteristic of magnetic-susceptibility paramagnetic effects, which corresponded to the hypointense regions on gradient-echo images. Energy-dispersive analysis and furnace atomic absorption spectrometry confirmed the presence of paramagnetic elements.

CONCLUSION It was shown that in vitro A fumigatus concentrates metal elements contained within the nutrient broth. These focal collections of calculated T2 values are caused at least partly by magnetic susceptibility effects.