Staining methods for magnetic resonance microscopy of the rat fetus.

PURPOSE

To develop a magnetic resonance histology (MRH) staining and fixation method by immersion to enhance the signal-to-noise ratio (SNR) with a paramagnetic contrast agent permitting microscopic acquisition within a 3-hour scan time.

MATERIALS AND METHODS

Methods were optimized for embryonic day 18.5 (E18.5) rat fetuses and imaging at 9.4T with an RF refocused spin-echo pulse sequence (TR/TE = 75 msec/5.2 msec). Fixation/staining was performed by immersion in Bouin's fixative containing varied concentrations of ProHance (from 10:1 to 500:1 Bouin's:ProHance) and for varied immersion durations (up to 24 hours).

RESULTS

The results showed a significant change in T1 and T2 relaxation times as a function of concentration of contrast agent and immersion duration. As the contrast agent penetrated the tissues, T1 was reduced as desired (typically by 10x), but at the same time T2 was profoundly reduced (typically by 3x) due to both protein cross-linking from the fixative and the high concentration of contrast agent. A systematic assessment of this staining protocol showed an increased SNR (by 5x) over that in unstained specimens.

CONCLUSION

This staining protocol reduced scan time for very-high-resolution images (19.5 microm) to only 3 hours, making MRH a routine tool for evaluating fetal development.