Measurement of T1, T2, and magnetization transfer properties during embryonic development at 7 Tesla using the chicken model

Purpose: To evaluate whether techniques of high field magnetic resonance imaging may be used to characterize embryonic tissue during proliferation and differentiation.

Materials and methods: Thirteen chicken embryos with incubation times between 5 days and 16 days have been measured in a small animal magnetic resonance imager (ClinScan, Bruker) at 7 Tesla using the built-in resonator. T1, T2-, and magnetization transfer imaging was performed using fast spin-echo with inversion recovery, half acquisition single shot turbo spin-echo, and spoiled gradient-echo sequences with and without off-resonance pulse, respectively. T1, T2, and magnetization transfer ratio (MTR) maps were calculated on a pixel-by-pixel basis.

Results: T1-, T2-, and MTR maps showed good image quality allowing for delineation of embryonic organs. During embryonic development, a decrease of T1 and T2 relaxation times was found, whereas, embryonic tissue typically showed an increase of magnetization transfer, for example, liver properties at day 5: T1 = 2431 +/- 163 ms, T2 = 122 +/- 12 ms, MTR = 9.2 +/- 4.2%; liver properties at day 16: T1 = 1763 +/- 89 ms, T2 = 71 +/- 4 ms, MTR = 16.9 +/- 2.2%.

Conclusion: Embryonic tissues show changing relaxation and magnetization transfer properties during development, therefore, high field MRI seems suitable for characterization of tissue replacement derived from embryonic stem cells.