Histological Properties of a Chemically Fixed Human Embryo Visualized with Quantitative Susceptibility Mapping.

A chemically fixed Carnegie stage 23 (approximately 56 days of gestation) human embryo specimen was imaged using 3D spin-echo and gradient-echo sequences in a static magnetic field strength of 4.74T, and a quantitative susceptibility map was calculated using the 3D gradient-echo image. The acquired 3D microscopic images (90 μm cube voxel size) clarified the relationship between R₂ (transverse relaxation rate), R₂* (apparent transverse relaxation rate), and magnetic susceptibility in the heart, liver, kidney, and spinal cord. The results suggested that the R₂* and magnetic susceptibility in each tissue were probably due to paramagnetic iron ions originating from erythrocytes. The large R₂* (~130 s^-1) and magnetic susceptibility (~0.122 ppm) in the liver were attributed to its hemopoietic function. A large magnetic susceptibility (~0.116 ppm) was also observed in the spinal cord, but we conclude that more detailed future studies are needed.