All experiments and procedures carried out on the animals were approved by the animal welfare committee of Capital Medical University and the approval ID is SCXK-(Army) 2007-004. The study sample was a 1-day-old mouse, provided by Laboratory Animal Science, Capital Medical University. Before imaging, the mouse was humanely sacrificed by intraperitoneal (ip) sodium pentobarbital injection overdose. The mouse was imaged after four hours of its death in order to avoid the small shifts of the body caused by the development of rigor mortis [7] . And then a piece of Kapton (Dupont, DE, USA) was used and rolled up into a tube. This kind of film is an electrical insulation material with outstanding thermal, mechanical and chemical properties. The mouse was constrained in the tube, and placed on the sample stage in a vertically up-side-down position.