Mirena is a progestin releasing device, it releases levonorgestrel into the uterus at a rate of 20 microgm/d. It has a T-shaped radiopaque frame, with its stem wrapped with a cylinder reservoir, composed of a polydimethylsiloxane-levonorgestrel mixture. Cu T 380A is another progestin releasing device. It has a polyethylene and barium sulfate, T-shaped frame wound with copper. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 32. Contraception.