Antimatter
It does have a use in medicine, because a special kind of scanner called the PET, which stands for positron emission tomography, uses positrons to go into the human body. Doctors can look at the way the positron changes into energy inside a person's body, and be able to tell if something is wrong inside a person. This kind of machine works differently than an X-ray machine or a magnetic resonance imaging (MRI) machine, and can help doctors see things that those other machines cannot see.