Imagine your flesh becoming transparent enough to see everything going on inside your body – or someone else’s. Yucky, but really interesting.

Throughout most of history, the only way to see inside the body was to cut it open, alive or dead. But with the discovery of X-rays 120 years ago, all that changed. X-rays are the same as light rays, but have a much shorter wavelength, meaning higher-energy photons, and can penetrate soft tissue and make the bones visible on a screen or photograph.

Thanks to scientific discoveries we now have many other ways of seeing inside your body, making visible different types of soft tissue, and parts where specific elements are concentrated.

Computed tomography, or a CT-scan, also uses X-rays, but combines high-resolution images from many directions using a computer. Sometimes chemicals called contrast agents are given, absorbing X-rays to highlight a specific region, such as the liver.

Maybe you’ve had an MRI-scan (magnetic resonance imaging). You were probably laid down inside a big white donut, in a strong magnetic field. You cannot feel that, but atomic nuclei are tiny magnets, and they can. When irradiated with radio waves of specific frequency, certain atoms emit a radio signal that can be detected. With the help of computers, this enables the position of selected elements to be imaged, for example the hydrogen in water or fat.

The electromagnets used in MRI have to be very strong, and generally use superconducting wires, which can carry very high electric currents when extremely cold. MRI scans are noisy, but perfectly safe.

A PET scan (positron emission tomography) is another way of seeing inside the body. Positrons are antimatter partners of electrons — almost the same but with a positive electric charge. One injects a radioactive positron-emitting isotope, usually made in a particle accelerator, into the bloodstream, inside a molecule that goes to a specific part of the body. For example, glucose will accumulate in an active region of the brain.

The positron immediately hits an electron and, being particles of antimatter and matter, they annihilate each other, creating two gamma-rays that fly off in opposite directions. Gamma-rays are like X-rays, but with even shorter wavelengths. Detecting the two gamma-rays allows an image to be built up showing where the annihilation occurred.

Don’t worry about the radioactivity; you probably have worse things to worry about.

These are just a few of the many ways to look inside your body. Science at your service.