Whole body scanning
Whole body contrast agents are more complicated than staining cells or tissues. Unlike cells and tissue sections, humans really are better doors than windows. Because we’re not very transparent, we cannot use normal light to see inside the body. Instead we must use other forms of light or even sound. Hospitals use radio waves, X-rays, gamma rays and ultrasound to look deep inside patients without having to resort to surgery.
High energy light beams called X-rays can be used to see through people - generally they work well for hard structures such as bone, but modern X-rays can be very clever.
Low energy light is usually called radio waves - the breakfast show on your favourite radio station is transmitted on radio-waves. They are also used in MRI scans.
Nuclear medicine uses very high energy light called gamma rays for PET and SPECT imaging. Gamma rays are even higher up the energy levels than X-rays.
High frequency sound can be used; t he image is formed from echoes. Submarines use sound instead of radar (sonar). Dolphins, bats, and occasionally people can also use sound to form a picture of the world.