The first medical imaging system was the X-ray machine. Being discovered in 1895 the x-ray predated much of the present knowledge of physics. It was not till 1909, 14 years later, that the modern model of the atoms started to take shape; and even then it was still incomplete compared to today’s (still developing) version. X-rays are actually gamma rays, though the naming conventions do vary. Basically, this is stream of protons, a component of the centre of an atom, being emitted from a source such as a decaying atom.
X-rays are useful because their travel is affected by the material they encounter. This principle is simple. Hard/dense materials like bone are difficult for an X-ray to penetrate; soft materials are easy to penetrate. A plate that is sensitive to X-rays works like a photography, showing a silhouette of any bones (or hard foreign object) in the body. This is rather like shining light through paper.
Of course the limitations of this method are obvious- only dense/hard objects can be seen on an X-ray. The soft tissues of the body are hard to distinguish on an X-ray, unless something else is introduces into the procedure.
With angiography a contrasting agent is used in to give an accurate visualization of organs and blood vessels. This contrasting agent is introduced into the body either orally or by injection, with the angiographic imaging techniques showing the path it takes through the body, and hence the body’s systems. Unlike x-rays it is very useful for shoeing the distinction between soft tissues. .
Different forms of medical imaging in radiology may use different techniques, but the underlying principles tend to fall into two types: either there are projected particles that distinguish dense materials from softer substances; or there are vibrations that bounce off objects to give an image, as in the case of Ultrasound. These two principles give us a lot of insight into an individual’s internal functioning.