X-Ray's are similair to visible light rays. Both x-rays and visible light rays consist of photon particles carried through electromagnetic energy. However, x-rays have shorter wavelengths and higher energies than the light rays you can see.
In an x-ray machine, high energy electrons are shot towards an element made up of heavy atoms, usually tungsten. This results in one of two atomic processes; the Bremsstrahlung or K-Shell emission. In the Bremsstrahlung, or braking radiation process,the velocity of the high energy electrons change as they swing around the tungsten nucleus and slow down. This results in a loss of energy in x-ray form. In the K-Shell emission process, the high energy electrons actually knock some of the tungsten atoms out of their k-shell, or lowest energy state. When a tungsten electron is knocked out of the lowest energy state, an electron from a higher energy state replaces it. Just like the Bremsstrahlung, energy is lost in the form of x-rays.
An x-ray machine consists of a cathode, which emits the high energy electons towards the anode, generally tungsten. The anode and cathode are contained in a lead case with a small opening, so that the x-rays are only emitted towards the patient.
On the other side of the patient is a camera that detects the x-rays after they pass through the patient's body. The x-ray energy is either absorbed or passed through the patient. This is why bones show up in x-rays. Calcium atoms are larger than other tissue, and can absorb the photon energy, while the energy passes through the smaller atoms of soft tissue. If a doctor wants to examine organs, the patient can ingest or be injected with what is called a contrast media, which consists of liquids that will absorb the x-ray photons.
The main differences between an x-ray and an MRI are the images they produce. An x-ray clearly shows the contrast between soft tissue and bone density. That is why it is often used to examine broken bones. An MRI image shows a better contrast between different kinds of soft issue. That is why it produces such detailed images of the brain and other tissues.
When X-Rays were discovered they represented an amazing medical breakthrough in non-evasive examination, and in some ways they still
do. They allow doctors to examine a patient without surgery, and therefore in a much safer manner. However, after the initial
x-ray craze between the 1940's and 1950's, scientists began to discover the negative side-effects of x-rays. X-ray's are so powerful,
they have the ability to knock electrons off of the atoms they hit. This produces ions, or negative atoms that produce abnormal chemical reactions
in the body. X-rays can also alter DNA. The resulting mutations often lead to birth defects or disease.
MRI is still a relatively new procedure when compared to x-ray. At this point, there are no known biological hazards associated with the MRI. MRI is more versitile than x-ray also, as it can be used to examine a wider variety of medical conditions. MRI does have a few disadvantages though. People who are claustrophobic have difficulties staying in the enclosed area. Some hospitals have open MRI machines that limit the amount of enclosed area. However, for patients with extreme claustrophobia, even an MRI in an open machine is too much to handle. Most patients are uncomfortable staying still during the exam, which can last up to 90 minutes Also, MRI machines usually have a weight limit of around 500 pounds, so obese people can not be examined. Patients wih pacemakers or other metal objects in their body usually can not be examined through MRI either, due to the extremely powerful magnets used. MRI's are much more expensive than other methods of examination also, including x-ray.