Medical imaging came to be at the turn of the twentieth century with the discovery of X-Rays and their power to penetrate the skin. Their short wave lengths and high energy allowed physicians to see broken bone, and chest X-Rays were used to in the early diagnosis of tuberculosis.

Computed Tomography, CT Scans, or CAT Scans Computed Axial Tomography were the second generation of X-Rays. Tomos is Greek for ?slice � or ?section �, graphia is describing. As named it describes an image of a particular cross section of the body. The technology was invented by people independently in 1972. A British Engineer and a South African born physicist working at Tufts University in Massachusetts. The engineer, Godfrey Hounsfield of EMI Labs in Great Britain won the Nobel Prize and was knighted, but shares credit with Allen Cormack for the invention.

The first CT scanners were installed between 1974 and 1976 and were only for the head. Whole body scanners came very quickly however, also in 1976. The first machines took several hours to acquire the raw data from a scan or slice, and took a few days to build an image from raw data. The equipment available today can scan 4 slices in 350 milliseconds, and scan an entire chest in 40 separate slices, and construct an image from the millions of data points in less than a second. Today the technology combines digital computers and a rotating X-ray that can show a detailed cross section image of organs. Physicians can window soft tissue, bone, and blood vessels to selectively view different areas of organs. CT scans give a better view of the different structures of the brain, than other imaging techniques.

Angiography is another form of X-Ray that is used to diagnose diseases of the blood vessels including the brain and heart. Originally Angiograms was used to diagnose blockages from plaque buildup, but more recently their use has been more for minimally invasive surgery of the blood vessels and arteries of the heart. Contrast liquids or dyes are intravenously injected into the area of interest to radiologist, cardiologist, or vascular surgeons who mainly use this technology. The biggest use has been in choosing whether coronary by-pass surgery or less invasive angioplasty is used in clearing blocked arteries.
Positron Emission Tomography or PET is a nuclear medicine scan that uses cross sectional data and reconstructs it as an image, much like CT scanning, but can see specific problems better such as brain tumors, and the heart and lungs.

The most recent innovation in PET has lung cancer patients inhaling a radionuclide or low level radioactive chemical rather than an oral or intravenous contrast medium. There is also SPECT which is similar to PET that uses a gamma camera, but is not as sensitive. PET cameras are much more expensive than SPECT cameras and are only in the largest medical centers.
MRI or Magnetic Resonance Imaging was first done on the brain in 1980 at Thorn-EMI Labs in England, and Nottingham University.

MRI works with magnetic resonance and radio waves of a certain frequency that create a cross sectional image of the body. When the radio waves are turned on and off, in the presence of the magnet, atoms in the body absorb and reflect them differently creating an image. The magnets used in MRI equipment are extremely expensive and come in several different types. The strength of these magnets is measured in Tesla Units, and range from 0.01 Tesla to 1.5 Tesla. The 1.5 Tesla can only be described as ?extreme � magnets, and have a magnetic field 30,000 stronger than the force of gravity, and cost millions of dollars.
There is an interesting web site that shows when magnets attack, when someone with out knowing the strength of the magnet brings a floor scrubber or welding tank into a room with an MRI machine to do some work. Picture after picture of floor scrubbers and pallet jacks picked up and slammed into the magnet, causing extremely expensive damage. The welding tank was going to be used to fix a leak in the fire sprinkler system, so it was turned off when they wheeled the tank in. When it flew across the room into the magnet it sparked a fire that burned the entire building down. That is why everything metal must come off before having an MRI.
The MRI machines themselves are a tube, with an opening of 55 cm to 65 cm. Open MRIs are available now. Approximately 3% of the population is too claustrophobic to spend any length of time in the MRI machine, so open MRI is done on them.
MRI has made diagnosing many injuries, particularly in sports medicine, and other illnesses practical where an invasive process of some kind would have been needed.