Computed axial tomography, commonly referred to as CAT scans or CT scans,
creates three-dimensional images from the two-dimensional X-ray pictures.
This process was invented in 1972 by Godfrey Newbold Hounsfield of EMI
Laboratories, except he used gamma rays instead of X-rays. During the same
period, the CAT scan system was independently created by Allan Mcleod
Cormack of Tufts University. As technology improved, the time it takes to
conduct a CAT scan has dramatically decreased. The first CAT scan machine
took 4.5 minutes of scanning and 1.5 minutes of processing to produce one
slice (a slice is a single three dimensional X-ray image produced by a CAT
scan), today a slice can be scanned and generated in one second. The dose of
X-ray radiation has decreased as technology has improved-although the
radiation dosage of CAT scans is higher than with regular X-rays.
Also, the ability to examine images from different angles has improved.
The
CAT scan process is very simple: “A patient undergoing a CT scan rests on a
moveable table at the center of a doughnut shaped scanner, which is about
2.4m (8 feet) tall. The CT scanner contains an X-ray source, which emits a
beam of X-rays; an X-ray detector, which monitors the number of X-rays that
strike various parts of its surface; and a computer.”1
The X-ray source and the X-ray detector are across from each other inside
the machine. As the machine spins, X-rays emitted by the X-ray source
travel through the patient’s body and are picked up by the detector on the
other side. Computer algorithms process each X-ray to produce a three
dimensional cross-section of the part of the body being examined. If
more than one part of the body is being scanned, the table will gradually
slide the patient through
the machine to generate several slices of the body. If the scan
focuses on blood vessels or intestines, barium or intravenous iodinated are
administered to the patient to highlight those areas. The patient may
also be given a liquid to make organs show up better. Highlighting
substances are most commonly used for scans of the chest, the abdomen, and
the pelvis. Sedatives may also be administered to the patient, as any
movement may distort the image.
CAT
scans are most commonly used to find possible bleeding or damage in the
brain and to create detailed images of the chest, the abdomen, the spine,
and the pelvis. CAT angiography is a relatively new procedure in which CAT
scans are used to create images of the inside of blood vessels, lungs, and
other hollow structures. Outside of the medical field they have little
practical application.
