Original CT scanners (1974 to 1987) would spin 360° in one direction and make an image (or slice), then spin 360° in the other direction to make a second slice. Between each slice, the machine would stop completely and reverse directions while the patient table was moved forward by an increment equal to the thickness of a slice.
In the mid-1980s, an innovation called the "power slip ring" allowed scanners to rotate continuously. This development led to a new type of CT called "spiral" or "helical" scanning.
Spiral And Helical CT
Spiral CT scanners image entire anatomic regions (like the abdomen or lungs) in 20 to 30 seconds. The scanner rotates continuously as the patient couch glides. And at that speed, most patients can hold their breath for the entire imaging session. That eliminates the possibility that image quality will suffer due to the motion associated with breathing.
The continuous nature of the images-there are no gaps between slices obtained through spiral scanning-means that the data can be reconstructed to provide three-dimensional images, displaying the entire volume of organs and vessels. This increases the likelihood that very small lesions will be detected.
Spiral CT has become the primary imaging technique for the chest, lungs, abdomen, and bones because of its ability to combine fast data acquisition and high resolution.
"Multi-Slice" Spiral CT Scanners
The newest "multi-slice" spiral CT scanners can acquire up to four slices in a single rotation and collect as much as eight times more data than previous state-of-the-art spiral CT scanners. This new technology will provide for more non-invasive imaging of a wider range of conditions in less time and with greater patient comfort.
"Virtual Reality" Imaging And Advanced 3D CT
New computer software and advanced computer systems combine with spiral CT to produce three-dimensional images that enable a growing number of non-invasive "virtual 
Endoscopy involves the use of an endoscope--a tiny camera at the end of a thin tube--to visualize the inside of certain organs, such as the colon. Virtual endoscopy performed with CT allows visualization of these same organ interiors without using an invasive endoscope.
Some virtual endoscopy procedures, like the placing of a stent inside a major blood vessel, were not possible with conventional endoscopy. Endoscopes could not be used to visualize the inside of blood vessels, but spiral CT can.
Multi-slice CT, combined with 3D reconstruction, is the newest technology for the management of heart disease and stroke.
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