There are two variations of the CAT scan (computed axial tomography) that are used in making cancer diagnoses:

• Spiral CAT scans, also called helical CAT scanning, use special slip-ring technology to create a continuously moving x-ray tube, which eliminates the bulky, time-consuming cables of earlier CAT scanning machines. As a result, the entire scan can be taken in a minute. Although there are still earlier generation CAT scan machines, spiral CAT scans are expected to soon entirely replace them.
  
  Spiral CAT scans have several advantages over the earlier version. Because the test is performed so quickly, it reduces distortion caused by inevitable movement during the longer scans as the patient breathes. A spiral CAT scan can frequently be taken during one breath-hold, which gives a much sharper image.
  
  The spiral CAT scan also yields results much faster. Results are available before the patient even leaves the testing site. Its high sensitivity marks it as particularly useful in the diagnosis of very small cancerous tumors in the lung. The use of spiral CAT scans in diagnosing gynecological conditions is still being investigated.
  
  A new technique known as virtual endoscopy uses a spiral CAT scan to allow physicians to see inside organs or other body structures without surgery or special instruments. A virtual colonoscopy, also known as a CAT colonography, is being studied as a potential screening technique for colon cancer.
  
  
• Combined PET/CAT scan. This technology combines CAT scans with another imaging procedure called positron emission tomography (PET scan). Positron emission tomography creates color pictures of chemical changes that occur in tissues, a process known as metabolic activity. Cancerous tumors are more active than normal tissues, so they appear as different colors, known as hot spots, on the PET scan. This technology shows promise, but it is currently available at only a handful of facilities.