New imaging technology that combines the power of CAT scans with the finesse of a PET scan can catch cancer and other diseases earlier, potentially boosting survival rates and cutting costs, researchers said on Wednesday.

The two types of scan are commonly used separately but the team at the University of Pennsylvania demonstrated a new way to combine them.

The CAT, or computerized axial tomography, scan uses a special barrage of X-rays to see through tissue while the PET, or positron emission tomography, scan can detect the kinds of metabolic changes associated with tumor growth.

University of Pennsylvania doctors on Wednesday unveiled the new imaging technology, which they called “time of flight” technology.

“We can use this PET/CAT to check for early indications of cancer or to see if the cancer has spread,” said Dr. Laurie Loevner, a neuroradiologist at the Hospital of the University of Pennsylvania. “We can also look to see if a particular therapy has been successful in treating the cancer.”

Once a patient has been injected with a radioactive isotope, the new technology allows doctors to measure to within half a billionth of a second the time difference in the detection of two gamma rays coming from the isotope. That allows for more accurate identification of the site of a lesion and a better image of any possible tumor.

At a news conference, Loevner cited the example of a patient who previously had cancer but was not clinically suspected of having a recurrence, and had only very mild symptoms of continuing illness. The new technology discovered that the patient’s cancer had indeed come back.

The technology is particularly valuable for obese patients - a growing sector of the population - whose body size makes detection and diagnosis of tumors difficult. Although mostly used with cancer patients, it also has applications in the fields of cardiology and neurology, doctors said.

The technology has been in experimental use at the Hospital of the University of Pennsylvania since November 2005, and began clinical use in June this year.

Launched this month by maker Philips Medical Systems, a unit of Philips Electronics NV, it is now also in use at Montefiore Medical Center in New York, and the University Hospital of Cleveland, Ohio, as well as in Europe and Japan.

Each unit costs about $2 million, a price that is expected to come down as its use spreads, said Dr. Joel Karp, a professor of radiology. He said the technology has the potential to reduce medical costs by eliminating the need for exploratory surgery or other treatment that turns out to be unnecessary.