When Maureen Scanlan had a painful kidney stone episode four years ago, she was pleased that her doctor ordered an annual regimen of CT scans to monitor her condition.
The scans involved hundreds of razor-thin X-rays of her innards stitched together by a computer into stunningly detailed 3-D images showing the size and location of the stone, down to the millimeter.
What she didn't realize was that the perfection of the images was a result of a radiation dose equivalent to more than a dozen standard abdominal X-rays -- all for a condition that though painful is relatively mundane.
"I never thought twice about it," said the 38-year-old mother of two from Westfield, N.J., who since learning of the radiation has been worried that the scans may have played a role in two miscarriages. "I knew there was radiation, but I didn't realize how strong it was."
Scanlan is part of an explosion in the use of one of the most revolutionary medical technologies of the last half century.
Introduced in the 1970s, computed tomography scans have become a standard procedure for such common problems as kidney stones, persistent headaches and appendicitis.
Doctors in the U.S. ordered 68.7 million CT scans last year, more than triple the number in 1995, according to IMV Medical Information Division, a medical market research group in Des Plaines, Ill.
Generating tens of billions of dollars in billing each year, CT scanning has become an economic engine for hospitals and doctors, and the once-exotic million-dollar devices are starting to be found in private practices.
"It's gotten into the culture of doctors," said Geoffrey Rubin, a Stanford University radiologist.
But with the boom has come a rising concern that the abundant use of radiation is beginning to have a subtle effect on the health of the nation.
Although the risk of a single CT scan to an individual is minuscule, even a tiny increase in radiation exposure spread over a large population can eventually add up to tens of thousands of cancer deaths a year.
A controversial study published last November in the New England Journal of Medicine estimated that CT scans administered today could cause up to 2% of cancer deaths in two or three decades.
The doctors who have embraced the technology in increasing numbers say the small increased risk is a minor price for a snapshot of the body so detailed it can delineate hidden infections of the sinuses, tiny blood clots in the lungs and thin layers of plaque on heart vessels.
"The problem is they are almost too good," said UCLA radiologist Dr. Jonathan Goldin. "People want to take a picture of everything just in case."
Some researchers estimate that up to a third of scans could have been avoided or replaced by safer technologies, such as ultrasound or magnetic resonance imaging.
"In 20 or 30 years, the radiation debate will be like the smoking debate today," Goldin said. "People will say, 'Why did I get this imaging in the first place?' "
In the basement of a Beverly Hills office building, Dr. Hooman Madyoon peered into a computer screen displaying a pristine black-and-white image of a heart caught mid-beat.
Rotating the picture, he zoomed in on an artery and traced its gnarly path in increments of less than half a millimeter.
Through a radiation-proof window in the next room, the machine, an upright doughnut with a table positioned in the center, was being prepared for the next patient.
"It's just a matter of time before this catches on everywhere," said Madyoon, whose practice has done about 8,500 scans since installing the $1.2-million machine four years ago.
The images are created using a revolving X-ray beam that clicks on for a few seconds, scanning the human body slice-by-slice as if it were a loaf of bread.
The scans can cost from a few hundred dollars for a single organ to a few thousand dollars for a full-body image.
Since the first CT scanner in the United States was purchased in 1973 by the Mayo Clinic in Rochester, Minn., the U.S. total has grown to 24,000 machines.
That amounts to 81 CT scanners in the U.S. for every million people -- almost three times the average for the rest of the industrialized world, according to a 2007 report from the McKinsey Global Institute, an economic research group. Only Japan has a higher density of machines at 93 per million people.
About 70% of the scanners are in hospitals. But with declining prices, a growing number are being installed in private practices and imaging centers.
Today, scanner manufacturers, including Siemens and General Electric Co., tout the ease of making money with the devices. Just two scans a day can pay for a machine and its operation over a five-year period, according to a Siemens sales brochure. Ten scans a day can bring in more than $400,000 a year in profit.
For diagnosis, CT can offer huge advantages over its main competitor, MRI, which avoids radiation but costs more and requires the patient to lie in a clanging cylinder for half an hour or longer.