Medical imaging, including X-rays and CT scans, let doctors see what's happening inside the body in great detail. More than 70 million such images are snapped annually, often with life-saving results.
But, with newer technologies, have come more powerful doses of radiation.
There are now growing concerns over safety.
Fran Gosnell is basically home-bound because of permanent internal injuries from cervical cancer treatment.
"Too much radiation," she explains, "And it wasn't regulated as it should have been."
Gosnell says her bladder, colon, and a major vein were damaged by radiation, more powerful than it was supposed to be.
In high therapeutic doses, experts know there is increased risk of dangerous side-effects.
But now, the FDA is investigating overdoses from diagnostic radiation. Diagnostic radiation is the same energy used in mammograms and X-rays.
In Los Angeles, more than 300 patients suffered radiation poisoning, after having CT scans.
"The effects won't show up for 20 years," says one victim. "I'm only 51. That means what I'll start having problems at age 70?"
There is very little oversight of radiation dosing. A facility typically monitors its own machines.
Experts say a single session in a CT scanner is like having 400 X-rays.
While one scan isn't a worry, multiple scans in a short period of time for some people, might be.
"There is a great potential for over-exposure to radiation, specifically in CT," says Texas Health Dallas medical physicist Messica Clements. "Exposure to radiation can increase your chance of cancer by 1 percent. So one in every 100 people could have an increased chance."
Clements monitors the scanners at Texas Health Dallas for accurate dosing to make sure patients aren't exposed to any more radiation than absolutely necessary.
In fact, medical radiation may cause 29,000 new cancers a year and 14,500 deaths, according to research published in the Archives of Internal Medicine.
Young people are at highest risk, partly because they have many years ahead to develop disease. Larger patients also have higher risk because more radiation is required to image their internal organs.
Doctors say short of radiation poisoning, which can result in lost hair and visible burns, there's no way for a person to know when they've been exposed to too much radiation.
"Much of the work on radiation sickness, radiation dosage, actually came on studies right after the second world war, related to the atomic bomb blast," explains Baylor radiologist Mark Fulmer. "Extrapolating data from an atomic bomb explosion to having your yearly chest X-ray in your doctor's office is kind of a hard, or not necessarily the right parallel to draw."
The best way to calculate even theoretical risks, say radiologists, is to compare imaging doses to radiation people soak up every day from the sun.
According to the FDA, a chest X-ray has the equivalent of 10 days of ordinary background radiation, a mammogram, three months.
An abdominal CT scan is like three years.
Despite that, radiologists say patients are often demanding.
"Radiation is always brought up," says Texas Health Dallas radiologist Dr. Douglas Baker, "And you still have some patients who insist on having exams done."
The potential for side effects is so real that North Texas medical centers are spending millions on new technologies that reduce exposure.
At Texas Health Dallas, there's a Flash CT, which scans faster and with less radiation.
Baylor Medical Center has a radiation safety committee.
"We presume that we might be inducing cancers from CT," says Baylor medical physicist Angela Bruner. "We're not sure yet, it depends on how it hits the body, but we want to do the right thing now to reduce that, so we formed this committee to do so."
For those who are worried, doctors suggest patients keep medical records of prior scans and ask questions before agreeing to medical imaging that might not be necessary.
"It's important that patients discuss this with their doctor," says Dr. Baker, "Ask, 'Why is this exam being performed? How is the information from the exam going to improve their health care? Are there alternative exams that don't require radiation, such as an MRI or ultrasound that can be performed instead?'"
There is no doubt that radiation for imaging and treatment can be lifesaving.
For Fran Gosnell, it has also been life-altering.
"I want them to be very aware of what they're getting into," says Gosnell, who wants others to hear her warning and know that what you can't see, can hurt you.