"Obesity is affecting the ability to image these people. We're having trouble finding out what's wrong," explained Dr. Raul N. Uppot, lead author of the study, and an assistant radiologist at Massachusetts General Hospital and an instructor in radiology at Harvard Medical School, both in Boston.

"When they come to the hospital, people are so concerned about the disease they have that they don't realize that being obese could hinder the ability to deliver health care," he said.

In fact, it could hinder it considerably, given medicine's ever-growing reliance on imaging technology such as X-rays and ultrasound.

"In the past 10 years or so, medicine has become so dependent on imaging," Uppot said. "Instead of doing very meticulous clinical examinations, a lot of doctors now rely on CT scans, ultrasounds, etcetera, to tell them what's happening inside the body. What happens when you're too big to fit on a table? Or you can fit on a table but the image is poor quality?"

The new study is published in the August issue of the journal Radiology.

The findings did not come as a surprise to outside experts. "The study shows more systemically what all of us felt was true anyway," said Dr. Levon Nazarian, professor of radiology and vice chairman for education at Thomas Jefferson University Hospital, in Philadelphia.

"Patients may not realize that there are two aspects to being overweight, one of which is the increased risk of a number of different diseases," Nazarian added. "They may not realize that once they actually get sick, their size is going to limit the ability to even tell them what's wrong."

According to official estimates, about two-thirds of adult Americans are overweight or obese, and the effect on individual health and the health-care system is considerable. Obese people are more likely to develop illnesses such as cancer, diabetes and heart disease. Hospitals have also had to "super-size" their wheelchairs and beds to accommodate the new generation of sick and overweight Americans.

To assess the effect of obesity on the quality of imaging exams, the researchers reviewed all radiology records from tests performed at Massachusetts General Hospital between 1989 and 2003. Specifically, they were looking at incomplete exams due to patient size.

"We looked at people who were able to fit on the imaging equipment and get the scan," Uppot said. "When radiologists read the film, they had trouble interpreting the film because the quality of the image was not very good because of [the patient's] size."

In 1989, 0.10 percent of inconclusive exams were due to patient size. By 2003, that number had almost doubled to 0.19 percent.

"What was most alarming was the increase," Uppot said. "The number itself was small."

Difficulties varied according to the type of imaging. By 2003, abdominal ultrasounds exhibited the most difficulty in giving a proper diagnosis (1.9 percent), followed by chest X-rays (0.18 percent), abdominal computed tomography (CT), abdominal X-rays, chest CT and magnetic resonance imaging (MRI).

Ultrasound sends high-frequency sound waves through the patient, where they bounce off internal organs and come back, like a submarine's sonar. But the thicker the fat, the less able the waves are to penetrate. A similar phenomenon is at work with X-rays, the study authors said.

CT scans and MRI have a different problem -- weight limitations of the table that holds the patient and the size of the opening on the imager.

"Many manufacturers have started to address the issue by increasing table weights," Uppot said.

The weight limit for CT scans has been increased from 450 pounds to 550 pounds. For MRI, the weight limit went from 350 to 550 pounds, he said.

But that doesn't solve the bigger problem. "We are now able to fit people on the machine. Then the issue is, what do you do?" Uppot said.

The imaging power can be increased on standard X-ray and CT machines, but this leads to an increase in radiation dose as well, he said.

"What we're realizing is that not only do obese people have increased health problems but our ability to deliver quality diagnostic imaging to them is limited," Uppot said. "A large patient can no longer walk into a hospital and say, 'I want the best quality care, let me get imaged and operated on.' If you're that big, there will be issues."

The problems don't stop with diagnosis. "It puts stress on personnel," said Dr. Jorge Guerra, professor of radiology at the University of Miami Miller School of Medicine. "X-ray personnel will be more prone to injury. We receive patients who are 400, 500, 600 pounds. It paralyzes our ability to provide care for other patients. We need special equipment, special beds, the imaging is lower quality so it takes longer to complete." Size also affects interventional radiology, or procedures meant to treat a patient, which is Guerra's specialty.

And as the University of Miami builds a new hospital, it is having to take into account that more than one-third of the patient population will be more than 350 pounds, he said.

More information

To learn more about obesity and how to control it, visit The Obesity Society.