Obese patients are straining imaging tools

Washington -- The burden of the nation's obesity epidemic is being carried on many levels.

The obvious -- that of increases in related morbidity and mortality -- continues to raise public health alarms. But downstream nuts-and-bolts issues involving the treatment of these patients also are emerging.

Not only are hospitals requiring larger wheelchairs and beds to accommodate patient's added girth, but radiology equipment is not always up to the task at hand. The problem is becoming more evident as growing numbers of extremely obese patients turn to gastric bypass surgery.

A study in the August Radiology found that rising obesity in the United States doubled the number of inconclusive diagnostic imaging exams between 1989 and 2003. Researchers assessed all exams done during that time at Massachusetts General Hospital to determine the effects of weight gain on imaging quality and diagnosis.

The problem is becoming more obvious, said the study's lead author, Raul Nirmal Uppot, MD, a radiologist at MGH. "No longer are obese people simply staying at home and living their lives, they are coming into the hospital to get gastric bypass surgery done."

At MGH, all patients undergo postoperative imaging to ensure that there are no leaks in the surgery site, the researchers said. But getting a clear image or even fitting a patient on a radiology table or through an imaging machine's "doughnut hole" opening is becoming more difficult.

During the past 20 years, obesity among adults has risen significantly in the United States. The latest data from the National Center for Health Statistics show that 30% of the nation's adults age 20 and older -- more than 60 million people -- are obese. This increase is not limited to adults. The percentage of young people who are overweight has more than tripled since 1980. Among children and teens ages 6-19, 16%, or more than 9 million, are considered overweight.

The researchers found that abdominal ultrasound was the most problematic imaging technology for producing clear pictures, followed by chest x-rays, abdominal CT scans, abdominal x-rays, chest CT scans and MRI exams of all parts of the body. Problems with CT and MRI scans arose because of the weight limitations of the imaging tables and the size of the imaging opening. Standard CT tables can accommodate patients weighing as much as 450 pounds, and MRI machines can obtain diagnostic-quality images in patients weighing up to 350 pounds.

For exams that require radiation exposure, such as x-rays and CT scans, the power can be increased on standard machines to attempt to produce a higher-quality image. But this approach also leads to the negative effect of increased radiation dose, although the risk is probably minimal, Dr. Uppot said.

MGH is purchasing MRI machines that accommodate larger people, he said. New machines are able to support people who weigh as much as 550 pounds. The diameter of the opening also will be larger.

The research team is now exploring how to improve image quality for these heavy patients and expects to publish their findings in about six months.