RSNA News - February 2005

Obesity Limits Image Quality, Diagnosis and Treatment

Manufacturers need to think about design changes and technological advancements to obtain better quality images for larger patients.
—Raul Uppot, M.D.

Raul Uppot, M.D., received a Research Trainee Prize at RSNA 2004 from C. Craig Blackmore, M.D., M.P.H.

When physicians at Massachusetts General Hospital (MGH) in Boston started to perform an increasing number of gastric bypass surgeries, they noticed a problem—radiologists couldn't assess obese patients due to limitations in radiology equipment.

That got Raul Uppot, M.D., thinking about the ability of radiology departments to provide quality diagnostic images of obese patients and make accurate diagnoses. During a scientific paper presentation at RSNA 2004, Dr. Uppot presented the findings of a 15-year retrospective study of radiologic exams at MGH. He earned an RSNA Research Trainee Prize for the research.

Dr. Uppot and his co-authors reviewed all five-million radiology studies performed between 1989 and 2003. They found that about 7,500 (0.15 percent) were marked, "limited by body habitus," meaning limited in quality due to the patient being overweight.

The researchers found that the percentage of the "limited" reports rose from 0.10 percent in 1989 to 0.19 percent in 2003, strongly correlating to the increase in obesity cases reported in Massachusetts during that approximate time period. In 1991, the state reported a nine percent obesity rate; in 2001, the number percentage rose to 16 percent.

The average age of the patient was 57.1 years. Female patients accounted for 62 percent. Ultrasound exams and chest x-rays were the radiology tests most limited by obesity.

Dr. Uppot said there is a relationship between the material that ultrasound waves have to penetrate, in this case body fat, and the degree of degradation of the resultant sonographic image. He said two possible solutions are to use a lower frequency transducer (lower frequency sound waves travel better over greater distances) or to position the organ of interest as close as possible to the transducer.

For x-rays, there is inadequate penetration through layers of fat. To solve this problem, Dr. Uppot suggested using a grid or increasing the radiation dose setting, adjusting the window and level settings or changing the speed of the film system.

As for CT and MR imaging, Dr. Uppot said it's all or nothing: "Either the patient fits on the equipment or not. At our hospital, a patient cannot weigh more than 425 pounds to go on the CT table or 325 pounds for the MR table."

In patients who can fit in the scanner gantry but still are at risk for potentially suboptimal image quality, one solution is to increase the dose of radiation. Another potential resolution is to buy a scanner with a larger gantry. "Manufacturers need to think about design changes and technological advancements to obtain better quality images for larger patients," he said. The Centers for Disease Control and Prevention reports nearly one third of the American population is obese.

Economic Impact: Underestimating the Cost

Dr. Uppot calculated the direct costs of incomplete radiologic exams at MGH at $100,000 for 2003. That figure is more than triple the 1995 cost of $28,000. "This is just the cost for the radiologic exams," he said. "These figures don't include further diagnostic testing costs, the cost of a longer hospital stay, the cost of missed diagnoses by doctors and the psychological cost to the patient."

To view the abstract for Dr. Uppot's research, go to rsna2004.rsna.org, click on Meeting Program in the left-hand column and then click Search at the top of the page. The direct link is rsna2004.rsna.org/rsna2004/V2004/conference/event_display.cfm?em_id=4406020.

This story was adapted from an article that appeared in the RSNA 2004 Daily Bulletin.