Obesity an Increasing Obstacle in Imaging Studies

BOSTON, July 25 -- The increase of obesity in the U.S. doubled the number of poor quality radiology reports, labeled "limited by body habitus," over 15 years, researchers here reported.

In a retrospective analysis of 5,253,014 dictated radiology reports at Massachusetts General Hospital from 1989 through 2003, the number of habitus-limited reports increased steadily from 0.10% in 1989, to 0.14% by 1995, and 0.19% by 2003, according to a report in the August issue of Radiology.

This trend occurred despite advances in imaging technology, said Raul Uppot, M.D., of Harvard Medical School, and colleagues. "Americans need to know that obesity can hinder their medical care when they enter a hospital," Dr. Uppot said.

From 1989 through 2003 the percentage of habitus-limited reports increased at a rate of 0.010% per year (95% confidence interval: 0.007%, 0.013%; P<0.001), they said. Overall, 778 (0.15%) of the more than five million reports were classified as habitus limited.

In a further analysis, the researchers found a significant difference (P<0.001), between the weight of 200 randomly selected patients (mean weight 239 pounds) with incomplete imaging reports and the weight of 200 age- and sex-matched controls (mean weight 162 pounds) whose reports were not habitus limited.

Significantly, Dr. Uppot, said, there was a positive correlation between the increase in the number of habitus-limited reports and an increase in the prevalence of obese individuals (BMI 30 or greater) in Massachusetts between 1991 and 2001 (r=0.868, P<0.03).

By 2003, the modalities most affected by obesity were abdominal ultrasound, having risen from 0.7 % to 1.9%, followed by chest radiography (0.19%), abdominal radiography, abdominal CT, chest CT, and MRI (for all anatomic regions), the researchers said.

The minimal effect of obesity on CT and MR imaging was understandable, the researchers said, as there was some selection bias. If patients met the table weight and gantry-size criteria, they could undergo the exam. "Current protocols for people who can fit in an imager are, for the most part, not limited by obesity," they wrote, but added that an increase in tube current and voltage for CT and x-rays, would improve diagnostic quality, but at the expense of increased radiation exposure.

The percentage of habitus-limited reports was small, the researchers said, yet increasingly radiologists are finding it difficult to fit obese patients on CT or MR tables. Standard CT tables can manage patients weighing up to 450 pounds; MR machines typically handle 350 pounds.

Limitations of the study included the inability to account for radiologists' biases, technologists' expertise, and equipment variations. The term "habitus limited" was not used universally by radiologists, they noted. The fact that the researchers could not correlate their findings with patients' actual body mass was another drawback.

Poor images as the result of obesity can have an economic effect on health care and can lead to misdiagnosis, further tests, and increased hospitalization, the investigators said. Other negative effects include increased stress on imaging systems and also on technologists and support staffers who must move these patients. The authors pointed out that other studies have shown that approximately 83% of technologists have reported some pain when moving obese patients.

Future prospective studies assessing a correlation between body mass and the quality of individual imaging modalities could help manufacturers and radiologists improve image quality in an increasing population of obese adults, Dr. Uppot said. But in the long term, he added, "this country must make cultural shifts that promote more exercise and a healthier diet."