"There are things that you can miss because the X-ray beams are just not able to penetrate deep enough," said study author Raul Uppot, a radiologist at Massachusetts General Hospital in Boston. The study is published in the August issue of the journal Radiology.

    In some cases, the quality can be so poor that doctors could fail diagnose small lung, abdominal and liver tumors, Uppot said.

    With 64 percent of the U.S. population either overweight or obese, the problem is worsening, but it represents a business opportunity for equipment makers and hospitals, he said.

    Canadian hospitals are also struggling with the difficulties of diagnosing an increasing number of obese patients.

    Stewart McNeil, patient equipment co-ordinator at Hamilton Health Sciences, said the hospital can rent over-sized equipment when it is called for, but noted that patients who are very obese are sometimes sent to nearby veterinary colleges.

    "The MRI and X-ray machines there are designed for horses," he said. "How would you feel?"

    Moreover, many older scanners also cannot support more than 400 pounds of weight, while in other cases, a patient's sheer girth can touch the sides of the scanner, making it difficult to get a clear image.

    Hospitals are supposed to replace their equipment every 10 years -- a guideline that is often ignored when the equipment is still functioning properly, said Robin Hesler, CEO of the Ontario Association of Medical Radiation Technologists.

    Meanwhile, Hesler said obese patients may be exposed to higher levels of radiation in some scans because more is needed to produce an image.

    Statistics Canada shows the nation's obesity rate has almost doubled in the past two decades -- jumping from 13 percent in 1978 to 23 percent in 2004. Enditem

    (Agencies)