Imaging Obese Patients a Weighty Task

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 - Rhino

More than one-third of Americans are obese and the number continues to climb. In June, the American Medical Association classified obesity as a disease, but the condition has challenged healthcare providers for decades, with radiology departments attempting to shoulder the weight of the obesity crisis and the logistical and technical hurdles it creates.

Even as imaging equipment has evolved to accommodate more weight and girth and software has been refined, there are still issues with image quality and radiation dose that can hinder the ability to make accurate diagnoses. 

“Obese patients can be difficult to image. There’s an extra layer of tissue between the machines and the organs of interest, so assessment may be impaired,” says Martin Gunn, MBChB, associate professor of radiology at the University of Washington School of Medicine in Seattle.

Poor image quality is a potential problem in all imaging modalities. “The overhanging rule is the more tissue you have, the harder it is for ultrasound and X-ray beams to penetrate,” says Raul Uppot, MD, of Harvard Medical School in Boston.

In response to the obesity epidemic and the demand for imaging services, manufacturers have adapted their equipment to allow for excess load. Tables can handle more weight—some machines can withstand more than 650 pounds—and gantry openings have gotten larger to allow for wider girth.

The changes, while making it possible to scan patients who once would have been impossible to image, are not cure-alls. Not every facility, for example, is able to acquire the necessary equipment.

“Hospitals that haven’t been able to get new equipment and are still using older equipment are still stuck with older weight limits,” says Leigh Shuman, MD, staff radiologist at Lancaster (Pa.) General Hospital. “We assume that because vendors have built new equipment that everyone’s got it, but that’s not true.”

Facilities with newer equipment may be able to provide imaging services to more patients, but radiology departments still face numerous obstacles once the patient gets to the imaging suite.

“There’s wear and tear on staff, and the number of medical professionals who have back injuries from moving obese patients is increasing,” Shuman says. “And many radiology departments try to have equipment for lifting like slings, but getting people trained to use them is expensive and can strain budgets.”

Gunn says his institution relies on cranes to help position patient to take the strain off staff. “We don’t put in new scanners anymore without putting in a crane at the same time.”

Once the patient is on the table, another challenge presents itself as the gantry aperture may be too small for the patient to fit through. Over the past several years, manufacturers have increased the gantry diameter to accommodate patients with a larger girth.

If a patient is still too large, however, radiologists may have to try other modalities, such as low field open MRI or ultrasound—which has no weight limitations via the scanner, however larger size makes penetrating extra soft tissue more challenging and may yield poor quality images, Uppot notes. They also may have to send patients to other facilities that have bariatric CT scanners.

Uppot and colleagues have had to turn to imaging equipment designed for other purposes. “We have a CT scanner that has a gantry opening 80 centimeters in diameter that we use for interventional purposes to fit patient and interventional equipment. It is also used to accommodate the occasional large patient who does not fit on our standard CT scans,” he says.

Larger gantry size, while allowing the patient to get into the machine, introduces another imaging obstacle. “We can’t increase the size of the gantry forever, because once we increase it, we increase the distance between the organs we need to see and the x-ray tube,” says Gunn. “Sometimes, we can only see part of the patient.”

Poor image quality & diagnostic dilemmas

Uppot says different tactics may be required to help with diagnosis, including in-hospital observation and even exploratory surgery.

Each modality presents different challenges for radiology staff, whether related to image quality or some other issue. X-ray images of larger patients often have foggy areas that hide critical details. One problem, Shuman explains, is created because photons get deflected by the extra tissue.

“We’ve gone about as far as we can go to eliminate scatter radiation,” says Shuman. “There are grids that try