Obesity has some hefty implications for imaging

One of the most intriguingly named scientific sessions at this year's ECR was "Fat radiology." You might think this consisted of a series of preaching-type lectures about how and why the profession has never had it so good. In fact, speakers from the Irish Republic and the U.S. focused on the implications of the growing number of obese patients for radiologists and clinicians and discussed whether more could be done to optimize imaging of this group.

Obesity is a huge public health challenge. The World Health Organization estimates it is already responsible for 2% to 8% of health costs and 10% to 13% of deaths in Europe. Its prevalence has tripled in many EU countries since the 1980s, and the numbers affected continue to rise alarmingly.

Children are of particular concern. The highest levels of childhood obesity in Europe are found in Spain, Portugal, the U.K, Italy, Greece, Malta, and Belgium, according to 2007 figures from the International Obesity Task Force. In each of these countries, around 30% of children are obese. In both Italy and the U.K., nearly twice as many boys aged five to 17 are obese than in Germany or the Czech Republic.

Fatter patients pose serious practical difficulties for imaging departments. Some of them are too large or heavy to undergo a scan, but manufacturers are responding by widening scanner bores and making patient tables more robust. A conventional CT unit may have a 70-cm diameter aperture and a 440-pound (200 kg) load limit, while MRI systems tend to have narrower bores. Some new machines have 90-cm-wide bores and can withstand loads of 680 pounds (310 kg).

Obtaining quality images is another problem. Due to the limited depth of signal penetration, ultrasound is difficult in people with a lot of subcutaneous fat, and accurate identification of gallstones and other conditions may be impossible. Canadian researchers have found that pregnant women who are overweight are more than 10 times more likely than women of normal weight to have their second trimester fetal screening recalled, and a second examination may not improve visualization (see lead news story in this edition).

Mammography findings may also be compromised if the patient's breasts are too large to fit within the imaging window. Similarly, in CT and MRI, attenuation from subcutaneous fat can make it harder to visualize central organs. Local staging of colon cancer with CT will have lower sensitivity, as will MRI-based staging for endometrial cancer.

The temptation for users of all modalities is to increase the power. But high-field MRI systems may not be available.

In CT, raising the kVp and mAs levels would mean obese patients will receive higher radiation doses, a hot issue in pediatrics.

If obesity levels continue to rise sharply, such dilemmas will become much more common. The pressures on healthcare professionals and vendors to find practical solutions look set to multiply.