Obesity affects ultrasound quality
Sharon Tiffin/Oak Bay News
Technician Helen Skinner helps Dr. Robert Koopmans with an ultrasound at Victoria General.
By Amy Dove
Oak Bay News
Aug 09 2006
Healthy lifestyles aren't enough - Canadians are still packing on the weight
Nestled in one of the healthiest corners of the world, even Greater Victoria's residents can't hide from the recent findings of a study correlating the link between obesity and incomplete diagnostic imagining scans.
"If you want to deliver some good news to Victoria - on a Canada-wide basis (we are) still about the healthiest city in the country," said Dr. Richard Eddy, Vancouver Island Health Authority radiologist.
But obesity is causing problems in local hospitals - especially in the ultrasound departments.
Obesity rates in Canada have nearly doubled over the last 20 years. In 2004 eight per cent of children and 23 per cent of adults were obese in Canada.
British Columbia showed the lowest provincial ratings according to Statistics Canada.
Rising obesity rates also effect the quality of diagnostic imaging - things like X-rays, ultrasounds, MRI and CT scans.
Despite a push towards healthier lifestyles, people are continuing to increase in size.
"The reality in front of you is, overall, Canadians on average are getting bigger. No one likes to be big, but the fact of the matter is they are."
While on average Victorians are not obese, local ultrasound technicians have noticed an increase in hazy, or blurry ultrasound pictures.
"It plays a role," noted Dr. Robert Koopmans, section head of ultrasound with VIHA.
"The detail you get and how confident you are that (the fetus) is normal depends on the quality of your ultrasound machine and, also, somewhat on the patient."
There is no defined point on the scale when obesity starts to interfere with a doctor's ability to properly use diagnostic imaging equipment. But for sensitive ultrasound equipment the trend toward heavier body sizes is reducing image quality.
"Our equipment is getting better so we are seeing more, but there is still a limitation if the patient is obese," said Dr. Sandra Seher, technical section head for ultrasound with VIHA.
Ultrasounds are more sensitive to patient size because of the physics behind sound waves, Seher explained. The more tissue the sonar waves have to travel through, the weaker the echo transmitted back.
This is increasingly a problem with pregnant patients as ultrasounds are the only scanning option to monitor the fetus. While other ultrasound patients can be referred for a CT scan or MRI, pregnant women are left in the dark.
"You may miss things," Koopmans said. "There is more uncertainty."
More than 50,000 ultrasound scans were conducted in 2005 in the Victoria area. About 30 per cent of them were on pregnant women.
The numbers of scans where obesity played a role is hard to pinpoint. There have been no formal studies - that Seher is aware of - that analyze the effects of obesity on how sound waves travel through the body.
"We can't put percentages on it really because you will have two patients the same size, both slightly overweight, and one might not be as hard to scan as the other."
There is no static weight that can be used as a gauge because of factors such as body tone and weight distribution.
Even though image quality is degraded on larger patients, the tool is still effective to some degree.
"There is always some information you get from every test you do. It is more of a grey area of how much you can see and how much you can't see," Seher said, noting it is rare for a test to provide no information.
While obesity is a health condition that doctors and patients deal with for its own reasons, the good news is that technology continues to improve.
"That sort of counteracts the problem that we have with patient size, but there certainly still are limitations," Seher said.
Ultrasounds aren't the only imaging procedure affected by obesity.
X-rays, MRI and CT scans all encounter problems when it comes to larger patients.
X-ray images become increasingly unclear the larger the patient - as thick layers of fat cloud internal structures, making it harder to decipher the results.
"The bigger you are, the harder it is to see through you," Eddy said.
MRI and CT scanners are capable of imaging larger patients, however, someone who weighs more than 450 pounds will not fit on the table.
"Occasionally you get somebody who is too big. It is not a question of not being able to see them well enough - you can't see them at all," Eddy said. Current MRI tables can accommodate up to 350 pounds while CT tables can hold up to 450 pounds.
While Eddy has never encountered a local patient exceeding the weight limit, there are no machines in the province capable of accommodating patients over 450 pounds.
And while the machine's manufacturers are starting to cater to the needs of a "larger" market need, it's a stretch to say there is a demand for the larger machines in Canada.
"The fact B.C. doesn't have a single one would pretty much tell you the answer to that."
Increasing machine capacity to address obesity is a reality however.
In the 1970s, when CT scans were developed, the tables could hold up to 200 pounds. By the early 1990s the limit was bumped up to 350 pounds and in 2005 the standard weight limit increased to its current 450 pounds.
And while there are not an inordinate number of obese patients utilizing B.C.'s health care system, the few who do require multiple resources.
Not only does obesity place individuals at a higher risk for conditions such as diabetes and heart disease, but also inconclusive tests often mean multiple tests are conducted.
"They use an incredible number of heath care resources," Eddy said. "It is just not good."
"Limited due to body habitus" - The Study
Researchers studied all radiological exams conducted at Massachusetts General Hospital between 1989 and 2003 under lead author and radiologist Dr. Raul Uppot. The research showed that 0.15 per cent of the more than five million cases studied were limited due to body size. On average the patients weighed 239 pounds (108 kg).
Abdominal ultrasounds presented the most difficulties when linked to obesity, followed by chest X-rays, abdominal CT scans and MRI scans.
The study reports that incomplete tests lead to further testing, hospitalization, misdiagnosis or the failure to make one.
Wear and tear on equipment is also noted since increased voltage and current settings are needed to produce quality images.
More than 66 per cent of the American adult population is overweight, obese or morbidly obese. The Department of Health and Human Services reports 12.5 million American children are overweight.
The study appears in the August issue of medical journal Radiology.
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