Americans have been living large, and it’s showing in their waistlines. But dieters aren’t the only ones who are battling the bulge?the medical community is finding itself challenged as well. Obstacles present themselves throughout the diagnosis and treatment of very obese patients, from the collection of simple information, such as an accurate weight, to the gathering of complex data, such as the results of an MR exam.
But these patients need care too, particularly since they are more likely to require it, and hospitals do not want to turn them away. The key to accommodating patients?at least in medical-imaging departments?is equipment, and manufacturers are responding with solutions meant to serve those outside of traditional means.
How Big Is Too Big?
Exactly what size is the patient who will experience challenges in medical imaging? There is no pat answer. A variety of factors, including height, weight, and body mass index (BMI), play a role. Ultimately, “too big” is whatever size the machine cannot support, either physically and/or mechanically.
With newer scanners supporting weight up to 600 pounds and featuring bore sizes larger than the average?which is about 60 cm for MR and 70 cm for CT?a patient who cannot be accommodated by available medical-imaging equipment is generally morbidly obese.
Unfortunately, the frequency with which these patients are seen has been increasing. The National Institutes of Health (NIH of Bethesda, Md) has collected data that indicates nearly one third of US persons aged 20+ years are obese; this represents 61.3 million adults, more than double the prevalence that previously existed in 1960 (30.9% in 2000 versus 13.3% in 1960). The increase in extreme obesity, represented by a BMI greater than 40, grew from 0.8% in 1960 to 4.7% in 2000; that figure was just 2.9% in 1988.
Extremely obese patients tend to suffer from conditions that require medical imaging for initial diagnosis and treatment, such as degenerative joint disease, diabetes, and hypertension. Unfortunately, the patient’s size limits the exam’s capability, a situation commonly referred to as limited by body habitus (LBBH).
LBBH: Too Big
A patient’s size limits have been documented. Researchers at the University of Washington School of Medicine (Seattle) examined the results of 100,000 mammograms and found that obese women had a 20% increased risk of a false positive than women defined as having a normal or thin weight. The full results were published in 2004.1
Later the same year, Raul N. Uppot, MD, a fellow in abdominal imaging and interventional radiology at Massachusetts General Hospital (Boston), presented a study at the annual meeting of the Radiological Society of North America (RSNA of Oak Brook, Ill).2 Reviewing the 15-year period from 1989 to 2003, Uppot and his colleagues determined that the portion of all radiologic exams determined inconclusive as a result of obesity nearly doubled, from 0.1% to 0.19%. The increase correlated to the growth of obesity in the state of Massachusetts, which rose from 9% in 1991 to 16% in 2001.
The report also found that the imaging exam most often filed as limited was abdominal ultrasound (1.5%), followed by chest X-ray (0.08%) and abdominal CT (0.04%). The direct costs of these incomplete radiologic exams was estimated to be approximately $100,000 in 2003, more than triple the 1995 cost of $28,000.
Frequency Expected to Rise
|Toshiba’s Kalare digital X-ray system shifts from vertical to horizontal for easier patient placement.|
With the prevalence of obesity expected to continue growing, facilities should expect to feel the weight of this impact more strongly. Such factors as geography, expertise, and equipment will influence the frequency with which these patients are seen.
“Any large facility will see these patients because it is so pervasive,” says Alan Berthe, product manager of X-ray at Toshiba America Medical Systems (TAMS of Tustin, Calif). “But those that specialize in bariatric procedures will necessarily see more.”
Facilities that invest in the capability to accommodate these patients also will see more of them. “We see these patients almost daily,” says Anthony J. Scuderi, MD, chairman and medical director of Laurel Highlands Advanced Imaging (Johnstown, Pa). “Before we purchased an open scanner, a 280-pound patient was the largest we saw. Now, we routinely see patients weighing 300 to 400 pounds.”
Challenge 1: Getting the Right Fit
Obese patients present a number of challenges, which generally fall into one of three areas: size, mobility, and image quality. Many of these obstacles fall upon the technologists, who have learned to be innovative. They also have been vocal, asking manufacturers to provide solutions, and vendors have been quick to respond.
The primary problem is size. If the patient cannot fit into the machine, he or she cannot undergo the exam. “This has been a problem historically with MR, because, with the 55- to 60-centimeter bore, people couldn’t fit,” says Anne Sheehan, marketing manager of the Magnetom Espree for Siemens Medical Solutions (Malvern, Pa). “Now, there are a variety of shapes and configurations in addition to the cylindrical bore. But even with an open magnet, there is still a point at which the patient cannot be squeezed in?the distance from the top of the table to the top of the magnet can be a problem.”
However, both MR and CT manufacturers have designed new equipment to feature larger or open bores and to bear greater weight. TAMS’ Vantage features a 60-cm internal bore; the next-generation CT from GE Healthcare (Waukesha, Wis) will feature an 80-cm bore; and open magnets are coming out in new configurations to fit larger patients. Ideally, these allow some room left over to fit coils and keep the patient comfortable, because uncomfortable patients tend to move, introducing artifact into the image.
Accessories and parts also have been modified. New coils for MR enable the technologist to lay the coils on the patient rather than wrapping the coils around the patient. Sheehan notes that Siemens Medical has developed coils that Velcro together and allow just half of one to be used, if that is all that is needed, to maximize signal to noise.
Similarly, the tables have been redesigned to bear more weight and maintain mobility. Newer equipment can support weight in the range of 450 to 600 pounds, depending on the model.
Challenge 2: Moving into Position
The table can play a key role in positioning the patient, so it is advantageous for its mobility to be maintained. “The system is designed to move its components rather than the patient,” Berthe says. But getting patients onto the table can present a challenge in itself.
Extremely obese patients often do not have the best mobility and could suffer shortness of breath as a result of narrowed airways. The technologist will help these patients, but excessive strain on the technologist can create ergonomic risks. Bob Giegerich, TAMS’ director of the MR business unit, has seen technologists slide the patient into the machine on a sheet. He says that it is a two-person job.
Berthe advises, “When possible, let the system do the work,” and he suggests footsteps and handrails for the patient and technologist to use. Even better are systems with tilting tables that allow the patient to stand, lean, and be lowered into position.
Scuderi praises the new scanner in his facility, which lowers almost all the way to the ground so the technologist does not have to lift the patient to get him or her off of the table. “It’s helpful when the table moves up, down, forward, and back,” he says.
Positioning the patient might not be as easy. “Markers, such as hip bones, are harder to find, making positioning more technologist and patient dependent,” says Sheehan, who feels the area in between the chest and pelvis can be the most challenging.
The goal is to position patients properly and keep them comfortable enough so that they can hold still. “If a patient doesn’t lie comfortably, he or she finds it difficult to stay still and instead moves around,” says Maurits Wolleswinkel, business director of open MR for Philips Medical Systems (Bothell, Wash). “If the patient is pretty large and asked to hold a strange position, the exam usually is unsuccessful.”
|This MR angiography (MRA) image (above left)?which took 24 seconds to acquire?shows the renal arteries. This MRI (above right) shows a 5’4″, 450-pound patient who was suffering from lower back pain. Both images were acquired using the Magnetom Espree 1.5T open bore MRI system from Siemens Medical Solutions, which provides patients access to medical-imaging options who traditionally have been unable to due to their size.|
Challenge 3: Obesity IQ
Movement negatively affects image quality, but this is not the only challenge presented in this area. By virtue of their size, obese patients are at a disadvantage in most modalities. Radiation, whether for X-ray or CT, can be limited by inadequate penetration or film size. Ultrasound waves might not be able to penetrate a large body size and will deliver poor image quality; indeed, quality could be compromised even in overweight patients (those with a BMI between 25 and 29). MR imaging of obese patients suffers from low signal to noise.
“If there is a large layer of fat over the gallbladder, you will have a harder time seeing it,” Sheehan says. Unfortunately, many of these issues cannot be controlled or have limits on how they can be modified.
CT machines can increase power and dose, but the human body can withstand only so much radiation before its associated risk becomes too severe. “The bigger patient has a larger cross-section for the beam to travel,” says Elmar M. Merkle, MD, associate professor of radiology at Duke University School of Medicine (Durham, NC). “CT radiation scatters, and you can increase the dose to improve quality, but you cannot do so infinitely; thus, the image will suffer.”
According to Kelly Piacsek, product manager of the functional and CT business, radiation oncology and bariatrics at GE Healthcare, “A lot can be done with hardware and software to improve the image quality for very large patients. You can increase the technical capability on the scanner to get enough power and current. We see a lot of range in bore size, tube power, and detector capability. Software optimizes how the CT is utilized, allowing the technologist to vary the protocol to adjust for the optimum dose.”
MR also relies on hardware and software solutions. Larger bores, coils, and tables help to acquire the image, while stronger field strengths and software image enhancement improve quality. Traditionally, open-bore magnets used lower field strengths, often 0.2T to 0.5T, but newer models have increased the open-bore capability to handle 1.0T and 1.5T field strength, making it possible to obtain better-quality images as well as perform newer applications.
“To image the extremely obese patient, you need high field strength magnets. Strengths of 0.2 to 0.5 Tesla do not provide adequate signal to noise, and sometimes it is just not possible to perform the exam with a longer acquisition time,” says Scuderi, who feels that the 1.5T magnet is a new standard helpful for large patients. Scuderi and his team also employ larger fields of view, alter MG matrices, adjust bandwidth, and use proper surface coils. “These all help to increase the signal,” he says.
Software techniques, such as fat saturation, also improve the image. “Fat gives off a bright signal, which saturation can eliminate,” says TAMS’ Giegerich.
Service for All
Sometimes, all of these hardware and software adjustments still are not enough. “Sometimes, you can’t produce a diagnosis. Ultrasound is often blind, the beam is not strong enough to penetrate, or the radiation exposure is too high,” Merkle admits.
In addition, some physicians do not necessarily trust the results. “The calculations behind this equipment are based on the 95th percentile,” Geigerich says. “These people fall into the 99th percentile and, therefore, the body calculations are off.”
Unfortunately, this problem exists for extremely obese patients throughout their care. “Whenever designing a piece of medical equipment, the manufacturer often takes into account 90 percent of the population. Those representing the extremes are not accommodated,” Wolleswink says. “As a result, these same patients find they cannot be helped with much of the equipment on the market.”
Even obtaining an accurate weight can be challenging. “I’ve seen patients weighed on meat scales, and even then, we couldn’t be sure of the final number,” Giegerich says.
But as their numbers increase, the inability to serve this group becomes unacceptable. “Even if you are turning just one or two patients away, it’s not ideal,” says GE Healthcare’s Piacsek. A facility wants to offer the same services that it can to thinner patients. And with manufacturers’ help, they are beginning to win the battle of the bulge.
Wren Davis is a contributing writer for Medical Imaging.
- Elmore JG, Carney PA, Abraham LA, et al. The association between obesity and screening mammography accuracy. Arch Intern Med. 2004;164:1140-1147. Available at: archinte.ama-assn.org. Accessed December 8, 2005.
- RSNA 2004 Meeting Program. Limited by body habitus: economic and quality control issues in the ability of a radiology department to provide diagnostic imaging to a fattening population. Available at: rsna2004.rsna.org. Accessed December 8, 2005.