New equipment, techniques sought for larger patients
New equipment, techniques sought for larger patients
Accompanying the growing demand for radiological services across the country is the growing physical size of the patients requesting those services. This demand has brought new challenges in terms of obesity and radiology. Can good quality images be obtained from an obese patient, and can that obese patient even fit on a machine?
In a 2004 study that initially addressed the obesity issue, Raul Uppot, MD, an assistant radiologist at Massachusetts General Hospital in Boston, and his colleagues found that images varied by modality. "The modality most limited in terms of obesity was ultrasound. At around 250 pounds, you started to notice the difficulty in imaging patients with ultrasound," he says.
Other modalities that were affected were chest radiographs, abdominal radiographs, and fluoroscopies, which ironically are used for obese patients seeking laparoscopic gastric bypass surgery. When Uppot and his colleagues examined tests performed between 1989 and 2003, they found that 0.10% of inconclusive exams were due to patient size in 1989, compared with 0.19% by 2003.
For other modalities such as CT and MRI, there were other issues, "but they weren't as great," Uppot says. "The main issue [for patients] was whether they could fit on the table."
If they could get on the table, adjustments could be made on a CT scanner, for example, to try to obtain better quality images and decreased "noise" from inadequate beam penetrations when compared to images made of a normal-sized person. These adjustments might result, though, in an increased radiation dose to the patient.
Will the patient damage the table?
Concerns have risen over patients who surpassed the weight limit of the table as specified by a manufacturer: They could damage a table or its motor mechanics. Usually, the cost of damage will not be covered if a heavier patient is placed on the table for imaging, which has led to a quandary for many health care institutions.
With these findings on obese patients and imaging equipment, manufacturers have begun to take notice. New fluoroscopic equipment is being introduced that is raising the table weight support limits from 350 pounds to upward of 550 to 700 pounds and increasing the bore diameter limits up to 70 cm.
New larger CT scans are being introduced that can accommodate upward of 680 pounds and have an increased gantry diameter of up to 90 cms. In comparison, most hospitals now have scans that are built to accommodate patients just up to 450 pounds. However, most of these new larger-bore CTs have been located in health care facilities for radiation oncology diagnosis and treatment. "They have not been used uniformly in radiology departments for diagnosis," Uppot said.
Some of the greater changes in diagnostic radiology equipment sizes have been occurring with MRIs. When patients are too large to fit inside the bore of a high-field MRI magnet, an open MRI system, with low-field magnets, could be used. The field strength of the magnets, would be in the area of 0.75 or 1 tesla.
But new larger closed units also have been introduced with 1.5 tesla. "The stronger the magnet, the better the quality of the images," says Jodi Hildestab, the radiology clinical coordinator manager with the Mayo Clinic in Jacksonville, FL. The clinic purchased its closed-unit MRI scanner, manufactured in 2004 by Siemens Medical Solutions, with U.S. headquarters in Malvern, PA. The table has a weight limit of 550 pounds and a bore opening of 70 cm in diameter (compared with the usual 60 cm diameter). The MRI scanner used by Mayo has one foot of free space between a patient's head and the magnet. At four feet long, the magnet allows more than 60% of exams to be completed with the patient's head outside the bore.
While the clinic doesn't encounter many morbidly obese patients, many patients do have weight issues. Using the larger unit has helped those patients and others feel less claustrophobic during the usual 45-minute period needed for an MRI scan, Hildestab says.
As manufacturers look at the idea that bigger is better, they may encounter some resistance. "There will be physics-related limitations," Uppot says. "Once you make the gantry diameter more than a certain diameter, [will it reach a point] where there will not be enough power for the X-ray beam to travel through the patient and get an image?"
For the current time, many radiology programs are facing the question of what to replace their imaging equipment with as it gets older. While equipment is available, from fluoroscopes to MRIs, that feature tables that can handle weights ranging from 500 to 700 pounds, Uppot suggests that weight load should not just be the predominating factor in making a selection.
"You have to see what the patient population of your institution is," he says. When he and his colleagues looked at his hospital's patient history over the past 10 years, they noted that only one patient ever came close to 700 pounds. Instead of just looking at upper weight capability, he suggested also examining the quality of the images produced by the machine and the level of service provided by the manufacturer, such as how quickly the manufacturer responds if the equipment breaks down.
In Uppot's recent investigations of what happens to patients who cannot fit on a table because of their size, he has disavowed one common misconception among physicians and radiologists: that they can use a CT at a local zoo. "I've tried to debunk that," he says. "I have called at least 20 zoos now across the country. There is not a single zoo that has a CT-machine that can accept larger patients."
Resources
Manufacturers producing radiological equipment to accompany larger sizes include:
- GE Healthcare Global Headquarters (U.S), Waukesha, WI. Phone: (800) 886-0815. Web: www.gehealthcare.com.
- Hitachi Medical Systems America, Twinsburg, OH. Phone: (800) 800-4925. Web: www.hitachimed.com.
- Philips Medical Systems Global Headquarters (U.S), Andover, MA. Phone: (978) 659-3000. Web: www.medical.philips.com.
- Shimadzu Medical Systems, Torrance, CA. Phone: (310) 217-8855. Web: www.shimadzu.com/products/medical/index.html.
- Siemens Medical Solutions, Malvern, PA. Phone: (800) SIEMENS or (610) 408-0920. Web: www.usa.siemens.com/medical.
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