June 2009
- Diabetic Patients Benefit from Non-contrast MRI
- Validating Improved Outcomes for Diabetic Patients
- D-THI Deepens Ultrasound's View
Diabetic Patients Benefit from Non-contrast MRI
During the past two decades, there has been a dramatic increase in obesity among U.S. residents, according to the Centers for Disease Control and Prevention; in 30 states, more than a quarter of the population is obese (see figure above). The rise in obesity has led, in turn, to an increase in the incidence of diabetes, presenting the radiology community with a fresh challenge: How can radiologists accurately and safely image patients with comorbidities ranging from slow blood flow to kidney disease?
"Vascular disease is obviously a huge problem in the diabetic population and is a major cause of morbidity and mortality, with limb loss and gangrene," according to Timothy Albert, MD, medical director of the Cardiovascular Diagnostic Center of Salinas Valley Memorial Healthcare System, Monterey, Calif. "At a minimum, it prevents patients from being active, so one of the things we try to emphasize in our community is the importance of aggressively working up this disease. If you can diagnose it, you can treat some patients with cholesterol medications, blood-pressure medications, and so on. For those who have a blockage, you can fix it."
In 2008, Salinas Valley installed a Vantage™ Atlas MRI system from Toshiba America Medical Systems, Inc. in Tustin, Calif., and began using the scanner's non-contrast protocol to image more than 90 percent of its patients. "We prefer to image these patients without contrast for a couple of reasons," Albert notes. "A lot of times, these diabetic patients have some early kidney disease (if not advanced kidney disease), and you've got issues with veins not getting enough contrast, especially in the lower extremities."
The 1.5T Atlas uses Toshiba's proprietary contrast-free imaging techniques. "In terms of image quality in the renal area, I'd say it's one-to-one with contrast-enhanced MRI. It's as good, if not even better; there's often some improvement, in that you can actually see the branching vessels better than when you're using contrast, which can wash the image out," Albert says.
Using non-contrast MRI, however, eliminates other timing issues, such as the need to take the scan while the contrast is flowing through the vessels at an optimal level. "Up to 5 percent of the time, even with an experienced technologist, you can miss it," he says, "and you'll still have problems with the veins getting enough contrast."
Use of the non-contrast technique improves workflow and throughput, Albert says, by eliminating the obstacles that come in tandem with using gadolinium or other contrast agents. "With contrast-enhanced imaging, there's always a certain percentage of patients whose exams you may need to redo," he notes. "IV issues themselves—plus the risk of reactions or complications from the IV (although low)—also contribute to the amount of time it can take to scan one patient."
There are throughput benefits specific to imaging the bariatric/diabetic population, he adds. "With diabetic patients, it can be hard to find a vein, and sometimes you can't get an IV the size you need for a rapid injection. You can spend 20 minutes looking for the right size IV," Albert says. "For patients with kidney disease, logistically, it's nice not to have to make sure you've got their latest kidney-function tests, because that can slow the process of getting patients through, and for patients who do have a contraindication for gadolinium, we're not dusting off the books and trying something new. This is what we do routinely."
Non-contrast MRI also saves money—well over $100 per study, according to Albert. "We're in a day and age when reimbursement is getting cut and cut, and this is a big way to save," he says. "It's not only the contrast bill, which could be up to $100 for the average study. You've also got IV supplies, and nursing time to put in the IV. We're working on some financial models to compare the two, but you're probably looking at saving up to $150 per study."
Albert emphasizes that while the non-contrast technique is particularly beneficial in imaging the diabetic population, it can be used on any patient. "There are a lot of misconceptions out there regarding who is the ideal patient for this," he says. "We've done a cross-section of patients of every size in the past year, and we've had very good results. This really is a robust technique."
Validating Improved Outcomes for Diabetic Patients
According to the American Diabetes Association, more than 75 percent of today's 23.6 million U.S. residents with diabetes will die of heart disease. Many of these diabetic individuals are asymptomatic for coronary heart disease (CHD) until their first heart attack, and there is no accepted method of detecting CHD, to date.
"Patients with diabetes have a risk of cardiovascular disease that is two to four times greater than that of nondiabetic patients," Donald Lappe, MD, chief of cardiology at Intermountain Medical Center, Salt Lake City, explains. "The ability to detect CHD in at-risk, asymptomatic patients will have a significant impact on the ability to improve their cardiac conditions and will help save lives."
To assess the viability of using 64-detector row CT to diagnose CHD in asymptomatic patients, Toshiba America Medical Systems, Inc. in Tustin, Calif., funded faCTor64, a 1,100-patient prospective study conducted by researchers at Intermountain Healthcare, Salt Lake City. Investigators will identify asymptomatic diabetic patients using Intermountain's diabetes database; then, they will compare two patient groups. Half will be evaluated for CHD using cardiac CT angiography (CTA) using the Toshiba Aquilion® CT system, while the other half will undergo traditional diabetes management. Researchers will follow both groups for five years to assess which group experiences better outcomes.
So far, 261 patients have been enrolled in the study, with 93 patients scanned; Intermountain hopes to complete enrollment by 2010. Using the Aquilion's Volume Imaging protocol, Intermountain researchers have been able to create up to five different reconstructions using data from a single acquisition, allowing them to review more aspects of the patients' cardiac function. Intermountain physicians also are able to develop their own CT protocols based on specific patient needs, and they can customize Toshiba's proprietary SURECardio software to reduce the amount of contrast, and the radiation dose, that patients receive.
Researchers say the study's initial results are promising. CHD has been diagnosed in approximately 75 percent of the scanned asymptomatic diabetic patients, and many of them also have high-grade, severe stenosis warranting revascularization. Several of the patients also have a defective anginal warning system, possibly providing a clue as to why they are asymptomatic, in spite of the severity of their CHD. The team at Intermountain also notes the results of the CTA scans have helped with patients' health management; many patients who need to lose weight or make other lifestyle changes have been more compliant after seeing their CT results.
D-THI Deepens Ultrasound's View
Ultrasound imaging of bariatric patients is often hampered by the limits of the modality's depth penetration. In some cases, larger patients cannot be imaged using the technology because of image-quality issues. Cassie Murvay is an ultrasound product manager for Toshiba America Medical Systems, Inc. in Tustin, Calif. She explains, "Ultrasound penetration depends on the frequency of the signal you're sending from the transducer. In order to penetrate deeper, you have to go to a lower frequency, but in order to get that, you sacrifice resolution and clarity."
To solve the frequency problem, Toshiba developed Differential Tissue Harmonic Imaging (D-THI), a proprietary technique designed to better penetrate dense tissue. D-THI, which is available on the company's Aplio™ XG and Xario™ XG ultrasound systems, sends a single signal consisting of two pulses—one at a low frequency and one at a high frequency.
"The two pulses give the penetration without losing the resolution," Murvay says, "so on larger, technically difficult patients, we can penetrate all the way through the liver, for example, and still have the resolution necessary for the diagnosis."
D-THI works by using enhanced effective bandwidth to capture the images. "This technology is ideal for use on any patient who is large or difficult to image," Murvay notes. "A lot of vascular imaging is done on diabetic patients, and D-THI can help penetrate large, edematous legs to get the vascular images needed. It's also beneficial in imaging dense livers, kidneys, pancreas—really, any abdominal imaging on bariatric patients can benefit from D-THI."
Using D-THI is faster than taking multiple images at a lower degree of depth coverage, and it easily accommodates bariatric patients who might otherwise require a different piece of equipment for scanning, improving throughput and saving imaging centers time and money. "It's a lifesaver for our customers who deal with bariatric patients," Murvay says.