Sixteen-slice CT is proving to be sweet with blossoming applications in cardiac and vascular imaging in addition to classic CT studies in the liver, pancreas and kidney. And 32-, 40- and 64-slice are promising even more punch for cardiac imaging as well as perfusion imaging and trauma.
The multislice CT era has dawned, and in the slice-wars, sixteen-slice technology is proving to be a tremendous hit. Elliot Fishman, MD, professor of radiology at Johns Hopkins University (Baltimore), contends, "CT will be the physical examination of the 21st century." Take for example the ER patient with abdominal pain. A surgeon could be called in to examine the patient and detect the probable etiology of the pain. Or the patient could undergo a 10 to 20 second CT scan to pinpoint the exact condition. But the latest and greatest scanners are extending the boundaries of CT far beyond routine abdominal studies and making cardiac CT reality. Fishman estimates that CT volume at Johns Hopkins has increased nearly 20 percent since deploying its 16-slice scanners two years ago.
Sixteen-slice CT scanners have been available for about two years, and many sites are finding that sixteen is the CT scanning sweet spot. Scott Lipson, MD, associate director of cardiac imaging at Long Beach Memorial Medical Center (Long Beach, Calif.), opines, "Going forward over the next five years, I think 16 will be the dominant technology. There are clear advantages of 16 over four- and eight-slice technology, and most single-slice scanners will be phased out and replaced with 16-slice scanners."
What is it that makes 16-slice so sweet? "It's the best of both worlds," according to Fishman. "We can do everything we did before on a four-slice scanner better and there are new applications [made possible by the 16-slice scanner's increased speed and improved resolution.]"
Johns Hopkins' radiology department relies on four Sensation 16 CT scanners from Siemens Medical Solutions (Malvern, Pa.) as its departmental workhorses. The scanners are used for classic CT applications-liver, pancreas and kidney studies-with better results than a four-slice scanner. The ultra-fast acquisition and sub-millimeter thin slices yield a high-resolution dataset for these bread-and-butter CT scans. For example, the 16-slice scanner can be used to create a vascular map of the liver with additional fine detail.
Lipson says the Aquilion 16 CFX scanner from Toshiba America Medical Systems (Tustin, Calif.) has made a tremendous difference for his practice. The practice realized increased CT utilization and improved patient care since upgrading from a four-slice scanner. One of the primary 16-slice applications is CT angiography, which is doable, but barely, on a four-slice scanner.
Lawrence Tanenbaum, section chief of MRI, CT and Neuroradiology at Edison Radiology Group (Edison, N.J.), says CT angiography is a prime example of how the GE Healthcare LightSpeed 16 makes a difference in clinical care. CT angiography provides better visualization than conventional angiography for conditions such as a leak in an aortic stent. What's more, because CT angiography replaces the conventional invasive procedure, it's possible for radiologists to diagnose patients who aren't candidates for an invasive procedure.
Other new applications made possible by 16-slice scanners include coronary artery studies and virtual colonoscopy. Coronary CT is the only way to visualize soft plaque, which is thought to play a role in half of heart attacks deaths-those that occur without evidence of an obstruction. And like CT angiography, virtual colonoscopy serves as a replacement for a conventional invasive procedure for many patients.
Sixteen-slice scanners enhance clinical care in other ways as well. For starters, the higher resolution means that radiologists are able to see things to make diagnoses that weren't possible before. "We can make more accurate diagnoses with the scanner," Tanenbaum explains. "Axial interpretation can be confusing at times. Adding the coronal and sagittal plane makes an enormous difference in the radiologist's ability to see subtle details." Lipson adds, "We're obtaining isotropic thin sections and multi-planar reconstruction on all patients, which has changed how we interpret studies."
The new, volume-based world does require a change in mindset and workflow. "You need a good PACS and 3D workstations to take advantage of what 16-slice scanners have to offer," Lipson explains. "Without these tools, you're using it like a single- or four-slice scanner." With the right tools, however, 16-slice technology can be integrated into a manageable workflow to enhance clinical care. (For more on CT and workflow, see "Efficient Pipelines Enhance Volumetric CT Utility" on page 28.)
BEYOND SIXTEEN SLICE
While the radiology community is still adjusting to the 'wow' and increased utility of 16-slice technology, the first 32- and 40-slice scanners are hitting the streets. The major impact is expected in cardiac applications, but the scanners will likely show some benefits in other areas such as perfusion imaging and trauma cases.
Joao A.C. Lima, MD, director of cardiovascular imaging and cardiology at Johns Hopkins University School of Medicine (Baltimore), has been using the Toshiba Aquilion 32 for three months. The new scanner is centrally located in the cardiology area to provide cardiologists with fast and easy access to the technology. The university is completing a number of research studies of the scanner. For example, researchers are attempting to see if CT angiography can reduce the length of stay for patients with indeterminate chest pain. Lima reports that he is seeing a steady increase in the number of clinical requests for 32-slice scans. A 32-slice scan can be used to locate bypass grafts on patients returning for a second surgery, and it's an effective substitute for catheterization for both high-risk patients and those who the cardiologist doesn't want to refer for catheterization. The Toshiba 32-slice scanner also is used to confirm clean arteries in patients undergoing valvular surgery, thus avoiding catheterization.
Lima says one of the primary advantages of the 32-slice scanner is that it allows cardiologist to see smaller vessels than a 16-slice scanner. According to Lima, as the number of detectors increases, the number of vessels that can't be seen drops-from 25 percent with a four-slice scanner to 10 to 12 percent with a 16-slice scanners. Results aren't in yet for the 32-slice scanner, but Lima predicts that the number won't be cut in half to 5 or 6 percent, but there will be an incremental gain. Lima provides a clear clinical example of the difference. "It's difficult to see coronary arteries with a high degree of calcification on a 16-slice scanner. Initial results indicate that the 32 [slice] provides acceptable accuracy."
Finally, although radiation dose does not dramatically increase as the number of detectors increases, Lima says that radiation dose can present an obstacle to making the technology more useful for preventative cardiology purposes. Lima is particularly concerned about radiation dose for patients who require a therapeutic procedure like cardiac catheterization immediately after the scan. Moreover, if CT is deployed for preventative cardiology, some patients could be scanned more often, thereby increasing the overall radiation dose. Toshiba, GE, Phillips' and Siemens all provide dose reduction tools to minimize this effect.
Phillips' Brilliance 40-slice scanner is being used in cardiology and beyond at Indiana University School of Medicine (Indianapolis). Jonas Rydberg, MD, associate professor of radiology at Indiana University School of Medicine, says Phillips' Brilliance 40-slice CT scanner resolves the classic compromise between speed and slice thickness. "With a 16-slice scanner, a CT of the chest, abdomen and pelvis required 2 breath-holds," he explains. "Now we can scan the entire body in a single breath-hold."
The Brilliance 40 provides finer detail further into the periphery than 16-slice scanners, resulting in more optimal cardiac studies, Rydberg says. The Brilliance 40 also reinvents post-processing time. Reconstruction typically takes five to 15 minutes with other multislice scanners, but Brilliance Workspace eliminates pre-processing to provide near-immediate image review. "This is an advantage in trauma cases where you are fighting against time," Rydberg points out.
Another patient population that could benefit from the souped up technology is children. Rydberg says, "We can reduce the amount of contrast media and with a fast scan, we don't have to sedate children as much as before."
W. Dennis Foley, MD, chief of digital imaging at Froedtert Hospital (Milwaukee, Wis.), uses GE's LightSpeed VCT for 64-slice imaging, but points out that a fully-featured 64-slice scanner could be modified to obtain a 32-slice exam. The slower scan speed, and resulting improved resolution, could be useful when imaging intracranial vessels.
In the last two years, sixteen-slice scanners have certainly proved their utility and value by enabling higher quality scans and making cardiac CT quite doable. While sweet sixteen is just right for many sites and applications, the next generation of CT scanning is burgeoning. Thirty-two and 40-slice scanners hit the market this year with pioneering sites exploring their advantages for cardiac CT, trauma, perfusion imaging and the multi-slice revolution, however, is still revving up. By the end of next year, all of the major CT vendors will have launched 64-slice scanners. Looking beyond the near future, most vendors have even higher slice scanners in the works.
Expanding CT Frontiers: The 64-Slice World
The major CT vendors are beginning to unveil 64-slice technology. GE Healthcare's debuted its LightSpeed VCT in June, and Siemens, Phillips' and Toshiba are expected to follow with their own 64-slice scanners later this year. Elliot Fishman, MD, professor of radiology at Johns Hopkins University (Baltimore), took a Siemens Sensation 64 for a trial run earlier this year and envisions a host of applications for 64-slice technology.
"Cardiac will be a slam dunk with 64-slice scanners," Fishman opines. "Studies that are barely doable on a 16 will be very doable on a 64."
With 64-slice scanners, cardiac CT scan time drops from 12 to 15 seconds to 5 to 8 seconds, further conquering cardiac motion issues. Fishman says, "With a 16-slice scanner, we can do a reasonable job with 80 percent of the patients in coronary imaging. With a 64-slice scanner, we'll probably be able to do everyone well."
W. Dennis Foley, MD, chief of digital imaging at Froedtert Hospital (Milwaukee, Wis.), has been using the GE's LightSpeed VCT for two months, and cardiac studies are a primary application. "The VCT is potentially very effective for coronary angiography for patients with disease in native arteries and evaluations for stenosis, angiographic stents and bypass grafts." Foley plans to complete a blinded study to compare the VCT to coronary arteriography. Another key application could be chest pain. A 64-slice CT scan could detect evidence of a heart attack, pulmonary embolism or aortic dissection.
Sixty-four slice CT technology also is expected to improve perfusion imaging. Foley says a fast scan can be used to obtain an angiogram and perfusion image to determine how to treat stroke patients. Thus, 64-slice scanners may be the bridge between CT and functional imaging. Changes in perfusion could indicate early angiogenesis or neovascularity and thus potentially more accurately identify patients at risk for certain types of cancer. "We want to use the 64-slice scanner to look at lesions and at the disease process," Fishman explains. "This is a way of increasing our sensitivity and detecting disease."
Will the introduction of 64-slice scanners banish 16-slice scanners to the radiology underworld? Not likely. Fishman explains, "For many applications and hospitals, 16 [slice] will be great. CT technology is not like computers."
"There will be an incremental benefit to 64-slice scanners, particularly in cardiac imaging," adds Scott Lipson, MD, associate director of cardiac imaging at Long Beach Memorial Medical Center (Long Beach, Calif.). "But for most people, the benefits of 64 over the 16 will be much smaller than the benefits of 16 over the four."
The CT frontier will not end with 64 slices; vendors are working on 256-slice technology, which could usher in a new era of functional CT imaging. Stay tuned.