Sixteen-slice CTs address sweet spot in U.S. market

Sales of 16-slice CTs led the industry to new heights last year, topping $1.3 billion in new unit sales to U.S. customers. Industry pundits expect even better numbers this year, as all three CT vendors are now in full production with 64-slice products. These units have grabbed the spotlight for their radiological and especially cardiological applications, but they are just the most visible facet of an increasingly complex CT market.

Whereas the evolution of CT scanners was once linear, progressing from four to eight, 16, 32, and finally 64 slices, this family tree has begun branching out. Specialty scanners are being built for niche applications. Vendors are manufacturing single-, dual-, and quadslice scanners for physician group practices, particularly ENTs, as well as small community hospitals and imaging centers. The most popular branch, however, is the 16-slice configuration.

Half of all CT sales at Toshiba this year have involved the Aquilion 16, according to Doug Ryan, director of Toshiba America's CT business unit. Other vendors report similar interest by customers. And once a CT is installed, it stays installed. Owners might shuffle it from one room or imaging center to another, but very few are traded in.

"Customers are moving their 16s to someplace else and then buying 32- or 64-slice technology," Ryan said. "We just don't see them coming back."

Sixteen-slice technology has settled into a sweet spot in radiology, as manufacturers sculpt their portfolios to fit it. Siemens this summer began U.S. deliveries of its Emotion 16, an air-cooled CT designed for routine radiological applications and priced below the Sensation 16. Eliminating the water chiller, otherwise needed to cool the x-ray tube, also makes the system more compact and easier to site.

GE Healthcare has reengineered its portfolio of 16-slice scanners into state-of-the-art systems, some with technology that's trickled down from the highest echelon. The Volara digital data acquisition system and Xtream FX workflow tools - developed for the company's 64-slice LightSpeed VCT - have migrated to the VFX series of LightSpeed 16s, as well as to scanners offering even fewer slices.

"It's kind of like 'Intel Inside,' where you are bringing a lot of the technology on the VCT down to these other products," said Bill Radaj, GE's general manager of CT for the Americas.

GE Healthcare has two high-power 16-slice LightSpeed scanners: the Pro16 80 and the Pro16 100, which complement the lower power LightSpeed 16. The two Pro systems differ primarily in the power of their generators and x-ray tubes.

"Anyone looking to do cardiac scanning would consider the Pro scanners versus the base LightSpeed 16," Radaj said.

Cardiac is the most demanding of all clinical CT applications. Any of the new legion of 64-slice devices may be the scanner of choice for such applications, but 16-slice scanners can do a lot in cardiology.

Siemens is targeting this cardiological niche for its Sensation 16. The system features a 0.4-second rotation time and a water chiller to cool its advanced x-ray tube called the Straton, which is more powerful - and cardiologically more capable - than the newly released Emotion 16.

Philips' customers may get into 16-slice scanners through the back door, buying 10- or even six-slice scanners, then field-upgrading to a 16. Field engineers can do this quickly because Philips uses the same detector in each CT, according to Richard Nelson, director of global field marketing for Philips. Owners of the Aquilion eight-slice scanner can upgrade to 16 slices in much the same way, adding channels to the existing detector. The driver behind such upgrades usually is an increasing number of patients or an interest in coronary CT angiography.

Interest in 16-slice scanners is building among cardiologists. For a while, Philips had hoped to direct at least some of those with such needs to its specially designed Brilliance CT Private Practice CV. The system, launched earlier this year, is optimized for cardiac scanning. The company initially reported strong interest among cardiologists but has since backed away from that claim.

"It hasn't sold quite as well as we thought it would," Nelson said. "We are seeing customers gravitating more toward a full-featured system, the regular radiology full-system 16-slice unit. We don't know why."

The use of CT to screen patients for coronary artery disease has been criticized in the past for suspect clinical benefit that did not justify patients' exposure to x-rays. Researchers at University Hospital in Ulm, Germany, however, have found that a standard 16-slice Brilliance CT was reasonably good at detecting significant obstructive coronary artery disease. They reported in the May 24 Journal of the American Medical Association sensitivity of 95%, specificity of 98%, positive predictive value of 87%, and negative predictive value of 99%, when comparing 16-slice CT to coronary angiography in the identification of coronary vasculature with greater than 50% narrowing.

Sixteen-slice scanners can whet an interest in cardiac applications but not satisfy it. That takes the biggest gun in the industry's portfolio: the 64-slice scanner, or at least a 32- or 40-slice scanner, which promises more detailed assessment of the coronaries than the 16 can deliver. Oncology, however, is well within the reach of 16-slice scanners.

Until recently, oncologists depended on single-slice CT simulators when planning radiotherapy. GE Healthcare was the first company to recognize the need for a multislice CT simulator, releasing its quadslice LightSpeed RT two years ago for this application. GE continues to offer this product. Philips leapfrogged to a 16-slice configuration with the commercial release of its Brilliance Big Bore in early summer. The wide-gantry system will have head-to-head competition when Toshiba comes out with its 16-slice Aquilion LB later this fall.

Multislice CT simulators have several advantages over their single-slice predecessors. The first is image resolution. CT images are the basis for digitally reconstructed radiographs from which virtual patient models are constructed. Single-slice simulators typically produce slices from 1.5 mm to 5 mm. The Brilliance Large Bore delivers submillimeter slices, an important consideration as data from thinner slices produce more accurate 3D models.

The second reason is tube heat. Single-slice scanners seldom produce more than 100 images, although many more may be needed to define a tumor. Sixteen-slice scanners easily produce 800 thin slices without excessive tube heating.

Third, multislice CT simulators do a better job than single-slice units at characterizing moving tumors, such as those in the lung. Subsecond rotation allows dynamic imaging, which can be used to quantify the extent of tumor motion. This allows more accurate therapy planning, better targeting of the tumor, and less collateral radiation to healthy tissues.

The popularity of 16-slice scanners may be short-lived. If the past is prelude, flagship CT scanners will soon jump forward again, this time to 128 or more slices. A prototype 256-slice scanner is already generating 4D images in Japan. This system, the result of a collaboration between Toshiba and the Japanese government, has successfully captured dynamic volumetric images of liver cancer (see related story, this issue). Other manufacturers are known to be experimenting with similar prototypes, as well as ones constructed from flat panels.

Vendors are equivocating, however, about when such advanced technology will enter the market. Technology ultimately will march forward, but 64-slice scanners may be enough to keep medicine busy for at least the next several years. These scanners provide the necessary coverage and speed to achieve coronary CTA and more than enough power to accomplish known radiological applications.

Consequently, scanners with even more slices may not be needed immediately, which means the workhorse of CT for the past three years might be able to keep its job well into the future.